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On the Relationship Between Gravity Waves and Tropopause Height and Temperature Over the Globe Revealed by COSMIC Radio Occultation Measurements

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On the Relationship between Gravity Waves and Tropopause Height and Temperature over the Globe Revealed by COSMIC Radio Occultation Measurements

  • Daocheng Yu 1, Xiaohua Xu 1,2,*, Jia Luo 1,3,
  • *
  • and Juan Li 1

1

School of Geodesy and Geomatics, Wuhan University, 129 Luoyu Road, Wuhan 430079, China; [email protected] (D.Y.); [email protected] (J.L.)

23

Collaborative Innovation Center for Geospatial Technology, 129 Luoyu Road, Wuhan 430079, China Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, 129 Luoyu Road, Wuhan 430079, China

*

Correspondence: [email protected] (X.X.); [email protected] (J.L.); Tel.: +86-27-68758520 (X.X.); +86-27-68778531 (J.L.)

ꢀꢁꢂꢀꢃꢄꢅꢆꢇ

ꢀꢁꢂꢃꢄꢅꢆ

Received: 4 January 2019; Accepted: 6 February 2019; Published: 12 February 2019

Abstract: In this study, the relationship between gravity wave (GW) potential energy (Ep) and the

tropopause height and temperature over the globe was investigated using COSMIC radio occultation

(RO) dry temperature profiles during September 2006 to May 2013. The monthly means of GW Ep with a vertical resolution of 1 km and tropopause parameters were calculated for each 5◦

×

5◦

longitude-latitude grid. The correlation coefficients between Ep values at different altitudes and

the tropopause height and temperature were calculated accordingly in each grid. It was found that

at middle and high latitudes, GW Ep over the altitude range from lapse rate tropopause (LRT) to

several km above had a significantly positive/negative correlation with LRT height (LRT-H)/ LRT

temperature (LRT-T) and the peak correlation coefficients were determined over the altitudes of

10–14 km with distinct zonal distribution characteristics. While in the tropics, the distributions of the

statistically significant correlation coefficients between GW Ep and LRT/cold point tropopause (CPT)

parameters were dispersive and the peak correlation were are calculated over the altitudes of 14–38

km. At middle and high latitudes, the temporal variations of the monthly means and the monthly

anomalies of the LRT parameters and GW Ep over the altitude of 13 km showed that LRT-H/LRT-T

increases/decreases with the increase of Ep, which indicates that LRT was lifted and became cooler

when GWs propagated from the troposphere to the stratosphere. In the tropical regions, statistically

significant positive/negative correlations exist between GW Ep over the altitude of 17–19 km and

LRT-H/LRT-T where deep convections occur and on the other hand, strong correlations exist between

convections and the tropopause parameters in most seasons, which indicates that low and cold

tropopause appears in deep convection regions. Thus, in the tropics, both deep convections and GWs

excited accordingly have impacts on the tropopause structure. Keywords: gravity waves; potential energy; tropopause; COSMIC

1. Introduction

The tropopause is the transition layer between the upper troposphere and the lower stratosphere,

which are distinct from one another in vertical mixing timescales, static stabilities, trace constituents,

and thermal balance [1]. The variations of the tropopause, which are the responses to any changes in the physical, chemical, and thermal characteristics of the two regions, are linked closely to the

stratosphere-troposphere exchange as well as climate variability and change [2–4].

Atmosphere 2019, 10, 75

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  • Different definitions and concepts exist for the determination of the tropopause [
  • 5]. The thermal

tropopause, which is also called the lapse rate tropopause (LRT), was defined by the Wor−ld1

Meteorological Organization (WMO) as the lowest level at which the lapse rate decreases to 2 K·km

or less, provided that the average lapse rate between this level and all higher levels within 2 km does

not exceed 2 K·km−1. LRT can be obtained from vertical profiles of atmospheric temperature and

are applied globally, both in the tropics and in the extra-tropics [6]. The cold point tropopause (CPT),

which is usually applied in the tropics, is the level of the temperature minimum as the temperature

decreases with height from the surface up to certain altitude and then increases at higher altitudes in the stratosphere [

exchange [2].

