scholarly journals The Role of Moisture in Summertime Low-Level Jet Formation and Associated Rainfall over the East Asian Monsoon Region

2015 ◽  
Vol 72 (10) ◽  
pp. 3871-3890 ◽  
Author(s):  
Ruidan Chen ◽  
Lorenzo Tomassini
Keyword(s):  
General Circulation ◽  
North China ◽  
Circulation Model ◽  
Moisture Flux ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Moisture Flux Convergence ◽  
Low Level ◽  
Low Level Jet

Abstract The southwesterly low-level jet (LLJ) located to the east of the Tibetan Plateau in southern China plays an important role in summertime convective initiation over north China. This study adopts a novel perspective and uses hindcast experiments in order to investigate the role of moisture in LLJ and associated heavy rainfall formation, employing a global atmospheric general circulation model (AGCM). In the sensitivity experiments, an increase of humidity in the inflow region leads to a weaker LLJ but stronger diurnal wind oscillations. The weaker LLJ is due to a decreased lower-tropospheric east–west pressure gradient resulting from a low pressure anomaly over southeastern China induced by deep convection and related condensational heating. On the other hand, the stronger diurnal variation of the LLJ originates from stronger day-and-night thermal differences over the sloping terrain, which is related to drier conditions over the mountain range. Moreover, the increased humidity and decreased LLJ counteract one another to impact precipitation in the outflow region. The change of precipitation is mainly determined by the altered moisture flux divergence. If the increase in humidity dominates, then the moisture flux convergence is enhanced and favors more precipitation over north China. Otherwise, if the decreased LLJ dominates, then the moisture flux convergence is reduced, which constrains precipitation. It is highlighted that the moist diabatic and dynamic processes are intimately coupled, and that a correct simulation of moisture flux convergence is vital for AGCMs to reproduce the LLJ-related precipitation, particularly the nocturnal precipitation peak, which is a deficiency in many current models.

scholarly journals Summertime precipitation in Hokkaido and Kyushu, Japan in response to global warming

2021 ◽  
Author(s):  
Daichi Takabatake ◽  
Masaru Inatsu
Keyword(s):  
Global Warming ◽  
Tropical Cyclones ◽  
General Circulation ◽  
Dynamical Downscaling ◽  
Circulation Model ◽  
Policy Decision ◽  
Moisture Flux ◽  
Specific Humidity ◽  
Future Climate Change ◽  
Moisture Flux Convergence

Abstract We analyzed a large ensemble dataset called the database for Policy Decision Making for Future climate change (d4PDF), which contains 60-km resolution atmospheric general circulation model output and 20-km resolution dynamical downscaling for the Japanese domain. The increase in moisture and precipitation, and their global warming response in June–July–August were described focusing on the differences between Hokkaido and Kyushu. The results suggested that the specific humidity increased almost following the Clausius Clapeyron relation, but the change in stationary circulation suppressed the precipitation increase, except for in western Kyushu. The + 4 K climate in Hokkaido would be as hot and humid as the present climate in Kyushu. The circulation change related to the southward shift of the jet stream and an eastward shift of the Bonin high weakened the moisture flux convergence via a stationary field over central Japan including eastern Kyushu. The transient eddy activity counteracted the increase in humidity, so that the moisture flux convergence and precipitation did not change much over Hokkaido. Because the contribution of tropical cyclones to the total precipitation was at most 10%, the decrease in the number of tropical cyclones did not explain the predicted change in precipitation.

scholarly journals Air, Sea, and Land Interactions of the Continental U.S. Hydroclimate

2009 ◽  
Vol 10 (2) ◽  
pp. 353-373 ◽  
Author(s):  
Vasubandhu Misra ◽  
P. A. Dirmeyer
Keyword(s):  
United States ◽  
General Circulation Model ◽  
General Circulation ◽  
Winter Season ◽  
Circulation Model ◽  
Moisture Flux ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Moisture Flux Convergence ◽  
The Mean

Abstract Multidecadal simulations over the continental United States by an atmospheric general circulation model coupled to an ocean general circulation model is compared with that forced by observed sea surface temperature (SST). The differences in the mean and the variability of precipitation are found to be larger in the boreal summer than in the winter. This is because the mean SST differences in the two simulations are qualitatively comparable between the two seasons. The analysis shows that, in the boreal summer season, differences in moisture flux convergence resulting from changes in the circulation between the two simulations initiate and sustain changes in precipitation between them. This difference in precipitation is, however, further augmented by the contributions from land surface evaporation, resulting in larger differences of precipitation between the two simulations. However, in the boreal winter season, despite differences in the moisture flux convergence between the two model integrations, the precipitation differences over the continental United States are insignificant. It is also shown that land–atmosphere feedback is comparatively much weaker in the boreal winter season.

