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91.
Yulong Ren Yaohui Li Zhaoxia Pu Tiejun Zhang Haixia Duan Wei Wang 《Acta Meteorologica Sinica》2018,32(5):758-767
Biogeophysical effects of land use and land cover (LULC) changes play a significant role in modulating climate on various spatial scales. In this study, a set of recent LULC products with a spatial resolution of 500 m was developed in China for update in RegCM4 (regional climate model version 4). Two sets of comparative numerical experiments were conducted to study the effects of LULC changes on near-surface temperature simulation. The results show that after LULC changes, areas of crops and mixed woodlands as well as urban areas increase over entire China, accompanied with greatly expanded mixed farming and forests/field mosaics in southern China, and reduced areas of 1) irrigated crops and short grasses in northern China and the Tibetan Plateau, and 2) semi-desert and desert in northwestern China. Improvements in the LULC data clearly result in more accurate simulations of the near-surface temperature. Specifically, increasing latent heat and longwave albedo due to enhanced LULC in certain areas lead to reduction in land surface temperature (LST), while changes in shortwave albedo and sensible heat also exert a great influence on the LST. Overall, these parameter adjustments reduce the biases in near-surface temperature simulation. 相似文献
92.
Haixia Duan Yaohui Li Tiejun Zhang Zhaoxia Pu Cailing Zhao Yuanpu Liu 《Acta Meteorologica Sinica》2018,32(3):469-490
This study investigated the performance of the mesoscale Weather Research and Forecasting (WRF) model in predicting near-surface atmospheric temperature and wind for a complex underlying surface in Northwest China in June and December 2015. The spatial distribution of the monthly average bias errors in the forecasts of 2-m temperature and 10-m wind speed is analyzed first. It is found that the forecast errors for 2-m temperature and 10-m wind speed in June are strongly correlated with the terrain distribution. However, this type of correlation is not apparent in December, perhaps due to the inaccurate specification of the surface albedo and freezing–thawing process of frozen soil in winter in Northwest China in the WRF model. In addition, the WRF model is able to reproduce the diurnal variation in 2-m temperature and 10-m wind speed, although with weakened magnitude. Elevations and land-use types have strong influences on the forecast of near-surface variables with seasonal variations. The overall results imply that accurate specification of the complex underlying surface and seasonal changes in land cover is necessary for improving near-surface forecasts over Northwest China. 相似文献
93.
An episode of persistent wintertime inversion over Salt Lake City, Utah and its vicinity from 1200 UTC 30 November to 0000 UTC 7 December 2010 is simulated using an advanced research version of the Weather Research and Forecasting model. The numerical simulations agree well with observed soundings in temperature, wind speed, and wind direction in the atmospheric boundary layer and above, although there are some differences near the surface due to the influence of complex terrain in the area. The characteristics of large-scale environmental conditions and their interactions with local-scale processes are analyzed to understand the factors that influence the onset and evolution of persistent inversions. It is found that the inversion formed mainly because of the interaction between the heating effect from a high-pressure ridge in the mid-troposphere and a near-surface cold pool due to the effects of radiation. During the following six to seven days, the high-pressure ridge was maintained and vertical motion very weak, allowing a persistent inversion to become established. Finally, the cold effect from a low-pressure trough in the mid-troposphere, combined with mixing due to vertical motion, led to extreme weakening of the persistent inversion. 相似文献
94.
To further investigate the influence of cloud base temperature, updraft velocity and precipitation particle constitution on cloud electrification, five thunderstorms in various regions of China were simulated by using the three-dimensional compressible hailstorm numerical model including inductive and non-inductive charging mechanisms. The results indicate that changes of cloud base temperature have an influence on the initial electrification. Comparison of the above cases shows that in the case of warm cloud base and moderate updraft velocity (< 20 m s− 1), active electrification occurred below the − 10 °C level before moving upward to the − 20 °C level. In contrast, when cloud base is cold and updraft velocity is intensive, the main charging region is at the − 20 °C or even higher level. In that case, the vertical extent of the main negative charge region becomes larger with the increase of cloud base temperature. Apart from the main dipolar or tripolar charge structure, some smaller charge regions with relatively high values of charge density may also appear. Frozen drops, originating mainly from supercooled raindrops, mainly get electrified through charging interactions with snow at or below the − 20 °C level. They are responsible for the negative charge region near the melting level at the initial stage of precipitation if there is a large supercooled raindrop content. Non-inductive charging during hail-snow collisions is rather weak, resulting in the charge density on hail of no more than − 0.01 nC m− 3. 相似文献
95.
