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Author: Singh, Shweta
Publisher: KIT Scientific Publishing
ISBN: 3731510685
Category : Science
Languages : en
Pages : 198
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Book Description
The impact of land-surface properties like vegetation, soil type, soil moisture, and the orography on the atmosphere is manifold. These features determine the evolution of the atmospheric boundary layer, convective conditions, cloud evolution and precipitation. The impact of model grid spacing and land-surface resolution on convective precipitation over heterogeneous surfaces is investigated using ICOsahedral Nonhydrostatic (ICON) simulations within the framework of the HD(CP)2 project.
Author: Singh, Shweta
Publisher: KIT Scientific Publishing
ISBN: 3731510685
Category : Science
Languages : en
Pages : 198
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Book Description
The impact of land-surface properties like vegetation, soil type, soil moisture, and the orography on the atmosphere is manifold. These features determine the evolution of the atmospheric boundary layer, convective conditions, cloud evolution and precipitation. The impact of model grid spacing and land-surface resolution on convective precipitation over heterogeneous surfaces is investigated using ICOsahedral Nonhydrostatic (ICON) simulations within the framework of the HD(CP)2 project.
Author: Wandel, Jan Lucas
Publisher: KIT Scientific Publishing
ISBN: 3731512491
Category : Science
Languages : en
Pages : 256
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Book Description
This study systematically investigates the representation of warm conveyor belts (WCBs) in large reforecast data sets of different numerical weather prediction models and evaluates the role of WCBs for the onset and life cycle of Atlantic-European weather regimes. The results emphasize the importance of accurate forecast of WCBs for sub-seasonal prediction on time scales beyond two weeks and tie the low forecast skill of blocked weather regimes over Europe to misrepresented WCBs.
Author: Pickl, Moritz
Publisher: KIT Scientific Publishing
ISBN: 373151236X
Category : Science
Languages : en
Pages : 250
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Book Description
Warm conveyor belts (WCBs) are weather systems that substantially modulate the large-scale extratropical circulation. As they can amplify forecast errors and project them onto the Rossby wave pattern, they are of high relevance for numerical weather prediction. This work elaborates on two aspects of WCBs in the context of ensemble forecasts: (1) sensitivities of WCBs to the representation of initial condition and model uncertainties, and (2) the role of WCBs for forecast error growth.
Author: Tiantian Xiang
Publisher:
ISBN:
Category : Boundary layer (Meteorology)
Languages : en
Pages : 194
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Book Description
Land surface fluxes of energy and mass developed over heterogeneous mountain landscapes are fundamental to atmospheric processes. However, due to their high complexity and the lack of spatial observations, land surface processes and land-atmosphere interactions are not fully understood in mountain regions. This thesis investigates land surface processes and their impact on convective precipitation by conducting numerical modeling experiments at multiple scales over the North American Monsoon (NAM) region. Specifically, the following scientific questions are addressed: (1) how do land surface conditions evolve during the monsoon season, and what are their main controls?, (2) how do the diurnal cycles of surface energy fluxes vary during the monsoon season for the major ecosystems?, and (3) what are the impacts of surface soil moisture and vegetation condition on convective precipitation? Hydrologic simulation using the TIN-based Real-time Integrated Basin Simulator (tRIBS) is firstly carried out to examine the seasonal evolution of land surface conditions. Results reveal that the spatial heterogeneity of land surface temperature and soil moisture increases dramatically with the onset of monsoon, which is related to seasonal changes in topographic and vegetation controls. Similar results are found at regional basin scale using the uncoupled WRF-Hydro model. Meanwhile, the diurnal cycles of surface energy fluxes show large variation between the major ecosystems. Differences in both the peak magnitude and peak timing of plant transpiration induce mesoscale heterogeneity in land surface conditions. Lastly, this dissertation examines the upscale effect of land surface heterogeneity on atmospheric condition through fully-coupled WRF-Hydro simulations. A series of process-based experiments were conducted to identify the pathways of soil moisture-rainfall feedback mechanism over the NAM region. While modeling experiments confirm the existence of positive soil moisture/vegetation-rainfall feedback, their exact pathways are slightly different. Interactions between soil moisture, vegetation cover, and rainfall through a series of land surface and atmospheric boundary layer processes highlight the strong land-atmosphere coupling in the NAM region, and have important implications on convective rainfall prediction. Overall, this dissertation advances the study of complex land surface processes over the NAM region, and made important contributions in linking complex hydrologic, ecologic and atmospheric processes through numerical modeling.
