Downloaded 10/07/21 07:51 PM UTC 1978 JOURNAL of ATMOSPHERIC and OCEANIC TECHNOLOGY VOLUME 35 Storms

OCTOBER 2018 L I M E T A L . 1977

Polarimetric Radar Signatures of a Rare Tornado Event over South Korea

S. LIM,S.ALLABAKASH, AND B. JANG Korea Institute of Civil Engineering and Building Technology, Goyang, South Korea

V. CHANDRASEKAR Colorado State University, Fort Collins, Colorado

(Manuscript received 13 March 2018, in ﬁnal form 28 August 2018)

ABSTRACT

The Korea Institute of Civil Engineering and Building Technology (KICT) made one of the first radar observations of a rare tornadic storm that occurred on 10 June 2014 in the Seoul metropolitan region, South Korea, using X-band dual-polarization radar. The tornado lasted for about 18 min, during which it destroyed about 20 greenhouses and injured several people. This tornado was rated at F0 on the Fujita scale. The KICT X-band dual-polarization radar was installed in the area northwest of Seoul to monitor storm development, measure rainfall, improve hazard mitigation, and disaster management. This paper presents the high- resolution (both spatial and temporal) polarimetric radar observations of the tornado, along with the radar parameters of reflectivity, differential reflectivity, Doppler velocity, and copolar correlation coefficient. The characteristic signatures of polarimetric variables, including the descending reflectivity core, weak echo hole, Doppler velocity couplet, and hook echo, are used to describe the tornado vortex and its development. In addition, the close range (about 5-km distance) observations of the hook echo show the high-resolution radar signatures of a weak echo region surrounded by high-reflectivity annular rings inside the tornado vortex. From development to dissipation, various finescale features are observed, including lofted tornadic debris and potential hail signatures. The high-resolution (close range) observations were also compared against low- resolution (long range) radar observations. The comparison shows that high-spatiotemporal, low-altitude, and close-range observations can be significantly advantageous for tornado detection and early warning.

1. Introduction Kumjian and Ryzhkov 2008; Lim et al. 2005). These polarimetric radar variables can also be used to distin- Weather radars are powerful remote sensing tools guish nonmeteorological scatterers (insects, dust, debris, for various meteorological applications, such as severe and birds) and hydrometeors (Ryzhkov et al. 2005). The weather monitoring and quantitative precipitation esti- polarimetric radars can be used to characterize tornadic mation. Over the last two decades, operational radars vortex signatures (Bluestein et al. 2007; Ryzhkov et al. have been significantly improved by the introduction of 2005). Dual-polarization radar transmits and receives dual-polarization capability. Dual-polarization radars electromagnetic waves in both vertical and horizontal have demonstrated the ability to discriminate between polarizations, which provides considerable information different types of hydrometeors. The combination of about the character of scatterers in the resolution vol- reflectivity factor at horizontal polarization Z , differ- h ume. The received polarimetric data can be used to ential reflectivity Z , and copolar correlation coefficient dr analyze and describe the structure of the tornadoes. r is used to extract information related to the size, hv The initial stage of the tornado may exhibit a descending shape, composition, and orientation of scatterers within reflectivity core (DRC) pattern (Rasmussen et al. 2006; the resolution volume (Bringi and Chandrasekar 2001; Byko et al. 2009). The DRC typically occurs prior to the development of the hook echo. The DRC signatures can Denotes content that is immediately available upon publication be used to detect tornadogenesis. DRCs may or may not as open access. be associated with tornadic storms. Rasmussen et al. (2006) performed the preliminary study on DRCs in which Corresponding author: S. Lim, [email protected] they described the characteristics of DRC in convective

DOI: 10.1175/JTECH-D-18-0041.1 Ó 2018 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1978 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35 storms. They also discussed the frequency of occurrence of supercell storm, which occurred on 4 May 2007, near DRCs prior to tornadic supercell storms. Subsequently, Greensburg, Kansas. They observed features such as WEH Kennedy et al. (2007) presented a statistical study of and WEC. The WEC is found in mode-1 (cyclic tornado DRCs and their relation to tornadic and nontornadic production) and mode-2 (long-track tornado production) storms. They suggested that DRCs are not necessarily tornadoes associated with low Zdr and low rhv, which in- present prior to tornadogenesis. Byko et al. (2009) also dicate lofted debris. They also found that high Zdr shield observed DRC features in various supercell thunder- and Zdr arc along the forward flank might represent large storms using mobile Doppler radar data. They described raindrops and size sorting, respectively. Houser et al. (2016) the classification of DRCs based on different precipitation observed the characteristics of a large violent tornado that events. According to this classification, type-I DRC are occurred on 24 May 2011, east of the dryline in western caused by stagnation of the midlevel flow, while type-II Oklahoma, using rapid scan X-band polarimetric mobile

DRC results from supercell cycling, and the low-level ro- Doppler radar. They analyzed the TDS using rhv iso- tation generates type-III DRC. Tornadic debris signatures surfaces, in addition to the Zh, Zdr, and Doppler velocity (TDS) of larger storms have been studied by several re- V features. Kumjian and Ryzhkov (2008) discussed the searchers using polarimetric radar variables. Ryzhkov et al. efficiency of rhv over Zdr at TDS detection. Bodine et al. (2005) observed tornadic supercells near the Oklahoma. (2014) analyzed statistical properties of TDS using dual- City, Oklahoma, metropolitan area. They found that the wavelength (S band and C band) polarimetric radar data, strong vortex in Doppler velocity and inside the hook which may improve the capability of tornado detection echo, the presence of low Zdr (,0.5 dB), low rhv (,0.8), and its damage survey. The authors observed an EF4- and high Zh (.45 dB) are associated with lofted debris. rated tornado that occurred on 10 May 2010 in Moore, They also reported that the presence of high Zdr values Oklahoma, and Oklahoma City. They made comparisons at the inflow region of the forward flank downdraft between S- and C-band radar measurements. The com- (FFD) indicates raindrop size sorting. Wurman and Gill parisons exposed that the TDS at S band exhibited higher

