The NOAA-National Geographic Society Waterspout Expedition (1993)

Abstract only small-medium-size waterspout funnels. Virtually no data were obtained for the waterspouts' spray This paper describes a field program conducted by NOAA and the vortices on the sea surface. The penetration data National Geographic Society in late August 1993 near Key West, found significant horizontal flow asymmetries, with Florida. The mission of the expedition was to obtain close-up peak values in one pass through a mature anticyclonic photographic documentation of waterspouts. Using a NOAA helicop- _1 ter as an observing platform, the participants dropped flares onto the waterspout of about 28 m s . Schwiesow et al. (1981) sea surface to visualize the airflow and filmed waterspouts using a found lidar-measured maximum velocities of up to state-of-the art motion picture camera and still cameras. Over a 29.6 m s"1 in waterspout funnels sampled aloft [aircraft dozen waterspouts/funnel clouds were observed, and the most altitudes were 95-615 m above mean sea level (MSL)]. detailed movies of spray vortices ever taken were obtained. Many questions remain about relationships between waterspout life cycle stages and associated velocity distributions with altitude in the vortex, de- 1. Introduction structive potential versus waterspout size and life cycle stage, and especially waterspout structure within Following a chance aerial encounter with a series of the parent cloud. Other questions arise concerning the waterspouts, Woodley et al. (1967) and Golden (1968) persistent wake noted by Golden (1974a) on the sea documented the structure and behavior of a large surface behind some intense spray vortices. waterspout that crossed Lower Matecumbe Key, The 1993 National Oceanic and Atmospheric Ad- Florida. Wind speeds up to 65 m s~1 were estimated by ministration (NOAA) National Geographic Society photogrammetry of movies taken from the light air- (NGS) waterspout expedition was a cooperative ven- craft, and an inferred three-dimensional conceptual ture born of both scientific interest and the needs of the model was also derived (Golden 1971). Subsequent society to gather unique photography for an upcoming studies shed light on the existence of intense anticy- television special, Cyclones (scheduled to air on NBC- clonic waterspouts and the existence of a waterspout TV in September 1995). The purpose of this unique life cycle (Golden 1974a,b). Later field experiments experiment was to use a stable platform, the NOAA/ confirmed the Lower Florida Keys as having the highest Aircraft Operations Center (AOC) Bell helicopter, annual waterspout frequency in the United States equipped with a special motion-suppressing camera (Golden 1977); moreover, data were taken with rug- mount and high-resolution Airreflex 16-mm movie ged instrumented aircraft penetrations (Leverson et camera, to photograph waterspouts at very close al. 1977) and with an airborne Doppler lidar (Schwiesow range. Both the photographic equipment and platform et al. 1981). The latter two field programs were con- used were unique for probing waterspouts at close ducted in the Key West, Florida, area during 1974 and range. In addition, a Cessna chase plane was com- 1976, respectively. Both were of very limited duration missioned by NGS and successfully filmed the heli- (about a week) and measurements were obtained for copter as it was orbiting waterspouts and recording high-speed movies. These data will be used in concert with concurrent still photography to obtain more accu- rate photogrammetric wind speed estimates than hith- 'National Oceanic and Atmospheric Administration, U.S. Weather Research Program Office, Silver Spring, Maryland. erto possible (Golden 1973, 1974b). +School of Meteorology, University of Oklahoma, Norman, Okla- homa Corresponding author address: Dr. Joseph H. Golden, NOAA/Office 2. Operations of Oceanic and Atmospheric Research, SSMC-3,1315 East-West Highway, Silver Springs, MD 20910. In final form 24 June 1994. The experiment ran from 22 to 28 August 1993. Our ©1994 American Meteorological Society base of operations was the National Weather Service

