Abstract
It is well reported that the 2015–16 El Niño event is one of the most intense and long lasting events in the 21st century. The quantified changes in the trace gases (Ozone (O3), Carbon Monoxide (CO) and Water Vapour (WV)) in the tropical upper troposphere and lower stratosphere (UTLS) region are delineated using Aura Microwave Limb Sounder (MLS) and Atmosphere Infrared Radio Sounder (AIRS) satellite observations from June to December 2015. Prior to reaching its peak intensity of El Niño 2015–16, large anomalies in the trace gases (O3 and CO) were detected in the tropical UTLS region, which is a record high in the 21st century. A strong decrease in the UTLS (at 100 and 82 hPa) ozone (~200 ppbv) in July-August 2015 was noticed over the entire equatorial region followed by large enhancement in the CO (150 ppbv) from September to November 2015. The enhancement in the CO is more prevalent over the South East Asia (SEA) and Western Pacific (WP) regions where large anomalies of WV in the lower stratosphere are observed in December 2015. Dominant positive cold point tropopause temperature (CPT-T) anomalies (~5 K) are also noticed over the SEA and WP regions from the high-resolution Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Position System (GPS) Radio Occultation (RO) temperature profiles. These observed anomalies are explained in the light of dynamics and circulation changes during El Niño.
Highlights
The Upper Troposphere and Lower Stratosphere (UTLS) is one of the important regions of the Earth’s atmosphere and crucial for the Earth’s energy balance [1]
water vapour (WV) acts as a major source of cooling in the upper troposphere whereas O3 is the main source for the warming in the lower stratosphere (LS)
The variability in the UTLS trace gases is strongly influenced by several dominant atmospheric oscillations such as quasi-biennial oscillation (QBO) and El Niño Southern Oscillation (ENSO)
Summary
The Upper Troposphere and Lower Stratosphere (UTLS) is one of the important regions of the Earth’s atmosphere and crucial for the Earth’s energy balance [1]. High troposphere temperatures in El Niño period, drought conditions generally observed over South East Asia (SEA) region with lot of biomass burning and forest fires [12,13,14]. It was reported that during the 2015–16 El Niño event, the large anomalies of WV and ice in the LS were observed in December 2015 over SEA and WP regions [7,25] This enhancement in WV was either due to the warm tropopause temperatures [7] or due to the 2015–16 QBO disruption [25]. We present the observed large anomalies of these trace gases in the tropical UTLS region during the recent strong El Nino event of 2015–16
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