Probing the dynamical features of intense pre-monsoon and summer monsoon deep convective systems using ARIES Stratosphere Troposphere Radar (206.5 MHz) over the Central Himalayan region 

2021 ◽  
Author(s):  
Aditya Jaiswal ◽  
Manish Naja ◽  
Samaresh Bhattacharjee
Keyword(s):  
Momentum Flux ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Heat Budget ◽  
Monsoon Season ◽  
Deep Convection ◽  
Himalayan Region ◽  
Upper Troposphere ◽  
Himalayan Foothills ◽  
Dynamical Features

<p>Deep convection is known to be critical for the transport of mass and momentum flux, heat and moisture throughout in the upper troposphere and lower stratosphere region. Hence it modifies the heat budget and general circulation in the atmosphere. Earlier studies have noted very strong instability in the atmosphere over Himalayan foothills, triggering occasional intense convection due to the orographic lifting of the low level moist flow.  However due to the lack of observational network over this complex terrain, a comprehensive analysis of these events and their impacts have not been done.</p><p>Recently a Stratosphere Troposphere Radar (wind profiler) operating at VHF frequency of 206.5 MHz has been installed at a high altitude site Aryabhatta Research Institute of Observational Sciences (ARIES) (29.4<sup>o</sup>N, 79.5<sup>o</sup> E, 1790 m amsl) in Nainital located in Himalayan foothills, a meteorologically sensitive subtropical region. Using the capability of VHF radar of detecting echoes from both clear air and precipitation,  intense deep convection systems were observed on May 5, 2020 and September 2, 2020. Both the events have been studied in details using the temporal and vertical evolution of  radar parameters like total backscattered power and spectral width. Reanalysis data from MERRA-2 and cloud fraction data of IR and Water Vapour channels of INSAT 3D has also been used to investigate underlying synoptic features of the event. Here, it is suggested that deep convection of the pre-monsoon season was induced due to moisture carried by the western disturbance. While the event in monsoon season was due to the easterly moist flow from the Bay of Bengal. The moisture in the mid - troposphere coupled with the orographic lift led to vigorous updrafts and downdrafts of magnitude reaching up to 16 m/s. Updrafts found to be extending well beyond the tropopause into the lower stratosphere region. From the temporal evolution of vertical wind velocity obtained from ST Radar, a clear demarcation between updrafts and downdrafts region was established during the mature phase of the event due to veering of the wind from lower to upper troposphere which also led to the tilting of the updraft cores. During the event the exchange of the vertical flux of horizontal momentum between upper troposphere and lower stratosphere has also been estimated. A significant enhancement (2 – 3 times) in mean zonal (<em>u'w</em>') and meridional component (<em>v'w')</em> of momentum flux has been observed during convection as compared to quiet period. In the upper troposphere and lower stratosphere region mean flux values even reached up to about 33 m<sup>2</sup> s<sup>-2</sup>. We feel that this study will help in providing the crucial insights of the dynamical features of meso-scale convective phenomenon in the central Himalayan region for the first time.</p>

scholarly journals The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

2015 ◽  
Vol 15 (11) ◽  
pp. 6467-6486 ◽  
Author(s):  
W. Frey ◽  
R. Schofield ◽  
P. Hoor ◽  
D. Kunkel ◽  
F. Ravegnani ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Transport Processes ◽  
Convective System ◽  
Upper Troposphere ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Transport And Mixing ◽  
The Impact

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of 50 ppbv. However, the passive carbon monoxide tracer exhibits an increase, while the observations show a decrease of about 10 ppbv, indicative of an erroneous model representation of the transport processes in the tropical tropopause layer. Furthermore, it could point to insufficient entrainment and detrainment in the model. The simulation shows a general moistening of air in the lower stratosphere, but it also exhibits local dehydration features. Here we use the model to explain the processes causing the transport and also expose areas of inconsistencies between the model and observations.

