scholarly journals Polar Low over the Barents Sea: Its Sensitivity to Surface Energy Fluxes and Condensational Heating

2020 ◽  
Vol 27 (3) ◽  
Author(s):  
D. A. Iarovaia ◽  
V. V. Efimov ◽  
◽  
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Numerical Experiments ◽  
Sensible Heat Flux ◽  
Mature Stage ◽  
Energy Fluxes ◽  
Cyclone Intensity ◽  
Surface Energy Fluxes ◽  
Polar Low ◽  
Phase Change Heat Transfer

Purpose. The aim of the paper is to study the polar low on January 18–20, 2017 using the sensitivity numerical experiments. The experiments were performed to analyse direct effect of the surface energy fluxes and condensational heating on the cyclone structure and intensity. Methods and Results. The Polar WRF model was used for the cyclone simulations. In order to study the cyclone direct response to the changes in the model, all the experiments started only after the polar low had reached its mature stage at 00:00 on January, 20. Five numerical experiments were performed, in which the following parameters were turned off: 1) sensible heat flux only, 2) latent heat flux only, 3) both surface energy fluxes, 4) phase change heat transfer in the atmosphere and 5) phase change heat transfer in the atmosphere as well as surface energy fluxes. The cyclone intensity was defined by the minimum sea level pressure in its center. Conclusions. It is shown that in all the numerical experiments, the cyclone intensity as well as its maximum wind speed at the model lowest level decreased. In experiments 1 and 2, the intensity decrease was nearly the same, i.e. at the mature stage, the sensible and latent heat fluxes were equally important for the cyclone intensity. In experiments 1, 3 and 5 (with the sensible heat flux turned off), the atmosphere static stability increased significantly due to considerable decrease of the air temperature at the model lowest level. In experiment 4, the planetary boundary layer became more unstable since evaporative cooling was turned off in the model. In experiments 1, 3 and 5, integral kinetic energy of the cyclone increased despite the fact that its intensity and maximum surface wind speed decreased. It is shown that such a response of the cyclone was, most probably, caused by decrease of the energy dissipation in the surface layer due to the increased atmospheric stability.

scholarly journals Evaluation of a Two-Source Snow–Vegetation Energy Balance Model for Estimating Surface Energy Fluxes in a Rangeland Ecosystem

2014 ◽  
Vol 15 (1) ◽  
pp. 143-158 ◽  
Author(s):  
Cezar Kongoli ◽  
William P. Kustas ◽  
Martha C. Anderson ◽  
John M. Norman ◽  
Joseph G. Alfieri ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Snow Cover ◽  
Sensible Heat Flux ◽  
Energy Balance Model ◽  
Balance Model ◽  
Sensible Heat ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract The utility of a snow–vegetation energy balance model for estimating surface energy fluxes is evaluated with field measurements at two sites in a rangeland ecosystem in southwestern Idaho during the winter of 2007: one site dominated by aspen vegetation and the other by sagebrush. Model parameterizations are adopted from the two-source energy balance (TSEB) modeling scheme, which estimates fluxes from the vegetation and surface substrate separately using remotely sensed measurements of land surface temperature. Modifications include development of routines to account for surface snowmelt energy flux and snow masking of vegetation. Comparisons between modeled and measured surface energy fluxes of net radiation and turbulent heat showed reasonable agreement when considering measurement uncertainties in snow environments and the simplified algorithm used for the snow surface heat flux, particularly on a daily basis. There was generally better performance over the aspen field site, likely due to more reliable input data of snow depth/snow cover. The model was robust in capturing the evolution of surface energy fluxes during melt periods. The model behavior was also consistent with previous studies that indicate the occurrence of upward sensible heat fluxes during daytime owing to solar heating of vegetation limbs and branches, which often exceeds the downward sensible heat flux driving the snowmelt. However, model simulations over aspen trees showed that the upward sensible heat flux could be reversed for a lower canopy fraction owing to the dominance of downward sensible heat flux over snow. This indicates that reliable vegetation or snow cover fraction inputs to the model are needed for estimating fluxes over snow-covered landscapes.

scholarly journals The role of improved soil moisture for the characteristics of surface energy fluxes in the ECMWF reanalyses

