scholarly journals Impact of geographic variations of the convective and dehydration center on stratospheric water vapor over the Asian monsoon region

2016 ◽  
Vol 16 (12) ◽  
pp. 7825-7835 ◽  
Author(s):  
Kai Zhang ◽  
Rong Fu ◽  
Tao Wang ◽  
Yimin Liu
Keyword(s):  
Water Vapor ◽  
Southeast Asia ◽  
Geographic Variation ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Boreal Summer ◽  
Monsoon Circulation ◽  
Monsoon Region ◽  
Geographic Variations ◽  
Asian Monsoon Region

Abstract. The Asian monsoon region is the most prominent moisture center of water vapor in the lower stratosphere (LS) during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using satellite observations from the Aura Microwave Limb Sounder (MLS) and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to geographic variations of convection and resultant variations of the dehydration center, of which the influence is comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest Asian monsoon region. Although the convective center is located over Southeast Asia, an anomalous increase of convection over the northwest Asia monsoon region increases local diabatic heating in the tropopause layer and air masses entering the LS are dehydrated at relatively warmer temperatures. Due to warmer dehydration temperatures, anomalously moist air enters the LS and moves eastward along the northern flank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the Southeast Asia monsoon region, dry anomalies appear in the LS. On a seasonal scale, this feature is associated with the monsoon circulation, convection and diabatic heating marching towards the northwest Asia monsoon region from June to August. The march of convection leads to an increasing fraction of the air mass to be dehydrated at warmer temperatures over the northwest Asia monsoon region. Work presented here confirms the dominant role of temperatures on water vapor variations and emphasizes that further studies should take geographic variations of the dehydration center into consideration when studying water vapor variations in the LS as it is linked to changes of convection and large-scale circulation patterns.

scholarly journals Impact of geographic variations of convective and dehydration center on stratospheric water vapor over the Asian monsoon region

2016 ◽  
Author(s):  
K. Zhang ◽  
R. Fu ◽  
T. Wang ◽  
Y. Liu
Keyword(s):  
Water Vapor ◽  
Geographic Variation ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Boreal Summer ◽  
Monsoon Circulation ◽  
Monsoon Region ◽  
Geographic Variations ◽  
Asian Monsoon Region ◽  
Air Mass

Abstract. The Asian monsoon region is the most prominent moisture center of lower stratospheric (LS) water vapor during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using the Aura Microwave Limb Sounder (MLS) satellite observations and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to the geographic variations of convection and resultant variations of dehydration center, comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest within the Asian monsoon region. Although convective center is located over the southeastern Asia, an anomalous increase of convection over the northwestern Asian monsoon region increases the local diabatic heating in the tropopause layer and air mass entering the LS that is dehydrated at relatively warm er temperatures. The warmer dehydration temperatures allow anomalously moist air enters the LS and then moves eastward along the northern frank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the southeastern Asian monsoon region, dry anomalies appear in the LS. On seasonal scale, this feature is associated with the march of the monsoon circulation, convection and diabatic heating towards the northwestern Asia monsoon from June to August, leading to an increasing fraction of the air mass to be dehydrated at warmer temperatures over the nort hwestern Asian monsoon region. Work presented here confirms the dominant role of temper atures and also emphasizes that one should take the geographic variations of dehydration center into consideration when studying water vapor variations in the LS, as it is linked to changes of convection and large-scale circulation.

scholarly journals Water vapor increase in the lower stratosphere of the Northern Hemisphere due to the Asian monsoon anticyclone observed during the TACTS/ESMVal campaigns

2018 ◽  
Vol 18 (4) ◽  
pp. 2973-2983 ◽  
Author(s):  
Christian Rolf ◽  
Bärbel Vogel ◽  
Peter Hoor ◽  
Armin Afchine ◽  
Gebhard Günther ◽  
...  
Keyword(s):  
Water Vapor ◽  
Northern Hemisphere ◽  
Asian Monsoon ◽  
Eastern China ◽  
Potential Temperature ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Air Mass ◽  
Air Masses ◽  
The Impact