A series of numerical simulations is conducted to understand the formation, evolution, and dissipation of an advection fog event over Shanghai Pudong International Airport (ZSPD) with the Weather Research and Forecasting (WRF) model. Using the current operational settings at the Meteorological Center of East China Air Traffic Management Bureau, the WRF model successfully predicts the fog event at ZSPD. Additional numerical experiments are performed to examine the physical processes associated with the fog event. The results indicate that prediction of this particular fog event is sensitive to microphysical schemes for the time of fog dissipation but not for the time of fog onset. The simulated timing of the arrival and dissipation of the fog, as well as the cloud distribution, is substantially sensitive to the planetary boundary layer and radiation (both longwave and shortwave) processes. Moreover, varying forecast lead times also produces different simulation results for the fog event regarding its onset and duration, suggesting a trade-off between more accurate initial conditions and a proper forecast lead time that allows model physical processes to spin up adequately during the fog simulation. The overall outcomes from this study imply that the complexity of physical processes and their interactions within the WRF model during fog evolution and dissipation is a key area of future research. 相似文献
96.
97.
The Florida peninsula in the USA has a frequent occurrence of sea breeze(SB)thunderstorms.In this study,the numerical simulation of a Florida SB and its associated convective initiation(CI)is simulated using the mesoscale community Weather Research and Forecasting(WRF)model in one-way nested domains at different horizontal resolutions.Results are compared with observations to examine the accuracy of model-simulated SB convection and factors that influence SB CI within the simulation.It is found that the WRF model can realistically reproduce the observed SB CI.Differences are found in the timing,location,and intensity of the convective cells at different domains with various spatial resolutions.With increasing spatial resolution,the simulation improvements are manifested mainly in the timing of CI and the orientation of the convection after the sea breeze front(SBF)merger into the squall line over the peninsula.Diagnoses indicate that accurate representation of geophysical variables(e.g.,coastline and bay shape,small lakes measuring 10-30 km2),better resolved by the high resolution,play a significant role in improving the simulations.The geophysical variables,together with the high resolution,impact the location and timing of SB CI due to changes in low-level atmospheric convergence and surface sensible heating.More importantly,they enable Florida lakes(30 km2 and larger)to produce noticeable lake breezes(LBs)that collide with the SBFs to produce CI.Furthermore,they also help the model reproduce a stronger convective squall line caused by merging SBs,leading to more accurate locations of postfrontal convective systems. 相似文献
98.
The Monte Carlo probability(MCP) model, which has been used for official tropical cyclone(TC) warnings to the public by the United States' National Hurricane Center(NHC), can estimate the probability of wind speed in the vicinity of a TC during the forecast period. It has been successful in the operational environment for many years.However, due to its strong dependence on a given forecast track(e.g., forecast from the NCEP Global Forecast System), the MCP model may generate a poor probability map for TCs near landfall. In this study, we proposed and tested a modified MCP method for TC forecasts near landfall. We first adjusted the MCP model by adding limits to the direction angle and motion distance to deal with the substantial change in TC moving direction and the low wind speeds during landfall. Then, we combined ensemble probability maps generated from ECMWF, United Kingdom Met Office(UKMO), and NCEP ensemble forecasts, obtained from The International Grand Global Ensemble(TIGGE), into the MCP model to configure a modified MCP model. Wind speed probability maps for the 0–120-h forecast from both the original and modified MCP models are compared. It is found that the modified MCP model can provide a better wind speed probability map during landfall, especially at wind speeds of 20–64 kt near TC landfall. The results from this study prove the benefits of combining the MCP model with ensemble forecasting in potential applications for improved TC forecasts. 相似文献