Extratropical-Tropical Interaction during Heavy Rainfall Events “Cloudbursts” Observed over Himalayan Region

Localized heavy rainfall events in the Himalayas, commonly known in the region as ”cloudbursts”, are one of the most devastating disasters to affect the Region. Because of the intense rainfall and occurrence mostly at night/early morning, these events cause extreme damage, particularly to human lives. Rainfall intensity during such events is generally more than 50mm/hr, while sometimes reaches 100mm/hr.

Observations have suggested that two basic synoptic situations synchronize during such events in Nepal. First, the monsoon trough/low pressure area shifts to the north of its normal position towards, the foothills of Himalayas. Second, westerly upper tropospheric wind relocates southward over Himalayas. We hypothesize that together these two changes enable a type of extratropical-tropical interaction to take place. We will analyze the role of extra-tropical tropical interaction on the formation of these events. We use composite analysis and case studies to explore the dynamics of these events.