(2000) characterized the Dimmit, Texas, tornado that values of Zh and rhv than at C band. The presence of low occurred on 3 June 1995, using Doppler on Wheels values (Zh and rhv) for C-band radar relative to S-band (DOW) mobile radar. They noticed that circular rings radar is probably a result of non-Rayleigh scattering effects. near the tip of the hook echo accompanied a strong Snyder et al. (2010) presented the differences between velocity couplet and stated that the inner low-reflectivity S-band and X-band radar observations during severe con- rings represent tornadic debris signatures and outer vective storms. They described the tornadic supercell high-reflectivity rings indicate precipitation particles. structure that occurred on 29 May 2004 (tornado passed Bluestein et al. (2007) used dual-polarization X-band through the state of Oklahoma), and the one that traversed mobile Doppler radar to identify tornadoes in super- between the towns of Medicine Lodge, Kansas, and Harper cells. The authors observed F2- (east of Attica, Kansas) in southwestern Kansas on 12 May 2004. During these and F0-rated (southwest of Harper, Kansas) tornadoes two cases, they observed that the low values of rhv and Zdr on 12 May 2004, near southern Kansas. They also ob- in the tornado core indicate debris signatures, specifi- served the cyclonic (northeast of Geary and northwest cally that Zdr arc in FFD represents size sorting and that of Calumet, Oklahoma) and anticyclonic (north of high Zh (45–55 dBZ) and high Zdr (3–4 dB) values in FFD Calumet) tornadoes near central Oklahoma on 29 May indicate heavy precipitation. Burgess et al. (2002) observed 2004. In these tornado events, they found that the debris the characteristics of an Oklahoma City tornado that ring exhibited values of Zdr , 0.5 dB, rhv , 0.5, and occurred on 3 May 1999. They found that the minimum Zh ;40 dBZ. They also reported that precipitation wraps reflectivity in the tornado core describes the centrifuging around the weak echo hole. Wakimoto et al. (2015) pre- of radar scatterers. They also compared high-resolution, sented the relationship between the hook echo, weak close-range (8 km) observations (using DOW radars) to echo hole (WEH), weak echo column (WEC), and ro- low-resolution, long-range (17–59 km) observations [using tational couplet with visual tornadic characteristics. In Weather Surveillance Radar-1988 Doppler (WSR-88D)]. their study, they presented photogrammetric analysis of a From the comparison, they determined the advantage of devastating tornado that occurred near El Reno, utilizing close-range observations and presented the loss of Oklahoma, (on 31 May 2013) with X-band mobile polari- tornado information for long-range measurements. metric radar observations. They observed weak hook echo All of the above studies described tornadic storm and weak velocity couplet during the early stage of the features such as DRC, WEH or bounded weak echo tornado and strong hook echo and prominent velocity region (BWER), TDS, hook echo, velocity couplet, Zh couplet during the intensified tornado case. Tanamachi et al. rings, Zdr arc, and Zdr shield using polarimetric radar (2012) presented data from 10 tornado events by a single variables. We also observed all these features, which can

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1979

TABLE 1. Important specifications of KICT and GDK TABLE 2. Radar scanning specifications: 10-min scan strategy (KMA) radar. [1 volume per 5 min (2 PPIs 1 10 RHIs), 1.5 km CAPPI per 1 min (58 and 68 PPIs), PPI EL: 108 every 5 min for volume]. Parameter KICT GDK Time Scan strategy CAPPI Volume Frequency 9410 6 30 MHz 2887 MHz Transmitter tube Magnetron Klystron 5 min 1. PPI EL: 58, AZ: 08–3608 (1 min) — Peak power output 8.0 kW 750 kW 2. RHI EL: 08–1808, AZ: 08–1808 — s (per channel) 3. RHI EL: 1808–08, AZ: 1628–3428 — s Max range coverage 50 km 250 km 1. PPI EL: 68, AZ: 3248–323.98 (1, 2 min) — Gain 41 dB 45 dB 2. RHI EL: 08–1808, AZ: 3248–1448 — s Polarization Dual linear, H and Single 3. RHI EL: 1808–08, AZ: 1268–3068 — s V channel 1. PPI EL: 58, AZ: 2888–287.98 (2, 3 min) s Range resolution 60 m 250 m 2. RHI EL: 08–1808, AZ: 2888–1088 — s Antenna diameter 1.8 m 8.5 m 3. RHI EL: 1808–08, AZ: 908–2708 — s Pulse repetition 2.0 KHz Short 250–1200 (Hz) 1. PPI EL: 68, AZ: 2528–251.98 (3, 4 min) s (maximum) Long 250–550 (Hz) 2. RHI EL: 08–1808, AZ: 2528–728 — s 3-dB beamwidth 1.48 1.08 3. RHI EL: 1808–08, AZ: 548–2348 — s 1. PPI EL: 58, AZ: 2168–215.98 (4, 5 min) — 2. RHI EL: 08–1808, AZ: 2168–368 — s be useful to describe the characteristics of the tornadic 3. RHI EL: 1808–08, AZ: 188–1988 — s storm event. The majority of the abovementioned PPI EL: 108, AZ: 1988–197.98 — s 8 8 8 studies observed tornadic storms at long-range dis- 5 min 1. PPI EL: 6 , AZ: 180 –179.9 (5, 6 min) — 2. RHI EL: 08–1808, AZ: 1808–08 — s tance from the radar and at low antenna elevation. Few 3. RHI EL: 1808–08, AZ: 3428–1628 — s studies observed DRC and Zdr arc patterns. The pres- 1. PPI EL: 58, AZ: 1448–143.98 (6, 7 min) — ent study is significant in many ways. It presents the first 2. RHI EL: 08–1808, AZ: 1448–3248 — s observation of a rare tornado event over South Korea 3. RHI EL: 1808–08, AZ: 3068–1268 — s 8 8 8 s with the tornadic storm observed at a very close range 1. PPI EL: 6 , AZ: 108 –107.9 (7, 8 min) 2. RHI EL: 08–1808, AZ: 1088–2888 — s (about 5 km) from the radar. It describes the impor- 3. RHI EL: 1808–08, AZ: 2708–908 — s tance of the high-resolution observations over low- 1. PPI EL: 58, AZ: 728–71.98 (8, 9 min) s resolution measurements. This paper also presents the 2. RHI EL: 08–1808, AZ: 728–2528 — s intriguing polarimetric radar signatures (e.g., DRC, 3. RHI EL: 1808–08, AZ: 2348–548 — s 8 8 8 velocity couplet, and BWER, along with strong vertical 1. PPI EL: 6 , AZ: 36 –35.9 (9, 10 min) — 2. RHI EL: 08–1808, AZ: 368–2168 — s wind shear and dryline) of the tornadic storm event, 3. RHI EL: 1808–08, AZ: 1988–188 — s which can be useful for early warnings. The significance PPI EL: 108, AZ: 1988–197.98 — s of high spatiotemporal radar observations for determining short-lived and weak tornado events is also presented in the present study. This paper is organized (37.66888N, 126.73898E). It provides valuable informa- as follows: Section 2 presents the Korea Institute of tion by monitoring severe weather events, which is useful Civil Engineering and Building Technology (KICT) for forecasting and for providing early warnings for pos- radar system and prevailing synoptic conditions for sible disaster prevention. The KICT radar operates at a the tornadic storm event. Development of the storm, frequency of 9.41 GHz. Its typical operating radius and interpretation of tornado debris signatures, and other maximum range coverage are 40 and 50 km, respectively. tornadic features are described in section 3.Thesig- The radar transmits and receives signals in both hori- nificance of the high-resolution and close-range po- zontal and vertical polarizations. It also consists of a larimetric radar observations is also provided in section 1.8 m, front-fed parabolic antenna with a peak output 3. Finally, a summary and the conclusions of this study power of 8 kW per channel. It provides high spatial- and are presented in section 4. temporal-resolution data. Important specifications of the system are summarized in Table 1. The KICT radar produces 6 plan position indicator (PPI) and 10 hemi- 2. Schematic description of the KICT radar spheric (i.e., 08–1808 in elevation) range–height indicator system and synoptic conditions for the (RHI) scans every 5 min. During the duration of the tornado formation tornadic storm, the quasi-horizontal data collection (i.e., For the first time, KICT radar observed a tornado, PPIs) alternates between 58 and 68 elevation angles (EL) which occurred on 10 June 2014, over South Korea. every minute, with the range resolution of 60 m. RHI This radar is operated and monitored by KICT, and it is scans are collected at 188 intervals in azimuth (AZ). The located approximately 20.6 km northwest of Seoul details of radar scanning specifications are given in Table 2.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1980 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG. 1. (a) Relative humidity and temperature proﬁles (900 hPa) at 0300, 0600, 0900, and 1200 UTC derived from the MERRA reanalysis data. The dotted line indicates the dryline. The dashed lines indicate isotherms. The white spaces represent the absence of the data. (b) Surface pressure, temperature, and wind proﬁles (900 hPa) at 0300, 0600, 0900, and 1200 UTC derived from the MERRA reanalysis data. The solid color lines represent the isobars and dashed lines indicate isotherms. (c) Wind patterns from lower (900 hPa) to upper (400 hPa) heights at 0900 UTC derived from the MERRA reanalysis data.