7]. The CPT is an import indicator of stratosphere-troposphere coupling and
The variations of the tropopause height and temperature show sub-seasonal, seasonal and

inter-annual variabilities [ 12] and are closely related to atmospheric waves [ 10 13 16], among which

the effects of Gravity waves (GWs) [10 17 18] are significant. Gravity waves (GWs) are usually excited

  • 8–
  • 8,
  • ,
  • –

  • ,
  • ,

in the troposphere and propagate upward, transferring energy, momentum, and water vapor and

depositing vertical mixing of heat [19], which affects tropopause temperature directly or indirectly [18].

GW activities play important roles in the global circulation and the temperature and constituent

structures, such as water vapor, ozone concentrations, and other chemical constituents [20,21].

  • Although there are a number of works on the variations of the structure of tropopause [22
  • –25]

  • and GW activities [21 26 27], studies on the relationship between GWs and the tropopause are
  • ,
  • ,

meager. Reference [10] investigated the structure and variability of temperature in the tropical

upper troposphere and lower stratosphere (UTLS) using the Global Positioning System Meteorology

(GPS/MET) data during April 1995 to February 1997. They found that much of the sub-seasonal

variability in CPT temperature and height appeared to be related to GWs or Kelvin waves. Using ~114 h mesosphere-stratosphere-troposphere (MST) radar data at Gadanki, references [17,28] studied the wind disturbances, tropopause height, and inertial gravity wave (IGW) associated with a tropical depression

passage, and they found that the tropopause height and IGW had similar periodograms, which

clearly showed that the tropopause height was modulated by inertial GW. Reference [18] investigated

the relationship between GWs and the temperature and height of CPT and water vapor over Tibet

using the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Radio

Occultation (RO) temperature data during June 2006 to February 2014. Their results showed that

GW potential energy (Ep), CPT temperature, and water vapor had good correlation with each other

and that GWs affected the CPT temperature and water vapor concentration in the stratosphere. These works about the relationship between GWs and tropopause were mainly focused on certain geographic regions. The effects of GW activity on the tropopause structure over the globe needs

further investigation.

The COSMIC RO temperature profiles with high vertical resolution, high accuracy, long-term

  • stability, and global coverage are ideal data sources to study the tropopause structures [
  • 4,25,29] and

  • are applicable to analyze the global characteristics of GW activity [21 30 31]. In this study, we used
  • ,
  • ,

COSMIC level 2 dry temperature (atmPrf) profiles during September 2006 to May 2013 to investigate

the relationship between GWs and the tropopause height and temperature over the globe. Data and

methods are introduced in Section 2. The results and analyses are presented in Section 3. Section 4

discusses the possible underlying mechanism. Finally, conclusions are given in Section 5.

2. Experiments

2.1. COSMIC RO Data

The COSMIC dry temperature profile is from near the ground up to 60 km with a good vertical

resolution (~1 km); however, due to the a priori information used in the inversion process and the

  • residual ionospheric effects, it typically exhibits increased noise at upper levels [27
  • ,32]. Although

COSMIC RO dry temperature data is used to analyze GW activity up to 50 km, it is indicated that

Atmosphere 2019, 10, 75

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the upper height level of the COSMIC temperature profiles most appropriate for GW study is below

40 km [27]. The vertical wavelengths of GW derived from COSMIC temperature are equal or greater

than 2 km [32]. This work uses COSMIC post-processed level 2 dry temperature profiles (atmPrf files)

of the version 2010.2640 from September 2006 to May 2013 produced by the COSMIC Data Analysis

and Archive Center (CDAAC) of the University Corporation for Atmospheric Research (UCAR) to

analyze the relationship between GWs and the tropopause.