2017 ◽  
Author(s):  
Wilhelm May
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Surface Energy ◽  
Moisture Content ◽  
Regional Differences ◽  
Soil Moisture Content ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract. In this study, the role that more realistic soil moisture has for the characteristics of surface energy fluxes in two sets of reanalyses performed at ECMWF is investigated. These are the standard set of reanalyses ERA-Interim (ERAInt) and the ERA-Interim/Land reanalyses of the land surface conditions (ERAInt/Land). In the latter, the ECMWF's land surface model has been forced with the meteorological fields from ERAInt, including an adjustment of precipitation based on the monthly mean values from the Global Precipitation Climatology Project data set. Adjusting precipitation has a distinct impact on the soil moisture content in the two sets of reanalyses. ERAInt is characterized by a general tendency to underestimate (overestimate) soil moisture in regions with a relatively high (low) soil moisture content. The differences in soil moisture between ERAInt and ERAInt/Land vary only slightly in the course of the year. This is not the case for precipitation, where the differences between the two sets of reanalyses vary markedly between different seasons. The direct impact of the regional differences in precipitation between ERAInt and ERAInt/Land on the corresponding deviations in soil moisture varies considerably by region. One reason is that the regional differences in precipitation vary by season, while the regional differences in soil moisture typically persist throughout the year. Another reason is that the specific nature of the interaction between precipitation and soil moisture diverges between different regions, depending on the climate conditions and on the degree to which the soil is saturated with moisture. The differences in soil moisture between the two sets of reanalyses have notable effects on the characteristics of surface energy fluxes. The nature of these effects differs by region and also by season, that is the coupling between soil moisture and the latent or the sensible heat flux is positive in one region or season, respectively, and negative in another one. In any case, the differences in the soil moisture content typically affect the latent and the sensible heat flux in opposite ways. Increases (decreases) in latent heat flux typically coincide with decreases (increases) in sensible heat flux. By this, the differences in soil moisture have a substantial impact on the partitioning of latent and sensible heat flux. The effect of the soil moisture differences on the evaporative fraction, for instance, is mainly governed by the impact on the latent heat flux because of the opposite effects on latent and sensible heat fluxes and, hence, only a weak impact on the total surface energy flux. The effect on the Bowen ratio, on the other hand, is for the most part controlled by the impact on the sensible heat flux, with higher (lower) values of the Bowen ratio in regions with increased (decreased) sensible heat flux.

Intercomparison of Spatially Distributed Models for Predicting Surface Energy Flux Patterns during SMACEX

2005 ◽  
Vol 6 (6) ◽  
pp. 941-953 ◽  
Author(s):  
Wade T. Crow ◽  
Fuqin Li ◽  
William P. Kustas
Keyword(s):  
Remote Sensing ◽  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Surface Temperature ◽  
Energy Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Energy Fluxes ◽  
Spatially Distributed

Abstract The treatment of aerodynamic surface temperature in soil–vegetation–atmosphere transfer (SVAT) models can be used to classify approaches into two broad categories. The first category contains models utilizing remote sensing (RS) observations of surface radiometric temperature to estimate aerodynamic surface temperature and solve the terrestrial energy balance. The second category contains combined water and energy balance (WEB) approaches that simultaneously solve for surface temperature and energy fluxes based on observations of incoming radiation, precipitation, and micrometeorological variables. To date, few studies have focused on cross comparing model predictions from each category. Land surface and remote sensing datasets collected during the 2002 Soil Moisture–Atmosphere Coupling Experiment (SMACEX) provide an opportunity to evaluate and intercompare spatially distributed surface energy balance models. Intercomparison results presented here focus on the ability of a WEB-SVAT approach [the TOPmodel-based Land–Atmosphere Transfer Scheme (TOPLATS)] and an RS-SVAT approach [the Two-Source Energy Balance (TSEB) model] to accurately predict patterns of turbulent energy fluxes observed during SMACEX. During the experiment, TOPLATS and TSEB latent heat flux predictions match flux tower observations with root-mean-square (rms) accuracies of 67 and 63 W m−2, respectively. TSEB predictions of sensible heat flux are significantly more accurate with an rms accuracy of 22 versus 46 W m−2 for TOPLATS. The intercomparison of flux predictions from each model suggests that modeling errors for each approach are sufficiently independent and that opportunities exist for improving the performance of both models via data assimilation and model calibration techniques that integrate RS- and WEB-SVAT energy flux predictions.

scholarly journals Surface energy fluxes on Chilean glaciers: measurements and models

2020 ◽  
Vol 14 (8) ◽  
pp. 2545-2565 ◽  
Author(s):  
Marius Schaefer ◽  
Duilio Fonseca-Gallardo ◽  
David Farías-Barahona ◽  
Gino Casassa
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Central Andes ◽  
Turbulent Fluxes ◽  
Tierra Del Fuego ◽  
Glacier Mass Balance ◽  
Positive Contribution ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Surface Melt

