scholarly journals Improvements of the coupled WRF-Lake model over Lake Nam Co, Central Tibetan Plateau

2020 ◽  
Vol 55 (9-10) ◽  
pp. 2703-2724
Author(s):  
Yang Wu ◽  
Anning Huang ◽  
Lazhu ◽  
Xianyu Yang ◽  
Bo Qiu ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Thermal Stratification ◽  
Roughness Length ◽  
Light Extinction ◽  
Nam Co ◽  
Light Extinction Coefficient ◽  
Surface Roughness Length ◽  
Lake Model ◽  
Lake Temperature ◽  
Lake Nam Co

Abstract A series of model sensitivity simulations are carried out to calibrate and improve the Weather Research and Forecasting Model coupled with a one-dimensional lake model (WRF-Lake) based on observations over Lake Nam Co. Using the default lake model parameters, the solution of WRF-Lake exhibits significant biases in both the lake thermodynamics and regional climatology, i.e., higher lake surface temperature (LST), earlier onset of summer thermal stratification, and overestimated near-surface air temperature and precipitation induced by the lake’s excessive warming and moistening impacts. The performance of WRF-Lake is improved through adjusting the initial lake temperature profile, the temperature of maximum water density (Tdmax), the surface roughness length, and the light extinction coefficient. Results show that initializing the water temperature with spring observation mitigates the LST overestimation and reduces the timing error of the onset of thermal stratification. By further adjusting Tdmax from 4 °C to the observed value of 3.5 °C, the LST increase from June to mid-July is enhanced and the buildup of thermal stratification is more accurately predicted. Through incorporating the parameterized surface roughness length and decreasing the light extinction coefficient, the model better reproduces the observed daily evolution of LST and vertical lake temperature profile. The calibrated WRF-Lake effectively mitigates the overestimation of over-lake air temperature at 2 m height and precipitation over regions downwind the lake. This suggests that an improved lake scheme within the coupled WRF-Lake is essential for realistically simulating the lake–air interactions and the regional climate over the lake-rich Tibetan Plateau.

The Role of Sublimation on the Surface Mass Balance of the Interior Greenland Ice Sheet

2021 ◽  
Author(s):  
Laura Dietrich ◽  
Hans Christian Steen-Larsen ◽  
Cécile Agosta ◽  
Xavier Fettweis ◽  
Anne-Katrine Faber ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Roughness Length ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Climate Signal ◽  
Surface Mass ◽  
Surface Roughness Length ◽  
Surface Snow ◽  
Precipitation Events

<p>Precipitation along with sublimation and deposition are the main contributors to the surface mass balance (SMB) in the accumulation area of the Greenland Ice Sheet (GrIS). However, precipitation events are rare and intermittent. In between precipitation events the surface snow continuously undergoes sublimation and deposition. Recent studies imply that these surface exchange processes influence the isotopic composition of the surface snow which is later archived as a climate record in ice cores. In order to understand the possible implications on the recorded climate signal, sublimation needs to be quantified on a local scale.</p><p>Here we present simulated SMB components for eight ice core drilling sites on the GrIS using the regional climate model MAR (Modèle Atmosphérique Régional). We validated MAR against in-situ flux observations at the East Greenland Ice Core Project site and found a high sensitivity of sublimation to the downward long wave flux and to the parameterization of the surface roughness length. We propose a surface roughness length optimized for the interior of the GrIS which is supported by our observations.</p><p>Our results show that in the GrIS accumulation area the mass turnover via sublimation and deposition can reach the same order of magnitude as precipitation. This highlights the importance of a better understanding of how the climate signal is imprinted in the surface snow isotopic composition.</p>

Surface roughness length dynamic over several different surfaces and its effects on modeling fluxes

2006 ◽  
Vol 49 (S2) ◽  
pp. 262-272 ◽  
Author(s):  
Yanlian Zhou ◽  
Xiaomin Sun ◽  
Zhilin Zhu ◽  
Renhua Zhang ◽  
Jing Tian ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Roughness Length ◽  
Surface Roughness Length

CORRECTION OF WIND SPEED DATA ACCORDING TO THE OPEN TERRAIN CONDITIONS

2019 ◽  
pp. 131-139
Author(s):  
D.O. Oshurok ◽  
O.Y. Skrynyk
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Roughness Length ◽  
Pearson Correlation ◽  
Aerodynamic Characteristics ◽  
Google Earth ◽  
Homogeneous Distribution ◽  
Heterogeneous Structure ◽  
Wind Speed Data ◽  
Surface Roughness Length

Wind speed spatial distribution over the territory of Ukraine built based on weather stations measurements has been analyzed. Interpolated field of wind speed averaged over 1981-2010 indicated fairly heterogeneous structure with a number of artificial spots of larger/smaller values compared to surrounding areas. The main reason of such heterogeneity might be associated with representativeness of observation site regarding the landscape zone. It is well known that surrounding obstacles have a great impact on wind flow in horizontal direction. In order to solve this problem we have corrected sub-daily wind speed data measured at 207 meteorological stations of Ukraine for the period of 1981-2010 according to the open terrain conditions and the standard height (10 m). Generally, aerodynamic characteristics (e.g. surface roughness length) of measurement sites are needed in order to perform such adjustment. However, the only usable parameter available at a climatological reference book is horizon closure degree. The research revealed significant relationship between this characteristic and wind speed records (Pearson correlation coefficient equals -0.58). Given that horizon closure degree could not be used in correction procedure directly, surface roughness length has been calculated for 10 stations and statistical relationship has been determined between these two parameters. Based on the obtained relation and additional information we have found roughness length for all 207 stations at eight directions. Supplementary materials for analysis included observation sites description and Google Earth snapshots as well. In the final step, there has been applied a correction formula derived from the neutral logarithmic profile of wind speed in the atmospheric surface layer. The output of the research is new database of corrected wind speed measurements for the multiyear period. These results have been compared with observations. Mean 30-yr corrected speeds are featured by more homogeneous distribution over Ukraine and mostly higher values (with positive mean spatial bias ~0.35 m/s). The applied method allowed us to remove uncertainties related to differences in vertical level of measurements and considerably eliminate influence of the micro-scale terrain inhomogeneity. Obtained datasets may facilitate to perform spatial interpolation and further development of Ukrainian Wind Atlas.