Abstract. The impact of air masses originating in Asia and influenced by the Asian monsoon anticyclone on the Northern Hemisphere stratosphere is investigated based on in situ measurements. A statistically significant increase in water vapor (H2O) of about 0.5 ppmv (11 %) and methane (CH4) of up to 20 ppbv (1.2 %) in the extratropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 during the HALO aircraft missions Transport and Composition in the UT/LMS (TACTS) and Earth System Model Validation (ESMVal). We investigate the origin of the increased water vapor and methane using the three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS). We assign the source of the moist air masses in the Asian region (northern and southern India, eastern China, southeast Asia, and the tropical Pacific) based on tracers of air mass origin used in CLaMS. The water vapor increase is correlated with an increase of the simulated Asian monsoon air mass contribution from about 10 % in August to about 20 % in September, which corresponds to a doubling of the influence from the Asian monsoon region. Additionally, back trajectories starting at the aircraft flight paths are used to differentiate transport from the Asian monsoon anticyclone and other source regions by calculating the Lagrangian cold point (LCP). The geographic location of the LCPs, which indicates the region where the set point of water vapor mixing ratio along these trajectories occurs, can be predominantly attributed to the Asian monsoon region.

scholarly journals Horizontal and Vertical Structures of the Northward-Propagating Intraseasonal Oscillation in the South Asian Monsoon Region Simulated by an Intermediate Model*

2007 ◽  
Vol 20 (16) ◽  
pp. 4278-4286 ◽  
Author(s):  
Hae-Kyung Lee Drbohlav ◽  
Bin Wang
Keyword(s):  
Phase Difference ◽  
Rossby Wave ◽  
3D Model ◽  
Asian Monsoon ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Monsoon Region ◽  
Wave Type ◽  
Asian Monsoon Region ◽  
Northward Propagation

Abstract The structures and mechanism of the northward-propagating boreal summer intraseasonal oscillation (BSISO) in the southern Asian monsoon region are simulated and investigated in a three-dimensional intermediate model (3D model). The horizontal structure of the intraseasonal variability in the 3D model depicts the Kelvin–Rossby wave–type disturbance, which may or may not produce the northward-propagating disturbance in the Indian Ocean, depending on the seasonal-mean background winds. Two experiments are conducted in order to identify what characteristic of seasonal-mean background can induce the northwestward-tilted band in the Kelvin–Rossby wave, whose overall eastward movement gives the impression of the northward propagation at a given longitude. When the prescribed boreal summer mean winds are excluded in the first experiment, the phase difference between the barotropic divergence tendency and convection disappears. Consequently, the Rossby wave–type convection forms a zonally elongated band. As a result, the northward propagation of convection at a given longitude disappears. When the easterly vertical shear is introduced in the second experiment, the horizontal and the vertical structures of BSISO become similar to that of the northward-propagating one. The reoccurrence of the northwestward-directed convective band and the phase difference between the barotropic divergence tendency and the convection suggest that the summer mean zonal winds in the boreal Indian summer monsoon region are a critical condition that causes the horizontal and vertical structures of northward-propagating BSISO in the southern Asian monsoon region.

scholarly journals Modeling sensitivity study of the possible impact of snow and glaciers developing over Tibetan Plateau on Holocene African-Asian summer monsoon climate

2008 ◽  
Vol 4 (6) ◽  
pp. 1265-1287 ◽  
Author(s):  
L. Jin ◽  
Y. Peng ◽  
F. Chen ◽  
A. Ganopolski
Keyword(s):  
Climate Change ◽  
Tibetan Plateau ◽  
Southeast Asia ◽  
South Asia ◽  
North Africa ◽  
Vegetation Cover ◽  
Asian Monsoon ◽  
The Tibetan Plateau ◽  
Monsoon Region ◽  
Asian Monsoon Region

Abstract. The impacts of various scenarios of snow and glaciers developing over the Tibetan Plateau on climate change in Afro-Asian monsoon region and other regions during the Holocene (9 kyr BP–0 kyr BP) are studied by using the coupled climate model of intermediate complexity, CLIMBER-2. The simulations show that the imposed snow and glaciers over the Tibetan Plateau in the mid-Holocene induce global summer temperature decreases, especially in the northern parts of Europe, Asia, and North America. At the same time, with the imposed snow and glaciers, summer precipitation decreases strongly in North Africa and South Asia as well as northeastern China, while it increases in Southeast Asia and the Mediterranean. For the whole period of Holocene (9 kyr BP–0 kyr BP), the response of vegetation cover to the imposed snow and glaciers cover over the Tibetan Plateau is not synchronous in South Asia and in North Africa, showing an earlier and a more rapid decrease in vegetation cover in North Africa from 9 to 6 kyr BP while it has only minor influence on that in South Asia until 5 kyr BP. Imposed gradually increased snow and glacier cover over the Tibetan Plateau causes temperature increases in South Asia and it decreases in North Africa and Southeast Asia during 6 kyr BP to 0 kyr BP. The precipitation decreases rapidly in North Africa and South Asia while it decreases slowly or unchanged during 6 kyr BP to 0 kyr BP with imposed snow and glacier cover over the Tibetan Plateau. The different scenarios of snow and glacier developing over the Tibetan Plateau would result in differences in variation of temperature, precipitation and vegetation cover in North Africa, South Asia and Southeast Asia. The model results show that the response of climate change in African-Asian monsoon region to snow and glacier cover over the Tibetan Plateau is in the way that the snow and glaciers amplify the effect of vegetation feedback and, hence, further amplify orbital forcing.

