Synoptic processes of winter precipitation in the Upper Indus Basin

Abstract

Abstract. Precipitation in the Upper Indus Basin is triggered by cross-barrier moisture transport. Winter precipitation events are particularly active in this region and are driven by an approaching upper troposphere Western Disturbance. Here statistical tools are used to decompose the winter precipitation timeseries into a wind and a moisture contribution. The relationship between each contribution and the Western Disturbances are investigated. We find that the wind contribution is not only related to the intensity of the upper troposphere disturbances but also to their thermal structure through baroclinic processes. Particularly, a short-lived baroclinic interaction between the Western Disturbance and the lower altitude cross-barrier flow occurs due to the shape of the relief. This interaction explains both the high activity of Western Disturbances in the area, as well as their quick decay as they move further east. We also revealed the existence of a moisture pathway from the Red Sea, to the Persian Gulf and the north of the Arabian Sea. A Western Disturbance strengthens this flow and steers it towards the Upper Indus Plain, particularly if it originates from a more southern latitude. In cases where the disturbance originates from the north-west, its impact on the moisture flow is limited, since the advected continental dry air drastically limits the precipitation output. The study offers a conceptual framework to study the synoptic activity of Western Disturbances as well as key parameters that explain their precipitation output. This can be used to investigate meso-scale processes or intra-seasonal to inter-annual synoptic activity.

Linking The North Atlantic Oscillation to Winter Precipitation Over The Western Himalaya Through Disturbances of The Subtropical Jet

“…It is known that both the latitude of the subtropical jet (Hunt et al, 2017) and its intensity (Hunt et al 2018) exert controls on WD behaviour over South Asia. In addition, the greater vertical wind shear exerted by a stronger jet is associated with more intense updrafts in WDs (Baudouin et al, 2021). As the NAO affects both of these jet characteristics, we can reasonably hypothesise that it will also modulate downstream WD behaviour.…”

Hydrological Extremes in Western Himalayas-Trends and Their Physical Factors

“…As our findings suggest an enhancement in both transient activity of westerly troughs and moisture flux convergence, it can be concluded that variability in dynamic responses of the atmosphere in conjunction with thermodynamic variations might be a major contributing factor for increasing trends of extreme precipitation over the region. Mediterranean, Caspian, Red and Arabian seas are primary contributors for eastward moisture advection towards WH leading to moisture availability for precipitation [74,75]. Here, we have tried to investigate the trends for winter seasonal moisture supply over WH (Figure 5n) through time series for VIMT which reveals a clear increasing trend in the moisture transport over WH through the years.…”

Dynamical and thermodynamical interactions in daily precipitation regimes in the Western Himalayas

“…Contrasting trends were observed in the frequency and intensity of extratropical disturbances in WH (Cannon et al ., 2015; Yadav et al ., 2017; Hunt et al ., 2019). Nevertheless, due to the topography, these disturbances are sustained in WH by their interaction with low‐level winds whereas they decay quickly in CH/EH (Baudouin et al ., 2021). Therefore, the meteorological processes that influence precipitation in the WH are distinct from those in the CH or the EH; hence, these processes must be categorized and studied independently.…”