共查询到20条相似文献，搜索用时 15 毫秒
1.
Sea surface temperature (SST) variations include negative feedbacks from the atmosphere, whereas SST anomalies are specified in stand-alone atmospheric general circulation simulations. Is the SST forced response the same as the coupled response? In this study, the importance of air–sea coupling in the Indian and Pacific Oceans for tropical atmospheric variability is investigated through numerical experiments with a coupled atmosphere-ocean general circulation model. The local and remote impacts of the Indian and Pacific Ocean coupling are obtained by comparing a coupled simulation with an experiment in which the SST forcing from the coupled simulation is specified in either the Indian or the Pacific Ocean. It is found that the Indian Ocean coupling is critical for atmospheric variability over the Pacific Ocean. Without the Indian Ocean coupling, the rainfall and SST variations are completely different throughout most of the Pacific Ocean basin. Without the Pacific Ocean coupling, part of the rainfall and SST variations in the Indian Ocean are reproduced in the forced run. In regions of large mean rainfall where the atmospheric negative feedback is strong, such as the North Indian Ocean and the western North Pacific in boreal summer, the atmospheric variability is significantly enhanced when air–sea coupling is replaced by specified SST forcing. This enhancement is due to the lack of the negative feedback in the forced SST simulation. In these regions, erroneous atmospheric anomalies could be induced by specified SST anomalies derived from the coupled model. The ENSO variability is reduced by about 20% when the Indian Ocean air–sea coupling is replaced by specified SST forcing. This change is attributed to the interfering roles of the Indian Ocean SST and Indian monsoon in western and central equatorial Pacific surface wind variations. 相似文献
2.
Over the mid-latitude North Pacific, there is a close relationship between interannual variations of the sea surface temperature (SST) and surface shortwave radiation during boreal summer. The present study evaluates this relationship in coupled model simulations, forced model simulations, and retrospective forecasts. It is found that the simulation of this relationship in climate models is closely related to the model biases in the meridional gradients of mean SST and surface shortwave radiation. A southward shift in the region of large mean meridional gradients leads to a similar southward shift in the region of large correlation between the SST and shortwave radiation variations. The relationship is enhanced (weakened) when the mean meridional gradients are stronger (weaker) compared to observations. The shortwave radiation?CSST correlation is weak in individual forced simulations because of the interference of internally generated shortwave radiation variations. The shortwave radiation?CSST correlation increases significantly in the ensemble mean due to reduction of internally generated variability. The long-lead Climate Forecast System (CFS) forecasts have a better simulation of the shortwave radiation?CSST correlation compared to the short-lead forecasts. Estimation based on the CFS ensemble forecasts indicates that the high-frequency atmospheric variations contribute importantly to the SST variability over the mid-latitude North Pacific during boreal summer. 相似文献
3.
Hiroaki Ueda Harumitsu Kuroki Masamichi Ohba Youichi Kamae 《Climate Dynamics》2011,37(11-12):2167-2179
Modulation of a monsoon under glacial forcing is examined using an atmosphere?Cocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air?Csea?Cland interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21?ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer convection. 相似文献
4.
J. A. Marengo I. F. A. Cavalcanti P. Satyamurty I. Trosnikov C. A. Nobre J. P. Bonatti H. Camargo G. Sampaio M. B. Sanches A. O. Manzi C. A. C. Castro C. D'Almeida L. P. Pezzi L. Candido 《Climate Dynamics》2003,21(5-6):459-475
This is a study of the annual and interannual variability of regional rainfall produced by the Center for Weather Forecasts and Climate Studies/Center for Ocean, Land and Atmospheric Studies (CPTEC/COLA) atmospheric global climate model. An evaluation is made of a 9-member ensemble run of the model forced by observed global sea surface temperature (SST) anomalies for the 10-year period 1982–1991. The Brier skill score and, Relative Operating Characteristics (ROC) are used to assess the predictability of rainfall and to validate rainfall simulations, in several regions world wide. In general, the annual cycle of precipitation is well simulated by the model for several continental and oceanic regions in the tropics and mid latitudes. Interannual variability of rainfall during the peak rainy season is realistically simulated in Northeast Brazil, Amazonia, central Chile, and southern Argentina–Uruguay, Eastern Africa, and tropical Pacific regions, where the model shows good skill. Some regions, such as northwest Peru–Ecuador, and southern Brazil exhibit a realistic simulation of rainfall anomalies associated with extreme El Niño warming conditions, while in years with neutral or La Niña conditions, the agreement between observed and simulated rainfall anomalies is not always present. In the monsoon regions of the world and in southern Africa, even though the model reproduces the annual cycle of rainfall, the skill of the model is low for the simulation of the interannual variability. This is indicative of mechanisms other than the external SST forcing, such as the effect of land–surface moisture and snow feedbacks or the representation of sub-grid scale processes, indicating the important role of factors other than external boundary forcing. The model captures the well-known signatures of rainfall anomalies of El Niño in 1982–83 and 1986–87, indicating its sensitivity to strong external forcing. In normal years, internal climate variability can affect the predictability of climate in some regions, especially in monsoon areas of the world. 相似文献
5.