scholarly journals Thermodynamic control of anvil cloud amount

2016 ◽  
Vol 113 (32) ◽  
pp. 8927-8932 ◽  
Author(s):  
Sandrine Bony ◽  
Bjorn Stevens ◽  
David Coppin ◽  
Tobias Becker ◽  
Kevin A. Reed ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
General Circulation ◽  
Deep Convection ◽  
Cloud Amount ◽  
General Circulation Models ◽  
Cloud Fraction ◽  
Thermodynamic Control ◽  
Upper Troposphere ◽  
High Clouds ◽  
Enhanced Stability

General circulation models show that as the surface temperature increases, the convective anvil clouds shrink. By analyzing radiative–convective equilibrium simulations, we show that this behavior is rooted in basic energetic and thermodynamic properties of the atmosphere: As the climate warms, the clouds rise and remain at nearly the same temperature, but find themselves in a more stable atmosphere; this enhanced stability reduces the convective outflow in the upper troposphere and decreases the anvil cloud fraction. By warming the troposphere and increasing the upper-tropospheric stability, the clustering of deep convection also reduces the convective outflow and the anvil cloud fraction. When clouds are radiatively active, this robust coupling between temperature, high clouds, and circulation exerts a positive feedback on convective aggregation and favors the maintenance of strongly aggregated atmospheric states at high temperatures. This stability iris mechanism likely contributes to the narrowing of rainy areas as the climate warms. Whether or not it influences climate sensitivity requires further investigation.

scholarly journals Trends in peroxyacetyl nitrate (PAN) in the upper troposphere and lower stratosphere over southern Asia during the summer monsoon season: regional impacts

2014 ◽  
Vol 14 (23) ◽  
pp. 12725-12743 ◽  
Author(s):  
S. Fadnavis ◽  
M. G. Schultz ◽  
K. Semeniuk ◽  
A. S. Mahajan ◽  
L. Pozzoli ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Monsoon Season ◽  
Michelson Interferometer ◽  
Temporal Trends ◽  
Nox Emissions ◽  
Summer Monsoon Season ◽  
Peroxyacetyl Nitrate ◽  
Upper Troposphere ◽  
India And China

Abstract. We analyze temporal trends of peroxyacetyl nitrate (PAN) retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) during 2002–2011 in the altitude range 8–23 km over the Asian summer monsoon (ASM) region. The greatest enhancements of PAN mixing ratios in the upper troposphere and lower stratosphere (UTLS) are seen during the summer monsoon season from June to September. During the monsoon season, the mole fractions of PAN show statistically significant (at 2σ) positive trends from 0.2 ± 0.05 to 4.6 ± 3.1 ppt yr−1 (except between 12 and 14 km) which is higher than the annual mean trends of 0.1 ± 0.05 to 2.7 ± 0.8 ppt yr−1. These rising concentrations point to increasing NOx (= NO + NO2) and volatile organic compound (VOC) emissions from developing nations in Asia, notably India and China. We analyze the influence of monsoon convection on the distribution of PAN in UTLS with simulations using the global chemistry–climate model ECHAM5-HAMMOZ. During the monsoon, transport into the UTLS over the Asian region primarily occurs from two convective zones, one the South China Sea and the other over the southern flank of the Himalayas. India and China host NOx-limited regimes for ozone photochemical production, and thus we use the model to evaluate the contributions from enhanced NOx emissions to the changes in PAN, HNO3 and O3 concentrations in the UTLS. From a set of sensitivity experiments with emission changes in particular regions, it can be concluded that Chinese emissions have a greater impact on the concentrations of these species than Indian emissions. According to SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) NO2 retrievals NOx emissions increases over India have been about half of those over China between 2002 and 2011.