The radar data are collected accounting for bias/error this phenomenon. Figure 1b illustrates that the high correction, the attenuation correction for rain (differ- pressure is characteristic of the west side of the Korean ential phase-based methodology), and data quality Peninsula, while inland Korean Peninsula experiences checking (Scarchilli et al. 1996) using algorithms detailed low pressure. The mixing of low-humidity (high pressure) by Chen et al. (2017). air with high-humidity (low pressure) air near the dryline The synoptic conditions have been described using may develop strong updrafts. We also observed the wind surface weather maps before and after tornado outbreak. patterns prior to the tornado outbreak. The wind patterns Figure 1a represents the relative humidity and temper- from lower to upper heights at 0900 UTC are shown in ature at 0300–1200 UTC. The dryline (dotted line) Fig. 1c. At lower heights (900 and 800 hPa) over the separates the high-humidity and low-humidity environ- mainland of the Korean Peninsula, the winds traverse at 2 ments. The west side of the Korean Peninsula experiences speeds of ;5ms 1 in the west and northeast directions. hot, dry air with low humidity and high temperature, while At a height of 700 hPa, the winds travel in the southeast 2 the mainland of the Korean Peninsula experiences warm, direction at a speed of ;7ms 1, while at 600 hPa, the 2 moist air consisting of high humidity and low tempera- winds are ;7ms 1 and eastward. At upper heights (500 2 tures. The dry and moist air converge along the dryline and and 400 hPa), the wind speed is strong at ;15 m s 1 causes instability on the ground, which is conducive to toward the east and northeast. Thus, Fig. 1c represents the development of storm events. Further, we used that the strong vertical wind shear exists prior to the de- surface pressure, temperature, and winds to examine velopment of the tornado with the upper-level winds

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1981

FIG.1.(Continued) blowing at high velocities relative to the low-level winds photographs of the tornado are shown in Fig. 2.The and the direction changes from lower to upper heights. center of the tornado and debris cloud reaching the This implies that the strong rotating updrafts lift the warm, ground are presented in Fig. 2a. The location of moist air (over the mainland of the Korean Peninsula) the tornado (the destroyed greenhouses) and the KICT into the thundercloud. The image of the mother cloud of radar are shown in Fig. 2b. The path of the tornado the tornado is shown in Fig. 2a. (during the mature stage) is depicted in Fig. 2c.The photographs depicting the damaged greenhouses and the hail (size ;1.5 cm) associated with this event are pre- 3. X-band polarimetric radar observation: Tornado sented in Figs. 2d and 2e, respectively. Data were col- signatures and analysis lected for the total tornadic storm duration from 1010 to

A tornado associated with a low-level mesocyclone 1059 UTC. The Zh, Zdr, rhv, V, and spectrum width (SW) passed through the Goyang province about 5.3 km were recorded for the total duration of the storm. northwest of the KICT radar. This tornado persisted a. Mesocyclone identiﬁcation for about 18 min, during which several people were injured and at least 20 greenhouses were destroyed. The It is interesting to look at these radar observations from tornado rated at F0 on the Fujita scale. The YTN News the perspective that it takes short-range measurements

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1982 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG.1.(Continued)

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1983

FIG. 2. (a) Images of debris cloud extending to the ground (YTN News), inset of the figure represents the mother cloud of the tornado. Arrows represent the funnel cloud. (b) Location of the tornado (destroyed greenhouses) from KICT, (c) path of the tornado over the Korean Peninsula, (d) destroyed greenhouses, and (e) hail associated with the event with the size of 1.5 cm. to detect this phenomenon (mesocyclone). The pres- invariant with respect to horizontal viewing angle ence of mesocyclones in supercells is often identified (shear pattern could be unchanged for the viewing 2 by hook echoes, a velocity couplet, and a weak echo angle ,458); and vertical vorticity greater than 0.01 s 1. region(WER)orBWER.Tornadoesmaybeassoci- These features and the criteria were met for this par- ated with a low-reflectivity eye (or WEH). Donaldson ticular storm case, and the storm produced 1.5-cm

(1970) and Suzuki et al. (2000) delineated the criteria hail. Furthermore, we have observed DRC and Zdr to detect tornado vortex signatures: persistence of a arc patterns (details are presented in the following velocity couplet, consisting of inbound and outbound sections). velocities with at least two consecutive elevation an- A mesocyclone was formed prior to the development gles and two subsequent scans; vortex shear pattern of the tornado. Figure 3 shows the variability of the

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1984 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG. 3. Evolution of (a) the rotational velocity and (b) the vorticity with respect to time for the total storm event.

