Abstract/Summary

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 analyzed 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 16-17 June 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.