scholarly journals Estimating the Influence of Evaporation and Moisture-Flux Convergence upon Seasonal Precipitation Rates. Part II: An Analysis for North America Based upon the NCEP–DOE Reanalysis II Model

2009 ◽  
Vol 10 (4) ◽  
pp. 893-911 ◽  
Author(s):  
Bruce T. Anderson ◽  
Alex C. Ruane ◽  
John O. Roads ◽  
Masao Kanamitsu
Keyword(s):  
Large Scale ◽  
Moisture Flux ◽  
Early Summer ◽  
Monsoon Circulation ◽  
Atmospheric Moisture ◽  
Storm Activity ◽  
Moisture Flux Convergence ◽  
Low Level ◽  
Low Level Jet ◽  
Northwestern Mexico

Abstract In this paper, a diagnostic metric—termed the local-convergence ratio—is used to analyze the contribution of evaporation and atmospheric moisture-flux convergence to model-based estimates of climatological precipitation over the North American continent. Generally, the fractional evaporative contribution is largest during spring and summer when evaporation is largest and decreases as evaporation decreases. However, there appears to be at least three regions with distinct spatiotemporal seasonal evolutions of this ratio. Over both the northern and western portions of the continent, the fractional evaporative contribution peaks in spring and early summer and decreases during fall and into winter. Over the northern portion, this fall decrease is related to an increase in atmospheric moisture-flux convergence associated with enhanced meridional moisture fluxes into the region; over the western coastal regions, the fall decrease in evaporative contribution is associated with a decrease in evaporation and an increase in total moisture-flux convergence, most likely associated with increased storm activity. In contrast, over the central portions of the continent, the fractional evaporative contribution to precipitation remains relatively low in spring—when enhanced low-level jet activity increases the low-level atmospheric moisture flux convergence into the region—and instead peaks in summer and fall—when the moisture-flux convergence associated with the low-level jet decreases and precipitation is balanced predominantly by local evaporation. Finally, over the southwestern United States and northwestern Mexico, the fractional evaporative contribution to precipitation is found to contain a wintertime minimum as well as a secondary minimum during summer. This latter feature is due to a substantial increase in low-level atmospheric moisture-flux convergence associated with the large-scale monsoon circulation that influences this region during this time.

scholarly journals Comprendre la dynamique atmosphérique pour mieux reconstituer l'altitude passée des chaînes de montagnes

2020 ◽  
pp. 023
Author(s):  
Svetlana Botsyun ◽  
Pierre Sepulchre ◽  
Camille Risi
Keyword(s):  
Tibetan Plateau ◽  
General Circulation ◽  
Circulation Model ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
Mountain Ranges ◽  
The Past ◽  
Il Y A ◽  
The Relationship ◽  
Composition Isotopique

Comprendre la dynamique de soulèvement d'une chaîne de montagne nécessite d'en estimer l'altitude passée. C'est le but de la paléoaltimétrie. La méthode la plus répandue utilise la composition isotopique en oxygène des roches carbonatées formées dans les sols et à partir des sédiments lacustres. Celle-ci reflète la composition de la pluie passée qui, dans le monde actuel et dans la plupart des chaînes de montagnes, s'appauvrit progressivement en isotopes lourds avec l'altitude. En supposant que cet appauvrissement reste valide dans le passé, l'altitude du plateau tibétain à l'Éocène (il y a environ 42 millions d'années) est estimée à 4 000 m environ. Mais d'autres marqueurs de l'altitude passée indiquent au contraire des altitudes inférieures à 2 000 m. La relation entre composition isotopique des pluies et altitude observée aujourd'hui s'applique-t-elle à l'Éocène ? C'est ce que nous avons essayé de vérifier en utilisant un modèle de circulation générale atmosphérique, LMDZ-iso. On trouve qu'à l'Éocène la circulation atmosphérique et les processus hydrologiques étaient tellement différents de l'actuel que les observations isotopiques dans les roches carbonatées se trouvent finalement être cohérentes avec des altitudes relativement faibles. Les différentes méthodes de paléo-altimétrie se retrouvent ainsi réconciliées et en accord avec un soulèvement récent (post-Éocène) du plateau tibétain. Understanding the uplift dynamics of a mountain range requires estimating past altitude. This is the purpose of the paleo-altimetry. The most commonly applied paleo-altimetry method is based on the isotopic oxygen composition of the carbonate archives. It reflects the composition of past rain, which at present-day and in the most mountain ranges becomes progressively more depleted in heavy isotopes with altitude. Assuming that this depletion remains valid in the past, the elevation of the Tibetan Plateau in the Eocene (about 42 millions years ago) is estimated to be about 4 000 m. However, other proxy data indicate on the contrary low altitudes. Is the relationship between the rain isotopic composition and the altitude that is observed today applicable to the Eocene? This is what we tried to verify using an atmospheric general circulation model, LMDZ-iso. We find that in the Eocene, the atmospheric circulation and hydrological processes were so different to the present-day that the isotopic observations in the Eocene carbonates are actually consistent with relatively low altitudes of the Plateau. This allows us to reconcile different methods of paleo-altimetry in agreement with more recent (post-Eocene) uplift of the Tibetan Plateau.