rotational velocity Vrot and vertical vorticity with vortex signature can be identified from a velocity cou- respect to time. The Vrot and vorticity are computed plet. The radar can measure the maximum unambiguous from the velocity couplet, Doppler velocity, which in the case of this storm event 2 was measured to be ;32 m s 1. Figure 3a shows the V 2 V V 5 max min , V 5 maximum velocity and increase of the rotational velocity (1025 UTC and af- rot 2 max terward) indicating the intensification of the tornado 5 Vmin minimum velocity , and vortex signature (TVS). From 1034 to 1040 UTC, it can ; 21 (1) be observed that the maximum in Vrot ( 24 m s ) implies strong TVS. During this time, the gate-to-gate 2(V 2 V ) wind shear (2 3 V or absolute difference between vertical vorticity 5 max min , (2) rot D Vmax and Vmin) also peaks with the maximum value 2 5 of ;48 m s 1. D distance between Vmax and Vmin . b. Evolution of the tornado Figure 3 represents the characteristics of the mesocyclone and tornado evolution pattern. According to Suzuki The development and dissipation stages of the tor- et al. (2000), Lee and White (1998),andDonaldson nado are rendered as conceptual diagrams of the po- (1970), the condition for mesocyclone detection is that larimetric radar variables. The conceptual diagrams of 21 vorticity should be greater than 0.01 s , as mentioned Zh, Zdr,andrhv are shown in Fig. 4. Figure 4a indicates above. This condition is achieved for the present storm the reflectivity associated with the DRC phenomenon event. Figure 3b shows that at 1010 UTC the vorticity is during the early stage of the tornado. Figure 4b rep- 2 0.05 s 1, denoting the onset of the mesocyclone. This resents most common features of tornadoes, such as vorticity is mostly consistent up to 1026 UTC, which WEH, debris, size soring, raindrops, and the Zdr arc indicates the onset of tornadogenesis. This tornado- exhibited in the polarimetric variables during the ma- genesis phenomenon is explained using the DRC pat- ture stage of the tornado and are mostly similar to tern in the following sections. From 1026 to 1033 UTC, Tanamachi et al. (2012). Additionally, circular rings the increasing trend of vorticity illustrates the in- are rendered in Zh as was done by Wurman and Gill tensification of the tornado (see next section). From (2000). A detailed description of all of these features is 1033 to 1040 UTC, vorticity is mostly constant, sug- given in the following sections. The early stage of the gesting the consistency of the tornadic pattern. After tornado has been described using PPI scans of mea-

1040 UTC, a trend of decreasing vorticity demonstrates sured Zh and V (shown in Fig. 5). In this stage, a weak the dissipation of the tornado. This pattern can also be hook echo and weak velocity couplet are formed along observed in rotational velocity (Fig. 3a). The tornado the vortex. The couplet, consisting of weak inbound

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1985

FIG. 4. Conceptual models of reflectivity, differential reflectivity, and copolar correlation coefficient of the tornado based on this case study. (a) (left) The PPI scan of reflectivity at 1028 UTC, and (right) the DRC pattern in Zh prior to tornadogenesis. (b) Tornadic features during mature stage: (left) WEH and concentric rings associated with the debris and hydrometeors, (middle) Zdr with the WEH, circular rings (debris and hydrometeors), and Zdr arc pattern, and (right) rhv with the WEH, debris, and hydrometeors signatures. and outbound velocities, represents the production of may be associated with the velocity couplet can indicate the weak rotating updraft. Additionally, we have also tornadogenesis. Rasmussen et al. (2006), Kennedy et al. observed the presence of DRC during the early stage (2007), Byko et al. (2009), Forbes (1981), and Lemon of the tornado. and Doswell (1979) documented the DRC signature in their studies using WSR-88D data. Byko et al. (2009) 1) DRC PATTERN noticed DRC using mobile, truck-borne radars (DOW Rasmussen et al. (2006) found that DRC is a blob-like radars). They presented high-resolution radar observa- echo segregated from the main echo, which evolves to tions (DOW) compared to Rasmussen et al. (2006) form as hook echo. They suggested that some DRCs that observations (WSR-88D). In this study, we are providing

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1986 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG. 5. (a)–(d) Evolution of the DRC pattern from 1022 to 1025 UTC. (left) PPI scans of reflectivity and (right) Doppler velocity with elevation angles 58 and 68. The marked circle in reflectivity represents the DRC and is also shown at the corresponding position in velocity data. (e)–(h) Evolution of the DRC pattern from 1026 to 1029 UTC. (left) PPI scans of reflectivity and (right) Doppler velocity with elevation angles 58 and 68. The marked circle in reflectivity represents the DRC and is also shown at the corresponding position in velocity data. The curved arrows in the velocity data indicate counterrotating vortices.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1987

FIG.5.(Continued)

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1988 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35 high-resolution X-band dual-polarization radar observa- ﬂank of updraft region (Lemon and Doswell 1979; tions to explore the DRC phenomenon. Rasmussen et al. Rasmussen et al. 2006; Byko et al. 2009). In the present (2006) observed the DRC at a long range of ;100 km study, we also assert that the hydrometeors from the from the radar, while Byko et al. (2009) noticed different main echo descend toward the rear side of the storm

DRCs at various distances ranging from 5 to 22 km from to develop the DRC pattern. The Zh, Zdr, and rhv cor- the DOW. In the present study, we observed the DRC responding to the DRC pattern are ;20 dBZ, ;2.5 dB, pattern at a very close range of ;5 km to the radar. Un- and ;0.9, respectively, indicating the presence of the like previous researchers who detected DRCs with low hydrometeors. elevation angles (0.58 and 1.58), this study used 58 and 2) BWER AND ECHO OVERHANG 68 elevation angles, which can catch the DRC pattern, possibly because of its high spatiotemporal resolution and From Fig. 5, it can be seen that the hook echo ex- close range observations. tended toward the south and rear side of the storm may Rasmussen et al. (2006) proposed three objective be referred to as echo overhang (Browning 1964), which conditions to describe DRC pattern: (i) An enhanced presents above WER. The corresponding vertical reflectivity pattern pendant from the echo overhang structure (RHI scan) at 1027 UTC is shown in Fig. 6. above WER, (ii) DRC pattern exceeding the minimum Figure 6a illustrates the presence of echo overhang on reflectivity by at least 4 dB following along the path of or above the low-reflectivity region, and the low- greatest reflectivity from the DRC reflectivity maximum reflectivity region surrounded (sides and top) by high- to the supercell echo core, and (iii) existence of DRC in reflectivity echoes may indicate BWER, which is often the rear right quadrant of the storm updraft. Rasmussen associated with updraft. The corresponding spectrum et al. (2006) and Byko et al. (2009) have expanded upon width (Fig. 6e), where the large spectrum width in- the DRC characteristics using reflectivity isosurface dicates strong upward flow of the wind, also supports the plots. Though we have not presented the isosurfaces of possibility of BWER presence. Figure 6c (Doppler ve- the reflectivity, the DRC pattern observed in this study locity) represents the convergence of the wind, which met the criteria put forth by Rasmussen et al. (2006). may indicate strong rotation of the wind updraft aloft. Figure 5 shows the evolution of the DRC pattern. The strong rotation of the wind can increase vertical Figure 5a represents the development of the hook echo vorticity, as observed from the vorticity pattern (Fig. 3), at 1022 UTC, where there is no appearance of the DRC where the enhancement of vorticity is observed at signature. At 1023 UTC [Fig. 5b(1)], a maximum re- 1027 UTC. The intense rotational updraft lifts the hy- flectivity echo of ;5dBZ is present at the rear flank of drometeors (hail, rain, and ice) and debris aloft into the the echo appendage, which appears like a dot-like echo storm. The tiny hydrometeors may fall down through detached from the main echo. This echo satisfies the the echo overhang and are recirculated into the cloud DRC criteria, given that it descends from the echo cap by the updraft flow. On the other hand, large raindrops/ and appears above WER, echo reflectivity (;5dBZ)is hail fall downward regardless of the updraft wind greater than the path of echo appendage reflectivity (Conway and Zrnic´ 1993). From Fig. 6, it is clearly evi-