Transport into the upper troposphere-lower stratosphere over North America

2020 ◽  
Author(s):  
Xinyue Wang ◽  
William Randel ◽  
Yutian Wu
Keyword(s):  
Gulf Of Mexico ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Deep Convection ◽  
Vertical Diffusion ◽  
Dynamical Mechanism ◽  
Upper Troposphere ◽  
The North ◽  
Budget Analysis

<p>We study fast transport of air from the surface into the North American upper troposphere-lower stratosphere (UTLS) during northern summer with a large ensemble of Boundary Impulse Response (BIR) idealized tracers. Specifically, we implement 90 pulse tracers at the Northern Hemisphere surface and release them during July and August months in the fully coupled Whole Atmosphere Community Climate Model (WACCM) version 5. We focus on the most efficient transport cases above southern U.S. (10°-40°N, 60°-140°W) at 100 hPa with modal ages fall below 10th percentile. We examine transport-related terms, including resolved dynamics computed inside model transport scheme and parameterized processes (vertical diffusion and convective parameterization), to pin down the dominant dynamical mechanism. Our results show during the fastest transport, air parcels enter ULTS directly above the Gulf of Mexico. The budget analysis indicates that strong deep convection over the Gulf of Mexico fast uplift the tracer into 200 hPa, and then is vertically advected into 100 hPa and circulated by the enhanced large-scale anticyclone. </p>

scholarly journals Annual cycle of water vapour in the lower stratosphere over the Indian Peninsula derived from Cryogenic Frost-point Hygrometer observations

2018 ◽  
Author(s):  
Maria Emmanuel ◽  
Sukumarapillai V. Sunilkumar ◽  
Muhsin Muhammed ◽  
Buduru Suneel Kumar ◽  
Nagendra Neerudu ◽  
...  
Keyword(s):  
Water Vapour ◽  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Deep Convection ◽  
Equatorial Station ◽  
Post Monsoon ◽  
Frost Point ◽  
Stratospheric Water Vapour

Abstract. In situ measurements of lower stratospheric water vapour employing Cryogenic Frost point Hygrometer (CFH) over two tropical stations, Trivandrum (8.53 °N, 76.87 °E) and Hyderabad (17.47 °N, 78.58 °E) over the Indian subcontinent are conducted as part of Tropical Tropopause Dynamics (TTD) monthly campaigns under GARNETS program. The annual variation of lower stratosphere (LS) water vapour clearly depicts the so called tape recorder effect at both the stations. The ascent rate of water vapour compares well with the velocity of Brewer-Dobson circulation and is slightly higher over the equatorial station when compared to the off-equatorial station. The column integrated water vapour in the LS varies in the range 1.5 to 4 g/m2 with low values during winter and high values during summer monsoon and post monsoon seasons and its variability shows the signatures of local dynamics. The variation in water vapour mixing ratio (WVMR) at the cold point tropopause (CPT) exactly follows the variation in CPT temperature. The difference in WVMR between the stations shows a semi-annual variability in the altitude region 18–20 km region with high values of WVMR during summer monsoon and winter over Hyderabad and during pre-monsoon and post-monsoon over Trivandrum. This difference is related to the influence of the variations in local CPT temperature and deep convection. The monsoon dynamics has a significant role in stratospheric water vapour distribution in summer monsoon season.

scholarly journals Balloon-borne measurements of temperature, water vapor, ozone and aerosol backscatter at the southern slopes of the Himalayas during StratoClim 2016-2017

2018 ◽  
Author(s):  
Simone Brunamonti ◽  
Teresa Jorge ◽  
Peter Oelsner ◽  
Sreeharsha Hanumanthu ◽  
Bhupendra B. Singh ◽  
...  
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Monsoon Season ◽  
Deep Convection ◽  
Lapse Rate ◽  
Boreal Summer ◽  
Aerosol Layer ◽  
Vertical Distributions ◽  
Aerosol Backscatter ◽  
Temperature Water

