排序方式： 共有93条查询结果，搜索用时 203 毫秒
31.
The East Asia-western North Pacific boreal summer intraseasonal oscillation simulated in GAMIL 1.1.1 总被引：1，自引：0，他引：1
We evaluate the performance of GAMIL1.1.1 in a 27-year forced simulation of the summer
intraseasonal oscillation (ISO) over East Asia (EA)-western North Pacific (WNP). The assessment
is based on two measures: climatological ISO (CISO) and transient ISO (TISO). CISO is the ISO
component that is phase-locked to the annual cycle and describes seasonal march. TISO is the
ISO component that varies year by year.
The model reasonably captures many observed features of the ISO, including the stepwise northward
advance of the rain belt of CISO, the dominant periodicities of TISO in both the South China
Sea-Philippine Sea (SCS-PS) and the Yangtze River Basin (YRB), the northward propagation of 30--50-day
TISO and the westward propagation of the 12--25-day TISO mode over the SCS-PS, and the zonal propagating
features of three major TISO modes over the YRB. However, the model has notable deficiencies. These
include the early onset of the South China Sea monsoon associated with CISO, too fast northward
propagation of CISO from 20oN to 40oN and the absence of the CISO signal south of 10oN,
the deficient eastward propagation of the 30--50-day TISO mode and the absence of a southward propagation
in the YRB TISO modes.
The authors found that the deficiencies in the ISO simulation are closely related to the model's biases in
the mean states, suggesting that the improvement of the model mean state is crucial for realistic
simulation of the intraseasonal variation. 相似文献
32.
Boreal summer quasi-monthly oscillation in the global tropics 总被引：1，自引：0，他引：1
Bin Wang Peter Webster Kazuyoshi Kikuchi Tetsuzo Yasunari Yanjun Qi 《Climate Dynamics》2006,27(7-8):661-675
The boreal summer intraseasonal oscillation (ISO) in the global tropics is documented here using a 7-year suite (1998–2004) of satellite measurements. A composite scenario was made of 28 selected events with reference to the oscillation in the eastern equatorial Indian Ocean (EIO), where the oscillation is most regular and its intensity is indicative of the strength of the subsequent northward propagation. The average oscillation period is about 32 days, and this quasi-monthly oscillation (QMO) is primarily confined to the tropical Indian and Pacific Oceans. Topics that were investigated are the partition of convective versus stratiform clouds, the vertical structure of precipitation rates, and the evolution of cloud types during the initial organization and the development of intraseasonal convective anomalies in the central Indian Ocean. During the initiation of the convective anomalies, the stratiform and convective rains have comparable rates; the prevailing cloud type experiences a trimodal evolution from shallow to deep convection, and finally to anvil and extended stratiform clouds. A major northwest/southeast-slanted rainband forms as the equatorial rainfall anomalies reach Sumatra, and the rainband subsequently propagates northeastward into the west Pacific Ocean. The enhanced precipitation in the west Pacific then rapidly traverses the Pacific along the Intertropical Convergence Zone, meanwhile migrating northward to the Philippine Sea. A seesaw teleconnection in rainfall anomalies is found between the southern Bay of Bengal (5–15°N, 80–100°E) and the eastern Pacific (5–15°N, 85–105°W). Local sea-surface temperature (SST)-rainfall anomalies display a negative simultaneous correlation in the off-equatorial regions but a zero correlation (quadrature phase relationship) near the equator. We propose that atmosphere–ocean interaction and the vertical monsoon easterly shear are important contributors to the northeastward propagation component of the intraseasonal rainband. The observed evidence presented here provides critical information for validating the numerical models, and it supports the self-induction mechanism theory for maintenance of the boreal summer ISO. 相似文献
33.