(,0dBZ) by about 5 dBZ, and lies at rear right quadrant dent that above 3 km, the presence of Zdr , 0.5 dB, of the storm. Additionally, this echo is associated with rhv , 0.8, and high Zh . 40 dBZ represents the TDS wind shear present in Doppler velocity with a weak (shown as ellipse; Bluestein et al. 2007; Schultz et al. velocity couplet that consists of inbound and outbound 2012), where the debris is transported to upper heights velocities (counterrotating velocity vortices) shown in through the updraft flow as mentioned above. The de- Fig. 5b(2). The progress of the DRC pattern is clearly bris signature associated with the tornadic touchdown visible from Fig. 5c to Fig. 5h. The DRC is apparent in has dimensions of horizontal size of about 1 km and Figs. 5g and 5h with a significant echo pattern. Figure 4a vertical extent of 1.5–2.5 km. shows the conceptual diagram of the DRC pattern. 3) INTENSIFICATION OF THE STORM From all these determinations (Fig. 5), it is inferred that the isolated reflectivity represents the DRC pattern. The The storm intensifies at 1030 UTC (see Fig. 3).

DRC connects with the main core and forms a hook- Figure 7 shows Zh, Zdr, V, and rhv scans at 1032 UTC, shaped echo during the intensification of the tornado. which represent the intensified tornado vortex. Figure 7a The rotational velocity presented in Fig. 3a shows an exhibits a well-defined hook echo and WEH in TVS and abrupt increment at 1029 UTC that may be due to the reflectivity gradient in the forward flank. Additionally, DRC phenomenon. This kind of feature is also observed intensified inbound and outbound velocities appear along by Rasmussen et al. (2006). The DRC formation may be the velocity couplet (Fig. 7c). The well-defined hook echo caused by deposition of the hydrometeors in the rear can indicate the mature stage of the tornado (Forbes

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1989

FIG. 6. The RHI scan of (a) reﬂectivity, (b) differential reﬂectivity, (c) Doppler velocity, (d) copolar correlation

coefﬁcient, and (e) SW at 1027 UTC. The inset of (a), shows the relative PPI scan of Zh, where the solid line indicates azimuthal direction of 3068–1258 is taken for RHI scan. In (a), BWER and echo overhang are represented by white and black markers, respectively. The convergence of the wind is represented by arrow markers in (c). The arrow marker in (e) indicates the presence of the updraft ﬂow. Ellipse illustrates the TDS.

1981; Markowski 2002; Broeke et al. 2008). During this WEH indicate the presence of rain or rain-and-hail stage, from Fig. 7, it can be seen that the hook echo mixed hydrometeors (Tanamachi et al. 2012). composed of low Zdr (;0 dB) and low rhv (,0.7) impli- From these observations, it is inferred that the low and cates the presence of randomly oriented nonmeteoro- high values of Zdr and rhv inside the tornado vortex il- logical scatterers lofted into the tornado core. This is lustrate lofted TDS (low values) and hydrometeors also evident from the SW pattern (Fig. 7e), which (high values), respectively (Kumjian and Ryzhkov 2008; 2 shows high values of SW .2ms 1 inside the TVS. It Bluestein et al. 2007; Ryzhkov et al. 2005; Tanamachi is also noted from Fig. 7 that the presence of high et al. 2012). The visual interpretations of the TDS can be values of Zdr (.2dB) and rhv (.0.9) around the seen in Fig. 4b.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1990 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG. 7. The PPI scans of (a) reflectivity, (b) differential reflectivity, (c) Doppler velocity, (d) copolar correlation coefficient, and (e) SW during the mature stage of the tornado (1032 UTC).

The aforementioned features (debris and precipita- region (,0dBZ), which is surrounded by high-reflectivity tion) are comprehensively described using the signifi- rings. The expanded view of the tornado vortex of Zh at cant characteristic of Zh rings. The Zh shown in Fig. 7 1032, 1033, 1034, 1035, and 1036 UTC scans is shown in represents the tornado core comprising a low-reflectivity Fig. 8. The inner low-reflectivity ring around the WEH,

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1991

FIG. 8. Expanded view of radar reflectivity shows ring patterns during the mature stage of the tornado (from 1032 to 1036 UTC). The inner low-reflectivity ring (debris) is surrounded by high-reflectivity rings (rain). which represents the debris signatures, is also called the 2000). The high-reflectivity rings are observed with re- debris ring. This ring also indicates that the debris is flectivity of ;15, ;25, and ;35 dBZ. They are associated centrifuged radially outward and upward in a cylindrical with a strong velocity couplet (not shown) and suggest manner from the center of the vortex (Wurman and Gill the presence of centrifuged hydrometeors and other

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1992 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35 scatterers (Snyder et al. 2010; Snow 1984; Dowell et al. Figure 9 also shows the high Zdr values present in the 2005). These ring-like patterns are also observed by forward ﬂank of the hook echo, which may be referred

Bluestein et al. (1993), Wurman et al. (1996),and to as the Zdr shield. Several authors (Kumjian and Wurman and Gill (2000). It can be noted that there is an Ryzhkov 2008; Broeke et al. 2008; Schuur et al. 2001) increase of reﬂectivity observed from inner rings to have observed these high Zdr features using S-, C-, and outer rings, as described above. The 1032 UTC scan X-band radars. Kumjian and Ryzhkov (2008) reported shows that the WEH is surrounded by semicircular (near that the Zdr arc is positively related to low-level storm- circular) rings, whereas the 1034, 1035, and 1036 UTC relative environmental helicity and also indicates an scans show the semicircular rings are converted into increase in streamwise vorticity. Romine et al. (2008) full circular rings. The ring-like patterns are visually stated that collision–coalescence of melted water drops rendered in the conceptual diagram (Fig. 4b). To the increases Zdr (high Zdr shield), while breakup decreases north of the tip of the hook, the high Zh (.30 dBZ) and Zdr, with a resulting balancing effect. Tanamachi et al. high Zdr (.3 dB; not shown) presented (especially at (2012) hypothesized that the high Zdr shield is caused by 1035 UTC) may represent the presence of centrifuged collision–coalescence and breakup processes (CCB) of large raindrops or the mixture of rain and hail. During raindrops. Thus, we speculate that the Zdr shield (Fig. 9) dissipation of the tornado, the weak echo region and the represents the large raindrops in the forward ﬂank of the rings have disappeared (1040 UTC and afterward). storm produced by melting of hail.