2.2. GW Ep

The potential energy (Ep) can well represent the feature of GW and is given by:

  • ꢂ
  • ꢃ

2

  • ꢀ
  • ꢁ

2

12

gN

T0

T

Ep =

(1) (2)

  • ꢂ
  • ꢃ

gT

∂T ∂z

g

N2 =

+

cP

where capacity,

g

is the gravitational acceleration, N is the Brunt-Väisälä frequency, cp is the isobaric heating

z

is the height, and T, and T0 is the background temperature and the temperature

perturbations caused by GWs, respectively. It is important to separate

temperature (T). The accurate Ep is based on the extraction of T0, which is given by:

T

and T0 from the raw COSMIC

T0 = T − T

(3)

We extracted Ep values from COSMIC RO temperature profiles following closely the method

used by references [21 32]. At first, the daily COSMIC temperature profiles between 8 km and 38 km

are gridded to 10◦ 15◦ latitude and longitude resolution with a vertical resolution of 0.2 km, based

,

×

on which the mean temperature of each grid is calculated for each height level. Then, the S-transform

was used for each latitude and altitude, obtaining the zonal wave number 0–6 which represents the

background temperature for zonal mean temperature. The S-transform is unique in that it provides

frequency-dependent resolution while maintaining a direct relationship with the Fourier spectrum [33].

In the next step, this background temperature was interpolated back to the positions of raw COSMIC

RO profiles and subtracted from T using Equation (3) to get the temperature perturbations T0. Finally,

GW Ep was calculated by Equations (1) and (2). To further analyze the relationship between GW Ep

and tropopause parameters, daily Ep values were binned and averaged in 5◦

grid cells with a vertical resolution of 1 km.

×

5◦ longitude–latitude

Following the above procedure, reference [34] presented an example of calculating the temperature

perturbation profile and the Ep profile corresponding to a COSMIC RO dry temperature profile. The temperature perturbation profile in Figure 1b of [34] presented a wavelike structure around

0 K, which is consistent with reference [21]. References [34,35] further investigated the seasonal and

interannual variations of the global stratospheric GW activities.

2.3. LRT and CPT Temperature and Height

COSMIC RO atmPrf products provided by CDAAC include the tropopause parameters, such as

the temperature and height of LRT and CPT. Reference [36] reported that the LRT temperature and height from COSMIC RO provided by CDAAC are consistent with those derived from the

high-resolution Modern-Era Retrospective Analysis for Research Application (MERRA).

In this work, the LRT and◦CPT ◦temperature and height, which were obtained directly from the

atmPrf files, were binned into 5

means of LRT height (LRT-H), LRT temperature (LRT-T), CPT height (CPT-H), and CPT temperature

(CPT-T) during September 2006 to May 2013 are shown in Figure 1. Because the CPT parameters are

×

5 longitude-latitude grids. The time-latitude plots of the monthly

Atmosphere 2019, 10, 75

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most applicable in the tropics [37], the variations of CPT-H and CPT-T are only shown for the latitude

region of 30◦ S–30◦ N.

  • Figure 1. Time-latitude plots of monthly means of (
  • a) lapse rate tropopause height (LRT-H), (

b) lapse

rate tropopause temperature (LRT-T), (

c

) cold point tropopause height (CPT-H), and ( ) cold point

d

tropopause temperature (CPT-T).

It can be seen from Figure 1a that the LRT-H is around 16 km in the tropics, while it decreases to

9 km in the polar regions, which is consistent with reference [23]. In the tropics, the LRT-H presents

significant seasonal variations with higher LRT in boreal winter and lower one in boreal summer.

While in middle and high latitudes, the seasonal variation of LRT-H is opposite. Figure 1b shows that

the LRT-T increases from the tropics to the poles. In the tropics and in the middle and high latitudes

of the Northern Hemisphere (NH), the LRT-T is higher in boreal summer and lower in boreal winter;

while in the middle and high latitudes of the Southern Hemisphere (SH), it presents the opposite

seasonal variation. The comparison between Figure 1a,b shows that LRT is higher and colder in the

tropics and lower and warmer at middle and high latitudes.

From Figure 1c, it can be seen that the CPT-H in the low latitudes is between 16–18 km and

presents the seasonal variation with higher and lower values in boreal winter and summer, respectively.

From Figure 1d, it is evident that the CPT-T is higher in boreal summer and lower in winter, which is

opposite to the seasonal variation of the CPT-H. So the CPT is higher and colder in boreal winter and

lower and warmer in summer, which is consistent with reference [38]. In the tropics, the parameters of

the LRT and CPT are close to each other and present similar seasonal variation patterns.