Sea surface temperature (SST) anomalies can induce anomalous convection through surface evaporation and low-level moisture
convergence. This SST forcing of the atmosphere is indicated in a positive local rainfall–SST correlation. Anomalous convection
can feedback on SST through cloud-radiation and wind-evaporation effects and wind-induced oceanic mixing and upwelling. These
atmospheric feedbacks are reflected in a negative local rainfall–SST tendency correlation. As such, the simultaneous rainfall–SST
and rainfall–SST tendency correlations can indicate the nature of local air–sea interactions. Based on the magnitude of simultaneous
rainfall–SST and rainfall–SST tendency correlations, the present study identifies three distinct regimes of local air–sea
interactions. The relative importance of SST forcing and atmospheric forcing differs in these regimes. In the equatorial central-eastern
Pacific and, to a smaller degree, in the western equatorial Indian Ocean, SST forcing dominates throughout the year and the
surface heat flux acts mainly as a damping term. In the tropical Indo-western Pacific Ocean regions, SST forcing and atmospheric
forcing dominate alternatively in different seasons. Atmospheric forcing dominates in the local warm/rainy season. SST forcing
dominates with a positive wind-evaporation feedback during the transition to the cold/dry season. SST forcing also dominates
during the transition to the warm/rainy season but with a negative cloud-radiation feedback. The performance of atmospheric
general circulation model simulations forced by observed SST is closely linked to the regime of air–sea interaction. The forced
simulations have good performance when SST forcing dominates. The performance is low or poor when atmospheric forcing dominates. 相似文献
6.
Hemantkumar S. Chaudhari Samir Pokhrel Sachiko Mohanty Subodh K. Saha 《Theoretical and Applied Climatology》2013,114(3-4):459-477
This study has identified probable factors that govern ISMR predictability. Furthermore, extensive analysis has been performed to evaluate factors leading to the predictability aspect of Indian Summer Monsoon Rainfall (ISMR) using uncoupled and coupled version of National Centers for Environmental Prediction Coupled Forecast System (CFS). It has been found that the coupled version (CFS) has outperformed the uncoupled version [Global Forecast System (GFS)] of the model in terms of prediction of rainfall over Indian land points. Even the spatial distribution of rainfall is much better represented in the CFS as compared to that of GFS. Even though these model skills are inadequate for the reliable forecasting of monsoon, it imparts the capacious knowledge about the model fidelity. The mean monsoon features and its evolution in terms of rainfall and large-scale circulation along with the zonal and meridional shear of winds, which govern the strength of the monsoon, are relatively closer to the observation in the CFS as compared to the GFS. Furthermore, sea surface temperature–rainfall relation is fairly realistic and intense in the coupled version of the model (CFS). It is found that the CFS is able to capture El Niño Southern Oscillation ISMR (ENSO-ISMR) teleconnections much strongly as compared to GFS; however, in the case of Indian Ocean Dipole ISMR teleconnections, GFS has the larger say. Coupled models have to be fine-tuned for the prediction of the transition of El Niño as well as the strength of the mature phase has to be improved. Thus, to sum up, CFS tends to have better predictive skill on account of following three factors: (a) better ability to replicate mean features, (b) comparatively better representation of air–sea interactions, and (c) much better portrayal of ENSO-ISMR teleconnections. This study clearly brings out that coupled model is the only way forward for improving the ISMR prediction skill. However, coupled model’s spurious representation of SST variability and mean model bias are detrimental in seasonal prediction. 相似文献
7.
