Relationship between Topography and Daytime Cloud Activity around Tibetan Plateau.

Abstract

The relationship between topography and daytime cloud activity over the Tibetan Plateau and surrounding areas was examined by using Geostationary Meteorological Satellite (GMS) Visible (VIS) and Infrared (IR) images during the premonsoon, and monsoon periods in 1998. Previous studies using IR images have already confirmed the strong diurnal variation of convective activity over the Tibetan Plateau. This study relies primarily on VIS images to analyze daytime cloud distribution because VIS images are more adaptable to low-level clouds and they offer better spatial resolution than IR images. IR images are used to judge whether cloud tops are high or low. High-level clouds are prominent over the large-scale (100-300 km) mountain ranges, but fewer clouds are observed in the major valleys in the plateau during premonsoon and monsoon periods at 15 Local Solar Time (LST), when the amount of cloud cover is at its maximum from 09 LST to 15 LST. However, the relationship between cloud distribution and topography is not always clear when the horizontal scale of the topography is less than 100 km.Less cloud coverage was observed over the plateau in the morning during the premonsoon period. On the contrary, clouds frequently appeared over the southeastern part of the plateau in the morning during the monsoon period. Low-level clouds often cover the southern slope of the Himalayas, and the frequency of cloud coverage exceeds 75% at 15 LST in the monsoon period. While the cloud tops are growing high elevation in the afternoon over the plateau, low-level clouds cover the southern slope of the Himalayas through the daytime (09-15 LST).

Characteristics of Diurnal Variations in Convection and Precipitation over the Southern Tibetan Plateau during Summer

“…Zonally elongated regions of high CCF are found near 28.5°N and 30.2°N, close to major mountain ranges C and D. High clouds are suppressed over valley B at 29.3°N. The CCF distribution is consistent with that shown by Kurosaki and Kimura (2002). At 21 LST (Fig.…”

“…Ueno (1998) showed that satellite-estimated precipitation is more likely to be over the major mountain ranges during the day (06 18 LST at 90°E) and over major valleys at night (18 06 LST). Kurosaki and Kimura (2002) used Geostationary Meteorological Satellite (GMS) visible and infrared data for both pre-monsoon and monsoon periods in 1998 to show that daytime (09 15 LST) clouds prevail over major mountain ranges of the TP. Such variations could be related to thermally induced local circulations driven by the topography of the TP.…”

Submonthly Variability of Convection and Circulation over and around the Tibetan Plateau during the Boreal Summer

“…Remarkable diurnal variation in convection occurs over the plateau during the summer (e.g., Murakami 1983;Nitta and Sekine 1994;Yanai and Li 1994;Fujinami and Yasunari 2001). The convection depends strongly on thermallydriven regional-scale circulations induced by plateau topography (Ueno 1998;Kuwagata et al 2001;Kurosaki and Kimura 2002). Nevertheless, few authors have investigated convective variability on submonthly timescales over the Tibetan Plateau.…”

A Case Study of a Heavy Rain over the Southeastern Tibetan Plateau

“…The temporal resolution is 3 h (UTC 00, 03, 06, 09, 12,15,18,21) and the spatial resolution is 0.25 • × 0.25 • . The daily aggregated precipitation is obtained by summing all 8 sets of 3-h precipitation totals for a given day.…”