Bulletin of the American Meteorological Society 2269

Unauthenticated | Downloaded 10/04/21 12:00 PM UTC showers, the cameraperson TABLE 1. List of participants. experienced some discom- fort due to the high-speed impact of the raindrops. The Name Affiliation Role in experiment primary still photographer J. Golden NOAA, Silver Spring, Maryland Chief scientist, and "flare flinger" were movie cameraperson seated to the rear of the H. Bluestein University of Oklahoma, Still photographer cameraperson, completely Norman, Oklahoma inside the helicopter. The duration of each flight G. Van den Berg NOAA, MacDill Air Force Base, Florida Helicopter pilot was approximately 1.5 h, D. Barr NOAA, MacDill Air Force Base, Florida Helicoptercopilot and the typical maximum D. Konop NOAA, Silver Spring, Maryland Flare flinger, coordinator range from Key West was around 40-50 km (Marathon R. Wells National Geographic Society Director to the east, and the Dry R. Poole National Geographic Society Movie cameraperson Tortugas to the west). The R. Chisolm National Geographic Society Movie cameraperson flight level was usually just under cloud base, around A. Donnelly National Geographic Society Assistant cameraperson 500-600 m MSL. Cloud D. Lindstrom National Geographic Society Sound base was measured for later E. Bracken State University of New York at Albany, Still photography, use in photogrammetric New York audiotapes analysis. Potentially water- T. Arruza West Palm Beach, Florida Still photography spout-producing parent clouds included primarily T. Koenig National Geographic Society Producer lines of rapidly building cu- C. Taylor National Geographic Society Associate producer mulus congestus and, to a lesser extent, isolated rapidly building cumulus congestus (Golden 1974b). If (NWS) office in Key West, which is located at the the cumulonimbus stage had been reached, the cloud airport on the southeastern side of the island. A list of was not likely to produce a waterspout. Signs of participants in the field program is given in Table 1. incipient waterspout formation were dark spots on the Forecast decisions were made on the basis of surface sea surface (Golden 1974a) and, initially, condensa- and upper-air observations and selected numerical tion funnels at cloud base. When a waterspout was model output from models at the National Meteoro- particularly well defined, the helicopter descended to logical Center. Days with weak low-level vertical shear, within 100-200 m MSL and hovered to permit close- in the absence of any well-organized tropical distur- up photography of the spray vortex. Efforts were bances, were ideal for waterspout-active cloud line developments (Golden 1974b). In addition, early morn- ing and early and late afternoon were given priority, based on climatology (Golden 1973). One difference from all previous field experiments, which surprised us a bit, was that most of the successful waterspout encounters were during the midday lunch hour, whereas the peak occurrence frequency is normally from 1600 to 1900 EDT (Golden 1973). The missions were flown on a NOAA Bell 212 helicopter, which can hold two crew members and eight passengers. On board the helicopter, a 16-mm ARRI-SR H camera was specially mounted on a shock-stabilized platform, the side doors of the helicopter were completely open, and the operator of the scientific movie camera (usually the first author, Fig. 1) was seated with his feet resting outside the right-hand FIG. 1. Photograph of the helicopter, with J. Golden operating the side of the helicopter. During passages through rain movie camera (photograph copyright National Geographic Society).

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC always made to obtain still photographs that showed cloud base and the sea surface, to allow for subsequent photogrammetric analysis of the movie films. Flares were dropped in the vicinity of waterspouts during vari- ous stages of their life cycles. The flares used to visualize the low- level flow were Mark-58 saltwater- activated marine markers, which give off a narrow white smoke plume and last for about 20 min.

