ALBERT

Description: 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 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. 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.

Description: Tropical cyclones (TCs) are deep convective synoptic scale systems and play an important role in modifying the thermal structure, tropical tropopause parameters and hence 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 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 TCs events, we generate the mean cyclone-centered composite structure for the tropopause parameters and removed from climatological mean obtained from averaging the GPS RO data from 2002–2013. Since the TCs include eye, eye walls and deep convective bands, we obtained the tropopause parameters based on radial distance from cyclone eye. In general, decrease in the CPH in the eye is noticed as expected. However, as the distance from cyclone eye increases by 3, 4, and 5° an enhancement in CPH (CPT), LRH (LRT) are observed. Lowering of CPH (0.6 km) and LRH (0.4 km) values with coldest CPT and LRT (2–3 K) within the 500 km radius from the TC centre is noticed. Higher (2 km) COH leading to the lowering of TTL thickness (2–3 km) is clearly observed. There exists multiple tropopause structures in the profiles of temperature obtained within 1° from centre of TC. These changes in the tropopause parameters are expected to influence the water vapour transport from troposphere to lower stratosphere and ozone from lower stratosphere to the upper troposphere and hence STE processes.

Description: Radiosondes are widely used to obtain basic meteorological parameters such as pressure (P), temperature (T), relative humidity (RH), and horizontal winds during the balloon ascent up to the altitude of balloon burst, usually ∼32–35 km. Data from the radiosondes released from Gadanki (13.5° N, 79.2° E), a tropical station in India, has been collected during the ascent and during the descent as well without attaching any parachute or its equivalent since the year 2008. In the present study an attempt has been made to characterize the radiosonde descent data with the main objective of exploring its usefulness and reliability for scientific purposes. We compared the data obtained during ascent and descent phases of the same sounding. The mean differences in T, RH and horizontal winds between ascent and descent data are found to be small and are sometimes even within the uncertainty of the measurements and/or expected diurnal variation itself. The very good consistency observed between the ascent and the descent data shows that one more profile of the meteorological parameters can be constructed within 3 h of time of balloon launch practically at no additional cost. Further checks are done by utilizing the 3 hourly radiosonde observations collected during the Tropical Tropopause Dynamics campaign conducted at Gadanki. In the process of checking the consistency between the radiosonde ascent and descent data, several new findings are arrived at and are reported in this study. In general, it has taken more than half-an-hour for the balloon to reach the ground from the burst altitude. It is also observed that the fall velocity is close to 10 m s−1 near the surface. Finally, it is suggested to record also the observations when the balloon is descending as this information is also useful for scientific purposes.

Description: Radiosondes are widely used to obtain basic meteorological parameters such as pressure (P), temperature (T), relative humidity (RH) and horizontal winds during the balloon ascent up to the altitude of balloon burst, usually ~ 32–35 km. Data from the radiosondes released from Gadanki (13.5° N, 79.2° E), a tropical station in India, have been collected during the ascent and during the descent as well without attaching any parachute or its equivalent since the year 2008. In the present study an attempt has been made to characterize the radiosonde descent data with the main objective of exploring its usefulness and reliability for scientific purposes. We compared the data obtained during ascent and descent phases of the same sounding. The mean differences in T, RH and horizontal winds between ascent and descent data are found to be small and are sometimes even within the uncertainty of the measurements and/or expected diurnal variation itself. The very good consistency observed between the ascent and the descent data shows that one more profile of the meteorological parameters can be constructed within 3 h of time of balloon launch practically at no additional cost. Further checks are done by utilizing the 3-hourly radiosonde observations collected during the Tropical Tropopause Dynamics campaigns conducted at Gadanki. In the process of checking the consistency between the radiosonde ascent and descent data, several new findings are arrived at and are reported in this study. In general, it has taken more than half an hour for the balloon to reach the ground from the burst altitude. It is also observed that the fall velocity is close to 10 m s−1 near the surface. Finally, it is suggested to record the observations also when the balloon is descending as this information is useful for scientific purposes.

Description: 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.

Description: 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.