The interannual variability of climate in the Amazon basin is studied using precipitation and river level anomalies observed near the March/April rainy season peak for the period 1980–86, supported by satellite imagery of tropical convection. Evaluation of this data in conjunction with the corresponding circulation and sea-surface temperature (SST) anomaly patterns indicates that abundant rainy seasons in Northern Amazonia are characterized by anomalously cold surface waters in the tropical eastern Pacific, and negative/positive SST anomalies in the tropical North/South Atlantic, accelerated Northeast trades and a southward displaced Intertropical Convergence Zone (ITCZ) over the Atlantic sector. Years with deficient rainfall show broadly opposite patterns.General circulation model (GCM) experiments using observed SST in three case studies were aimed at testing the teleconnections between SST and Amazon climate implied by the empirical analysis. The GCM-generated surface fields resemble the corresponding observers fields most closely over the tropical Pacific and, with one exception, over the tropical Atlantic as well. The modeled precipitation features, along the Northwest coast of South America, anomalies of opposite sign to the North and South of the equator, in agreement with observations and results from a different GCM. Similarities in simulations run from different initial conditions, but using the same global SST, indicate broad consistency in response to common boundary forcing. 相似文献
8.
Dependence of Indian monsoon rainfall on moisture fluxes across the Arabian Sea and the impact of coupled model sea surface temperature biases 总被引：2，自引：2，他引：0
The Arabian Sea is an important moisture source for Indian monsoon rainfall. The skill of climate models in simulating the monsoon and its variability varies widely, while Arabian Sea cold sea surface temperature (SST) biases are common in coupled models and may therefore influence the monsoon and its sensitivity to climate change. We examine the relationship between monsoon rainfall, moisture fluxes and Arabian Sea SST in observations and climate model simulations. Observational analysis shows strong monsoons depend on moisture fluxes across the Arabian Sea, however detecting consistent signals with contemporaneous summer SST anomalies is complicated in the observed system by air/sea coupling and large-scale induced variability such as the El Ni?o-Southern Oscillation feeding back onto the monsoon through development of the Somali Jet. Comparison of HadGEM3 coupled and atmosphere-only configurations suggests coupled model cold SST biases significantly reduce monsoon rainfall. Idealised atmosphere-only experiments show that the weakened monsoon can be mainly attributed to systematic Arabian Sea cold SST biases during summer and their impact on the monsoon-moisture relationship. The impact of large cold SST biases on atmospheric moisture content over the Arabian Sea, and also the subsequent reduced latent heat release over India, dominates over any enhancement in the land-sea temperature gradient and results in changes to the mean state. We hypothesize that a cold base state will result in underestimation of the impact of larger projected Arabian Sea SST changes in future climate, suggesting that Arabian Sea biases should be a clear target for model development. 相似文献
9.
Interdecadal change in the relationship of southern China summer rainfall with tropical Indo-Pacific SST 总被引：1，自引：0，他引：1
Renguang Wu Song Yang Zhiping Wen Gang Huang Kaiming Hu 《Theoretical and Applied Climatology》2012,108(1-2):119-133
The present study investigates the interdecadal change in the relationship between southern China (SC) summer rainfall and tropical Indo-Pacific sea surface temperature (SST). It is found that the pattern of tropical Indo-Pacific SST anomalies associated with SC summer rainfall variability tends to be opposite between the 1950–1960s and the 1980-1990s. Above-normal SC rainfall corresponds to warmer SST in the tropical southeastern Indian Ocean (SEIO) and cooler SST in the equatorial central Pacific (ECP) during the 1950–1960s but opposite SST anomalies in these regions during the 1980–1990s. A pronounced difference is also found in anomalous atmospheric circulation linking SEIO SST and SC rainfall between the two periods. In the 1950–1960s, two anomalous vertical circulations are present between ascent over SEIO and ascent over SC, with a common branch of descent over the South China Sea that is accompanied by an anomalous low-level anticyclone. In the 1980–1990s, however, a single anomalous vertical circulation directly connects ascent over SC to descent over SEIO. The change in the rainfall–SST relationship is likely related to a change in the magnitude of SEIO SST forcing and a change in the atmospheric response to the SST forcing due to different mean states. A larger SEIO SST forcing coupled with a stronger and more extensive western North Pacific subtropical high in recent decades induce circulation anomalies reaching higher latitudes, influencing SC directly. Present analysis shows that the SEIO and ECP SST anomalies can contribute to SC summer rainfall variability both independently and in concert. In comparison, there are more cases of concerted contributions due to the co-variability between the Indian and Pacific Ocean SSTs. 相似文献
10.