scholarly journals Land Cover Change Effects on the Climate of the La Plata Basin

2012 ◽  
Vol 13 (1) ◽  
pp. 84-102 ◽  
Author(s):  
Seung-Jae Lee ◽  
Ernesto Hugo Berbery
Keyword(s):  
Surface Roughness ◽  
Land Cover ◽  
Surface Temperature ◽  
River Basin ◽  
Land Surface ◽  
Roughness Length ◽  
Sensible Heat Flux ◽  
Near Surface ◽  
La Plata ◽  
Surface Roughness Length

Abstract Deforestation and replacement of natural pastures by agriculture have become a common practice in the La Plata River basin in South America. The changes in land cover imply changes in the biophysical properties of the land surface, with possible impacts on the basin’s hydroclimate. To help understand to what extent the climate could be affected, and through which processes, ensembles of seasonal simulations were prepared using the Weather Research and Forecasting Model for a control case and a scenario assuming an expansion of the agricultural activities to cover the entire basin. The La Plata River basin shows different climate responses to the land cover changes depending on the region. The northern part of the basin, where forests and savanna were replaced by crops, experiences an overall increase in albedo that leads to a reduction of sensible heat flux and near-surface temperature. A reduction of surface roughness length leads to stronger low-level winds that, in turn, favor a larger amount of moisture being advected out of the northern part of the basin. The result is a reduction of the vertically integrated moisture flux convergence (VIMFC) and, consequently, in precipitation. In the southern part of the basin, changes from grasslands to crops reduce the albedo and thus increase the near-surface temperature. The reduction in surface roughness length is not as large as in the northern sector, reducing the northerly moisture fluxes and resulting in a net increase of VIMFC and, thus, in precipitation. Notably, advective processes modify the downstream circulation and precipitation patterns over the South Atlantic Ocean.

scholarly journals Impact of Urban Surface Roughness Length Parameterization Scheme on Urban Atmospheric Environment Simulation

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Meichun Cao ◽  
Zhaohui Lin
Keyword(s):  
Surface Roughness ◽  
Roughness Length ◽  
Urban Morphology ◽  
Atmospheric Environment ◽  
Urban Surface ◽  
Parameterization Scheme ◽  
Roughness Parameters ◽  
Surface Roughness Length ◽  
Environment Simulation ◽  
The Impact

In this paper, the impact of urban surface roughness lengthz0parameterization scheme on the atmospheric environment simulation over Beijing has been investigated through two sets of numerical experiments using the Weather Research and Forecasting model coupled with the Urban Canopy Model. For the control experiment (CTL), the urban surfacez0parameterization scheme used in UCM is the model default one. For another experiment (EXP), a newly developed urban surfacez0parameterization scheme is adopted, which takes into account the comprehensive effects of urban morphology. The comparison of the two sets of simulation results shows that all the roughness parameters computed from the EXP run are larger than those in the CTL run. The increased roughness parameters in the EXP run result in strengthened drag and blocking effects exerted by buildings, which lead to enhanced friction velocity, weakened wind speed in daytime, and boosted turbulent kinetic energy after sunset. Thermal variables (sensible heat flux and temperature) are much less sensitive toz0variations. In contrast with the CTL run, the EXP run reasonably simulates the observed nocturnal low-level jet. Besides, the EXP run-simulated land surface-atmosphere momentum and heat exchanges are also in better agreement with the observation.

scholarly journals Sensitivity Analysis of the High-Resolution WISE-WRF Model with the Use of Surface Roughness Length in Seoul Metropolitan Areas

Atmosphere ◽  
2016 ◽  
Vol 26 (1) ◽  
pp. 111-126 ◽  
Author(s):  
Joon-Bum Jee ◽  
Min Jang ◽  
Chaeyeon Yi ◽  
Il-Sung Zo ◽  
Bu-Yo Kim ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Surface Roughness ◽  
High Resolution ◽  
Roughness Length ◽  
Metropolitan Areas ◽  
Wrf Model ◽  
Surface Roughness Length

scholarly journals Influence of sea surface roughness length parameterization on Mistral and Tramontane simulations

2016 ◽  
Vol 13 ◽  
pp. 107-112 ◽  
Author(s):  
Anika Obermann ◽  
Benedikt Edelmann ◽  
Bodo Ahrens
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Wind Direction ◽  
Roughness Length ◽  
Western Mediterranean ◽  
Sea Surface ◽  
Surface Roughness Length ◽  
Sea Surface Roughness ◽  
Simulated Wind ◽  
Simulated Wind Speed

Abstract. The Mistral and Tramontane are mesoscale winds in southern France and above the Western Mediterranean Sea. They are phenomena well suited for studying channeling effects as well as atmosphere–land/ocean processes. This sensitivity study deals with the influence of the sea surface roughness length parameterizations on simulated Mistral and Tramontane wind speed and wind direction. Several simulations with the regional climate model COSMO-CLM were performed for the year 2005 with varying values for the Charnock parameter α. Above the western Mediterranean area, the simulated wind speed and wind direction pattern on Mistral days changes depending on the parameterization used. Higher values of α lead to lower simulated wind speeds. In areas, where the simulated wind speed does not change much, a counterclockwise rotation of the simulated wind direction is observed.

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