4) ZDR ARC SIGNATURE 5) HAIL SIGNATURE

Another striking feature, the Zdr arc, has been ob- Hail signatures are usually found at higher Zh served in this tornadic storm event. The Zdr arc may not (.45 dBZ), lower Zdr (22–0.5 dB), and lower rhv (0.9–0.96) be present in all tornadoes and is a rapid phenomenon. than in rain (Bringi and Chandrasekar 2001; Mason 1971).

Occasionally, it is also present in nontornadic storms. The According to Ryzhkov et al. (2005), rhv does not drop high Zdr arc pattern is observed at 1036 (Fig. 9a)and below 0.85 for hail signatures. We have observed these 1037 UTC (Fig. 9b). Figure 9 clearly shows that the high hail features from the polarimetric measurements dur-

Zdr arc appears along the southern edge of FFD and is ing intensification of the storm (1030 UTC). Figure 10 collocated with the high spatial gradient of Zh.TheZdr shows the high Zh (.50 dBZ), low Zdr (;0 dB), and low arc signature is indicative of strong, low-level wind shear, rhv (,0.96) values at the 1030 UTC scan (marked with as a result of fast size sorting of hydrometeors. The up- an ellipse). From these observations, it can be inferred draft also plays an important role in the formation of the that values of high Zh,lowZdr,andlowrhv signal the hail Zdr arc. The large hydrometeors descending from the reaching to the ground. The ground observation of the hail cloud will rapidly reach the ground, because of their associated with this tornadic storm is shown in Fig. 2d, higher terminal fall velocity. Since the large drops expe- which indicates the diameter of the hail to be ;1.5 cm. rience less time in the air, these drops are not advected by The tornado occluded and dissipated 1040 UTC and the winds. On the other hand, the updraft continues to afterward, which can be observed from the vorticity suspend the smaller particles aloft for a longer period of pattern in Fig. 3. From 1041 UTC, the decreasing trend time, because of their lower fall speeds. Therefore, the of vorticity illustrates the dissipation of the storm. smaller drops are advected farther by the updraft than During this stage, the hook echo and the WEH features larger drops, such that the smaller particles are trans- weakened and finally disappeared. The velocity couplet ported farther downstream, deeper into the storm is less prominent and reflectivity rings also disappear (Browning 1964). This leads to sorting of the particles during this stage. Additionally, the debris is replaced by based on size, where the larger particles are placed below the raindrops. the smaller hydrometeors. Thus, the larger hydrometeors c. The significance of the high-resolution and produce high Z arc signatures. These high Z arc values dr dr close-range observations at ;4dBandgreaterin Fig. 9 represent the larger raindrops or hail. Further, high rhv (;0.95; figure not shown) This section focuses on the comparison between the associated with Zdr arc also indicates the larger raindrops. close-range (high resolution) and long-range (low reso- The strong inbound and outbound velocity (figure not lution) observations of the tornadic storm event. KICT shown) corresponding to the Zdr arc represent the stronger radar produces both high temporal- and spatial- rotation of the winds and size sorting of the particles. The resolution observations. The Gwangduk-san (GDK) magnitude and curvature of the Zdr are indicative of the radar (S band) is operated and monitored by the Korea potential of the low-level rotation. The visual renderings of Meteorological Administration (KMA) in South Korea.

Zdr arc pattern shown in Fig. 4b. The GDK radar produces lower radial and temporal

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1993

FIG. 9. PPI scans of (left) differential reﬂectivity and (right) reﬂectivity at 1036 and 1037 UTC. The black marker

in Zdr represents the Zdr arc pattern, with the same position marked in Zh. The arrow mark in Zdr indicates the Zdr shield in FFD. observations compared to KICT radar. The location of ;5 and ;75 km away from the KICT and GDK radars, the tornado was closer to the KICT radar (;5 km) than respectively. Figure 11b shows the reflectivity and the GDK radar (;75 km). Hence, the KICT radar could Doppler velocity patterns at the mature stage of the better observe the tornado with its high temporal and tornado. The PPI reflectivity and velocity scans of GDK spatial resolution. The maximum coverage range of the (left column of panels) and KICT radars (right column GDK radar is 240 km, with range and azimuthal reso- of panels) were performed at 1030 UTC. The GDK ra- lutions of 250 m and ;18, respectively. The GDK radar dar scans are performed at 08 elevation, while the KICT operates at 15 elevation angles from 08 to 24.98 over a radar scans are performed at 58 and 68 elevations. The period of 10 min. Altitude of the KICT radar is 50 m left (GDK observations) and right column (KICT ob- above mean sea level (MSL), whereas that of the GDK servations) of the chart correspond to range resolutions radar is 1030 m (MSL). The important specifications and of 250 and 60 m, respectively. A well-defined hook echo the differences between the KICT and GDK radars are and an intensified velocity couplet are observed from the shown in Table 1. KICT radar observations. Even though GDK radar Figure 11a shows the overlapping area between the shows an obscured hook echo, it is not possible to de- ranges of the KICT and GDK radars. Because of the scribe tornadic features from this data, and there is no short range of KICT radar, higher-resolution tornado clear evidence of velocity couplet signature. The green observations could be obtained. The radars are sepa- rhombus in the GDK radar plots indicates the location rated from each other by 79 km. The tornado formed of the KICT radar and the rectangular box represents

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1994 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

FIG. 10. The full RHI scans (08–1808 scan) along the 758–2518 azimuth of (a) reflectivity, (b) differential reflectivity, (c) Doppler velocity, (d) copolar correlation coefficient, and (e) SW at 1030 UTC (during storm intensification).The black ellipse indicates the presence of the rain/hail signature. the observational area covered by the KICT radar, GDK radar. The KICT radar has 60-s time resolution, where the tornado was formed. From these observa- whereas the GDK radar has 10-min time resolution. tions, it is important to note that the close range and Additionally, the range resolution of the KICT radar high-resolution observations are advantageous over (60 m) is better than that of the GDK radar (250 m). low-resolution measurements to describe the tornadic Furthermore, the KICT radar can provide a closer look features, and that it is possible that the low-resolution into the details of the tornadic events. Therefore, it is observations may lose tornadic information. From quite evident that the KICT radar with high-resolution Fig. 11b, it is observed that the KICT radar with observations is advantageous in its capacity to more high resolution has the following advantages over the clearly show the features of tornadic storms.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1995

FIG. 11. (a) Observation overlapping coverage areas of KICT (small blue circle) and GDK (big black circle). (b) Comparison of GDK and KICT radar observations during mature/developing stage of the tornado (1030 UTC). (left) GDK radar observations (at 08 elevation) and (right) KICT radar observations (at 58 elevation). (top) Re- ﬂectivity and (bottom) Doppler velocity. Green triangle markers and rectangular boxes shown in GDK observations indicate location and observation area of the KICT radar, respectively.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1996 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35

