Monsoon

About: Monsoon is a research topic. Over the lifetime, 16087 publications have been published within this topic receiving 599888 citations.

Short circuit of water vapor and polluted air to the global stratosphere by convective transport over the Tibetan Plateau

Abstract: During boreal summer, much of the water vapor and CO entering the global tropical stratosphere is transported over the Asian monsoon/Tibetan Plateau (TP) region. Studies have suggested that most of this transport is carried out either by tropical convection over the South Asian monsoon region or by extratropical convection over southern China. By using measurements from the newly available National Aeronautics and Space Administration Aura Microwave Limb Sounder, along with observations from the Aqua and Tropical Rainfall-Measuring Mission satellites, we establish that the TP provides the main pathway for cross-tropopause transport in this region. Tropospheric moist convection driven by elevated surface heating over the TP is deeper and detrains more water vapor, CO, and ice at the tropopause than over the monsoon area. Warmer tropopause temperatures and slower-falling, smaller cirrus cloud particles in less saturated ambient air at the tropopause also allow more water vapor to travel into the lower stratosphere over the TP, effectively short-circuiting the slower ascent of water vapor across the cold tropical tropopause over the monsoon area. Air that is high in water vapor and CO over the Asian monsoon/TP region enters the lower stratosphere primarily over the TP, and it is then transported toward the Asian monsoon area and disperses into the large-scale upward motion of the global stratospheric circulation. Thus, hydration of the global stratosphere could be especially sensitive to changes of convection over the TP.

Mediterranean Moisture Source for an Early-Holocene Humid Period in the Northern Red Sea

Abstract: Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.

Relative contribution of monsoon precipitation and pumping to changes in groundwater storage in India

Abstract: The depletion of groundwater resources threatens food and water security in India. However, the relative influence of groundwater pumping and climate variability on groundwater availability and storage remains unclear. Here we show from analyses of satellite and local well data spanning the past decade that long-term changes in monsoon precipitation are driving groundwater storage variability in most parts of India either directly by changing recharge or indirectly by changing abstraction. We find that groundwater storage has declined in northern India at the rate of 2 cm yr−1 and increased by 1 to 2 cm yr−1 in southern India between 2002 and 2013. We find that a large fraction of the total variability in groundwater storage in north-central and southern India can be explained by changes in precipitation. Groundwater storage variability in northwestern India can be explained predominantly by variability in abstraction for irrigation, which is in turn influenced by changes in precipitation. Declining precipitation in northern India is linked to Indian Ocean warming, suggesting a previously unrecognized teleconnection between ocean temperatures and groundwater storage. Groundwater storage has declined in northern India and increased in southern India over the past decade. Trend analysis shows that much of this variability can be explained by changes in irrigation in response to monsoon precipitation.

A Hydrological Definition of Indian Monsoon Onset and Withdrawal

Abstract: A diagnostic criterion that retrospectively assesses the onset and withdrawal dates of the Indian monsoon is derived from variability in the large-scale hydrologic cycle. The method is proposed as an improved means with which to understand interannual variability in the monsoon transitions as compared to criteria that rely heavily on rainfall variability over limited spatial domains (e.g., individual Indian districts). The hydrologic cycle is chosen as a key physical basis for monitoring the monsoon due to the essential roles played by zonal and meridional gradients in water vapor, clouds, and rainfall in driving the large-scale monsoon circulation. Moreover, as rainfall is greater than evaporation in wet monsoonal areas, lateral transports of water vapor are required for the existence of monsoonal rains. To diagnose onset and withdrawal, vertically integrated moisture transport (VIMT) is therefore used instead of rainfall, which over the large scale is often poorly measured and modeled. In contrast to rainfall, VIMT is generally well modeled and observed, and its variability, particularly over the Arabian Sea, is substantial during both monsoon onset and withdrawal. An index, named the hydrologic onset and withdrawal index (HOWI), is thus formed from those regions where VIMT variability is pronounced at the beginning and end of the monsoon season. The HOWI offers several advantages as the index is based on fields that are better modeled and measured than rainfall, and the index is indicative of the transition in the largescale monsoon circulation rather than being highly sensitive to synoptic variability and the spatial complexity of the monsoon transitions. The HOWI is shown to be both robust to bogus monsoon onsets and reflective of the timing, rather than the spatial character, of the transitions. Analysis of interannual variability in monsoon onset and withdrawal dates based on the HOWI reveals robust associations that are weak and insignificant when assessed using other onset criteria. For example, the associations between total June‐July‐August‐September (JJAS) rainfall and both monsoon onset and withdrawal are weak (correlations are weaker than 20.11) when onset dates from the Indian Meteorological Department (IMD) or other objective methods are considered. However, the HOWI criterion shows strong correlations between total JJAS rainfall and both onset (0.30) and withdrawal (20.49). Thus, the length of the monsoon season is shown to be strongly related to its overall strength. In addition, while the correlation between IMD onset date and