Monsoon

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

Monsoon prediction : Why yet another failure?

Abstract: 1–3 of 2002, with the all-India summer monsoon (June–September) rainfall (ISMR) being 19% less than the long-term average, led to considerable co ncern in the meteorological community since none of the pr edictions had suggested a large deficit in the ISMR. This was irrespective of whether the predictions were based on empir ical models used in the country for generating oper ational/ experimental forecasts, or generated in the different ce ntres in the world using the atmospheric general circulation mo dels 1 . Fortunately, the unanticipated failure of the Indian mo nsoon in the summer of 2002, was followed by the summer monsoon of 2003 for which the ISMR was 2% more than the average 4 . However, the relief was short-lived since the summer monsoon of 2004 has again been a drought (defined as a summer monsoon season for which the deficit in ISMR is larger than 10% of the long-term average), with the ISMR being 87% of the average. As in 2002, neither the forecast of the India Meteorological Depar tment (IMD) for the ISMR nor the predictions from the international ce ntres using atmospheric general circulation models (GCMs), suggested that there would be a drought. Clearly, it is far more important to generate accurate predictions of droughts/ excess rainfall seasons than of flu ctuations within 10% of the average. The variation of the summer monsoon rainfall from year to year is not coherent over the Indian region. Ge nerally, while some regions experience above-average rainfall, others suffer from deficit. Thus the anomalies (difference from the long-term average) of the summer monsoon rainfall are positive over some of the meteorological subdivisions and negative for others, particularly in the so -called normal years (i.e. with the magnitude of the ISMR anomaly <10% of the average). During droughts, rainfall over the vast majority of the subdivisions is deficit. This is illu strated in Figure 1 in which anomalies of the su mmer monsoon rainfall for the meteorological subdivisions (e xpressed as a percentage of the long-term average) for the droughts of 2002 and 2004 and the 2003 normal monsoon season are shown. The variation of the all -India rainfall is also generally not coherent within the monsoon season. Thus, in 2002 there was an unprecedented deficit of 49% in the all -India average rainfall in July, while the rainfall was close to the average during all the other months. In 2004, the all -India rainfall was close to the average in June and August, but well b elow the average in July and September (June: 100%, July: 81 %, August: 95% and September: 71%). This year, predictions were also made for the rainfall pa tterns of July and

Asynchronous glaciation at Nanga Parbat, northwestern Himalaya Mountains, Pakistan

Abstract: We present a new glacial chronology demonstrating asynchroneity between advances of Himalayan glaciers and Northern Hemisphere ice-sheet volumes. Glaciers at Nanga Parbat expanded during the early to middle Holocene ca. 9.0–5.5 ka. No major advances at Nanga Parbat during the last global glacial stage of marine oxygen isotope stage 2 (MIS-2) between 24 and 11 ka were identified. Preliminary evidence also indicates advances between ca. 60 and 30 ka. These periods of high ice volume coincide with warm, wet regional climates dominated by a strong southwest Asian summer monsoon. The general lack of deposits dating from MIS-2 suggests that Nanga Parbat was too arid to support expanded ice during this period of low monsoon intensity. Advances during warm, wet periods are possible for the high-altitude summer accumulation glaciers typical of the Himalayas, and explain asynchronous behavior. However, the Holocene advances at Nanga Parbat appear to have been forced by an abrupt drop in temperature ca. 8.4–8.0 ka and an increase in winter precipitation ca. 7–5.5 ka. These results highlight the overall sensitivity of Himalayan glaciation to orbital forcing of monsoon intensity, and on millennial or shorter time scales, to changes in North Atlantic circulation.