The characteristics of the temporal and spatial variability of the LRT and CPT heights and

temperatures shown in Figure 1 are generally consistent with those of the available literatures. Thus,

the tropopause parameters provided by CDAAC is reliable and can be applied to this study.

2.4. Statistical Method

The monthly means of GW Ep with a vertical resolution of 1 km and tropopause parameters

were calculated for each 5◦

and the tropopause heights and temperatures were subtracted from the monthly means to get the

corresponding monthly anomalies, as shown by equation (4):

×

5◦ longitude-latitude grid. The annual cycle of Ep at each height layer

n

1

  • ∆F = F −
  • F

i,j

(4)

  • i,j
  • i,j

∑

ni=1

where n is the number of years. i = 1, 2, . . . . . . n is the

in one year.

i

th year and j = 1, 2, . . . . . . 12 is the

j

th month

F

i,j

and ∆F represents the monthly mean and the monthly anomaly of Ep at certain

i,j

Atmosphere 2019, 10, 75

5 of 15

height layer or of tropopause parameters for the

j

th month in the

i

th year, respectively. In each grid,

the correlation coefficient between GW Ep for certain height interval and the tropopause parameters

was calculated accordingly.

3. Results

3.1. Calculation Example

GW Ep and the LRT-H at a certain grid (50◦ N, 25◦ W) is taken as an example in this section.

The time series of the monthly means and the monthly anomalies of GW Ep at the altitude of 13 km

and the LRT-H over this grid are shown in Figure 2. The monthly anomalies were calculated by the

statistical method presented in Section 2.4.

Figure 2.

(a) The monthly means and (b) the monthly anomalies time series of gravity wave potential

  • ◦
  • ◦

energy (GW Ep) at 13 km and the LRT-H over the grid (50 N, 25 W).

From Figure 2a, it can be seen that the Ep monthly means (blue solid line) at 13 km over this grid fluctuated mainly between 2.5 J·kg−1 and 10 J·kg−1, while LRT-H monthly means (red dotted

line) oscillated mainly between 10 km and 12 km. The temporal variation pattern of Ep was similar

to that of LRT-H, which means that high values of Ep correspond to high values of LRT-H and vice versa. The Pearson correlation coefficient between the two lines shown in Figure 2a is 0.62, which

passes through the significance test of the confidence level of 99%. Figure 2b shows that Ep monthly

anomalies fluctuate between −2 J·kg−1 and 4 J·kg−1, while LRT-H monthly anomalies fluctuated between −0.5 km and 0.5 km. The Pearson correlation coefficient between the two lines shown in Figure 2b was 0.39, which also passes through the significance test of the confidence level of

99%. The correlation coefficient between the monthly anomalies was smaller than that between the

monthly means.

3.2. The Vertical Structure of the Correlation Between Ep and Tropopause Parameters

To investigate the vertical structure of the correlation between Ep and LRT and CPT parameters,

we gave the longitude-altitude cross sections of Pearson correlation coefficients between the time series of Ep and those of LRT-H (LRT-T) and CPT-H (CPT-T) over different latitudes in Figures 3

and 4, respectively.

Figure 3 shows the longitude-altitude cross sections of the Pearson correlation coefficients between

Ep and LRT-H and between Ep and LRT-T at 70◦ N, 0◦, and 50◦ S, which can represent high, low, and middle latitude, respectively. The comparisons between the subfigures in Figure 3 show that the vertical distributions of the correlation coefficients between GW Ep and LRT-H vary greatly at

◦

different latitudes. It is shown in Figure 3a that, at 70 N, the statistically significant Pearson correlation

coefficients between Ep values and LRT-H are mostly positive and are large at the altitudes between

Atmosphere 2019, 10, 75

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the height of LRT and 14 km, while the correlation coefficients of Ep values and LRT-H were small and

not statistically significant below the LRT-H or above 14 km.

At the equator, the distributions of the correlation coefficients that are statistically significant are

◦

dispersed, as shown in Figure 3b. At 50 S, Ep mostly has a significant positive correlation with LRT-H

between the height of LRT and 14 km, as shown in Figure 3c.