3. Summary of field program

The synoptic conditions re- mained undisturbed for the duration of the field program. Nearby soundings at Key West on the days we saw the largest waterspouts are shown in Fig. 2. These soundings, which are representative of all the soundings at Key West In- ternational Airport, were charac- terized by extremely weak vertical shear of the horizontal wind in the lower troposphere and abundant low-level moisture and convective instability in the lowest 3 km. Wind speeds were, at most, around 5 m s-1 below 500 mb, and the shear in the lowest 6 km was 5 m s_1 (6 km-1) or less. The low-level moist layer extended through a relatively deep layer; dewpoint depressions were generally on the order of 5°C at least up to 700 mb. The convective available potential energy of each sounding was in excess of 1500 J kg-1, with some as high as 3500- 3900 J kg-1. Thus, the nearby envi- ronments could thermodyna- mically support strong updrafts. A FIG. 2. NWS sounding at Key West for (a) 0800 EDT 24 August 1993 and (b) 0800 EDT key scientific question that could not 28 August 1993. Temperature (thick solid line) and dewpoint (thick dashed line), skewed be addressed by this experiment is abscissa in °C, and logarithmic ordinate in mb. Winds plotted to right; partial, half, and whole the mesoscale structure of the near wind barbs represent less than 2.5,2.5, and 5 ms-1, respectively. Wind speed in m s~1 plotted near wind barbs; tens unit of wind direction plotted at end of wind barbs. Waterspouts occurred environment of waterspout active to the west (a) for several hours later, and to the northeast (b) for an hour later. cloud lines (Simpson et al. 1986). Future field experiments should address this issue of the cloud line environment. It Corresponding surface data are plotted in Fig. 3 for should be noted that Key West will be getting one of the times of the two largest waterspouts. Pressures at the NWS NEXRAD Doppler radars in early 1996. all observing stations in south Florida were within 1-

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC 1.5 mb of each other during the entire experiment. 4. In the subset of all Table 2 observations for which Surface winds were nearly always under 5 ms-1. we could discern rotation, the rotation was cyclonic. Table 2 lists the 15 waterspouts/funnel clouds In one instance, two waterspouts were observed observed from the helicopter. The locations of some of side by side. Lightning was not noted when water- the more prominent waterspouts are indicated in Fig. spouts were in progress; lightning was rarely seen at

TABLE 2. Operations summary (all times given in EDT).

24 August 1993

Flight 1 • funnel cloud/waterspout (1138-1147) • funnel cloud (1149) • funnel cloud/waterspout (1156-1205)

Flight 2 • no waterspouts observed • waterspout observed from ground to northwest of Key West (1810-1817) • funnel cloud observed from ground to west of Key West (1818-1819)

25 August 1993

Flight 3 • funnel cloud (1640-1448) • funnel cloud/waterspout (1647) • funnel cloud/waterspout (1652-1701) (boat went through spray vortex as it dissipated, filmed from copter)

26 August 1993

Flight 4a • funnel cloud (1021 -1022) (stopped to refuel at Marathon Key) Flight 4b • no waterspouts observed Flights • two funnel clouds (1709-after 1714) • funnel cloud time unknown (tape was garbled)

27 August 1993

Flight 6 • no waterspouts observed Flight 7 • no waterspouts observed Flight 8 • funnel cloud/waterspout (1829-1837)

28 August 1993

Flight 9 FIG. 3. Surface data for south Florida at (a) 1200 EDT 24 August • waterspout (0844-time unknown) 1993 and (b) 1000 EDT28 August 1993. Temperature and dewpoint • funnel cloud/waterspout (0851-0910) plotted in °C; wind barbs as in Fig. 2. Sea level pressure plotted in • two funnel clouds/waterspouts (0911 -0926) tens of mb, without the leading "10." Wind direction (tens and Flight 10 hundreds units only) and wind speed in kt plotted below pressure. • no waterspouts observed Waterspouts occurred to the west and northeast of Key West for (a) and (b), respectively.

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC Figure 8 shows a wake and the spray vortex, in addition to a wave train of swells off to the side of the waterspout. Figure 9 illustrates the use of the smoke flares to visualize the low- level flow in the vicinity of the waterspouts. Figure 10 shows a relatively long persistent wake trailing the spray ring of a dissipating waterspout.

