The Woods Hole Oceanographic Institution surface mooring with ORV Sagar Nidhi in the background.

Consistent with earlier studies, this analysis reveals that net surface heat flux primarily controls the ML heat balance. The penetrative component of shortwave radiation plays a crucial role in the ML heat budget in the BoB, especially during the spring warming phase when the ML is thin. During winter and summer, vertical processes contribute significantly to the ML heat budget. During winter, the presence of a strong barrier layer and a temperature inversion (warmer water below the ML) leads to warming of the ML by entrainment of warm subsurface water into the ML. During summer, the barrier layer is relatively weak, and the ML is warmer than the underlying water (i.e., no temperature inversion); hence, the entrainment cools the mixed layer. The contribution of horizontal advection to the ML heat budget is greatest during winter when it serves to warm the upper ocean. In general, the residual term in the ML heat budget equation is quite large during the ML cooling phase compared to the warming phase when the contribution from vertical heat flux is small.

RESUMENLos Himalayas desempeñan un papel importante en el clima y el tiempo meteorológico de la India, y controlan tanto las perturbaciones del oeste (PO) durante el invierno como el monzón del suroeste durante el verano. En los meses de invierno (diciembre a marzo), los vientos del oeste asociados con PO causan precipitaciones, en ocasiones asociadas a fuertes nevadas y extensas avalanchas sobre Himachal Pradesh. Por tal motivo, el presente estudio analiza la variabilidad temporal de la frecuencia de PO y de diversos índices de precipitación (como número de días húmedos y lluviosos, días con precipitación fuerte y muy fuerte, e intensidad de la precipitación de 1977 a 2007) en Himachal Pradesh durante el invierno. También se analizan las caracterís-ticas sinópticas asociadas con PO intensas que provocaron fuertes precipitaciones sobre la región durante el Himachal Pradesh ocurre sobre todo como resultado de las PO, tanto la precipitación total como los días con precipitación fuerte y muy fuerte han disminuido en la región. El análisis también muestra una disminución de alrededor de 25% en los días de precipitación fuerte y de 13% en la precipitación invernal total sobre Himachal Pradesh respecto de su media respectiva (de 1977 a 2007). ABSTRACTThe Himalayas have an important role in Indian weather and climate, since they control the western disturbances (WDs) during winter and the southwest monsoon during summer. During the winter months (December to March), westerly winds associated with WDs cause precipitation, sometimes along with heavy snowfall, extensive avalanches, etc., over Himachal Pradesh. Therefore, this study examined the temporal variability in the winter months frequency of WDs and various precipitation indices like wet days, rainy days, rather heavy and heavy precipitation days, and precipitation intensity during 1977 to 2007 over Himachal Pradesh. The study also examined synoptic features associated with intense WDs that caused heavy precipitation over the region trend in the frequency of WDs over this region. Since winter precipitation in Himachal Pradesh mainly occurs due to WDs, total winter precipitation and frequency of rather heavy and heavy precipitation days have decreased over the region. The analysis also shows a decrease of about 25% in heavy precipitation days and of 13% in total winter precipitation from their respective mean (from 1977 to 2007) over Himachal Pradesh.

No abstract