scholarly journals Ten Years of Measurements of Tropical Upper-Tropospheric Water Vapor by MOZAIC. Part I: Climatology, Variability, Transport, and Relation to Deep Convection

2007 ◽  
Vol 20 (3) ◽  
pp. 418-435 ◽  
Author(s):  
Zhengzhao Luo ◽  
Dieter Kley ◽  
Richard H. Johnson ◽  
Herman Smit
Keyword(s):  
Water Vapor ◽  
Asian Monsoon ◽  
Deep Convection ◽  
Seasonal Migration ◽  
Specific Humidity ◽  
Tropical Atlantic ◽  
Monsoon Region ◽  
Tropical Africa ◽  
Asian Monsoon Region ◽  
The Mean

Abstract Ten years (1994–2004) of measurements of tropical upper-tropospheric water vapor (UTWV) by the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) are investigated over three regions—the tropical Atlantic, tropical Africa, and the Asian monsoon region—to determine the UTWV climatology and variability on multiple scales and to understand them in relation to moisture transport and deep convection. The seasonal migration of upper-tropospheric humidity (UTH) keeps pace with that of the ITCZ, indicating the convective influence on UTH distribution. Some significant regional differences are identified with the tropical Africa and the Asian monsoon regions being moister than the tropical Atlantic. UTH generally increases with height by 10%–20% relative humidity with respect to ice (RHi) from about 300 to 200 hPa, and the differences are larger in the deep Tropics than in the subtropics. The probability density functions of tropical UTH are often bimodal. The two modes stay rather constant; differences in the mean value are largely due to the variations in the proportion of the two modes as opposed to changes in the modes themselves. In the deep Tropics, the moisture level frequently reaches ice supersaturation, the most notable case being the near-equatorial Asian monsoon region during the wet season when ice supersaturation is observed 46% of the time. Interannual variations are observed in association with the 1997–98 ENSO event. A warming of about 1–2 K is observed for all three regions equatorward of roughly 15°. Specific humidity also increases somewhat for the tropical Atlantic and tropical Africa, but the increase in temperature outweighs the increase in specific humidity such that RH decreases by 5%–15% RHi. In addition to the ENSO-related variation, MOZAIC also sees increases in both RH and specific humidity over tropical Africa from 2000 onward. Moisture fluxes are computed from MOZAIC data and decomposed into contributions from the mean circulation and from eddies. The flux divergence, which represents the moisture source/sink from horizontal transport, is also estimated. Finally, the MOZAIC climatology and variability are revisited in relation to deep convection obtained from the International Satellite Cloud Climatology Project (ISCCP).

scholarly journals Precipitation-Top Heights of Heavy Orographic Rainfall in the Asian Monsoon Region

2016 ◽  
Vol 73 (8) ◽  
pp. 3009-3024 ◽  
Author(s):  
Shoichi Shige ◽  
Christian D. Kummerow
Keyword(s):  
Relative Humidity ◽  
Heavy Rainfall ◽  
Asian Monsoon ◽  
The Philippines ◽  
Winter Monsoon ◽  
Boreal Summer ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Low Level ◽  
Orographic Rainfall

