Papers by Suvarna Fadnavis
AGU Fall Meeting Abstracts, Dec 1, 2020
Annales Geophysicae, Nov 25, 2008
Spatiotemporal characteristics of the ozone quasibiennial oscillation (QBO) over the tropical-sub... more Spatiotemporal characteristics of the ozone quasibiennial oscillation (QBO) over the tropical-subtropical stratosphere (40 • S-40 • N) have been examined by analyzing data from the Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) for the period 1992-1999. A combination of regression analysis and wavelet analysis combines to act as an accurate QBO filter. Wavelet analysis provides inter-annual variability of amplitude and phase of the ozone QBO in the vertical structure of tropical-subtropical stratosphere. It gives minute details of phase propagation and descend rates, which can be used as input to models. Latitude-height structure shows evidence of a secondary meridional circulation induced by the QBO as double peak structure at the equator with maximum amplitude at two pressure levels 30 hPa and 9 hPa and a node at 14 hPa. The equatorial maxima are out of phase with each other. The maximum amplitude (∼1.4 ppmv) of the ozone QBO was observed near the equator at 10 hPa. Descent rate of the easterly phase is greater than westerly. The lag correlation of the ozone QBO with circulation and variation of descent rates in the vertical structure of the stratosphere are examined in detail. In the equatorial upper stratosphere ozone anomalies descent with the rate ∼1.5 km/month but in tropics and subtropics (above 2 hPa) they propagate upward. Keywords. Atmospheric composition and structure (Middle atmosphere-composition and chemistry)-Meteorology and atmospheric dynamics (Middle atmosphere dynamics; Waves and tides) 1 Introduction A Quasi Biennial Oscillation (QBO) in equatorial zonal wind is a dominant characteristic of the lower stratosphere. The
Annales Geophysicae, Nov 3, 2004
To study the mesospheric temperature inversion, daily temperature profiles obtained from the Halo... more To study the mesospheric temperature inversion, daily temperature profiles obtained from the Halogen Occultation Experiment (HALOE) aboard the Upper Atmospheric Research Satellite (UARS) during the period 1991-2001 over the Indian tropical region (0-30 • N, 60-100 • E) have been analyzed for the altitude range 34-86 km. The frequency of occurrence of inversion is found to be 67% over this period, which shows a strong semiannual cycle, with a maximum occurring one month after equinoxes (May and November). Amplitude of inversion is found to be as high as 40 K. Variation of monthly mean peak and bottom heights along with amplitude of inversions also show the semiannual cycle. The inversion layer is detected most frequently in the altitude range of 70-85 km, with peak height ranging from 80 to 83 km and that of the bottom height from 72 to 74 km. A comparison of frequency of temperature inversion with that obtained from Rayleigh lidar observations over Gadanki (13.5 • N, 60-100 • E) is found to be reasonable. The seasonal variation of amplitude and frequency of occurrence of temperature inversion indicates a good correlation with seasonal variation of average ozone concentration over the altitude range of the inversion layer.
Annales Geophysicae, Sep 13, 2006
To investigate the effects of decadal solar variability on ozone and temperature in the tropical ... more To investigate the effects of decadal solar variability on ozone and temperature in the tropical stratosphere, along with interconnections to other features of the middle atmosphere, simultaneous data obtained from the Halogen Occultation Experiment (HALOE) aboard the Upper Atmospheric Research Satellite (UARS) and the Stratospheric Aerosol and Gas Experiment II (SAGE II) aboard the Earth Radiation Budget Satellite (ERBS) during the period 1992-2004 have been analyzed using a multifunctional regression model. In general, responses of solar signal on temperature and ozone profiles show good agreement for HALOE and SAGE II measurements. The inferred annual-mean solar effect on temperature is found to be positive in the lower stratosphere (max 1.2±0.5 K / 100 sfu) and near stratopause, while negative in the middle stratosphere. The inferred solar effect on ozone is found to be significant in most of the stratosphere (2±1.1-4±1.6% / 100 sfu). These observed results are in reasonable agreement with model simulations. Solar signals in ozone and temperature are in phase in the lower stratosphere and they are out of phase in the upper stratosphere. These inferred solar effects on ozone and temperature are found to vary dramatically during some months, at least in some altitude regions. Solar effects on temperature are found to be negative from August to March between 9 mb-3 mb pressure levels while solar effects on ozone are maximum during January-March near 10 mb in the Northern Hemisphere and 5 mb-7 mb in the Southern Hemisphere.
