Dynamics of dry air intrusion over India during summer monsoon breaks

A Mechanism for the Summer Monsoon Precipitation Variability Over Northwest India Driven by Moisture Deficit Transport

“…The northwestern India (NWI) has an arid climate, with a considerable inter‐annual variability in the rainfall. One of the reasons for the relatively less amount of the rainfall over this region is the dry air being advected from the northern Arabian Sea and the adjacent land regions by the summer monsoon circulation (Singh & Sandeep, 2022). In addition, the progression and onset of the monsoon are determined by the dynamical interaction of moist low‐level flow from the Arabian Sea with mid‐level dry air from western and central Asia (Parker et al., 2016; Volonté et al., 2020).…”

“…A strong influx of moisture deficit air occurred at 850‐hPa over the northern Arabian Sea and from the adjacent arid regions during break spells when SRA ≤ −1 (Figure 6). This increase is strengthened and also propagated toward continental India via northwestern part of Indian landmass after the onset of break leading to demise of convection over NWI and some parts of central India due to increase in atmospheric static stability (Emanuel et al., 2008; Singh & Sandeep, 2022). In addition, the transport of moisture deficit air takes place due to strengthening of the westerly flow followed by the formation of anomalous cyclonic circulation pattern over the northern flank of the Arabian Sea at 25°N between 60°E and 70°E.…”

“…The monsoon low-level circulation transports moisture to the continental India, which results in copious amount of rainfall. A recent study argues that the arm of the monsoon low-level flow across the northern Arabian Sea transports saturation deficit air toward the continental India, primarily during the break phase of summer monsoon (Singh & Sandeep, 2022). The role of this dry air intrusion on the subseasonal and interannual variability of summer monsoon was not explored earlier.…”

“…We defined moisture deficit (qd) as the difference between saturation specific humidity and specific humidity. Daily linear regression analysis of the moisture (or saturation) deficit transport vectors ( V qd; Singh and Sandeep (2022)) at 850‐hPa on daily SRA is performed and its lead‐lag regression coefficients spatial patterns are computed for the period 1981–2019. Further, an EOF analysis is performed on seasonal mean MSLP anomalies over the domain 5°N−35°N, 50°E−90°E during JA season and its first two leading modes principal components are used to perform linear regression analysis on the precipitation and moisture deficit transport vectors ( V qd) at 850‐hPa.…”

“…However, a significant deficit in rainfall activity is observed during the strengthening of dry air intrusion from the Middle East desert, which prevents the monsoon’s onset from spreading northwest and suppresses convection activity over continental India (Bhat, 2006; Krishnamurti et al., 2010). Furthermore, a recent study by Singh and Sandeep (2022) reported a huge reservoir of moisture deficit in the northern and western Arabian Sea at lower troposphere, which acts as a primary source, and the low‐level jet (LLJ) acts as the primary carrier, transporting dry air to continental India during ISM break phases, ultimately weakening convection activity over the Indian landmass. Therefore, like moisture flux, moisture deficit flux is also a critical parameter to analyze for understanding the dynamics of convection activity.…”