Seasonal variations, trend in the tropopause height/temperature over Indian stations and its modulations by SST anomalies of east Pacific Ocean

Global warming due to increase in the Green House Gases is now well known. There are several studies, also, suggesting discernible changes over the years in respect of meteorological parameters like, rainfall events, frequency and intensity of tropical cyclones/hurricanes, maximum/minimum temperature, SST of oceans etc, on regional as well as global scale. The present study besides finding out seasonal variations in tropopause height and temperature across each 5° latitude over India based on a longer data set, has demarcated the locations where significant trend in respect of temperature and height was observed over Indian region on annual scale besides investigating the possible causes of this trend. The study has also confirmed significant linear associationship between tropopause temperature/height over Indian stations and SST anomalies of east Pacific Ocean with SST leading by one year.

Determination of Tropical Belt Widening Using Multiple GNSS Radio Occultation Measurements

In the last decades, Global navigation satellite systems (GNSS) have provided an exceptional opportunity to retrieve atmospheric parameters globally through GNSS radio occultation (GNSS-RO). In this paper, data of 12 GNSS-RO missions from June 2001 to November 2020 with high resolution were used to investigate the possible widening of the tropical belt along with the probable drivers and impacts in both hemispheres. Applying both lapse rate tropopause (LRT) and cold point tropopause (CPT) definitions, the global tropopause height shows increase of approximately 36 m/decade and 60 m/decade, respectively. Moreover, the tropical edge latitude (TEL) estimated based on two tropopause height metrics, in the northern hemisphere (NH) and southern hemisphere (SH), are different from each other. For the first metric, subjective method, the tropical width from GNSS has expansion behavior in NH with ~ 0.41°/decade and a minor expansion in SH with ~ 0.08°/decade. In case of ECMWF Reanalysis v5 (ERA5) there is no significant contraction in both NH and SH. For Atmospheric Infrared Sounder (AIRS), there are expansion behavior in NH with ~ 0.34°/decade and strong contraction in SH with ~ −0.48°/decade. Using the second metric, objective method, the tropical width from GNSS has expansion in NH with ~ 0.13°/decade, and no significant expansion in SH. In case of ERA5, there is no significant signal in NH while SH has a minor contraction. AIRS has an expansion with ~ 0.13°/decade in NH, and strong contraction in SH with ~ −0.37°/decade. The variability of tropopause parameters (temperature and height) is maximum around the TEL locations at both hemispheres. The total column ozone (TCO) shows increasing rates globally, and the rate of increase at the SH is higher than that of the NH. There is a good agreement between the spatial and temporal patterns of TCO variability and the TEL location estimated from GNSS LRT height. Carbon dioxide (CO2), and Methane (CH4), the most important greenhouse gases (GHGs) and the main drivers of global warming, have a global increasing rate and the increasing rate of the NH is similar to that of the SH. The spatial pattern in the NH is located more pole ward than its equivalent at the SH. Both surface temperature and precipitation increase in time and have strong correlation with GNSS LRT height. Both show higher increasing rates at the NH, while the precipitation at the SH has slight decrease and the surface temperature increases. The surface temperature shows a spatial pattern with strong variability, which broadly agrees with the TEL locations. The spatial pattern of precipitation shows northward occurrence. In addition, Standardized Precipitation Evapotranspiration Index (SPEI) has no direct connection with the TEL behavior.

The Combined QBO and ENSO Influence on Tropical Cyclone Activity over the North Atlantic Ocean

The Quasi-Biennal Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO) largely modulate the zonal wind in the tropics. Previous studies showed that QBO phases produce changes in deep convection through an increase/decrease in the tropopause height over the tropics and subtropics. This study investigates the combined effects of QBO and ENSO on tropical cyclone activity by modulating tropopause height. We found that tropopause height increases over the Gulf of Mexico, the Caribbean region, and the Western North Atlantic Ocean during La Niña + QBOW, allowing deeper tropical convection to develop over those regions. As a consequence, TC activity over those regions is not only increased in number but also enhanced in intensity. Conversely, during El Niño + QBOE, most deep tropical convection is inhibited over those same regions due to the decrease in tropopause height over the subtropics. We conclude that QBO effects on TCs and deep convection should be studied in combination with ENSO. Additional comparative studies using long record data at high vertical resolution are needed to fully understand to what extent QBO interacts with ENSO in the lower tropical stratosphere and upper tropical troposphere.