11.
R. Justin Small Shang-Ping Xie Eric D. Maloney Simon P. de Szoeke Toru Miyama 《Climate Dynamics》2011,36(5-6):867-890
Intraseasonal variability in the eastern Pacific warm pool in summer is studied, using a regional ocean?Catmosphere model, a linear baroclinic model (LBM), and satellite observations. The atmospheric component of the model is forced by lateral boundary conditions from reanalysis data. The aim is to quantify the importance to atmospheric deep convection of local air?Csea coupling. In particular, the effect of sea surface temperature (SST) anomalies on surface heat fluxes is examined. Intraseasonal (20?C90?day) east Pacific warm-pool zonal wind and outgoing longwave radiation (OLR) variability in the regional coupled model are correlated at 0.8 and 0.6 with observations, respectively, significant at the 99% confidence level. The strength of the intraseasonal variability in the coupled model, as measured by the variance of outgoing longwave radiation, is close in magnitude to that observed, but with a maximum located about 10° further west. East Pacific warm pool intraseasonal convection and winds agree in phase with those from observations, suggesting that remote forcing at the boundaries associated with the Madden?CJulian oscillation determines the phase of intraseasonal convection in the east Pacific warm pool. When the ocean model component is replaced by weekly reanalysis SST in an atmosphere-only experiment, there is a slight improvement in the location of the highest OLR variance. Further sensitivity experiments with the regional atmosphere-only model in which intraseasonal SST variability is removed indicate that convective variability has only a weak dependence on the SST variability, but a stronger dependence on the climatological mean SST distribution. A scaling analysis confirms that wind speed anomalies give a much larger contribution to the intraseasonal evaporation signal than SST anomalies, in both model and observations. A LBM is used to show that local feedbacks would serve to amplify intraseasonal convection and the large-scale circulation. Further, Hovm?ller diagrams reveal that whereas a significant dynamic intraseasonal signal enters the model domain from the west, the strong deep convection mostly arises within the domain. Taken together, the regional and linear model results suggest that in this region remote forcing and local convection?Ccirculation feedbacks are both important to the intraseasonal variability, but ocean?Catmosphere coupling has only a small effect. Possible mechanisms of remote forcing are discussed. 相似文献
12.
Most estimates of the skill of atmospheric general circulation models (AGCMs) for forecasting seasonal climate anomalies have been based on simulations with actual observed sea surface temperatures (SSTs) as lower boundary forcing. Similarly estimates of the climatological response characteristics of AGCMs used for seasonal-to-interannual climate prediction generally rest on historical simulations using "perfect" SST forecasts. This work examines the errors and biases introduced into the seasonal precipitation response of an AGCM forced with persisted SST anomalies, which are generally considered to constitute a good prediction of SST in the first three-month season. The added uncertainty introduced by the persisted SST anomalies weakens, and in some cases nullifies, the skill of atmospheric predictions that is possible given perfect SST forcing. The use of persisted SST anomalies also leads to changes in local signal-to-noise characteristics. Thus, it is argued that seasonal-to-interannual forecasts using AGCMs should be interpreted relative to historical runs that were subject to the same strategy of boundary forcing used in the current forecast in order to properly account for errors and biases introduced by the particular SST prediction strategy. Two case studies are examined to illustrate how the sensitivity of the climate response to predicted SSTs may be used as a diagnostic to suggest improvements to the predicted SSTs. 相似文献
13.
