Surface temperature modulations induced by Rossby Wave Breaking over Indian region

Abstract

Upper-level Rossby Wave Breaking (RWB) significantly affects surface weather patterns in the subtropical Indian region through influencing wind circulation often resulting in extremes in rainfall and surface temperatures. While the impact of RWB on rainfall is relatively well understood, its role in modulating surface temperatures within the Indian subcontinent is less explored. This study examines the link between pre-monsoon (March to May) RWB events and the occurrence of extreme surface temperatures and heatwaves by considering long-term data of 43 years between 1979 and 2021. We identify 139 RWB events using a potential vorticity (PV) contour searching algorithm over the Indian sub-continent. Our analysis reveals a significant amplification in temperature both to the west and east of the breaking PV streamers. These temperature anomalies, which last for 3–4 days during the breaking events, strongly correlate with the maximum day of breaking. Further, regression analyses explain the reasons behind the temperature enhancement mainly on the western and eastern flank of RWB. It indicates a positive association between upper-level PV anomalies and anticyclonic circulations at 250 hPa, along with subsidence at 500 hPa, leading to drier conditions in the western and eastern regions of the PV streamers. Additionally, the decomposition of temperature anomalies during RWB events reveals that surface warming is primarily driven by diabatic heating on both sides of the centroid, with stronger adiabatic heating in regions of upper-level anticyclonic circulation and significant temperature advection predominantly on the western side of the centroid, resulting in dry weather and the poleward movement of warm air toward the ridges near the PV streamers.

Keywords

• temperature
• Rossby Wave Breaking
• climatology
• potential vorticity