Abstract Over coastal mountain ranges of the Asian monsoon region, heavy orographic rainfall is frequently associated with low precipitation-top heights (PTHs). This leads to conspicuous underestimation of rainfall using microwave radiometer algorithms, which conventionally assume that heavy rainfall is associated with high PTHs. Although topographically forced upward motion is important for rainfall occurrence, it does not fully constrain precipitation profiles in this region. This paper focuses on the thermodynamic characteristics of the atmosphere that determine PTHs in tropical coastal mountains of Asia (Western Ghats, Arakan Yoma, Bilauktaung, Cardamom, Annam Range, and the Philippines). PTHs of heavy orographic rainfall generally decrease with enhanced low- and midlevel relative humidity, especially during the summer monsoon. In contrast, PTHs over the Annam Range of the Indochina Peninsula increase with enhanced low-level and midlevel relative humidity during the transition from boreal summer to winter monsoon, demonstrating that convection depth is not simply a function of humidity. Instead, PTHs of heavy orographic rainfall decreased with increasing low-level stability for all monsoon regions considered in this study, as well as the Annam Range during the transition from boreal summer to winter monsoon. Therefore, low-level static stability, which inhibits cloud growth and promotes cloud detrainment, appears to be the most important parameter in determining PTHs of heavy rainfall in the Asian monsoon region.

scholarly journals Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region

2006 ◽  
Vol 6 (4) ◽  
pp. 8069-8095 ◽  
Author(s):  
R. Zhan ◽  
J. Li ◽  
A. Gettelman
Keyword(s):  
Water Vapor ◽  
Summer Monsoon ◽  
Arabian Sea ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
West Pacific ◽  
Intraseasonal Variations ◽  
Asian Summer

Abstract. This study investigates intraseasonal oscillations (ISOs) of upper tropospheric water vapor (UTWV) in the Asian monsoon region in boreal summer by using data with high spatial and temporal resolution from the AIRS instrument. There are robust intraseasonal cycles with periods of 30–60 days and 10–20 days in the UTWV field over both South Asia and East Asia. The 30–60-day oscillation accounts for more than 60 percent of the total variance. For the 30–60-day mode, the source and propagating signature of the UTWV disturbances are distinct in two monsoon sub-systems. Two patterns in the 30–60 day oscillation are seen: a South Asian pattern that originates on the western side of the Arabian Sea and moves eastward, and an East Asian pattern that develops over West Pacific and moves westward. The 10–20-day mode exhibits a uniform westward propagating signature from West Pacific to the Arabian Sea. The Asian summer monsoon region is identified as a main source for UTWV, so another special interest in this study is the relationship between monsoon activity and the 30–60-day oscillation of UTWV. The data show that the upper troposphere is moistened following intense monsoon convection with lags about 5–10 days. An examination of the low level circulation reveals that wet and dry periods in UTWV are closely related to active and break (inactive) periods in monsoon convection, suggesting that the Asian summer monsoon plays an important role in the intraseasonal variations of UTWV. Similar variability is seen in water vapor from European Center for Medium-Range Weather Forecasts (ECMWF) analyses.

Intercomparison of Deep Convection over the Tibetan Plateau–Asian Monsoon Region and Subtropical North America in Boreal Summer Using CloudSat/CALIPSO Data

2011 ◽  
Vol 24 (8) ◽  
pp. 2164-2177 ◽  
Author(s):  
Yali Luo ◽  
Renhe Zhang ◽  
Weimiao Qian ◽  
Zhengzhao Luo ◽  
Xin Hu
Keyword(s):  
North America ◽  
Tibetan Plateau ◽  
Asian Monsoon ◽  
Deep Convection ◽  
Local Environment ◽  
Boreal Summer ◽  
The Tibetan Plateau ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Cloud Tops

Abstract Deep convection in the Tibetan Plateau–southern Asian monsoon region (TP–SAMR) is analyzed using CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data for the boreal summer season (June–August) from 2006 to 2009. Three subregions are defined—the TP, the southern slope of the plateau (PSS), and the SAMR—and deep convection properties (such as occurrence frequency, internal vertical structure, system size, and local environment) are compared among these subregions. To cast them in a broader context, four additional regions that bear some similarity to the TP–SAMR are also discussed: East Asia (EA), tropical northwestern Pacific (NWP), and western and eastern North America (WNA and ENA, respectively). The principal findings are as follows: 1) Compared to the other two subregions of the TP–SAMR, deep convection over the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection over the TP are closely related to the unique local environment, namely, a significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context in which all seven regions are brought together, deep convection in the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. A similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo (e.g., 0 and 10 dBZ), and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed. Hence, the difference between the TP and SAMR is more of a general contrast between subtropical land regions and tropical oceanic regions during the boreal summer. 3) Deep convection over the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon flow. 4) Results from a comparison between the daytime (1:30 p.m.) and nighttime (1:30 a.m.) overpasses are largely consistent with researchers’ general understanding of the diurnal variation of tropical and subtropical deep convection.

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