4. Summary and conclusions Chen and Chandrasekar (2016). We also advocate that the high spatial and temporal radar observations have For the first time, a tornadic storm was observed by great potential for determining short-lived and weak the high-resolution KICT X-band dual-polarization ra- tornadic storms. The DRC associated with velocity dar on 10 June 2014 over the Korean Peninsula. The 2 couplet (vorticity . 0.01 s 1) and WER signatures along structure of the tornado was analyzed using polarimetric with strong vertical wind shear can be used for early variables such as Z , Z , r , V, and SW. The present h dr hv warning of tornadic storm event. The hook echo and study drew from several conclusions presented by pre- debris signatures represent the intensity of the tornado. vious research studies. The structure of the tornadic We also conclude that the high-resolution radar obser- storm was most similar to the conceptual model de- vations are more useful to the forecasters for accurate scribed by Tanamachi et al. (2012). The presence of estimation of the severe weather events. DRC associated with WER and velocity couplet com- Additional data are required to describe the detailed posed of counterrotating vortices may indicate torna- structure of the tornadic storm events over this region. dogenesis. The precipitation falls through the rotating For future studies, we suggest that numerical simulation updraft, with hydrometeors that descend from the main models are required to comprehensively characterize echo to form the DRC (similar to Rasmussen et al. the tornado formation, development, and dissipation. 2006). Vorticity pattern reveals the evolution of the Additionally, three-dimensional patterns of the data to tornado associated with a mesocyclone. In accordance clearly describe the debris signatures, wind, and inten- with Ryzhkov et al. (2005), high-spatial-resolution radar sity of the tornado are also needed. More statistical observations required to detect TVS were also observed studies are recommended to explore the relation be- in the present study. The intensified tornado is observed tween the DRC and tornadogenesis. This information by the strong inbound and outbound velocities of the could be helpful to forecast the tornadic storm and its couplet and a well-defined hook echo at tornado vortex. potential damage on the ground. The peak inbound and outbound velocities generated 6 21 by the tornado were measured to be 24 m s . The Acknowledgments. This work was supported by KICT BWER associated with the strong updraft indicates the Strategic Research Project (Development of Driving transportation of the debris and hydrometeors aloft. Environment Observation, Prediction and Safety Tech- Ryzhkov et al. (2005) concluded that if the location of nology Based on Automotive Sensors). The participation the tornado is at a long distance from the radar, then of V. Chandrasekar is supported by the Hazard SEES those observations cannot be useful to detect the debris program. and size sorting of the hydrometeors. In the current study, the tornado was located very close to the radar REFERENCES at a distance of about 5 km. The low values of Zdr and rhv presented in the weak echo region illustrate the lofted Bluestein,H.B.,J.G.Ladue,H.Stein,D.Speheger,andW.F.Unruh, tornadic debris signatures (Bluestein et al. 2007; 1993: Doppler radar wind spectra of supercell tornadoes. Mon. Tanamachi et al. 2012; Ryzhkov et al. 2005). The exis- Wea. Rev., 121, 2200–2222, https://doi.org/10.1175/1520-0493(1993) 121,2200:DRWSOS.2.0.CO;2. tence of the Zdr arc at the rear side of the FFD reveals ——, M. M. French, R. L. Tanamachi, S. Frasier, K. Hardwick, the development of low-level rotation and the hydro- F. Junyent, and A. L. Pazmany, 2007: Close-range observa- meteor size sorting (Ryzhkov et al. 2005; Kumjian and tions of tornadoes in supercells made with a dual polarization, Ryzhkov 2008). Inside the hook echo, the WEH is sur- X-band, mobile Doppler radar. Mon. Wea. Rev., 135, 1522– 1543, https://doi.org/10.1175/MWR3349.1. rounded by high Z and Z rings. These high Z and Z h dr h dr Bodine, D. J., R. D. Palmer, and G. Zhang, 2014: Dual-wavelength rings associated with the strong velocity couplet repre- polarimetric radar analyses of tornadic debris signatures. sent the centrifuged hydrometeors (Tanamachi et al. J. Appl. Meteor. Climatol., 53, 242–261, https://doi.org/ 2012). Features of the hail are described from low Zdr 10.1175/JAMC-D-13-0189.1. Bringi, V. N., and V. Chandrasekar, 2001: Polarimetric Doppler collocated with high values of Zh and low rhv. The KICT Weather Radar: Principles and Applications.Cambridge radar observations (high resolution and short range) University Press, 636 pp. clearly describe the features of the storm, which the Browning, K. A., 1964: Airflow and precipitation trajectories GDK radar observations cannot sufficiently do (low within severe local storms which travel to the right of the resolution and long range). From analysis of the results, winds. J. Atmos. Sci., 21, 634–639, https://doi.org/10.1175/ , . it is clear that the high-spatiotemporal, low-altitude, and 1520-0469(1964)021 0634:AAPTWS 2.0.CO;2. Burgess,D.W.,M.A.Magsig,J.Wurman,D.C.Dowell,and close-range radar observations were very useful for Y. Richardson, 2002: Radar observations of the 3 May 1999 tornado detection, as also shown by the Collaborative Oklahoma City tornado. Wea. Forecasting, 17, 456–471, https:// Adaptive Sensing of the Atmosphere (CASA) program doi.org/10.1175/1520-0434(2002)017,0456:ROOTMO.2.0.CO;2.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L . 1997