Abstract. The Asian summer monsoon anticyclone (ASMA) is a major meteorological system of the upper troposphere-lower stratosphere (UTLS) during boreal summer. It is known to be enriched in tropospheric trace gases and aerosols, due to rapid lifting from the boundary layer by deep convection and subsequent horizontal confinement. Given its dynamical structure, the ASMA offers a very efficient pathway for the transport of pollutants to the global stratosphere. Detailed understanding of the ASMA structure and processes requires accurate in-situ measurements. Here we present balloon-borne measurements of temperature, water vapor, ozone and aerosol backscatter conducted within the StratoClim project from two stations at the southern slopes of the Himalayas. In total we performed 63 balloon soundings during two main monsoon-season campaigns, in August 2016 in Nainital, India (NT16AUG) and July–August 2017 in Dhulikhel, Nepal (DK17), and one brief post-monsoon campaign in Nainital in November 2016 (NT16NOV). These measurements provide unprecedented insights into the ASMA thermal structure and its relations to the vertical distributions of water vapor, ozone and aerosols. To study the structure of the UTLS during the monsoon season, we adopt the thermal definition of tropical tropopause layer (TTL), and define the region of altitudes between the lapse rate minimum (LRM) and the cold-point tropopause (CPT) as the Asian Tropopause Transition Layer (ATTL). Further, based on air mass trajectories, we define the Top of Confinement (TOC) level of ASMA, which divides the lower stratosphere (LS) into a Confined LS (CLS), below the TOC and above the CPT, and a Free LS (FLS), above the TOC. Using these thermodynamically-significant boundaries, our analysis reveals that the composition of the UTLS is affected by deep convection up to altitudes 1.5–2 km above the CPT due to the horizontal confinement effect of ASMA. This is shown by enhanced water vapor mixing ratios in the Confined LS compared to background stratospheric values in the Free LS, observed in both NT16AUG (+0.5 ppmv) and DK17 (+0.75 ppmv), and by enhanced aerosol backscatter of the Asian tropopause aerosol layer (ATAL) extending into the Confined LS, as observed in NT16AUG. The CPT was 600 m higher in altitude and 5 K colder in DK17 compared to NT16AUG and strong ozone depletion was found in the ATTL and CLS in DK17, suggesting stronger convective activity during DK17 compared to NT16AUG. An isolated water vapor maximum in the Confined LS, about 1 km above the CPT, was also found in DK17, which we argue is due to overshooting convection hydrating the CLS. These evidence show that the vertical distributions and variability of water vapor, ozone and aerosols in the Asian UTLS are controlled by the top height of the anticyclonic confinement in ASMA, rather than by CPT height as in the conventional understanding of TTL, and suggest that the ASMA contributes to moistening the global stratosphere and to increase its aerosol burden.

scholarly journals Forcing of the Upper-Tropospheric Monsoon Anticyclones

2019 ◽  
Vol 76 (7) ◽  
pp. 1937-1954 ◽  
Author(s):  
Leong Wai Siu ◽  
Kenneth P. Bowman
Keyword(s):  
General Circulation ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Warm Season ◽  
Circulation Model ◽  
Western Hemisphere ◽  
North American Monsoon ◽  
Upper Troposphere ◽  
Forcing Mechanisms ◽  
Good Agreement

Abstract During the boreal warm season (May–September), the circulation in the upper troposphere and lower stratosphere is dominated by two large anticyclones: the Asian monsoon anticyclone (AMA) and North American monsoon anticyclone (NAMA). The existence of the AMA has long been linked to Asian monsoon precipitation using the Matsuno–Gill framework, but the origin of the NAMA has not been clearly understood. Here the forcing mechanisms of the NAMA are investigated using a simplified dry general circulation model. The simulated anticyclones are in good agreement with observations when the model is forced by a zonally symmetric meridional temperature gradient plus a realistic geographical distribution of heating based on observed tropical and subtropical precipitation in the Northern Hemisphere. Model experiments show that the AMA and NAMA are largely independent of one another, and the NAMA is not a downstream response to the Asian monsoon. The primary forcing of the NAMA is precipitation in the longitude sector between 60° and 120°W, with the largest contribution coming from the subtropical latitudes within that sector. Experiments with idealized regional heating distributions reveal that the extratropical response to tropical and subtropical precipitation depends approximately linearly on the magnitude of the forcing but nonlinearly on its latitude. The AMA is stronger than the NAMA, primarily because precipitation in the subtropics over Asia is much heavier than at similar latitudes in the Western Hemisphere.

scholarly journals Large differences in reanalyses of diabatic heating in the tropical upper troposphere and lower stratosphere