A version of the National Centre for Atmospheric Research (NCAR) coupled climate model is integrated under current climate
conditions and in a series of experiments with climate forcings ranging from modest to very strong. The purpose of the experiments
is to investigate the nature and behaviour of the climate feedback/sensitivity of the model, its evolution with time and climate
state, the robustness of model parameterizations as forcing levels increase, and the possibility of a “runaway” warming under
strong forcing. The model is integrated for 50 years, or to failure, after increasing the solar constant by 2.5, 10, 15, 25,
35, and 45% of its control value. The model successfully completes 50 years of integration for the 2.5, 10, 15, and 25% solar
constant increases but fails for increases of 35% and 45%. The effective global climate sensitivity evolves with time and
analysis indicates that a new equilibrium will be obtained for the 2.5, 10, and 15% cases but that runaway warming is underway
for the 25% increase in solar constant. Feedback processes are analysed both locally and globally in terms of longwave and
shortwave, clear-sky/surface, and cloud forcing components. Feedbacks in the system must be negative overall and of sufficient
strength to balance the positive forcing if the system is to attain a new equilibrium. Longwave negative feedback processes
strengthen in a reasonably linear fashion as temperature increases but shortwave feedback processes do not. In particular,
solar cloud feedback becomes less negative and, for the 25% forcing case, eventually becomes positive, resulting in temperatures
that “run away”. The conditions under which a runaway climate warming might occur have previously been investigated using
simpler models. For sufficiently strong forcing, the greenhouse effect of increasing water vapour in a warmer atmosphere is
expected to overwhelm the negative feedback of the longwave cooling to space as temperature increases. This is not, however,
the reason for the climate instability experienced in the GCM. Instead, the model experiences a “cloud feedback” warming whereby
the decrease in cloudiness that occurs when temperature increases beyond a critical value results in an increased absorption
of solar radiation by the system, leading to the runaway warming. 相似文献
34.
Lin Liu Shang-Ping Xie Xiao-Tong Zheng Tim Li Yan Du Gang Huang Wei-Dong Yu 《Climate Dynamics》2014,43(5-6):1715-1730
The performance of 21 Coupled Model Intercomparison Project Phase 5 (CMIP5) models in the simulation of the Indian Ocean Dipole (IOD) mode is evaluated. Compared to CMIP3, CMIP5 models exhibit a similar spread in IOD intensity. A detailed diagnosis was carried out to understand whether CMIP5 models have shown improvement in their representation of the important dynamical and thermodynamical feedbacks in the tropical Indian Ocean. These include the Bjerknes dynamic air-sea feedback, which includes the equatorial zonal wind response to sea surface temperature (SST) anomaly, the thermocline response to equatorial zonal wind forcing, the ocean subsurface temperature response to the thermocline variations, and the thermodynamic air-sea coupling that includes the wind-evaporation-SST and cloud-radiation-SST feedback. Compared to CMIP3, the CMIP5 ensemble produces a more realistic positive wind-evaporation-SST feedback during the IOD developing phase, while the simulation of Bjerknes dynamic feedback is more unrealistic especially with regard to the wind response to SST forcing and the thermocline response to surface wind forcing. The overall CMIP5 performance in the IOD simulation does not show remarkable improvements compared to CMIP3. It is further noted that the El Niño-Southern Oscillation (ENSO) and IOD amplitudes are closely related, if a model generates a strong ENSO, it is likely that this model also simulates a strong IOD. 相似文献
35.
The representative concentration pathways: an overview 总被引：20，自引：4，他引：16
Detlef P. van Vuuren Jae Edmonds Mikiko Kainuma Keywan Riahi Allison Thomson Kathy Hibbard George C. Hurtt Tom Kram Volker Krey Jean-Francois Lamarque Toshihiko Masui Malte Meinshausen Nebojsa Nakicenovic Steven J. Smith Steven K. Rose 《Climatic change》2011,109(1-2):5-31
This paper summarizes the development process and main characteristics of the Representative Concentration Pathways (RCPs), a set of four new pathways developed for the climate modeling community as a basis for long-term and near-term modeling experiments. The four RCPs together span the range of year 2100 radiative forcing values found in the open literature, i.e. from 2.6 to 8.5 W/m2. The RCPs are the product of an innovative collaboration between integrated assessment modelers, climate modelers, terrestrial ecosystem modelers and emission inventory experts. The resulting product forms a comprehensive data set with high spatial and sectoral resolutions for the period extending to 2100. Land use and emissions of air pollutants and greenhouse gases are reported mostly at a 0.5?×?0.5 degree spatial resolution, with air pollutants also provided per sector (for well-mixed gases, a coarser resolution is used). The underlying integrated assessment model outputs for land use, atmospheric emissions and concentration data were harmonized across models and scenarios to ensure consistency with historical observations while preserving individual scenario trends. For most variables, the RCPs cover a wide range of the existing literature. The RCPs are supplemented with extensions (Extended Concentration Pathways, ECPs), which allow climate modeling experiments through the year 2300. The RCPs are an important development in climate research and provide a potential foundation for further research and assessment, including emissions mitigation and impact analysis. 相似文献
36.
