Tropical Tropopause Dynamics

In recent years “Tropical Tropopause” has been receiving immense scientific interest because of its sensitivity to anthropogenic activities leading to climate change. The focus is mainly on chemistry, dynamics, radiation as well as transport within the Tropical Tropopause region/layer (TTL). There is an immediate need to link the TTL processes to climate, which requires the inclusion of radiation and chemistry in the conceptual framework. Convection in the tropics plays a key role in redistributing trace gases and aerosols in the upper Troposphere–lower stratosphere (UTLS) region, and the interaction between cloud dynamics, radiation and microphysics is of fundamental importance in these processes. Among these the convective detrainment and the effect of overshooting convection on the heat balance of the TTL remain elusive. With a view to address this important and complex interplay, particularly over Indian region, a focused field experiment “Tropical Tropopause Dynamics (TTD)” has been formulated under the CAWSES-India program of ISRO since 2004. The science objectives being addressed are:

(i) Temporal evolution of TTL on shorter time scales and its association with convection
(ii) Characteristics of turbulence structure in the troposphere/TTL at shorter time scales
(iii) Effect of cirrus in modulating the thermal structure of TTL
(v) Association between cirrus, convection and turbulence
(iv) Role of waves in modulating cirrus and thermal structure.

As part of this program, SPL and NARL jointly conducted scientific experiments at Trivandrum [8.5°N, 77°E] and Gadanki [13.5°N, 79.2°E] using balloons, lidar and radars during the period December 2010 to March 2014 [40 campaigns]. Simultaneous radiosonde soundings were carried out from both stations, at 3 h interval for three consecutive days in each month at 02:30, 05:30, 08:30, 11:30, 14:30, 17:30, 20:30 and 23:30 IST.

For further details on the data, please contact: Dr. S. V. Sunilkumar ( This email address is being protected from spambots. You need JavaScript enabled to view it.)



Since 2014, the TTD Experiments have been continued under the GARNETS (GPS Aided Radiosonde Network Experiment for Stratosphere-troposphere Studies) program as part of TDP (R&D) of SPL, VSSC.  Cryogenic frost-point hygrometer (CFH),Ozonesonde and radiosonde flights are carried out over Trivandrum, Hyderabad, Kharagpur and Haringhata under GARNETS program. The program aimed the “Quantification of moisture transport into the lower stratosphere and investigation on the role of tropopause dynamics in the vertical transport of moisture over the Indian monsoon region and its influence on the cirrus formation, chemistry and thermodynamics”. The main scientific objectives are:

(i) Study of the seasonal cycle of water vapour and ozone in the Upper Troposphere and Lower stratosphere (UTLS) region 

(ii) Examination of the impact of deep convection on the Tropical Tropopause and its role in the moisture budget of the UTLS 

(iii) Investigation of the Troposphere – Stratosphere exchange (STE) over the Indian region


Though present in trace amounts in the UTLS region, water vapour has profound influence in modulating the weather and climate of the Earth-atmosphere system. South Asian Monsoon region is the main entry point for water vapour and other species to the global lower stratosphere in summer monsoon season.  In this context, the scope of the work is: 

(i) Direct measurements of trace species (e.g., water vapour) in the UTLS region are scarce due to difficulties in measuring trace amount of water vapour at low temperatures; hence the UTLS over South Asian Monsoon Region is least explored.

(ii) For the first time, designed an approach and conducted direct / in situ measurements in the UTLS region (systematic and regular experiments), over the deep convective hotspots (deep convective and outflow regions) & non-hotspots of Indian region.

(iii) Development of a methodology utilizing ground-based (in situ) and space-based observations (KALPANA-1, INSAT-3D/3DR, SAPHIR-MeghaTropiques, MLS, CALIPSO) and global re-analysis dataset for the studies of the UTLS dynamics.


