Effect of tropical cyclones on the tropical tropopause parameters observed using COSMIC GPS RO data

Abstract

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.

Effect of tropical cyclones on the stratosphere–troposphere exchange observed using satellite observations over the north Indian Ocean

“…These results compare well with higher WVMR observed on the eastern side of cyclones over Atlantic and Pacific oceans (Ray and Rosenlof, 2007). These results also compare well with those reported by Ravindra Babu et al (2015), who used GPS-RO measured relative humidity (RH) and found enhancement in RH on the eastern side of the centre in the upper troposphere (10-15 km) over the north Indian Ocean. Higher WVMR values observed on the eastern side of the cyclone centre might be due to the upper level anticyclonic circulation over the cyclones.…”

“…However, our quantification of the cross-tropopause flux will not be affected by this limitation as earlier studies revealed that the maximum STE occurs during the mature to peak stage of the cyclone. Details on the selection of 16 cyclones are presented in Ravindra Babu et al (2015). In Fig.…”

“…We also calculated the difference of tropopause parameters for different cyclone intensities (figures are not shown). Figure 3 shows the cyclonecentred composite of the mean difference in the tropopause parameters (CPH, LRH, CPT, LRT, COH, and TTL thickness) between climatological mean (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) and individual tropopause parameters observed during cyclones (irrespective of cyclone intensity), and more detailed results on the effect of TCs on the tropopause variations and mean temperature structure in UTLS region during TCs can be found in Ravindra Babu et al (2015). We have reported that the CPH (LRH) is lowered by 0.6 km (0.4 km) in most of the areas within a 500 km radius of the cyclone centre, and the temperature (CPT/LRT) is more or less colder or equal to the climatological values from the area around 1000 km from the cyclone centre.…”

“…The wind information is taken from ERA-Interim, and the tropopause temperature and pressure within 500 km of the cyclone centre is estimated from COSMIC GPS-RO measurements (Ravindra Babu et al, 2015). These values are considered for the maximum intensity day for each of the 16 cyclones and the respective cross-tropopause flux is estimated.…”

“…A detailed review on the effect of TCs on the UTLS can be found in same report. Recently, Ravindra Babu et al (2015) reported the effect of cyclones on the tropical tropopause parameters using temperature profiles obtained from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System radio occultation (GPS-RO) measurements. Many studies have been carried out on the role of extratropical cyclones in STE (for example Reutter et al, 2015 and references therein), though the quantitative estimates of STE provided by these case studies varied considerably.…”