Eddy transport, wave–mean flow interaction, and Eddy forcing during the 2013 Uttarakhand extreme event in the reanalysis and S2S retrospective forecast data. (21st June 2022)

• Record Type: Journal Article
• Authors: Kalshetti, Mahesh; Chattopadhyay, Rajib; Hunt, Kieran M. R.; Phani, R.; Joseph, Susmitha; Pattanaik, D. R.; Sahai, A. K.
• Is Part Of: International journal of climatology. Volume 42:Number 16(2022)
• Page Start: 8248
• Page End: 8268
• Publication Date: 2022-06-21
• Subjects: extratropical–tropical teleconnection -- extreme events -- Indian monsoon -- subseasonal forecasts; Climatology -- Periodicals; Climat -- Périodiques; Climatologie -- Périodiques; 551.605
• DOI: 10.1002/joc.7706
• Languages: English
• ISSNs: 0899-8418

Abstract

Abstract: In this study, to explore the wave–mean interaction during the monsoon season, we investigate (a) the potential role of transient eddy forcing and the wave–mean interaction on the monsoon weather during the June 2013 heavy rainfall event over the Himalayan regions (especially the Uttarakhand State of India and the nearby regions) and (b) how they are captured in a set of operational models. Some studies have pointed out how prolonged breaks can occur due to extratropical trough incursions. However, there is a lack of clarity on how transient eddy forcing associated with such interactions can lead to modulation of monsoonal circulation or whether such interaction can lead to heavy rainfall events. E‐vector fields are analysed to quantify the eddy forcing from extratropical transient eddies and the feedback mechanism between transient eddies and the mean flow during June 2013. Analysis reveals that along with local factors (orography, moisture convergence), the large‐scale heavy rainfall event over the Uttarakhand region during June 16–17, 2013 was influenced by eddy forcing due to the intrusion of extratropical Rossby waves over the Indian region. The location of eddy affects the location of regional occurrence of the eddy‐mean interaction. Model hindcast analysis results suggest that operational models cannot forecast the upper‐level eddy forced circulation patterns, and the improper representation of the E‐vector divergence field leads to the underestimation of intensity and the spatial pattern of rainfall. Abstract : The study proposes a diagnostic framework using E‐vectors to analyse and understand the extratropical transient eddy forcing over Indian region during the monsoon season. The framework can be used both in observation/reanalysis data and operational forecast models. The analysis is based on a case study of the 2013 Uttarakhand (India) extreme rainfall event over the Himalayan region. The study indicates that the transient eddy forcing can force extreme rainfall events in addition to other forcings.