Under GARNETS program: 

o Systematic balloon-borne experiments/campaigns are conducted at Trivandrum and Hyderabad in all seasons (2014-2017] and over Kolkata region [Kharagpur and Haringhata] during pre-monsoon and summer-monsoon seasons [2016-2019].

o Conducted campaign mode balloon-borne experiments at Thumba, Trivandrum during deep convective events (BUREVI cyclone period) and fair-weather conditions in November 2020.

o Systematic monthly campaigns (CFH, Ozonesonde and Radiosonde flights) are being continued at Trivandrum. 


Science Results obtained from GARNETS program

(i) Seasonal/annual variation of water vapour in the lower stratosphere (LS) and the effect of local/regional dynamics on these variabilities:

1. Variabilities of water vapour in the lower regime of the LS (LS1; tropopause to 21 km) showing signatures of local/regional dynamics; tropopause temperature in winter and convection in all other seasons. LS1 contributes 50-70 % of the column integrated lower stratospheric water vapour (IWVLS) [ Atmos. Chem. & Phy. Diss., doi: 10.5194/acp-2018-630]

(ii) Quantitative assessment of moisture budget in the UTLS during summer monsoon: Role of monsoon dynamics 

Direct in situ observations (CFH observations) shows a water vapour enhancement of ~40-250 % in the upper troposphere and an increase of 0.5-1 ppmv (10-40 %) in the amount of water vapour entering into the lower stratosphere with respect to pre-monsoon [Atmos. Res., doi: 10.1016/ j.atmosres.2020.105336]

(iii) Role of cirrus clouds and atmospheric waves in modulating the water vapour distribution in the UTLS over Indian monsoon region is delineated.

The altitude structure of mean relative humidity with respect to ice (RHi) from CFH observations showed a double peak structure in the UTLS, with one peak around 12-14 km and another peak around 14-16 km. Examination of temperature anomalies due to atmospheric waves and occurrence of cirrus clouds revealed that the cirrus cloud is present only during the cold phase of the waves in the TTL.

(iv) Contrasting features of turbulence in the troposphere over Indian Peninsula

Convective instability exists in the upper troposphere even under clear air conditions; their generation mechanism could be wave breaking. The reduction in static stability causing convective instability in the 10-15 km region under in-cloud conditions could be due to saturation layers and/or sublimation of ice crystals beneath cirrus layers. Compared the occurrence of turbulence from Thorpe method and critical value of Ri. This study shows that the Thorpe method appears to be good in identifying convectively induced turbulence than the dynamically (shear) induced turbulence [J.Atmos.Sol.Terr. Phys., doi:  105179].

(v) Effect of meteorology on the variability of ozone in the troposphere and lower stratosphere region over a tropical station Thumba:

Ozone exhibits a clear annual variation in the lower troposphere (0-2 km) with winter maximum (49.2±3.6 ppbv) and summer monsoon minimum (21.9±0.7 ppbv). The relative standard deviation (RSD) is 20-30 % in the troposphere, 5% in the stratosphere and  the TTL [J. Atmos. Sol.-Terr. Phys., 215, 105567, doi: 2021.105567]

(vi) Spatial and diurnal variability of tropospheric water vapour over oceanic region.

Latitudinal variation of column Integrated Water Vapour (IWV) from Arabian Sea to Equatorial Indian Ocean is ~10 kg/m2. Hydration due to convection can lead to and enhancement of ~10-15 kg/m2. The amplitude of diurnal variation is less over deep ocean (~±2 kg/m2), when compared to offshore sea (~±3 kg/m2) and land (~±5 kg/m2).


Validation Experiments carried out using GARNETS data

The balloon-borne experiments conducted at different locations are used to validate the measurements by satellite and ground-based instruments. The details are given below:

(i) Validated SAPHIR onboard Megha-Tropiques, MLS onboard Aura, ERA-interim/MERRA datasets with balloon-borne Cryogenic Frost-point Hygrometer (CFH) over India [IEEE-Transactions of Geosciences and Remote sensing, 2018,].

(ii) Assessment of INSAT-3D/3DR derived parameters over India has been carried out by comparing the temperature and humidity profiles with radiosonde (in situ) measurements [IEEE-Transactions of Geosciences and Remote sensing, 2020, doi : 10.1109/TGRS.2019.2960277].