Using observations of rainfall and SST analysis it is shown that there is a robust relationship with two-season lag between the austral summer (December–January–February [DJF]) Equatorial Amazon (EA) rainfall and the following boreal summer season (June–July–August [JJA]) Intra-Americas Seas (IAS) Sea Surface Temperature Anomalies (SSTA). It is observed that in wetter than normal austral summer seasons over EA, the SSTA in the IAS are cooler than normal in the following JJA season. This teleconnection also manifests in the ocean heat content of the IAS region. Our analysis indicates that the net surface heat flux into the ocean (particularly the surface longwave and the shortwave radiative fluxes) dictates the strongest influence on the JJA Caribbean SSTA, the core region of the IAS where the observed teleconnection with EA rainfall is strongest. This study also finds that this teleconnection is in fact a manifestation of the remote ENSO forcing on the Caribbean SSTA through its modulation of the EA rainfall anomalies. In a wet DJF year over EA, the Atlantic Inter-Tropical Convergence Zone (ITCZ) moves further southward than climatology. This causes the dry limb of the associated overturning circulation of the Atlantic ITCZ to reside over the Caribbean Sea region in the subsequent March–April–May and JJA seasons. As a result of this large-scale descent in the wet DJF year over EA, there is a net decrease in the heat flux into the ocean from increased emission of surface longwave radiation in the presence of anomalously dry atmosphere. In a dry DJF year over EA the Atlantic ITCZ is nearly co-located in the core region of the IAS, which is northward than the climatological location, resulting in the descending limb of the overturning location to be located further south of the Caribbean Sea leading to warmer SSTA. 相似文献
14.
1998年和2016年北大西洋海温异常对中国夏季降水影响的数值模拟研究 总被引：3，自引：0，他引：3
基于1979-2016年ERA-Interim再分析资料和CAM5.3模式,研究了2016年和1998年北大西洋海温异常对中国夏季降水以及大尺度环流的可能影响及其机制。结果表明,这两年前夏（6-7月）长江中下游及其以南地区降水均异常偏多,但1998年降水异常较2016年更为显著。后夏（8月）,2016年长江以南地区降水异常偏多,长江-黄河流域降水异常偏少,而1998年降水异常分布与之相反。2016年和1998年夏季中国东部降水异常的差异与西北太平洋对流层低层异常反气旋以及欧亚中高纬度环流变化的共同作用直接相关。敏感性数值试验的结果表明,北大西洋海温异常的显著差异是导致2016年和1998年夏季中国东部降水以及大尺度环流异常存在明显差异的重要原因之一。一方面,北大西洋海温异常可以通过改变欧亚中高纬度环流进而对中国夏季降水产生影响。1998年北大西洋海温异常自热带至副极地呈类似"+ - +"型分布,这种海温异常型能够在前夏欧亚中高纬度地区激发出双阻型的环流异常响应。2016年北大西洋海温异常自热带至副极地呈相对弱的"- + -"型分布,欧亚中高纬度环流异常响应总体偏弱。另一方面,北大西洋海温异常还可以通过影响热带纬向环流进而对西北太平洋对流层低层异常反气旋起调制作用。1998年北大西洋海温异常对夏季西北太平洋异常反气旋起增强作用,这与热带印度洋-太平洋海温的强迫作用相协调。然而,2016年北大西洋海温异常则有利于西北太平洋异常反气旋的减弱,这与热带印度洋-太平洋海温的强迫作用相反。因此,在这3个大洋的协同作用下,2016年和1998年前夏西北太平洋异常反气旋均偏强,但前者的振幅弱于后者。在后夏,1998年西北太平洋对流层低层仍受异常反气旋控制,2016年则为异常气旋控制。 相似文献
15.
This study investigates summer rainfall variability in the South China Sea (SCS) region and the roles of remote sea surface temperature (SST) forcing in the tropical Indian and Pacific Ocean regions. The SCS summer rainfall displays a positive and negative relationship with simultaneous SST in the equatorial central Pacific (ECP) and the North Indian Ocean (NIO), respectively. Positive ECP SST anomalies induce an anomalous low-level cyclone over the SCS-western North Pacific as a Rossby-wave type response, leading to above-normal precipitation over northern SCS. Negative NIO SST anomalies contribute to anomalous cyclonic winds over the western North Pacific by an anomalous east–west vertical circulation north of the equator, favoring more rainfall over northern SCS. These NIO SST anomalies are closely related to preceding La Niña and El Niño events through the “atmospheric bridge”. Thus, the NIO SST anomalies serve as a medium for an indirect impact of preceding ECP SST anomalies on the SCS summer rainfall variability. The ECP SST influence is identified to be dominant after 1990 and the NIO SST impact is relatively more important during 1980s. These Indo-Pacific SST effects are further investigated by conducting numerical experiments with an atmospheric general circulation model. The consistency between the numerical experiments and the observations enhances the credibility of the Indo-Pacific SST influence on the SCS summer rainfall variability. 相似文献
16.
