Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

Abstract

<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>

Stratospheric intrusion into the troposphere during the tropical cyclone Nilam (2012)

“…The enhanced turbulence is attributed to the KHI, which plays a significant role in the STE process by modulating or weakening the tropical tropopause. Observational (Baray et al, 1999;Das, 2009;Das et al, 2015;Venkat Ratnam et al, 2016) and simulation (Leclair de Bellevue et al, 2007;Das et al, 2011) studies have shown that stratospheric air could intrude into the middle and upper troposphere during a tropical cyclone. On the contrary, Cairo et al (2008) have shown that there is no stratospheric intrusion during a tropical cyclone.…”

“…A few observational studies suggest that two-way transport at the ULTS region, i.e. upward flux of humid tropospheric air into the troposphere, after which downward flux of ozone-rich stratospheric air into the troposphere can occur during intense convective activity (Venkat Ratnam et al, 2016). This forms a circulation pattern of air mass in the UTLS region with respect to (w.r.t.)…”

“…Many observational studies have shown that the organized convective system associated with a tropical cyclone plays a significant role in the exchange of ozone and water vapour between the stratosphere and the troposphere (Baray et al, 1999;Leclair de Bellevue et al, 2007;Cairo et al, 2008;Das, 2009;Zhan and Wang, 2012;Das et al, 2015;Rowe and Hitchman, 2015;Venkat Ratnam et al, 2016). Zhan and Wang (2012) have found 25% enhancement in STE during the active tropical cyclone season as compared to the inactive season.…”

Tropical cyclones impact on tropopause and the lower stratosphere vapour based on satellite data

“…Earlier studies have shown that TCs moisten the upper troposphere (Su et al ., 2006; Ray and Rosenlof, 2007). TCs also can modify the tropical tropopause temperature, creating favourable conditions for water vapour exchange between the stratosphere and troposphere (Das et al ., 2011; Venkat Ratnam et al ., 2016). During the evolution stage of a storm over midlatitude, water vapour transported from troposphere to the lower stratosphere by the storm based on satellite observation (Stvák et al ., 2008).…”

Long‐Term Observations of Stratosphere‐Troposphere Exchange Using MST Radar and Aura MLS Measurements Over a Tropical Station Gadanki

“…Bourqui and Trepanier (2010) have found that on a global scale, 25–50% sources are from middle‐latitude stratospheric intrusion. There are many studies which detail with episodic (instantaneous short time scale from minutes to hour) stratospheric ozone intrusion, that is, STT associated with convective processes (e.g., Baray et al, 1999; Cairo et al, 2008; Das, 2009; Das et al, 2016; Das, Ratnam, Uma, Subrahmanyam, et al, 2016; Kumar & Uma, 2009; Venkar Ratnam et al, 2016; Zhan & Wang, 2012). In addition to the conventional methods, there are many observational evidences of STT over the globe using radar operating at VHF range (e.g., mesosphere‐stratosphere‐troposphere (MST) radar) (Das, 2009; Das et al, 2008; Das, Ratnam, Uma, Subrahmanyam, et al, 2016; Gage & Green, 1982; Hocking et al, 2007; Kumar & Uma, 2009; Rao et al, 2008).…”