Abstract. The surface energy fluxes of glaciers determine surface melt, and their adequate parametrization is one of the keys to a successful prediction of future glacier mass balance and freshwater discharge. Chile hosts glaciers in a large range of latitudes under contrasting climatic settings: from 18∘ S in the Atacama Desert to 55∘ S on Tierra del Fuego. Using three different methods, we computed surface energy fluxes for five glaciers which represent the main glaciological zones of Chile. We found the main energy sources for surface melt change from the Central Andes, where the net shortwave radiation is driving the melt, to Patagonia, where the turbulent fluxes are an important source of energy. We inferred higher surface melt rates for Patagonian glaciers as compared to the glaciers of the Central Andes due to a higher contribution of the turbulent sensible heat flux, less negative net longwave radiation and a positive contribution of the turbulent latent heat flux. The variability in the atmospheric emissivity was high and not able to be explained exclusively by the variability in the inferred cloud cover. The influence of the stability correction and the roughness length on the magnitude of the turbulent fluxes in the different climate settings was examined. We conclude that, when working towards physical melt models, it is not sufficient to use the observed melt as a measure of model performance; the model parametrizations of individual components of the energy balance have to be validated individually against measurements.

scholarly journals Distinguishing between early- and late-covering crops in the land surface model Noah-MP: impact on simulated surface energy fluxes and temperature

2020 ◽  
Vol 17 (10) ◽  
pp. 2791-2805
Author(s):  
Kristina Bohm ◽  
Joachim Ingwersen ◽  
Josipa Milovac ◽  
Thilo Streck
Keyword(s):  
Land Use ◽  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Land Surface Model ◽  
Surface Model ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract. Land surface models are essential parts of climate and weather models. The widely used Noah-MP land surface model requires information on the leaf area index (LAI) and green vegetation fraction (GVF) as key inputs of its evapotranspiration scheme. The model aggregates all agricultural areas into a land use class termed “cropland and pasture”. In a previous study we showed that, on a regional scale, the GVF has a bimodal distribution formed by two crop groups differing in phenology and growth dynamics: early-covering crops (ECC; e.g., winter wheat, winter rapeseed, winter barley) and late-covering crops (LCC; e.g., corn, silage maize, sugar beet). That result can be generalized for central Europe. The present study quantifies the effect of splitting the land use class cropland and pasture of Noah-MP into ECC and LCC on surface energy fluxes and temperature. We further studied the influence of increasing the LCC share, which in the study area (the Kraichgau region, southwest Germany) is mainly the result of heavily subsidized biomass production, on energy partitioning at the land surface. We used the GVF dynamics derived from high-resolution (5 m × 5 m) RapidEye satellite data and measured LAI data for the simulations. Our results confirm that the GVF and LAI strongly influence the partitioning of surface energy fluxes, resulting in pronounced differences between simulations of ECC and LCC. Splitting up the generic crop into ECC and LCC had the strongest effect on land surface exchange processes in July–August. During this period, ECC are at the senescence growth stage or already harvested, while LCC have a well-developed ground-covering canopy. The generic crop resulted in humid bias, i.e., an increase in evapotranspiration by +0.5 mm d−1 (latent heat flux is 1.3 MJ m−2 d−1), decrease in sensible heat flux (H) by 1.2 MJ m−2  d−1 and decrease in surface temperature by −1 ∘C. The bias increased as the shares of ECC and LCC became similar. The observed differences will impact the simulations of processes in the planetary boundary layer. Increasing the LCC share from 28 % to 38 % in the Kraichgau region led to a decrease in latent heat flux (LE) and a heating up of the land surface in the early growing season. Over the second part of the season, LE increased and the land surface cooled down by up to 1 ∘C.

scholarly journals Quantifying Surface Energy Fluxes in the Vicinity of Inland-Tracking Tropical Cyclones

2013 ◽  
Vol 52 (12) ◽  
pp. 2797-2808 ◽  
Author(s):  
Theresa K. Andersen ◽  
David E. Radcliffe ◽  
J. Marshall Shepherd
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Tropical Cyclones ◽  
Sensible Heat Flux ◽  
Surface Energy Fluxes ◽  
Warm Core ◽  
South Central ◽  
Surface Latent Heat Flux ◽  
Central United States ◽  
Modern Era