Heights of Cb clouds around Chhatrapati Shivaji International (C.S.I.) airport, Mumbai - Diurnal and seasonal variations

Lkkj & bl 'kks/k&i= esa 1990&99 ds o"kksZa ds nkSjku ekSle dk;kZy;] N=ifr f’kokth vUrjjk"Vªh; ¼lh- ,l- vkbZ-½ gokbZ vM~Ms esa ,df=r fd, x, jsMkj ds vk¡dM+ksa ds vk/kkj ij gokbZ vM~Ms ds lehi 200 fd- eh- dh ifjf/k esa 6 fd- eh- ls Åij vFkok blls vkSj vf/kd Å¡pkbZ ij QSys diklh es?kksa ¼lh- ch-½ dk v/;;u fd;k x;k gSA blesa lh- ch- lSyksa dh dqy la[;k ds ekSleh] ekfld vkSj ?kaVsokj forj.k vkSj mudh Å¡pkb;ksa] lh- ch- lfgr fnuksa dh la[;k] {kksHkeaMyh; lhek dh Å¡pkbZ rd igq¡pus okys lh- ch- lSyksa] foiqy lh- ch- es?kksa ds cuus ds izkFkfedrk okys LFkkuksa vkSj mudh xfr dh tk¡p djds mu ij fopkj&foe’kZ fd;k x;k gSA lh- ,l- vkbZ- gokbZ vM~Ms eqEcbZ ds lehi lh- ch- es?kksa ds fodkl ds fy, mÙkjnk;h flukfIVd fLFkfr;ksa dk Hkh irk yxk;k x;k gS vkSj mu ij fopkj&foe’kZ Hkh fd;k x;k gSA Based on radar data collected at the Meteorological Office, Chhatrapati Shivaji International (C.S.I.) airport, Mumbai during the years 1990-99, a study has been made on cumulonimbus (Cb) clouds with their height of top 6 km or more over an area having a radius of 200 km around the airport. The seasonal, monthly and hourly distribution of the total number of Cb cells and their heights, number of days with Cb, Cb cells that reached tropopause height, the preferred places of formation of large Cb clouds and their movement have been examined and discussed. The synoptic situation(s) responsible for the development of Cb clouds around C.S.I. airport, Mumbai have also been identified and discussed.

Retrieval of Stratospheric HNO3 and HCl Based on Ground-Based High-Resolution Fourier Transform Spectroscopy

Vertical profiles and stratospheric HNO3 and HCl columns are retrieved by ground-based high resolution Fourier transform infrared spectroscopy (FTIR) remote sensing measurements at the Hefei site in China. The time series of stratospheric HNO3 and HCl columns from January 2017 to December 2019 showed similar annual variation trends, with an annually decreasing rate of (−9.45 ± 1.20)% yr−1 and (−7.04 ± 0.81)% yr−1 for stratospheric HNO3 and HCl, respectively. The seasonal amplitudes of stratospheric HNO3 and HCl are 2.67 × 1015 molec cm−2 and 4.76 × 1014 molec cm−2 respectively, both reaching their maximum in March and their minimum in September, due to the tropopause height variation. Further, HNO3 and HCl data were used to compare with Microwave Limb Sounder (MLS) satellite data. MLS satellite data showed similar seasonal variations and annual rates with FTIR data, and the stratospheric HNO3 and HCl columns of the two datasets have correlation coefficients (r) of 0.87 and 0.88, respectively. The mean bias between satellite and FTIR data of stratospheric HNO3 and HCl columns are (−8.58 ± 12.22)% and (4.58 ± 13.09)%, respectively.

Evaluations of the characteristics of the Tropo-Strato-Mesopause height and temperature variability over Bahir Dar, Ethiopia (11.60 N, 37.30 E) using SABER

The height profile of atmospheric temperature data between 12 km and 100 km was obtained from SABER/TIMED satellite instruments during the year 2016 and used to characterize the three atmospheric pauses temporal variability of height and temperature over Bahir Dar, Ethiopia ( N, E). The daily, monthly, and frequency distributions of tropopause-stratopause-mesopause height and temperature are investigated. From the frequency distribution, we had found that of the tropopause-stratopause-mesopause height 17 km, 48 km, and 98 km with the corresponding temperature 192 k, 268 k, and 148 k. The decrement (cooling) trend lines of tropopause height 0.7 and its corresponding tropopause increment temperature has been ~1.5 . The stratopause and mesopause trend lines of height are insignificant and the corresponding decrement (cooling) temperatures are ~3 and ~13 respectively. The mean monthly maximum heights of tropopause 19 km in May with a corresponding maximum temperature of 201 k in September. The maximum stratopause height 49.5 km in February and July and its temperature 268 k and 267 k in February and April respectively. The maximum mesopause height 98 km, 95 km, 97 km in March, Jun, and November respectively, and its maximum temperature 196 k and 198 k in January and July respectively.