C. J. C. Reason 《Meteorology and Atmospheric Physics》1998,69(1-2):49-65
Summary An important pattern of interannual variability in the southern African region is one where sea surface temperature (SST) in neighbouring waters, particularly in the Agulhas Current, its retroflection region and outflow across the southern midlatitudes of the Indian Ocean, is anomalously warm or cool. Evidence exists of significant rainfall anomalies over large parts of southern Africa during these warm or cool SST events. Here, a general circulation model is used to study the response of the atmosphere in the region to an idealised representation of these SST anomalies. The induced atmospheric circulation and precipitation anomalies over the adjacent southern African landmass on intraseasonal through to interannual time scales are investigated.A nonlinear response to the SST anomalies is found in that the changes to the model atmosphere when warm SST forcing is used are not the reverse (in either pattern or magnitude) to that when cold SST forcing is imposed. For the warm SST anomaly, it is found that the atmospheric response is favourable for enhancement of the original SST anomaly on scales up to, and including, annual. However, as the scale becomes interannual (i.e., 15–21 months after imposition of the anomaly), the model response suggests that damping of the original SST anomaly becomes likely. However, no such coherent timescale dependent response is found when the cold SST anomaly is impose. It is suggested that the relationship of the SST anomaly to the background seasonal climatology may help explain this fundamental difference in the response.Examination of the circulation and rainfall patterns under warm SST forcing indicates that there are significant anomalies over large parts of southern Africa on all scales from intraseasonal through to interannual. On the south coast, rainfall anomalies result from enhanced evaporation of moisture off the SST anomaly. Over the interior, changer in the convergence of moist air streams together with suggestions of a shift in the Walker circulations between southern Africa and the bordering tropical South Atlantic and Indian Oceans appear to be associated with the rainfall anomalies. Similar mechanisms of rainfall perturbation are found when the cold SST anomaly is imposed; however, there is a significant response only on intra-annual to interannual scales. In all cases, the magnitude of the rainfall anomalies accumulated over a 90 day season were of the order of 90–180 mm, and therefore represent a significant fraction of the annual total of many areas. These model results re-inforce previous observational work suggesting that SST anomalies south of Africa, particularly in the retroflection region of the Agulhas Current, are linked with significant rainfall anomalies over the adjacent subcontinent.With 12 Figures 相似文献
17.
Xiouhua Fu June-Yi Lee Pang-Chi Hsu Hiroshi Taniguchi Bin Wang Wanqiu Wang Scott Weaver 《Climate Dynamics》2013,41(3-4):1067-1081
The present study assesses the forecast skill of the Madden–Julian Oscillation (MJO) observed during the period of DYNAMO (Dynamics of the MJO)/CINDY (Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011) field campaign in the GFS (NCEP Global Forecast System), CFSv2 (NCEP Climate Forecast System version 2) and UH (University of Hawaii) models, and revealed their strength and weakness in forecasting initiation and propagation of the MJO. Overall, the models forecast better the successive MJO which follows the preceding event than that with no preceding event (primary MJO). The common modeling problems include too slow eastward propagation, the Maritime Continent barrier and weak intensity. The forecasting skills of MJO major modes reach 13, 25 and 28 days, respectively, in the GFS atmosphere-only model, the CFSv2 and UH coupled models. An equal-weighted multi-model ensemble with the CFSv2 and UH models reaches 36 days. Air–sea coupling plays an important role for initiation and propagation of the MJO and largely accounts for the skill difference between the GFS and CFSv2. A series of forecasting experiments by forcing UH model with persistent, forecasted and observed daily SST further demonstrate that: (1) air–sea coupling extends MJO skill by about 1 week; (2) atmosphere-only forecasts driven by forecasted daily SST have a similar skill as the coupled forecasts, which suggests that if the high-resolution GFS is forced with CFSv2 forecasted daily SST, its forecast skill can be much higher than its current level as forced with persistent SST; (3) atmosphere-only forecasts driven by observed daily SST reaches beyond 40 days. It is also found that the MJO–TC (Tropical Cyclone) interactions have been much better represented in the UH and CFSv2 models than that in the GFS model. Both the CFSv2 and UH coupled models reasonably well capture the development of westerly wind bursts associated with November 2011 MJO and the cyclogenesis of TC05A in the Indian Ocean with a lead time of 2 weeks. However, the high-resolution GFS atmosphere-only model fails to reproduce the November MJO and the genesis of TC05A at 2 weeks’ lead. This result highlights the necessity to get MJO right in order to ensure skillful extended-range TC forecasting. 相似文献
18.