AbstractTropical cyclones (TCs) typically weaken or transition to extratropical cyclones after making landfall. However, there are cases of TCs maintaining warm-core structures and intensifying inland unexpectedly, referred to as TC maintenance or intensification events (TCMIs). It has been proposed that wet soils create an atmosphere conducive to TC maintenance by enhancing surface latent heat flux (LHF). In this study, “HYDRUS-1D” is used to simulate the surface energy balance in intensification regions leading up to four different TCMIs. Specifically, the 2-week magnitudes and trends of soil temperature, sensible heat flux (SHF), and LHF are analyzed and compared across regions. While TCMIs are most common over northern Australia, theoretically linked to large fluxes from hot sands, the results revealed that SHF and LHF are equally large over the south-central United States. Modern-Era Retrospective Analysis for Research and Applications (MERRA) 3-hourly LHF data were obtained for the same HYDRUS study regions as well as nearby ocean regions along the TC path 3 days prior (prestorm) to the TC appearance. Results indicate that the simulated prestorm mean LHF is similar in magnitude to that obtained from MERRA, with slightly lower values overall. The modeled 3-day mean fluxes over land are less than those found over the ocean; however, the maximum LHF over the 3-day period is greater over land (HYDRUS) than over the ocean (MERRA) for three of four cases. It is concluded that LHF inland can achieve similar magnitudes to that over the ocean during the daytime and should be pursued as a potential energy source for inland TCs.

scholarly journals Measurement of Surface Energy Fluxes from Two Rangeland Sites and Comparison with a Multilayer Canopy Model

2012 ◽  
Vol 13 (3) ◽  
pp. 1038-1051 ◽  
Author(s):  
Gerald N. Flerchinger ◽  
Michele L. Reba ◽  
Danny Marks
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Sensible Heat Flux ◽  
Theory Approach ◽  
Turbulent Transfer ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Transfer Equations ◽  
K Theory ◽  
Canopy Model

Abstract Rangelands are often characterized by a patchy mosaic of vegetation types, making measurement and modeling of surface energy fluxes particularly challenging. The purpose of this study was to evaluate surface energy fluxes measured using three eddy covariance systems above and within two rangeland vegetation sites and use the data to improve simulations of turbulent energy fluxes in a multilayer plant canopy model: the Simultaneous Heat and Water (SHAW) model. Model modifications included adjustment of the wind profile roughness parameters for sparse canopies, extending the currently used K-theory approach to include influence of the roughness sublayer and stability functions within the canopy, and in a separate version of the model, introducing Lagrangian far-field turbulent transfer equations (L theory) in lieu of the K-theory approach. There was relatively little difference in simulated energy fluxes for the aspen canopy using L-theory versus K-theory turbulent transfer equations, but L theory tracked canopy air temperature profiles better during the growing season. Upward sensible heat flux was observed above aspen trees, within the aspen understory, and above sagebrush throughout the active snowmelt season. Model simulations confirmed the observed upward sensible flux during snowmelt was due to solar heating of the aspen limbs and sagebrush. Thus, the eddy covariance (EC) systems were unable to properly quantify fluxes at the snow surface when vegetation was present. Good agreement between measured and modeled energy fluxes suggest that they can be measured and simulated reliably in these complex environments, but care must be used in the interpretation of the results.

scholarly journals The annual cycle of meteorological variables and the surface energy balance on Berkner Island, Antarctica

1999 ◽  
Vol 29 ◽  
pp. 49-54 ◽  
Author(s):  
Carleen Reijmer ◽  
Wouter Greuell ◽  
Johannes Oerlemans
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Sensible Heat Flux ◽  
Balance Model ◽  
Mean Annual Temperature ◽  
Annual Average ◽  
Surface Energy Fluxes ◽  
Summer Temperatures

AbstractIn February 1995 an automatic weather station (AWS) was placed on Thyssen Hohe, the south dome of Berkner Island, Antarctica. A fairly complete 3 year meteorological dataset of hourly average data was obtained. The mean annual temperature is about –24°C. The annual mass balance is about +180 mm we. Summer temperatures stay below 0°C, which implies that no melt takes place. Because the AWS is located on a dome, katabatic winds are not active, the wind direction is variable (directional constancy 0.38) and the wind speed relatively low (4.5 ms−1). Annual average variables are compared with data from Recovery Glacier AWS and Halley station.The measurements are used to evaluate the surface energy fluxes for the 3 year period by using a surface energy-balance model. The annual average gain of energy from the sensible-heat flux ( + 10.8 W m–2) is balanced by a negative net radiative flux (–9.1 W m−2) and a small negative latent-heat flux (-1.7 W rrT2). The annual subsurface flux is small.

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