(iii) Validated Pisharoty sondes (B3 series) measured temperature and humidity profiles by comparing with WMO accepted radiosondes (Graw, iMet and Meisei) [Feedback provided to RFAD/AVN & SCL].

(iv) Validation of wind measurements from a 53MHz ST radar located at Haringhata (University of Calcutta) with collocated radiosonde launches [Radio Science, 2021, under review].


Publications in referred journals (under GARNETS)

1. Sunilkumar. S. V, M. Muhsin, M. Emmanuel, G. Ramkumar, K. Rajeev, S. Sijikumar. (2016). Balloon-borne cryogenic frost-point hygrometer observations of water vapour in the tropical upper troposphere and lower stratosphere over India: First results. J. Atmos. Sol.-Terr. Phys., 140, 86–93.

2. Sunilkumar. S. V, M. Muhsin, M. Venkat Ratnam, K. Parameswaran, B. V. Krishna Murthy, M. Emmanuel (2017). Boundaries of Tropical Tropopause layer (TTL): A new perspective based on thermal and stability profiles. J. Geophys. Res. Atmos., 122, doi: 10.1002/2016JD025217. 

3. Emmanuel. M, S. V. Sunilkumar, M. Muhsin, B. Suneel Kumar, N. Nagendra, P. R. Satheesh Chandran, G. Ramkumar, K. Rajeev (2018). Inter-comparison of Cryogenic Frost-point Hygrometer observations with SAPHIR, MLS, COSMIC, radiosonde and reanalysis datasets over Indian Peninsula. IEEE-Transactions on Geoscience and Remote Sensing, doi: 10.1109/TGRS.2018.2834154.

4. Emmanuel. M, S. V. Sunilkumar, M. Muhsin., B. Suneel Kumar, N. Nagendra, G. Ramkumar, Rajeev. K, Parameswaran. K (2018). Annual cycle of water vapour in the lower stratosphere over the Indian Peninsula derived from Cryogenic Frost-point Hygrometer observations. Atmos. Chem. & Phy. Diss., doi: 10.5194/acp-2018-630.

5. Muhsin. M, S. V. Sunilkumar, M. Venkat Ratnam, K. Parameswaran, K. Mohanakumar, S. Mahadevan, K. Murugadass, P. M. Muraleedharan, B. Suneel Kumar, N. Nagendra, M. Emmanuel, P. R. Satheesh Chandran, N. Koushik, G. Ramkumar, B. V. Krishna Murthy (2019), Contrasting features of tropospheric turbulence over the Indian peninsula, J. Atmos. Sol.-Terr. Phys., doi:  105179.

6. Kumar, A.H. and S. V. Sunilkumar (2020). Assessment of INSAT-3D Retrieved Temperature and Water Vapour With Collocated Radiosonde Measurements Over Indian Region, IEEE Transactions on Geoscience and Remote Sensing, 58, 6, 4000-4005, DOI: 10.1109/TGRS.2019.2960277

7. Emmanuel. M, S. V. Sunilkumar, M. Muhsin, K. Parameswaran, P. R. Satheesh Chandran, B. Suneel Kumar, A. Maitra, A. N. V. Satyanarayana, N. Nagendra, (2020). Effect of monsoon dynamics and deep convection on the upper troposphere lower stratosphere water vapour over Indian monsoon region, Atmos. Res., doi: 10.1016/ j.atmosres.2020.105336.

8. Satheesh Chandran. P. R, S. V. Sunilkumar, M. Muhsin, M. Emmanuel, Geetha Ramkumar, Prabha R Nair (2021), Effect of meteorology on the variability of ozone in the troposphere and lower stratosphere region over a tropical station Thumba (8.5°N, 76.9°E), J. Atmos. Sol.-Terr. Phys., 215, 105567, doi: 2021.105567.


For further details, please contact: Dr. S. V. Sunilkumar (sv_sunilkumar[at]vssc[dot]gov[dot]in)