Figure 3. Longitude-altitude cross sections of Pearson correlation coefficients between Ep and LRT-H

d) 70◦ N, (b e) 0◦ and (c f) 50◦ S.

(left column), and between Ep and LRT-T (right column) at (a, , ,

The regions where the correlation coefficients pass through the significance test of the confidence level

of 95% are marked with crosses. The LRT height is represented by black dotted lines (a–f).

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  • A Climatology of the Tropical Tropopause Layer

    A Climatology of the Tropical Tropopause Layer

    Journal of the Meteorological Society of Japan, Vol. 80, No. 4B, pp. 911--924, 2002 911 A Climatology of the Tropical Tropopause Layer A. GETTELMAN National Center for Atmospheric Research, Boulder, CO, USA and P.M. de F. FORSTER Department of Meteorology, University of Reading, Reading, UK (Manuscript received 4 June 2001, in revised form 17 September 2001) Abstract The tropical tropopause layer (TTL) is a transition region between the troposphere and the strato- sphere. In this study the vertical extent of the TTL is diagnosed from radiosonde and ozonesonde profiles in the tropics and a climatology of this layer is presented. The radiative balance in the TTL is also characterized. The TTL is locally defined as extending from the level of the lapse rate minimum at 10– 12 km to the cold point tropopause (CPT) at 16–17 km. The minimum in lapse rate represents the level of maximum convective impact on upper tropospheric temperatures, which is found to closely correspond to a minimum in ozone. Variations in this level are correlated with convective activity as measured by satellite brightness temperatures and Outgoing Longwave Radiation (OLR). At the cold point, the TTL height is nearly uniform throughout the tropics, and has a pronounced annual cycle. There are regional variations in the altitude of the lower boundary of the TTL. Interannual variations of the TTL result from changes in the large scale organization of convective activity, such as from the El-Nin˜ o Southern Oscillation (ENSO). Over the last 40 years, records indicate an increase (200–400 m) in the height of both the cold point tropopause and the level of minimum lapse rate.
  • Characteristics of the Tropical Tropopause Inversion Layer Using High

    Characteristics of the Tropical Tropopause Inversion Layer Using High

    Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-1182 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 17 December 2018 c Author(s) 2018. CC BY 4.0 License. Characteristics of the tropical tropopause inversion layer using high- resolution temperature profiles retrieved from COSMIC GNSS Radio Occultation Noersomadi Noersomadi1,2, Toshitaka Tsuda1, Masatomo Fujiwara3 5 1Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji, 611-0011, Japan 2National Institute of Aeronautics and Space (LAPAN), Bandung, 40173, Indonesia 3Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan Correspondence to: Noersomadi ([email protected]) Abstract. Using COSMIC GNSS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved 10 temperature profiles with 0.1 km vertical resolution in the upper troposphere and lower stratosphere (UTLS). We investigated the global distribution of static stability (N2) and the characteristics of the tropopause inversion layer (TIL) in the tropics, where a large change in temperature gradient occurs associated with sharp variations of N2. We show the variations of the mean N2 profiles in conventional height coordinates as well as in coordinates relative to both the Lapse Rate Tropopause (LRT) and the Cold Point Tropopause (CPT). When the N2 profiles are averaged relative to CPT height, there is 15 a very thin (<1 km) layer with average maximum N2 in the range 11.0–12.0 × 10−4 s−2. The mean and standard deviation of the tropopause sharpness (S-ab), defined as the difference between the maximum N2 (maxN2) and minimum N2 (minN2) within ±1 km of the CPT, is (10.5 ± 3.7) × 10−4 s−2.
  • PHAK Chapter 12 Weather Theory

