Tropical tropopause layer evolution during 2015–16 El Niño event inferred from COSMIC RO measurements

Abstract

The detailed evolution of different tropical tropopause layer (TTL) parameters, such as tropopause height (cold point (CPH)/lapse rate (LRH)/convective (COH)), its corresponding temperature (CPT/LRT/COT) and TTL thickness in response to recent 2015–16 El Niño event are delineated using high-resolution Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Radio Occultation (RO) measurements. Distinct TTL anomalies are noticed between June-July-August (JJA), September-October-November (SON), and December -January-February (DJF) seasons during 2015–16 El Niño event. A pronounced positive anomaly in the CPH and LRH (~0.8 km) is noticed in JJA over most of the tropical equatorial region, whereas, in DJF, positive anomalies mostly concentrate over off equatorial central Pacific (CP) and eastern Pacific (EP) regions. Interestingly, prominent higher positive anomalies are evident in the convective outflow level altitude (~1 km) particularly over the tropical CP and EP regions in JJA and DJF. The CPT and LRT exhibit strong negative anomalies (>4 K) over CP and EP regions and positive anomalies over the western Pacific region in all the seasons. However, significant positive CPT and LRT anomalies are evident over the Atlantic region in DJF. In contrast, the COH (COT) and TTL thickness anomalies are well-matched with the outgoing long wave radiation anomalies compared to the CPH and LRH (CPT and LRT) anomalies. Overall, the observed TTL parameters exhibit similar El Niño signatures as observed for the other events. However, the 2015–16 El Niño event was one of strongest summer ENSO events in the 21st century compared to the previous events. As a result, prominent warm tropopause temperatures are evident over the WP region during JJA and these anomalies reaches maximum in DJF. The observed changes in the TTL parameters are explained in the context of circulation and convection changes over the tropics.