Byko, Z., P. Markowski, Y. Richardson, J. Wurman, and E. Adlerman, Rasmussen, E. N., J. M. Straka, M. S. Gilmore, and R. Davies- 2009: Descending reflectivity cores in supercell thunderstorms Jones, 2006: A preliminary survey of rear-flank descending observed by mobile radars and in a high-resolution numerical reflectivity cores in supercell storms. Wea. Forecasting, 21, simulation. Wea. Forecasting, 24, 155–186, https://doi.org/10.1175/ 923–938, https://doi.org/10.1175/WAF962.1. 2008WAF2222116.1. Romine, G. S., D. W. Burgess, and R. B. Wilhelmson, 2008: A dual- Chen, H., and V. Chandrasekar, 2016: Real-time tornado detection polarization-radar-based assessment of the 8 May 2003 and wind retrieval with high resolution X-band Doppler radar Oklahoma City area tornadic supercell. Mon. Wea. Rev., 136, network. Proc. Int. Geoscience and Remote Sensing Symp., 2849–2870, https://doi.org/10.1175/2008MWR2330.1. Beijing, China, Institute of Electrical and Electronics Engineers, Ryzhkov, A. V., T. J. Schuur, D. W. Burgess, and D. S. Zrnic´, 2005: 2150–2153, https://doi.org/10.1109/IGARSS.2016.7729555. Polarimetric tornado detection. J. Appl. Meteor., 44, 557–570, ——, S. Lim, V. Chandrasekar, and B. J. Jang, 2017: Urban hydro- https://doi.org/10.1175/JAM2235.1. logical applications of dual-polarization X-band radar: Case Scarchilli, G., V. Gorgucci, V. Chandrasekar, and A. Dobaie, 1996: study in Korea. J. Hydrol. Eng., 22, E5016001, https://doi.org/ Self-consistency of polarization diversity measurement of 10.1061/(ASCE)HE.1943-5584.0001421. rainfall. IEEE Trans. Geosci. Remote Sens., 34, 22–26, https:// Conway,J.W.,andD.S.Zrnic´, 1993: A study of embryo production and doi.org/10.1109/36.481887. hail growth using dual-Doppler and multiparameter radars. Mon. Schultz, C. J., and Coauthors, 2012: Dual-polarization tornadic Wea. Rev., 121, 2511–2528, https://doi.org/10.1175/1520-0493(1993) debris signatures part I: Examples and utility in an operational 121,2511:ASOEPA.2.0.CO;2. setting. Electron. J. Oper. Meteor., 13, 120–137. ö Donaldson, R. J., Jr., 1970: Vortex signature recognition by a Schuur, T. J., A. V. Ryzhkov, D. S. Zrnic´, and M. Sch nhuber, Doppler radar. J. Appl. Meteor., 9, 661–670, https://doi.org/ 2001: Drop size distributions measured by a 2D video dis- 10.1175/1520-0450(1970)009,0661:VSRBAD.2.0.CO;2. drometer: Comparison with dual-polarization radar data. Dowell, D. C., C. R. Alexander, J. M. Wurman, and L. J. Wicker, J. Appl. Meteor., 40, 1019–1034, https://doi.org/10.1175/ 1520-0450(2001)040,1019:DSDMBA.2.0.CO;2. 2005: Centrifuging of hydrometeors and debris in tornadoes: Snow, J. T., 1984: On the formation of particle sheaths in columnar Radar-reflectivity patterns and wind-measurement errors. Mon. vortices. J. Atmos. Sci., 41, 2477–2491, https://doi.org/10.1175/ Wea. Rev., 133, 1501–1524, https://doi.org/10.1175/MWR2934.1. 1520-0469(1984)041,2477:OTFOPS.2.0.CO;2. Forbes, G. S., 1981: On the reliability of hook echoes as tornado Snyder, J. C., H. B. Bluestein, G. Zhang, and S. J. Frasier, 2010: indicators. Mon. Wea. Rev., 109, 1457–1466, https://doi.org/ Attenuation correction and hydrometeor classification of high- 10.1175/1520-0493(1981)109,1457:OTROHE.2.0.CO;2. resolution, X-band, dual-polarized mobile radar measurements Houser, J. L., H. B. Bluestein, and J. C. Snyder, 2016: A finescale radar in severe convective storms. J. Atmos. Oceanic Technol., 27, examination of the tornadic debris signature and weak-echo re- 1979–2001, https://doi.org/10.1175/2010JTECHA1356.1. flectivity band associated with a large, violent tornado. Mon. Wea. Suzuki, O., H. Niino, H. Ohno, and H. Nirasawa, 2000: Tornado- Rev., 144, 4101–4130, https://doi.org/10.1175/MWR-D-15-0408.1. producing mini supercells associated with Typhoon 9019. Kennedy, A., J. M. Straka, and E. N. Rasmussen, 2007: A statistical Mon. Wea. Rev., 128, 1868–1882, https://doi.org/10.1175/ study of the association of DRCs with supercells and torna- 1520-0493(2000)128,1868:TPMSAW.2.0.CO;2. does. Wea. Forecasting, 22, 1191–1199, https://doi.org/10.1175/ Tanamachi, R. L., H. B. Bluestein, J. B. Houser, S. J. Frasier, and 2007WAF2006095.1. K. M. Hardwick, 2012: Mobile, X-band, polarimetric Doppler Kumjian, M. R., and A. V. Ryzhkov, 2008: Polarimetric signatures radar observations of the 4 May 2007 Greensburg, Kansas, in supercell thunderstorms. J. Appl. Meteor. Climatol., 47, tornadic supercell. Mon. Wea. Rev., 140, 2103–2125, https:// 1940–1961, https://doi.org/10.1175/2007JAMC1874.1. doi.org/10.1175/MWR-D-11-00142.1 Lee, R. R., and A. White, 1998: Improvement of the WSR-88D me- Van Den Broeke, M. S., J. M. Straka, and E. N. Rasmussen, 2008: socyclone algorithm. Wea. Forecasting, 13, 341–351, https://doi.org/ Polarimetric radar observations at low levels during tornado , . 10.1175/1520-0434(1998)013 0341:IOTWMA 2.0.CO;2. life cycles in a small sample of classic southern plains super- Lemon, L. R., and C. A. Doswell III, 1979: Severe thunderstorm cells. J. Appl. Meteor. Climatol., 47, 1232–1247, https://doi.org/ evolution and mesocyclone structure as related to tornado- 10.1175/2007JAMC1714.1. genesis. Mon. Wea. Rev., 107, 1184–1197, https://doi.org/10.1175/ Wakimoto, R. M., N. T. Atkins, K. M. Butler, H. B. Bluestein, 1520-0493(1979)107,1184:STEAMS.2.0.CO;2. K. Thiem, J. Snyder, and J. Houser, 2015: Photogrammetric Lim, S., V. Chandrasekar, and V. N. Bringi, 2005: Hydrometeor analysis of the 2013 El Reno tornado combined with mobile classification system using dual polarization radar measure- X-band polarimetric radar data. Mon. Wea. Rev., 143, 2657– ments: Model improvements and in situ verification. IEEE 2683, https://doi.org/10.1175/MWR-D-15-0034.1. Trans. Geosci. Remote Sens., 43, 792–801, https://doi.org/10.1109/ Wurman, J., and S. Gill, 2000: Finescale radar observations of the TGRS.2004.843077. Dimmitt, Texas (2 June 1995), tornado. Mon. Wea. Rev., 128, Markowski, P. M., 2002: Hook echoes and rear-flank downdrafts: A 2135–2164, https://doi.org/10.1175/1520-0493(2000)128,2135: review. Mon. Wea. Rev., 130, 852–876, https://doi.org/10.1175/ FROOTD.2.0.CO;2. 1520-0493(2002)130,0852:HEARFD.2.0.CO;2. ——, J. M. Straka, and E. N. Rasmussen, 1996: Fine-scale Doppler Mason, B. J., 1971: The Physics of Clouds. 2nd ed. Oxford University radar observations of tornadoes. Science, 272, 1774–1777, Press, 671 pp. https://doi.org/10.1126/science.272.5269.1774.

Unauthenticated | Downloaded 10/07/21 07:51 PM UTC