The stratospheric ozone rich cold intrusion during El‐Niño over the Indian region: Implication during the Indian summer monsoon

Abstract

AbstractOzone in the upper troposphere is a dominant radiative constituent. In this study, we investigate ozone variability due to stratospheric intrusions in the upper troposphere over India and associated radiative impacts during monsoon breaks co‐occurring with El Niño using the ECHAM5‐HAMMOZ, Global‐Chemistry‐climate model simulations, and ERA‐Interim reanalysis data. Our analysis shows that during El Niño, deep stratospheric intrusions occur at the North India‐Tibetan Plateau (NI‐TP) region and the eastern edge of the monsoon anticyclone. These intrusions lead to an enormous increase in ozone amounts (~100 ppb) in the upper troposphere over India. The intrusions frequently penetrate deep into the troposphere which enhances the surface ozone levels by ~10–20 ppb and augments radiative forcing by ~0.33 W m−2 at the top of the atmosphere. The stratospheric intrusions are associated with the eastward‐moving wave train (composed of cyclonic and anticyclonic circulations) in the upper troposphere emanating from the anomalously warm east Pacific, traversing towards NI‐TP locale. This wave train transport extra‐tropical cold air mass, producing an anomalous cooling of ~1.6–2 K in the upper troposphere over NI‐TP. The upper tropospheric anomalous cooling seems to act as a dominating factor opposing the heating due to enhanced ozone. The wave train likewise intensifies Rossby wave breaking, facilitating stratospheric intrusions, enhancing the anomalous subsidence over the NI‐TP region. Our analysis shows that break days with El Niño substantiate with simultaneous occurrence of (a) RWB, (b) transport of cold air mass via WT‐1 and (c) subsidence by El Niño circulation. These factors lead to exacerbation of deficit rainfall.