*2.2. Atmosphere Infrared Radio Souder Data*

AIRS is one of six instruments onboard Aqua, which is part of NASA's EOS of satellites launched into Earth orbit on 4 May 2002. Version 6 Level 2 data of CO is utilized in the present study. AIRS CO is retrieved with horizontal resolution of 45 km at nadir, in a swath of width about 1600 km. This orbit gives global coverage in the tropics every 2 days. The retrieval uses a cloud-clearing methodology providing the CO with sensitivity that peaks around 500 hPa, with ∼0.8–1.2 degrees of freedom of signal for 50–70% of scenes.

## *2.3. COSMIC GPS RO Data*

The temperature profiles obtained from the COSMIC GPS RO were utilized for the present study. The GPS RO data were downloaded from the COSMIC Data Analysis and Archive Centre (CDAAC) website (http://cosmic-io.cosmic.ucar.edu/cdaac/index.html). COSMIC GPS RO is a joint Taiwan–U.S. mission, which is a constellation of six microsatellites equipped with GPS receivers [37]. These satellites were launched in early 2006 and started providing data from April 2006. It provides 2000–2500 occultations for a day over the entire globe. There are different vertical resolutions available for COSMIC GPS RO data but for the present study we used 200 m resolution temperature (atmPrf) profiles available at CDAAC website only which is freely available for the public use. Note that these data are validated with a variety of techniques, including GPS radiosonde data and matched very well, particularly in the UTLS region [38–40]. A comprehensive introduction to the RO method for remote sensing of the atmosphere and ionosphere was presented by Liou et al. [41]. Deployment of COSMIC was presented by Fong et al. [42] and its constellation spacecraft system performance after one year in orbit was presented by Fong et al. [43]. Later, follow-on mission of COSMIC, that is COSMIC-2 and its deployment were introduced by Fong et al. [44] and [45], respectively. The suitability and importance of the GPS RO data for different topics of the atmospheric research (e.g., gravity wave studies [46–50], tropopause structure [51], tropical cyclones [52,53], etc.) were well reported in the literature.