Remote Sensing of Atmospheric Hydrogen Fluoride (HF) over Hefei, China with Ground-Based High-Resolution Fourier Transform Infrared (FTIR) Spectrometry

Remote sensing of atmospheric hydrogen fluoride (HF) is challenging because it has weak absorption signatures in the atmosphere and is surrounded by strong absorption lines from interfering gases. In this study, we first present a multi-year time series of HF total columns over Hefei, China by using high-resolution ground-based Fourier transform infrared (FTIR) spectrometry. Both near-infrared (NIR) and mid-infrared (MIR) solar spectra suites, which are recorded following the requirements of Total Carbon Column Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC), respectively, are used to retrieve total column of HF (THF) and column-averaged dry-air mole fractions of HF (XHF). The NIR and MIR observations are generally in good agreement with a correlation coefficient (R) of 0.87, but the NIR observations are found to be (6.90 ± 1.07 (1σ)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the XHF over Hefei showed a maximum monthly mean value of (64.05 ± 3.93) pptv in March and a minimum monthly mean value of (45.15 ± 2.93) pptv in September. The observed XHF time series from 2015 to 2020 showed a negative trend of (−0.38 ± 0.22) % per year. The variability of XHF is inversely correlated with the tropopause height, indicating that the variability of tropopause height is a key factor that drives the seasonal cycle of HF in the stratosphere. This study can enhance the understanding of ground-based high-resolution remote sensing techniques for atmospheric HF and its evolution in the stratosphere and contribute to forming new reliable remote sensing data for research on climate change.

Attribution of the Principal Components of the Summertime Ozone Valley in the Upper Troposphere and Lower Stratosphere

The key factors affecting the variation of the ‘ozone valley’, which appears during the boreal summer in the upper troposphere and lower stratosphere (UTLS) over the South Asian High (SAH) and its adjacent areas, have not been determined. This study has performed statistical analysis to improve the understanding of the roles of the sea surface temperature (SST), tropopause height, and the West Pacific Subtropical High (WPSH) on the ozone valley. Based on the European Center for Medium-Range Weather Forecasts Interim Re-Analysis (ERA5), Modern Era Retrospective Analysis for Research and Applications dataset version 2 (MERRA2), and the Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) observation dataset, we examined the principal components of the zonal deviation of the total column ozone (TCO*) in the UTLS by applying the empirical orthogonal function (EOF), Liang-Kleeman information flow method, regression analysis, and composite analysis. The variations of the TCO* anomalies show three dominant modes, namely the east-west dipole mode in the low latitude region, the east-west tripole mode in the middle latitude region, and the south-north mode. According to the regression analysis and information flow, the three leading principal components of TCO* variations are related to the SST near Indonesia and the western Pacific Ocean in low latitudes, the tropopause height over the Iranian Plateau (IP), and the strength of the SAH over the eastern part of the Tibetan Plateau (TP), which is linked to the synchronousness between the SAH and the WPSH. For the east-west dipole mode in the low latitude region, composite analysis shows the interaction between the atmosphere and ocean causes the strengthening of the southern trough at 850 hPa and the divergence at 200 hPa, resulting in a decrease of the TCO* in the UTLS near the low latitude region around the TP. For the east-west tripole mode in the middle latitude region, the composite analysis shows obvious negative anomalies over the IP, where the TCO* reduces and the extent of the ozone valley over the IP increases with the rise of the tropopause. Comparatively, the south-north mode shows obvious positive anomalies over the TP, where the TCO* increases and the extent of the ozone valley over the TP decreases with a weak SAH. This mode is closely related to the location of the WPSH. In summary, the leading factors affecting the three dominant modes for the variations of the TCO* anomalies are SST, tropopause height, and the WPSH.

Identification of Tropopause Height with Atmospheric Refractivity

Investigation of the structure and variation of the tropopause is crucial for the development of an in-depth understanding of water-vapor exchange processes, the concentrations and nature of chemicals within the tropopause, and their role in climate change and the ecosphere. At present, the common methods used for the estimation of tropopause height are limited by their reliance on area, an overdependence on atmospheric temperature, and the use of many different data types, and thus lack strong generality. Therefore, this study used atmospheric refractivity data from multiple sources to determine the tropopause height. An objective covariance transform method was applied to identify transitions in a refractivity profile. The refractivity tropopause height was compared with the bending angle tropopause (BAT)/cold point tropopause (CPT)/lapse rate tropopause (LRT) height derived from radio occultation (RO) and radiosonde data and revealed a good agreement. An initial analysis of tropopause structure and seasonal changes derived from refractivity method afforded results that were consistent with existing research results, which proved the validity of the method. The refractivity method was also used to analyze various types of data downloaded from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Data Analysis and Archive Center (CDAAC), and show that this method is suitable for the analysis of RO data, radiosonde, reanalysis and analysis/forecast data. A series of experiments were used to verify the generality and utility of the refractivity covariance transform method to determine tropopause height, which will be useful for the analysis of long-term variations in tropopause height.