Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the north Indian Ocean during 2007-2013 on the STE processes is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) radio occultation (RO) measurements, and ozone and water vapour concentrations in the UTLS region are obtained from Aura Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km of the centre of the tropical cyclone. In our earlier study, we observed a decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K), and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within 500 km of the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from the cyclone centre, whereas the enhancement in the water vapour in the lower stratosphere is more significant on the south-east side, extending from 500 to 1000 km away from the cyclone centre. The cross-tropopause mass flux for different intensities of cyclones is estimated and it is found that the mean flux from the stratosphere to the troposphere for cyclonic storms is 0.05 ± 0.29 × 10 −3 kg m −2 , and for very severe cyclonic storms it is 0.5 ± 1.07 × 10 −3 kg m −2 . More downward flux is noticed on the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget, and consequentially the STE in the UTLS region.

Abstract. Tropical cyclones (TCs) are deep convective synoptic-scale systems that play an important role in modifying the thermal structure, tropical tropopause parameters and hence also modify stratosphere-troposphere exchange (STE) processes. In the present study, high vertical resolution and high accuracy measurements from COSMIC Global Positioning System (GPS) radio occultation (RO) measurements are used to investigate and quantify the effect of tropical cyclones that occurred over Bay of Bengal and Arabian Sea in the last decade on the tropical tropopause parameters. The tropopause parameters include cold-point tropopause altitude (CPH) and temperature (CPT), lapse-rate tropopause altitude (LRH) and temperature (LRT) and the thickness of the tropical tropopause layer (TTL), that is defined as the layer between convective outflow level (COH) and CPH, obtained from GPS RO data. From all the TC events, we generate the mean cyclone-centred composite structure for the tropopause parameters and removed it from the climatological mean obtained from averaging the GPS RO data from 2002 to 2013. Since the TCs include eye, eye walls and deep convective bands, we obtained the tropopause parameters based on radial distance from the cyclone eye. In general, decrease in the CPH in the eye is noticed as expected. However, as the distance from the cyclone eye increases by 300, 400, and 500 km, an enhancement in CPH (CPT) and LRH (LRT) is observed. Lowering of CPH (0.6 km) and LRH (0.4 km) values with coldest CPT and LRT (2-3 K) within a 500 km radius of the TC centre is noticed. Higher (2 km) COH leading to the lowering of TTL thickness (2-3 km) is clearly observed. There are multiple tropopause structures in the profiles of temperature obtained within 100 km from the centre of the TC. These changes in the tropopause parameters are expected to influence the water vapour transport from the troposphere to the lower stratosphere, and ozone from the lower stratosphere to the upper troposphere, hence influencing STE processes.

L a b o r a t o r y f o r Space S c i e n c e s NASA Goddard Space F l i g h t C e n t e r G r e e n b e l t , Maryland ABSTRACT V a r i a t i o n s i n t h e e l e c t r o n d e n s i t y d i s t r i b u t i o n of t h e t o p s i d e i o n o s p h e r e ( i n c l u d i n g t h e h e i g h t of t h e Fa peak) obt a i n e d from A l o u e t t e I d u r i n g t h e g r e a t m a g n e t i c s t o r m of 17-18 A p r i l 1965 a r e a n a l y z e d . i n g on t h e p h a s e of t h e m a g n e t i c storm. S p e c i f i c a l l y , enhancement is a s s o c i a t e d w i t h t h e p o s i t i v e p h a s e and t h e asymmetric p a r t of t h e main p h a s e , w h i l e d e p l e t i o n of t h e t o p s i d e i o n o s p h e r e o c c u r s d u r i n g t h e s y m m e t r i c p a r t of t h e s t o r m main p h a s e o v e r a l a t i t u d er a n g e c o r r e s p o n d i n g t o L v a l u e s g r e a t e r t h a n 3. A s s o c i a t e d w i t h t h i s d e p l e t i o n is a r e d i s t r i b u t i o n of i o n i z a t i o n i nd i c a t i n g t h a t t h e t o p s i d e i o n o s p h e r e d u r i n g t h e s y m m e t r i c main p h a s e c o n s i s t s p r i m a r i l y of 0 ( w i t h H+ b e i n g d e p l e t e d ) . The + enhancement of t o p s i d e i o n i z a t i o n d u r i n g t h e p o s i t i v e p h a s e of t h e storm a p p e a r s t o b e a s s o c i a t e d w i t h t h e c o m p r e s s i o n of t h e d a y t i m e magnetosphere d u r i n g t h a t p h a s e of t h e storm.The d e p l e t i o n seems t o b e a s s o c i a t e d w i t h t h e e x p a n s i o n of f i e l d t u b e s due t o t h e p r e s e n c e of t h e h i g h e n e r g y -d e n s i t y r i n g c u r r e n t plasma a s o b s e r v e d on s a t e l l i t e s c a u s i n g a n upward f l u

Over the Indian region, changes in the tropopause parameters during pre-monsoon to monsoon seasons have been reported. However, no study exists to date dealing with the Indian summer monsoon (ISM) onset signatures on the tropopause parameters. In the present study, the climatological structure of the tropical tropopause layer during the onset phase of ISM is delineated by using long-term (2006-2017) radiosonde observations over Gadanki (13.5 N, 79.2 E). A prominent transition in the tropopause parameters from pre-monsoon to monsoon is noticed and the transition is initiated from the day of ISM onset. Continuous decrease (increase) of tropopause altitude (temperature) is perceived after the ISM onset. The ozonesonde observations clearly show the strong enhancement in the ozone mixing ratio in the lower stratosphere (~16-20 km) after the ISM onset. This clearly demonstrates the instantaneous warming of the tropopause region after the ISM onset in addition to the latent heat release due to the precipitation. Transitions from pre-monsoon to monsoon in the tropopause parameters are influenced strongly by onset of ISM which was attributed as seasonal changes earlier. These results provide strong evidence on the ISM onset signatures on the tropical tropopause parameters.

<p><strong>Abstract.</strong> Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10<sup>−3</sup> kg m<sup>−2</sup> and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10<sup>−3</sup> kg m<sup>−2</sup>. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.</p>