Summertime ENSO-North African-Asian jet teleconnection and implications for the Indian monsoons

Recent findings indicate that ENSO may modulate the strength of the Indian monsoons by altering the meridional tropospheric temperature gradient between Asia and the equatorial Indian Ocean. Here we show that during northern hemisphere summertime El Nino events both colder upper tropospheric temperatures and increased vorticity anomalies are observed within the North African-Asian (NAA) jet. The temperature response within the NAA jet is the dominant ENSO-related change to the meridional tropospheric temperature gradient between Asia and the equatorial Indian Ocean. Forced solutions of the linearized barotropic vorticity equation indicate that these anomalies within the NAA jet are a response to northern hemisphere summertime El Nino-related convective activity over the equatorial Pacific Ocean. Additional experiments indicate that westward propagating anomalies in both the tropics and middle latitudes produce the anomaly response within the NAA jet. These findings suggest that the teleconnection linking ENSO and the monsoons is mediated by the response of the NAA jet to westward propagating Rossby waves.