Variability of the Cold Season Climate in Central Asia. Part II: Hydroclimatic Predictability

Abstract Central Asia (CA) is subjected to a large variability of precipitation. This study presents a statistical model, relating precipitation anomalies in three subregions of CA in the cold season (November–March) with various predictors in the preceding October. Promising forecast skill is achieved for two subregions covering 1) Uzbekistan, Turkmenistan, Kyrgyzstan, Tajikistan, and southern Kazakhstan and 2) Iran, Afghanistan, and Pakistan. ENSO in October is identified as the major predictor. Eurasian snow cover and the quasi-biennial oscillation further improve the forecast performance. To understand the physical mechanisms, an analysis of teleconnections between these predictors and the wintertime circulation over CA is conducted. The correlation analysis of predictors and large-scale circulation indices suggests a seasonal persistence of tropical circulation modes and a dynamical forcing of the westerly circulation by snow cover variations over Eurasia. An EOF analysis of pressure and humidity patterns allows separating the circulation variability over CA into westerly and tropical modes and confirms that the identified predictors affect the respective circulation characteristics. Based on the previously established weather type classification for CA, the predictors are investigated with regard to their effect on the regional circulation. The results suggest a modification of the Hadley cell due to ENSO variations, with enhanced moisture supply from the Arabian Gulf during El Niño. They further indicate an influence of Eurasian snow cover on the wintertime Arctic Oscillation (AO) and Northern Hemispheric Rossby wave tracks. Positive anomalies favor weather types associated with dry conditions, while negative anomalies promote the formation of a quasi-stationary trough over CA, which typically occurs during positive AO conditions.

Download Full-text

Effect Of Eurasian Snow Cover On Summer Climate Of The Northern Hemisphere: A GCM Study

Annals of Glaciology ◽

10.1017/s0260305500009447 ◽

1990 ◽

Vol 14 ◽

pp. 364 ◽

Cited By ~ 1

Author(s):

Tetsuzo Yasunari ◽

Akio Kitoh ◽

Tatsushi Tokioka

Keyword(s):

Snow Cover ◽

Land Surface ◽

General Circulation ◽

Large Scale ◽

General Circulation Models ◽

Late Winter ◽

Hydrological Process ◽

Eurasian Snow Cover ◽

Eurasian Snow ◽

Snow Cover Extent

Observational studies have shown that Eurasian snow-cover anomalies during winter-through-spring seasons have a great effect on anomalies in atmospheric circulation and climate in the following summer season through snow albedo feedback (Hahn and Shukla, 1976; Dey and Bhanu Kumar, 1987). Morinaga and Yasunari (1987) have revealed that large-scale snow-cover extent over central Asia in late winter, which particularly has a great effect on the circulation over Eurasia in the following season, is closely related to the Eurasian pattern circulation (Wallace and Gutzler, 1981) in the beginning of winter. Some atmospheric general circulation models (GCM) have suggested that not only the albedo effect of the snow cover but also the snow-hydrological process are important in producing the atmospheric anomalies in the following seasons (Yeh and others, 1984; Barnett and others, 1988). However, more quantitative evaluations of these effects have not yet been examined. For example, it is not clear to what extent atmospheric anomalies are explained solely by snow-cover anomalies. Spatial and seasonal dependencies of these effects are supposed to be very large. Relative importance of snow cover over Tibetan Plateau should also be examined, particularly relevant to Asian summer monsoon anomalies. Moreover, these effects seem to be very sensitive to parameterizations of these physical processes (Yamazaki, 1988). This study focuses on these problems by using some versions of GCMs of the Meteorological Research Institute. The results include the evaluation of total snow-cover feedbacks as part of internal dynamics of climatic change from 12-year GCM integration, and of the effect of anomalous snow cover over Eurasia in late winter on land surface conditions and atmospheric circulations in the succeeding seasons.

Download Full-text

Effects Of Eurasian Snow Cover On Atmospheric Circulation In The Northern Hemisphere

Annals of Glaciology ◽

10.1017/s0260305500009162 ◽

1990 ◽

Vol 14 ◽

pp. 348

Author(s):

Yuki Morinaga ◽

Tetuzo Yasunari

Keyword(s):