4. Conclusions

The helicopter, which transported us easily and quickly to waterspouts, is a platform that is more stable than a small airplane and is therefore more suitable for photography. A helicopter might be considered as a possible vehicle for carrying instruments in tornado field experiments. Not only could FIG. 4. Locations of some of the more prominent waterspouts documented in the jt be used to get to the desired loca- Lower Florida Keys, 21-26 August 1993. Dark boundaries delineate primary envelope tions much more auicklv than can be of warm, shallow water (depths less than 3 m). all in most cloud lines, especially before precipitation had begun. However, cloud-water lightning was observed after the decay of some waterspouts in nearby heavy showers, and we then departed for another cloud line. The most unusual event documented was the landfall of a waterspout in the hour before sunset on 26 August 1993 on a tiny island about 11 km northeast of Key West and the reemergence of the spray vortex on the other side of the tiny island. A day earlier, we watched (and filmed) in horrified amazement as a large boat, which was observed heading for a waterspout's spray vortex, penetrated it as the spray vortex decayed. Many of the life cycle features reported by Golden (1974a) were observed: the first stage of many inter- cepted waterspouts was indicated by a dark spot on the sea surface. Most of the condensation funnels associated with the waterspouts appeared to be hollow, with a surrounding shell of turbulent condensate. Spiral patterns (or rings) were observed on the water beneath some funnel clouds (Fig. 5). Waterspouts initially tended to be nearly stationary (Fig. 6) and then picked up forward speed later on, apparently in response to nearby shower formation (Fig. 7). Surprisingly, Fig. 6 shows a frigate bird hovering below, near the waterspout. We often noted birds soaring under cloud base, getting a free ride in the subcloud-layer updrafts near FIG. 5. Funnel cloud pendant from cloud base, and ring in sea waterspouts. Figure 7 shows a wake in the sea surface, surface below, at 1145 EDT 24 August 1993 (photograph copyright which looks like a tail connected to the spray vortex. H. Bluestein).

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC FIG. 6. Waterspout, with circular spray vortex on the sea surface, FIG. 7. Waterspout, with spray vortex and wake on the sea at 1200 EDT 24 August 1993. A bird is visible in front of the surface, at 1201 EDT 24 August 1993 (photograph copyright H. condensation funnel (photograph copyright H. Bluestein). Bluestein).

done on the ground in vans (e.g., Bluestein and Unruh 1989), but it can provide a better visual perspective on important near-surface air motions in and around the tornado (Pauley and Snow 1988). The main disadvan- tages of the helicopter are its large expense, the limited payload capacity, the possible danger of airborne debris near tornadoes and lightning, and possible interference to onboard remote sensing systems from the helicopter's blades. A number of very high quality 16-mm movies were obtained that will be photogrammetrically analyzed. These movies are of much higher resolution, stability, and quality than those obtained during any of the waterspout field programs in the late 1960s and mid- 1970s (Golden 1974a). The perspective of the sea state as seen from above allowed us to obtain detailed spray vortex movies, which will be photogrammetrically analyzed so that estimates of the surface wind speeds can be computed. The photographs of the sea state near waterspouts revealed, as shown in earlier field programs, a train of regularly spaced swells on one side of the spray vortex, long wakes, and spiral patterns. We suggest

FIG. 8. Waterspout, with spray vortex, wake, and train of wave on that the interaction between an intense vortex, such as the sea surface, at 0912 EDT 28 August 1993 (photograph copyright a waterspout, and a shallow ocean be simulated with H. Bluestein). a coupled ocean-atmosphere numerical model to see if it is possible to make deductions about the vortex from visual characteristics of the ocean surface.

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC We observed a large number of waterspouts near appear to hold great potential for providing much more Key West, in comparison with the relatively few water- detailed understanding of waterspout wind speeds spouts observed from NWS at Key West or reported and structure. Consideration might also be given to by mariners to NWS. The existing waterspout clima- using a shallow-draw speedboat as a platform for tology therefore likely underestimates significantly carrying instruments. Any of these experiments would (perhaps by an order of magnitude) the frequency of have to be organized with great attention to safety, as occurrence of waterspouts in the Florida Keys. Seri- was the case here. ous consideration should be given to testing small radars and lidars in the vicinity of waterspouts before Acknowledgments. The NGS (coproducers Teri Koenig and use in tornado field experiments, because the prob- Richard Wells) and NOAA (Deputy Undersecretary Douglas Hall ability of safe and successful close-range encounters and Rear Admiral Sigmund Petersen, Office of NOAA Corps Opera- tions) provided the primary funding. Mr. DaneKonop, NOAA Office with waterspouts is much higher than that with torna- of Public Affairs, was a key team member (flare flinger) who does. However, the typical waterspout is much smaller persevered in organizing and securing critical NOAA support for the (on the order of a few tens of meters in diameter) than project. H. Bluestein was supported in part by NSF Grant ATM- the typical tornado (on the order of hundreds of meters 9019821. Some of the graphics were produced by the Geosciences in diameter), and there may be serious resolution Computing Network at the University of Oklahoma. D. Henize (NWS, Key West) and his coworkers kindly provided use of their problems, because the radar beam may be wider than facilities and assisted us in many ways. The NOAA AOC provided a large majority of waterspouts. Airborne Doppler the Bell helicopter and crew, and the expertise of the pilots Gary Van lidars or narrow, millimeter-wavelength Dopper radars den Berg and Deborah Barr is gratefully acknowledged.