    PHAK Chapter 12 Weather Theory

    Chapter 12 Weather Theory Introduction Weather is an important factor that influences aircraft performance and flying safety. It is the state of the atmosphere at a given time and place with respect to variables, such as temperature (heat or cold), moisture (wetness or dryness), wind velocity (calm or storm), visibility (clearness or cloudiness), and barometric pressure (high or low). The term “weather” can also apply to adverse or destructive atmospheric conditions, such as high winds. This chapter explains basic weather theory and offers pilots background knowledge of weather principles. It is designed to help them gain a good understanding of how weather affects daily flying activities. Understanding the theories behind weather helps a pilot make sound weather decisions based on the reports and forecasts obtained from a Flight Service Station (FSS) weather specialist and other aviation weather services. Be it a local flight or a long cross-country flight, decisions based on weather can dramatically affect the safety of the flight. 12-1 Atmosphere The atmosphere is a blanket of air made up of a mixture of 1% gases that surrounds the Earth and reaches almost 350 miles from the surface of the Earth. This mixture is in constant motion. If the atmosphere were visible, it might look like 2211%% an ocean with swirls and eddies, rising and falling air, and Oxygen waves that travel for great distances. Life on Earth is supported by the atmosphere, solar energy, 77 and the planet’s magnetic fields. The atmosphere absorbs 88%% energy from the sun, recycles water and other chemicals, and Nitrogen works with the electrical and magnetic forces to provide a moderate climate.
  • Changes of the Tropical Tropopause Layer Under Global Warming

    Changes of the Tropical Tropopause Layer Under Global Warming

    1 Changes of the tropical tropopause layer under global warming ∗ 2 Pu Lin 3 Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 4 David Paynter, Yi Ming and V. Ramaswamy 5 Geophysical Fluid Dynamics Laboratory / NOAA, Princeton, NJ ∗ 6 Corresponding author address: Pu Lin, Program in Atmospheric and Oceanic Sciences, Princeton 7 University, Princeton, NJ. 8 E-mail: [email protected] Generated using v4.3.1 (5-19-2014) of the AMS LATEX template1 ABSTRACT 9 We investigate changes in the tropical tropopause layer (TTL) in response 10 to carbon dioxide increase and surface warming separately in an atmospheric 11 general circulation model, and find that both effects lead to a warmer tropical 12 tropopause. Surface warming also results in an upward shift of the tropopause. 13 We perform a detailed heat budget analysis to quantify the contributions from 14 different radiative and dynamic processes to changes in the TTL temperature. 15 When carbon dioxide increases with fixed surface temperature, a warmer TTL 16 mainly results from the direct radiative effect of carbon dioxide increase. With 17 surface warming, the largest contribution to the TTL warming comes from the 18 radiative effect of the warmer troposphere, which is partly canceled by the ra- 19 diative effect of the moistening at the TTL. Strengthening of the stratospheric 20 circulation following surface warming cools the lower stratosphere dynami- 21 cally and radiatively via changes in ozone. These two effects are of compa- 22 rable magnitudes. This circulation change is the main cause of temperature 23 changes near 63 hPa, but is weak near 100 hPa.
  • Jet Streams of the Atmosphere

    Jet Streams of the Atmosphere

    Jet Streams of the Atmosphere By Herbert Riehl Department of Atmospheric Science Colorado State University Fort Collins, Colorado May 1962 CER62HR35 Jet Streams of the Atmosphere by Herbert Riehl Technical Report No. 32 Department of Atmospheric Science Colorado State University Fort Collins. Colorado May 1962 The price for this report is $1.50. Copies may be obtained from the Department of Atmospheric Science Colorado State University Fort Collins, Colorado JET STREAMS OF THE ATMOSPHERE by Herbert Riehl Colorado State University With a chapter on The Jet Stream and Aircraft Operations by Cdr. J. W. Hinkelman, Jr., USN Technical Paper Number 32 Department of Atmospheric Science Colorado State University Fort Collins. Colorado May 1962 CER62HR35 FOREWORD The presence of jet streams in the atmosphere is one of the most important and exciting facts in the field of Atmospheric Science. The practical impact created by the narrow bands of high wind speed goes far beyond air route planning, downstream with the current, upstream at a judicious distance from the core. Missile flight planning must take account of this current. The cloud systems that bring rain and snow to the ground often are shaped by the jet stream and in their turn may react on it. Many features of surface cli­ mate are closely related to jet stream incidence. In the field of theory, the observed concentration of kinetic energy into narrow cores is a highly challenging problem. No theory of the general circulation and of the daily weather disturbances will be satisfactory without an explanation of the wind concentration and its role in the mechanics and energy transformations of the atmosphere.