Research Square (Research Square), Jan 27, 2023
The variability and trend of ozone (O 3) in the Upper troposphere and Lower Stratosphere (UTLS) o... more The variability and trend of ozone (O 3) in the Upper troposphere and Lower Stratosphere (UTLS) over the Asian region needs to be accurately quanti ed. A major challenge for understanding ozone chemistry is sparse observations in the region and thus the representation of precursor gases in model emission inventories. Here, we evaluate ozonesonde measurements during August 2016 at Nainital, in the
Zenodo (CERN European Organization for Nuclear Research), Jun 30, 2022
Copernicus GmbH, Dec 8, 2016
The study by Roy et al focuses on the radiative and dynamic impact of enhanced NOx emissions from... more The study by Roy et al focuses on the radiative and dynamic impact of enhanced NOx emissions from China and India during the summer monsoon period. The increased NOx emissions are comparable to the observed increase over a 10 year period in the first decade of this millennium. This makes the study especially interesting as it describes a recent development and not a future case scenario. The results presented are interesting as NOx emissions change O3 fields in the monsoon region. The
Journal Of Geophysical Research: Atmospheres, Jan 27, 2023
Deep convection associated with tropical cyclones leads to stratosphere‐troposphere exchange (STE... more Deep convection associated with tropical cyclones leads to stratosphere‐troposphere exchange (STE), which affects the upper‐tropospheric ozone concentrations in the vicinity of the cyclones. This study estimates the ozone enhancements over India due to the North Indian Ocean (NIO) cyclones‐driven STE. Indicators such as stratospheric fraction and potential vorticity calculated using the reanalysis data sets suggest that roughly 70% of the cyclones show anomalously high stratospheric intrusions. Aircraft observations over different locations across India also show elevated ozone concentrations in the mid‐to‐upper troposphere on cyclone days. Further, ozone and stratospheric ozone tracer concentrations from Goddard Earth Observing System‐Chemistry simulations and the Copernicus Atmosphere Monitoring Service reanalysis data sets show up to 40 ppb of excess upper tropospheric ozone over India, of which stratospheric ozone accounts for roughly 60%. Stratospheric intrusion due to the Bay of Bengal and the Arabian Sea cyclones affected the upper tropospheric ozone amounts over North and South India, respectively. The stratospheric ozone was observed to propagate downwards into the troposphere, often reaching ∼600 hPa and, in some cases, even the surface.
Frontiers in Environmental Science, Oct 3, 2022
Frontiers in Environmental Science, Aug 24, 2022
The high level of aerosol pollution in South Asia has a measurable impact on clouds, radiation, a... more The high level of aerosol pollution in South Asia has a measurable impact on clouds, radiation, and precipitation. Here, exploring multiple observational data sets and simulations of the state-of-the-art ECHAM6-HAMMOZ chemistryclimate model, we report that the reduction in anthropogenic emissions during the COVID-19 lockdown period has enhanced precipitation by 5-25% over India. This precipitation enhancement is the result of the combined effect of an enhancement in cloud cover, a reduction in aerosol induced cloud invigoration and dynamical changes. We observed that the increase in cloud cover was associated with a reduction in cloud base height and an increase in the effective radius of cloud particles which led to an increase in cloud water content. In response to sudden emission reduction, an anomalous northward moisture transport was observed adding convection and precipitation over the Indian region. Importantly, we show that there is an advantage of anthropogenic pollution reduction for water availability in addition to benefits of air quality, human health, and crop yield.