FIG. 9. Waterspout, with spray vortex and wake on sea surface, FIG. 10. Wake and spray vortex on the sea surface, from a at 0912 EDT 28 August 1993. Smoke plumes from two flares are dissipating waterspout, at 0925 EDT 28 August 1993 (photograph visible near the sea surface (photograph copyright H. Bluestein). copyright H. Bluestein).

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Unauthenticated | Downloaded 10/04/21 12:00 PM UTC References Leverson, V., P. C. Sinclair, and J. H. Golden, 1977: Waterspout wind, temperature, and pressure structure deduced from a Bluestein, H. B., and W. P. Unruh, 1989: Observations of the wind aircraft measurements. Mon. Wea. Rev., 105,725-733. field in tornadoes, funnel clouds, and wall clouds with a portable Pauley, R. L., and J. T. Snow, 1988: On the kinematics and Doppler radar. Bull. Amer. Meteor. Soc., 70,1514-1525. dynamics of the 18 July 1986 Minneapolis tornado. Mon. Wea. Golden, J. H., 1968: Waterspouts at Lower Matecumbe Key, Florida, Rev., 116,2731-2736. September 2,1967. Weather,23,103-114. Schwiesow, R. L., R. E. Cupp, P. C. Sinclair, and R. F. Abbey Jr., , 1971: Waterspouts and tornadoes over South Florida. Mon. 1981: Waterspout velocity measurements by airborne Doppler Wea. Rev.,99,146-154. lidar. J. Appl. Meteor.,20,341-348. , 1973; Some statistical aspects of waterspout formation. Simpson, J., B. R. Morton, M. C. McCumber, and R. S. Penc, 1986: Weatherwise,26,108-117. Observations mechanisms of GATE waterspouts. J. Atmos. , 1974a: The life cycle of Florida Keys' waterspouts. I. J. Appl. Sci., 43,753-782. Meteor., 13,676-692. Woodley, W. L., J. H. Golden, and B. C. Halter, 1967: Aircraft , 1974b: Scale-interaction implications for the waterspout life observations in the immediate vicinity of two waterspouts. Mon. cycle. II. J. Appl. Meteor., A3,693-709. Wea. Re v., 95,799-803. , 1977: An assessment of waterspout frequencies along the U.S. East and Gulf Coasts. J. Appl. Meteor., 16,231-236.

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The Representation of Cumulus Convection in Numerical Models Meteorological Monograph No. 46

Cumulus convection is perhaps the most complex and perplexing subgrid-scale process that must be represented in numerical models of the atmosphere. It has been recognized that the water vapor content of large parts of the atmosphere is strongly controlled by cloud microphysical processes, yet scant attention has been paid to this problem in formulating most existing convection schemes. This monograph is the fruit of the labors of many of the leading specialists in convection and convective parameterization to discuss this and other issues. Its topics include: an overview of the problem; a review of "classical" convection schemes in widespread use; the special problems associated with the representation of convection in mesoscale and climate models; the parameterization of slantwise convection; and some recent efforts to use explicit numerical simulations of ensembles of convective clouds to test cumulus representations. American ©1994 American Meteorological Society. Hardbound, B&W, 246 pp., $65 list\$45 members Meteorological

(includes shipping and handling). Please send prepaid orders to: Order Department, American # Meteorological Society, 45 Beacon St., Boston, MA 02108-3693. SOCiety

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