2013 ◽  
Vol 13 (18) ◽  
pp. 9565-9576 ◽  
Author(s):  
J. S. Wright ◽  
S. Fueglistaler
Keyword(s):  
Turbulent Mixing ◽  
Lower Stratosphere ◽  
Heat Budget ◽  
Radiative Heating ◽  
Japan Meteorological Agency ◽  
Latent Heating ◽  
Moist Convection ◽  
Climate Data ◽  
Upper Troposphere ◽  
Tropical Upper Troposphere

Abstract. We present the time mean heat budgets of the tropical upper troposphere (UT) and lower stratosphere (LS) as simulated by five reanalysis models: the Modern-Era Retrospective Analysis for Research and Applications (MERRA), European Reanalysis (ERA-Interim), Climate Forecast System Reanalysis (CFSR), Japanese 25-yr Reanalysis and Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS), and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis 1. The simulated diabatic heat budget in the tropical UTLS differs significantly from model to model, with substantial implications for representations of transport and mixing. Large differences are apparent both in the net heat budget and in all comparable individual components, including latent heating, heating due to radiative transfer, and heating due to parameterised vertical mixing. We describe and discuss the most pronounced differences. Discrepancies in latent heating reflect continuing difficulties in representing moist convection in models. Although these discrepancies may be expected, their magnitude is still disturbing. We pay particular attention to discrepancies in radiative heating (which may be surprising given the strength of observational constraints on temperature and tropospheric water vapour) and discrepancies in heating due to turbulent mixing (which have received comparatively little attention). The largest differences in radiative heating in the tropical UTLS are attributable to differences in cloud radiative heating, but important systematic differences are present even in the absence of clouds. Local maxima in heating and cooling due to parameterised turbulent mixing occur in the vicinity of the tropical tropopause.

Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport

Science ◽  
2012 ◽  
Vol 337 (6090) ◽  
pp. 78-81 ◽  
Author(s):  
Adam E. Bourassa ◽  
Alan Robock ◽  
William J. Randel ◽  
Terry Deshler ◽  
Landon A. Rieger ◽  
...  
Keyword(s):  
Sulfur Dioxide ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Volcanic Eruptions ◽  
Volcanic Aerosol ◽  
Upper Troposphere ◽  
Asian Summer

The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO2) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO2 was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.

scholarly journals Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

2015 ◽  
Vol 15 (20) ◽  
pp. 11477-11499 ◽  
Author(s):  
S. Fadnavis ◽  
K. Semeniuk ◽  
M. G. Schultz ◽  
M. Kiefer ◽  
A. Mahajan ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Peroxyacetyl Nitrate ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Asian Summer ◽  
Emission Change ◽  
Transport Patterns

Abstract. The Asian summer monsoon involves complex transport patterns with large-scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry–climate model ECHAM5–HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species peroxyacetyl nitrate (PAN), NOx and HNO3 from various monsoon regions, to the UTLS over southern Asia and vice versa. Simulated long-term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon season (June–September) in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM), the North American monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere (UT). Remote transport also occurs in the extratropical UT where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. Sensitivity experiments with ECHAM5–HAMMOZ for simultaneous NOx and non-methane volatile organic compounds (NMVOCs) emission change (−10 %) over ASM, NAM and WAM confirm similar transport. Our analysis shows that a 10 % change in Asian emissions transports ~ 5–30 ppt of PAN in the UTLS over Asia, ~ 1–10 ppt of PAN in the UTLS of northern subtropics and mid-latitudes, ~ 7–10 ppt of HNO3 and ~ 1–2 ppb of ozone in UT over Asia. Comparison of emission change over Asia, North America and Africa shows that the highest transport of HNO3 and ozone occurs in the UT over Asia and least over Africa. The intense convective activity in the monsoon regions is associated with lightning and thereby the formation of additional NOx. This also affects the distribution of PAN in the UTLS. Simulations with and without lightning show an increase in the concentrations of PAN (~ 40 %), HNO3 (75 %), NOx (70 %) and ozone (30 %) over the regions of convective transport. Lightning-induced production of these species is higher over equatorial Africa and America compared to the ASM region. This indicates that the contribution of anthropogenic emissions to PAN in the UTLS over the ASM is higher than that of lightning.

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