Author: Muhammad Javed Shaikh
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Author: Chao Jih-Ping
Publisher:
ISBN:
Category : Cloud physics
Languages : en
Pages : 152
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Book Description
Author: Jonathan Craig Collier
Publisher:
ISBN:
Category :
Languages : en
Pages :
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This study evaluates the simulation of tropical precipitation by the Community Climate Model, Version 3, developed at the National Center for Atmospheric Research. For an evaluation of the annual cycle of precipitation, monthly-mean precipitation rates from an ensemble of CCM3 simulations are compared to those computed from observations of the TRMM satellite over a 44-month period. On regional and sub-regional scales, the comparison fares well over much of the Eastern Hemisphere south of 10°S and over South America. However, model - satellite differences are large in portions of Central America and the Caribbean, the southern tropical Atlantic, the northern Indian Ocean, and the western equatorial and southern tropical Pacific. Since precipitation in the Tropics is the primary source of latent energy to the general circulation, such large model - satellite difference simply large differences in the amount of latent energy released. Differences are seasonally-dependent north of 10°N, where model wet biases occur in realistic wet seasons or model-generated artificial wet seasons. South of 10°N, the model wet biases exist throughout the year or have no recognizable pattern. For an evaluation of the diurnal cycle of precipitation, hourly-averaged precipitation rates from the same ensemble of simulations and for the same 44-month period are compared to observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. Comparisons are made for 15° longitude x 10° latitude boxes and for larger geographical areas within the Tropics. The temporally- and spatially-averaged hourly precipitation rates from CCM3 and from TRMM are fit to the diurnal harmonic by the method of linear least-squares regression, and the phases and the amplitudes of the diurnal cycles are compared. The model's diurnal cycle is too strong over major land masses, particularly over South America (by a factor of 3), and is too weak over many oceans, particularly the northwestern Tropical Pacific (by a factor of 2). The model-satellite phase differences tend to be more homogeneous. The peak in the daily precipitation in the model consistently precedes the observations nearly everywhere. Phase differences are large over Australia, Papua New Guinea, and Saharan Africa, where CCM3 leads TRMM by 4 hours, 5 to 6 hours, and 9 to11 hours respectively. A model sensitivity experiment shows that increasing the convective adjustment time scale in the model's deep convective parameterization reduces its positive amplitude bias over land regions but has no effect on the phase of the diurnal cycle.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Book Description
We analyze simulations of the global climate performed at a range of spatial resolutions to assess the effects of horizontal spatial resolution on the ability to simulate precipitation in the continental United States. The model investigated is the CCM3 general circulation model. We also preliminarily assess the effect of replacing cloud and convective parameterizations in a coarse-resolution (T42) model with an embedded cloud-system resolving model (CSRM). We examine both spatial patterns of seasonal-mean precipitation and daily-timescale temporal variability of precipitation in the continental United States. For DJF and SON, high-resolution simulations produce spatial patterns of seasonal-mean precipitation that agree more closely with observed precipitation patterns than do results from the same model (CCM3) at coarse resolution. However, in JJA and MAM, there is little improvement in spatial patterns of seasonal-mean precipitation with increasing resolution, particularly in the Southeast. This is owed to the dominance of convective (i.e., parameterized) precipitation in these two seasons. We further find that higher-resolution simulations have more realistic daily precipitation statistics. In particular, the well-known tendency at coarse resolution to have too many days with weak precipitation and not enough intense precipitation is partially eliminated in higher-resolution simulations. However, even at the highest resolution examined here (T239), the simulated intensity of the mean and of high-percentile daily precipitation amounts is too low. This is especially true in the Southeast, where the most extreme events occur. A new GCM, in which a cloud-resolving model (CSRM) is embedded in each grid cell and replaces convective and stratiform cloud parameterizations, solves this problem, and actually produces too much precipitation in the form of extreme events. However, in contrast to high-resolution versions of CCM3, this model produces little improvement in spatial patterns of seasonal-mean precipitation compared to models at the same resolution using traditional parameterizations. Thus, our results suggest that using an embedded ''Cloud Resolving Model'' in a high-resolution GCM might provide the best representation of spatial and temporal variability of mid-latitude continental precipitation.
Author: Xu Deng
Publisher:
ISBN:
Category : Rain and rainfall
Languages : en
Pages : 60
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Book Description
This study aims to analyze what processes are mainly responsible for nocturnal convective precipitation during the 1991-2000 period for May-June-July over the Great Plains. Firstly, based on the Weather Research and Forecasting model (WRF) coupled with the NCAR Community Land Model (CLM) and the North American Regional Reanalysis (NARR) reanalysis data, the simulations of the diurnal cycles of LLJ and the convective precipitation are examined. Then, the LLJ-related moisture transport is evaluated since the moisture supply is critical for the development of the heavy rainfall. Results show that the WRF model fails to simulate the nocturnal peak rainfall shown in the reanalysis data. The failure in simulating nocturnal maximum precipitation is related to the bias occurring in the modeled nighttime moisture flux divergence/convergence, which suggests that the nocturnal peak convective precipitation may the result of the large-scale processes. To further figure out the mechanisms controlling the nighttime convection, based on the composite analysis, three 10-case groups are classified: (a) cases that the WRF cannot simulate the timing of the nocturnal peak convective precipitation; (b) cases that the timing of the nocturnal maximum rainfall can be simulated in the model; (c) cases that the maximum precipitation is shown during the afternoon hours in both the NARR data and the WRF model. The comparisons among the three groups suggest that the suppression of daytime convective precipitation and the favoring of nighttime convective precipitation over the Great Plains is closely related to the diurnal cycle of zonal circulation, which is induced by the mountain-plain baroclinic instability. In addition, during nighttime, the intensified anomalous southerly wind, together with the southward forcing above, may have a positive effect on the maintenance of the mountain-plain circulation.
Author: D B. Clark
Publisher:
ISBN:
Category :
Languages : en
Pages :
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