评估了耦合气候系统模式FGOALS海洋同化试验对西北太平洋夏季降水和SST相关关系的模拟技巧,并对比了相应的观测海温强迫试验（AMIP）和历史气候模拟试验结果。结果显示,FGOALS海洋同化试验对亚洲季风区大部分海域夏季SST年际变化有较高的模拟技巧,但其对菲律宾以东海域模拟技巧较低。在西北太平洋夏季降水-SST相关关系方面,同化试验部分地再现了南海和菲律宾以东海域降水超前SST变化1个月和同时二者的负相关关系,优于AMIP试验但逊于自由耦合模拟试验。同化试验对SST倾向-降水相关关系的模拟技巧亦介于AMIP试验和自由耦合试验之间。观测中,西北太平洋夏季降水与环流异常受日界线附近和赤道东印度洋海洋大陆地区海温异常的遥强迫,并通过改变到达海表的净短波辐射通量影响局地SST异常,导致局地海温-降水和局地海温倾向-降水的负相关关系。在AMIP试验中,遥强迫导致的西北太平洋地区环流异常较之观测偏弱,由于缺少局地海气耦合过程,在西北太平洋多数地区表现为海温对大气的强迫作用,即SST-降水正相关关系。FGOALS同化试验和自由耦合试验考虑了局地海气耦合过程,虽然低估了遥强迫对西北太平洋地区夏季环流异常的影响,依然部分模拟出局地降水-SST负相关关系但较之观测偏弱。同时,自由耦合试验高估了西北太平洋20°N以南地区海温异常对大气环流异常的强迫,使得其对中国南海和日本岛以南海域SST-降水负相关关系的模拟稍优于同化试验。 相似文献
19.
The sensitivity of different atmospheric forcing on the simulation of Sea Surface Temperature (SST) in the Indian Ocean is examined using Regional Ocean Modeling System (ROMS). Model simulations using three different atmospheric forcings from the National Centers for Environmental Prediction (NCEP; 2.5 deg), National Centre for Medium Range Weather Forecasting (NCMRWF; 0.25 deg) and TropFlux (0.5 deg) are analyzed here. Model sensitivity to the atmospheric forcing is studied by analyzing the response of SST and mixed layer depth (MLD) using statistical methods. Results show that the response of NCMRWF and TropFlux forcing was almost similar in capturing the variability of SST in comparison with the corresponding observations. But NCEP was unable to capture SST variability, especially over the central part of the Arabian Sea (AS). It is shown that deeper MLD simulations by NCEP forcing due to the high magnitude of wind resulted in an unrealistic simulation of SST. 相似文献
20.
GFS物理过程包在GRAPES区域模式中的实施及改进:单柱试验 总被引：3，自引：2，他引：1
将NCEP的中期全球预报系统（GFS）整套物理过程包引入GRAPES区域模式,并利用美国ARM计划（Atmospheric Radiation Measurement Program）南部大平原外场1997年夏加强观测资料,对GRAPES模式中原有物理过程和GFS物理过程进行了单柱试验的测试和比较,评估了两组物理过程的模拟性能。单柱试验结果表明GFS试验模拟的位温和水汽混合比演变更为准确;到地短波和长波辐射的误差更小;其模拟的地面向上潜热通量与观测更为接近,而原物理过程试验的感热偏大;GFS试验对2 m气温最高和最低值的模拟也比原有物理过程更接近观测。进一步分析降水的模拟发现,两组物理过程对强降水过程均有很好的预报能力,但对中等强度降水存在漏报或者发生时间偏晚的倾向,此外还存在对小雨的空报。在3个降水事件的模拟中,GFS试验模拟的降水误差小于原物理过程试验。最后还对两组试验中明显的降水过程漏报和降水延迟进行了分析,对GFS物理过程包中对流参数化的对流触发方式的修改,可改进此次降水的模拟,进而通过更准确的反馈过程,改善对大尺度场的模拟。 相似文献