Snow Cover ◽

Atmospheric Circulation ◽

Northern Hemisphere ◽

Large Scale ◽

Time Lag ◽

Summer Monsoon Rainfall ◽

Hydrological Process ◽

Eurasian Snow Cover ◽

Eurasian Snow ◽

Snow Cover Extent

Effects of Eurasian snow cover were first noted by Blanford (1884) who found an inverse relationship between summer monsoon rainfall over India and winter snow cover over the Himalayas. Hahn and Shukla (1976) confirmed it by using satellite-derived data and their work stimulated succeeding studies on the interaction between large-scale snow cover and atmosphere. Matson and Wiesnet (1981) showed that interannual variation of northern hemisphere snow cover is dominated by Eurasian snow cover, both showing similar trends and fluctuations during 1967–79. Recent studies (Barnett, 1988) also noted that Eurasian snow cover has a greater feedback potential than that of North America on hemispheric-scale climatic anomalies. Though the importance has been thus recognized, not many studies have been done on the interaction between Eurasian snow cover and large-scale atmospheric circulation anomalies. Morinaga and Yasunari (1987) studied lag correlations between satellite-derived snow-cover extent over central Asia and the 500 mb-geopotential height field in the Northern Hemisphere (1967–84), and indicated that so-called Eurasian pattern (Wallace and Gutzler, 1981) in December brings large snow-cover extent in February; in turn, February snow cover has a considerable lingering effect on the atmosphere in April. This study present further results on the time-lag teleconnections of the atmosphere associated with Eurasian snow-cover anomalies and their physical implications including the evaluation of snow-hydrological process.

Download Full-text

Effect Of Eurasian Snow Cover On Summer Climate Of The Northern Hemisphere: A GCM Study

Annals of Glaciology ◽

10.3189/s0260305500009447 ◽

1990 ◽

Vol 14 ◽

pp. 364-364 ◽

Cited By ~ 1

Author(s):

Tetsuzo Yasunari ◽

Akio Kitoh ◽

Tatsushi Tokioka

Keyword(s):

Snow Cover ◽

Land Surface ◽

General Circulation ◽

Large Scale ◽

General Circulation Models ◽

Late Winter ◽

Hydrological Process ◽

Eurasian Snow Cover ◽

Eurasian Snow ◽

Snow Cover Extent

Observational studies have shown that Eurasian snow-cover anomalies during winter-through-spring seasons have a great effect on anomalies in atmospheric circulation and climate in the following summer season through snow albedo feedback (Hahn and Shukla, 1976; Dey and Bhanu Kumar, 1987). Morinaga and Yasunari (1987) have revealed that large-scale snow-cover extent over central Asia in late winter, which particularly has a great effect on the circulation over Eurasia in the following season, is closely related to the Eurasian pattern circulation (Wallace and Gutzler, 1981) in the beginning of winter.Some atmospheric general circulation models (GCM) have suggested that not only the albedo effect of the snow cover but also the snow-hydrological process are important in producing the atmospheric anomalies in the following seasons (Yeh and others, 1984; Barnett and others, 1988).However, more quantitative evaluations of these effects have not yet been examined. For example, it is not clear to what extent atmospheric anomalies are explained solely by snow-cover anomalies. Spatial and seasonal dependencies of these effects are supposed to be very large. Relative importance of snow cover over Tibetan Plateau should also be examined, particularly relevant to Asian summer monsoon anomalies. Moreover, these effects seem to be very sensitive to parameterizations of these physical processes (Yamazaki, 1988).This study focuses on these problems by using some versions of GCMs of the Meteorological Research Institute. The results include the evaluation of total snow-cover feedbacks as part of internal dynamics of climatic change from 12-year GCM integration, and of the effect of anomalous snow cover over Eurasia in late winter on land surface conditions and atmospheric circulations in the succeeding seasons.

Download Full-text

Effects Of Eurasian Snow Cover On Atmospheric Circulation In The Northern Hemisphere

Annals of Glaciology ◽

10.3189/s0260305500009162 ◽

1990 ◽

Vol 14 ◽

pp. 348-348

Author(s):

Yuki Morinaga ◽

Tetuzo Yasunari

Keyword(s):

Snow Cover ◽

Atmospheric Circulation ◽

Northern Hemisphere ◽

Large Scale ◽

Time Lag ◽

Summer Monsoon Rainfall ◽

Hydrological Process ◽

Eurasian Snow Cover ◽

Eurasian Snow ◽

Snow Cover Extent

Effects of Eurasian snow cover were first noted by Blanford (1884) who found an inverse relationship between summer monsoon rainfall over India and winter snow cover over the Himalayas. Hahn and Shukla (1976) confirmed it by using satellite-derived data and their work stimulated succeeding studies on the interaction between large-scale snow cover and atmosphere. Matson and Wiesnet (1981) showed that interannual variation of northern hemisphere snow cover is dominated by Eurasian snow cover, both showing similar trends and fluctuations during 1967–79. Recent studies (Barnett, 1988) also noted that Eurasian snow cover has a greater feedback potential than that of North America on hemispheric-scale climatic anomalies.Though the importance has been thus recognized, not many studies have been done on the interaction between Eurasian snow cover and large-scale atmospheric circulation anomalies. Morinaga and Yasunari (1987) studied lag correlations between satellite-derived snow-cover extent over central Asia and the 500 mb-geopotential height field in the Northern Hemisphere (1967–84), and indicated that so-called Eurasian pattern (Wallace and Gutzler, 1981) in December brings large snow-cover extent in February; in turn, February snow cover has a considerable lingering effect on the atmosphere in April.This study present further results on the time-lag teleconnections of the atmosphere associated with Eurasian snow-cover anomalies and their physical implications including the evaluation of snow-hydrological process.

Download Full-text