An eight member ensemble of ECHAM5-HAMMOZ simulations for the year 2003 is analyzed to study the ... more An eight member ensemble of ECHAM5-HAMMOZ simulations for the year 2003 is analyzed to study the transport of aerosols in the Upper Troposphere and Lower Stratosphere (UTLS) during the Asian Summer Monsoon (ASM). Simulations show persistent maxima in black carbon, organic carbon, sulfate, and mineral dust aerosols within the anticyclone in the UTLS throughout the ASM (period from July to September) when convective activity over the Indian subcontinent is highest. Model simulations indicate boundary layer aerosol pollution as the source of this UTLS aerosol layer and identify ASM convection as the dominant transport process. Evidence of ASM transport of aerosols into the stratosphere is observed in HALogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction. The impact of aerosols in the UTLS region is analyzed by evaluating the differences between simulations with (CTRL) and without aerosol (HAM-off) loading. The transport of anthropogenic aerosols in the UTLS increases cloud ice, water vapour and temperature, indicating that aerosols play an important role in enhancement of cloud ice in the Upper-Troposphere (UT). Aerosol induced circulation changes include a weakening of the main branch of the Hadley circulation and increased vertical transport around the southern flank of the Himalayas and reduction in monsoon precipitation over the India region.
Zenodo (CERN European Organization for Nuclear Research), Oct 31, 2022
Atmospheric Chemistry and Physics, Jan 27, 2017
Atmospheric Chemistry and Physics, Aug 15, 2018
The highly vibrant Asian summer monsoon (ASM) anticyclone plays an important role in efficient tr... more The highly vibrant Asian summer monsoon (ASM) anticyclone plays an important role in efficient transport of Asian tropospheric air masses to the extratropical upper troposphere and lower stratosphere (UTLS). In this paper, we demonstrate long-range transport of Asian trace gases via eddy-shedding events using MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) satellite observations, ERA-Interim reanalysis data and the ECHAM5-HAMMOZ global chemistry-climate model. Model simulations and observations consistently show that Asian boundary layer trace gases are lifted to UTLS altitudes in the monsoon anticyclone and are further transported horizontally eastward and westward by eddies detached from the anticyclone. We present an event of eddy shedding during 1-8 July 2003 and discuss a 1995-2016 climatology of eddy-shedding events. Our analysis indicates that eddies detached from the anticyclone contribute to the transport of Asian trace gases away from the Asian region to the western Pacific (20-30 • N, 120-150 • E) and western Africa (20-30 • N, 0-30 • E). Over the last two decades, the estimated frequency of occurrence of eddy-shedding events is ∼ 68 % towards western Africa and ∼ 25 % towards the western Pacific. Model sensitivity experiments considering a 10 % reduction in Asian emissions of non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO x) were performed with ECHAM5-HAMMOZ to understand the impact of Asian emissions on the UTLS. The model simulations show that transport of Asian emissions due to eddy shedding significantly affects the chemical composition of the upper troposphere (∼ 100-400 hPa) and lower stratosphere (∼ 100-80 hPa) over western Africa and the western Pacific. The 10 % reduction of NMVOCs and NO x Asian emissions leads to decreases in peroxyacetyl nitrate (PAN) (2 %-10 % near 200-80 hPa), ozone (1 %-4.5 % near ∼ 150 hPa) and ozone heating rates (0.001-0.004 K day −1 near 300-150 hPa) in the upper troposphere over western Africa and the western Pacific. forts to implement several mitigation strategies (Ohara et al., 2007). In situ observations, satellite measurements, trajectory analysis and model simulations show long-range transport of Asian trace gases to remote locations (e.g. North America, Europe) (Liang et al., 2004). The transported trace gases change the radiative balance, dynamics and chemical composition at the respective locations (Vogel et al., 2016). Satellite observations show increasing trends in sev-Published by Copernicus Publications on behalf of the European Geosciences Union.
Advances in Space Research, 2023
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Papers by Suvarna Fadnavis