scholarly journals Sensitivity of the tropical climate to an interhemispheric thermal gradient: the role of tropical ocean dynamics

2018 ◽  
Vol 9 (1) ◽  
pp. 285-297 ◽  
Author(s):  
Stefanie Talento ◽  
Marcelo Barreiro
Keyword(s):  
Seasonal Cycle ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Ocean Dynamics ◽  
Thermocline Depth ◽  
Thermal Forcing ◽  
Tropical Ocean ◽  
Slab Ocean

Abstract. This study aims to determine the role of the tropical ocean dynamics in the response of the climate to extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a reduced gravity ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics oppose the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates strong warming in the central-eastern basin from April to August balanced by cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Niño–Southern Oscillation, weakening its amplitude and low-frequency behaviour.

scholarly journals Sensitivity of the tropical climate to an interhemispheric thermal gradient: the role of tropical ocean dynamics

2017 ◽  
Author(s):  
Stefanie Talento ◽  
Marcelo Barreiro
Keyword(s):  
Seasonal Cycle ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Ocean Dynamics ◽  
Thermocline Depth ◽  
Thermal Forcing ◽  
Tropical Ocean ◽  
Slab Ocean

Abstract. This study aims to determine the role of the tropical ocean dynamics in the response of the climate to an extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a Reduced Gravity Ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of an extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics opposes the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates a strong warming in the centre-east of the basin from April to August balanced by a cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Niño Southern Oscillation, weakening its amplitude and low-frequency behaviour.

scholarly journals Reexamination of the Late Pliocene Climate over China Using a 25-km Resolution General Circulation Model

2019 ◽  
Vol 32 (3) ◽  
pp. 897-916 ◽  
Author(s):  
Qing Yan ◽  
Ting Wei ◽  
Zhongshi Zhang
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
East Asian ◽  
Circulation Model ◽  
Northwest China ◽  
Precipitation Change ◽  
The Tibetan Plateau ◽  
Model Resolution ◽  
Geological Evidence ◽  
Late Pliocene

Simulations of past warm climate provide an opportunity to better understand how the climate system may respond to increased greenhouse gas emissions. Using the ~25-km-resolution Community Atmosphere Model, version 4 (CAM4), we examine climate change over China in the Late Pliocene warm period (3.264–3.025 Ma) and further explore the influences of different sea surface temperature (SST) forcings and model horizontal resolutions. Initial evaluation shows that the high-resolution CAM4 performs well in capturing the climatological distribution of present-day temperature, precipitation, and low-level monsoon circulations over China. Based on the standard Pliocene Research, Interpretation and Synoptic Mapping (version 4; PRISM4) boundary conditions, CAM4 predicts an increase of annual mean temperature by ~0.5°C over China in the Late Pliocene relative to the preindustrial era, with the greatest warming in northwest China but cooling in southwest China. Enhanced annual mean precipitation is observed in the Late Pliocene over most of China except for northwest China where precipitation is decreased. The East Asian summer (winter) monsoon is intensified (weakened) in the Late Pliocene as suggested by geological evidence, which is attributed to the enhanced (reduced) land–sea thermal contrast. The East Asian monsoon domain exhibits a northwestward expansion in the Late Pliocene, especially over the Tibetan Plateau. Additionally, our results indicate that the modeled climate change is sensitive to the Late Pliocene SST forcings and model resolution. Particularly, different SST forcings [PRISM4-based vs Pliocene Model Intercomparison Project (PlioMIP)-based SSTs] affect the modeled phase change of summer monsoon and the associated precipitation change, while model resolution (~25 vs 400 km) mainly impacts precipitation change.

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