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
37.
Ki-Seon Choi Chun-Chieh Wu Yuqing Wang 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(4):391-397
The effect of ENSO on landfalling tropical cyclones (TCs) over the Korean Peninsula is examined. It is found that although the landfalling frequency does not show any statistically significant difference among ENSO phases, the landfalling tracks are shifted northward in response to the decrease in Niño-3.4 index. In the neutral ENSO phase, many TCs pass through mainland China before landfalling over the Korean Peninsula due to the westward expansion of the western North Pacific subtropical high. Therefore, the landfalling TC intensity over the Korean Peninsula in the neutral phase is similar to that in the La Niña phase because more than half of those TCs made landfall over mainland China. However, it is found that the preceding winter ENSO phases are not related to the landfalling TC activity over the Korean Peninsula during summer. 相似文献
38.
Huijun Wang Yongjiu Dai Song Yang Tim Li Jingjia Luo Bo Sun Mingkeng Duan Jiehua Ma Zhicong Yin Yanyan Huang 《大气和海洋科学快报》2022,15(1):2-11
过去几十年,气候变化和极端气候事件造成的经济损失和灾害显著增加.虽然全球的科学家在理解和预测气候变异方面做出了巨大的努力,但当前在气候预测领域仍然存在几个重大难题.2020年,依托于国家自然科学基金基础科学中心项目的气候系统预测研究中心(CCSP)成立了,该中心旨在应对和处理气候预测领域的三大科学难题:厄尔尼诺-南方涛动(ENSO)预测,延伸期天气预报,年际-年代际气候预测,并为更加准确的气候预测和更加有效的灾害防御提供科学依据.因此,本文介绍了CCSP的主要目标和面对的科学挑战,回顾了CCSP在季风动力过程,陆-气相互作用和模式开发,ENSO变率,季节内振荡,气候预测等方面已取得的重要研究成果.未来CCSP将继续致力于解决上述领域的关键科学问题. 相似文献
39.
The article considers the reasons for the underestimation of the wind speed by the WRF-ARW model when simulating downslope windstorms in the Russian Arctic. Simulation results for the Tiksi windstorm, for which sensitivity tests were carried out, appeared to be weakly dependent on the initial and boundary conditions, topography resolution, and boundary layer parameterization. Wind speed underestimation was mostly related to improper land use and the highly overestimated roughness length, which are used in the model. Reduction of the roughness length in accordance with the observations leads not only to a quantitative change in the wind speed in the boundary layer, but to qualitative changes in the dynamics of the flow. Wind underestimation in simulations with the overestimated roughness was caused by the jet stream unrealistically jumping over the lee slope and wake formation in the station area, while jet stream stayed near the surface and propagated to the station area in simulations with the modified roughness length. Modification of land use and roughness length in Tiksi and other regions where downslope windstorms are observed (Novaya Zemlya, Pevek, Wrangel Island) led to a decrease in wind speed modelling error by more than 2.5 times. 相似文献
40.
The problem of determining the absolute velocity of marine currents, including its barotropic component, is revisited. A generalization of the classical Needler’s formula is discussed for a Boussinesq fluid and it is shown that the steady flow solution can be deduced from a variational principle that uses the constants of motion existing in the problem. A simple model of a steady flow is considered when the Bernoulli function consists of two terms. The first term is proportional to the square of Ertel’s potential vorticity and the second term is a quadratic function of the fluid buoyancy. This model is applied to mimic the circulation in the western Mediterranean Sea near the African coast. Alternatively, “potential temperature – salinity” coordinates are applied to construct the stream-tubes and infer the steady flow velocity in the simplest case of the Bernoulli function being proportional to the product of the above two variables. 相似文献