How Much Do Different Land Models Matter for Climate Simulation? Part I: Climatology and Variability

2010 ◽  
Vol 23 (11) ◽  
pp. 3120-3134 ◽  
Author(s):  
Jiangfeng Wei ◽  
Paul A. Dirmeyer ◽  
Zhichang Guo ◽  
Li Zhang ◽  
Vasubandhu Misra
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Latent Heat ◽  
General Circulation ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Maximum Temperature ◽  
Daily Maximum Temperature ◽  
Time Step ◽  
The Impact

Abstract An atmospheric general circulation model (AGCM) is coupled to three different land surface schemes (LSSs), both individually and in combination (i.e., the LSSs receive the same AGCM forcing each time step and the averaged upward surface fluxes are passed back to the AGCM), to study the uncertainty of simulated climatologies and variabilities caused by different LSSs. This tiling of the LSSs is done to study the uncertainty of simulated mean climate and climate variability caused by variations between LSSs. The three LSSs produce significantly different surface fluxes over most of the land, no matter whether they are coupled individually or in combination. Although the three LSSs receive the same atmospheric forcing in the combined experiment, the inter-LSS spread of latent heat flux can be larger or smaller than the individually coupled experiment, depending mostly on the evaporation regime of the schemes in different regions. Differences in precipitation are the main reason for the different latent heat fluxes over semiarid regions, but for sensible heat flux, the atmospheric differences and LSS differences have comparable contributions. The influence of LSS uncertainties on the simulation of surface temperature is strongest in dry seasons, and its influence on daily maximum temperature is stronger than on minimum temperature. Land–atmosphere interaction can dampen the impact of LSS uncertainties on surface temperature in the tropics, but can strengthen their impact in middle to high latitudes. Variations in the persistence of surface heat fluxes exist among the LSSs, which, however, have little impact on the global pattern of precipitation persistence. The results provide guidance to future diagnosis of model uncertainties related to LSSs.

Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

2013 ◽  
Vol 17 (14) ◽  
pp. 1-22 ◽  
Author(s):  
Allison L. Steiner ◽  
Dori Mermelstein ◽  
Susan J. Cheng ◽  
Tracy E. Twine ◽  
Andrew Oliphant
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Atmospheric Aerosols ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Environmental Drivers ◽  
Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

scholarly journals Processes Controlling Sea Surface Temperature Variability of Ningaloo Niño

2020 ◽  
Vol 33 (10) ◽  
pp. 4369-4389 ◽  
Author(s):  
Yaru Guo ◽  
Yuanlong Li ◽  
Fan Wang ◽  
Yuntao Wei ◽  
Zengrui Rong
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Heat Loss ◽  
Latent Heat ◽  
General Circulation ◽  
Sea Surface ◽  
Turbulent Heat ◽  
Sst Warming ◽  
Latent Heat Loss

AbstractA high-resolution (3–8 km) regional oceanic general circulation model is utilized to understand the sea surface temperature (SST) variability of Ningaloo Niño in the southeast Indian Ocean (SEIO). The model reproduces eight Ningaloo Niño events with good fidelity and reveals complicated spatial structures. Mesoscale noises are seen in the warming signature and confirmed by satellite microwave SST data. Model experiments are carried out to quantitatively evaluate the effects of key processes. The results reveal that the surface turbulent heat flux (primarily latent heat flux) is the most important process (contribution > 68%) in driving and damping the SST warming for most events, while the roles of the Indonesian Throughflow (~15%) and local wind forcing are secondary. A suitable air temperature warming is essential to reproducing the reduced surface latent heat loss during the growth of SST warming (~66%), whereas the effect of the increased air humidity is negligibly small (1%). The established SST warming in the mature phase causes increased latent heat loss that initiates the decay of warming. A 20-member ensemble simulation is performed for the 2010/11 super Ningaloo Niño, which confirms the strong influence of ocean internal processes in the redistribution of SST warming signatures. Oceanic eddies can dramatically modulate the magnitudes of local SST warming, particularly in offshore areas where the “signal-to-noise” ratio is low, raising a caution for evaluating the predictability of Ningaloo Niño and its environmental consequences.

scholarly journals Fetch Effect on Flux-Variance Estimations of Sensible and Latent Heat Fluxes of Camellia Sinensis

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 299
Author(s):  
Noman Ali Buttar ◽  
Hu Yongguang ◽  
Josef Tanny ◽  
M Waqar Akram ◽  
Abdul Shabbir
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Soil Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Effect Of Temperature ◽  
Sensible Heat ◽  
Fine Wire

Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.

Wind Speed, Surface Flux, and Convection Coupling from CYGNSS Data

2021 ◽  
Author(s):  
Eric Maloney ◽  
Hien Bui ◽  
Emily Riley Dellaripa ◽  
Bohar Singh
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface Wind ◽  
Surface Flux ◽  
Surface Wind Speed ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Boreal Summer

<p>This study analyzes wind speed and surface latent heat flux anomalies from the Cyclone Global Navigation Satellite System (CYGNSS), aiming to understand the physical mechanisms regulating intraseasonal convection, particularly associated with the Madden-Julian oscillation (MJO). The importance of wind-driven surface flux variability for supporting east Pacific diurnal convective disturbances during boreal summer is also examined. An advantage of CYGNSS compared to other space-based datasets is that its surface wind speed retrievals have reduced attenuation by precipitation, thus providing improved information about the importance of wind-induced surface fluxes for the maintenance of convection. Consistent with previous studies from buoys, CYGNSS shows that enhanced MJO precipitation is associated with enhanced wind speeds, and that associated surface heat fluxes anomalies have a magnitude about 7%-12% of precipitation anomalies. Thus, latent heat flux anomalies are an important maintenance mechanism for MJO convection through the column moist static energy budget. A composite analysis during boreal summer over the eastern north Pacific also supports the idea that wind-induced surface flux is important for MJO maintenance there. We also show the surface fluxes help moisten the atmosphere in advance of diurnal convective disturbances that propagate offshore from the Colombian Coast during boreal summer, helping to sustain such convection.  </p>

scholarly journals Estimation of the Latent Heat Flux over Irrigated Short Fescue Grass for Different Fetches

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 322
Author(s):  
Francesc Castellví ◽  
Pedro Gavilán
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The Other ◽  
Sensible Heat ◽  
Surface Renewal ◽  
Residual Method ◽  
Flux Footprints

Often in agrometeorology the instrumentation required to estimate turbulent surface fluxes must be installed at sites where fetch is not sufficient for a sector of wind directions. For different integrated flux-footprints (IFFP) thresholds and taking as a reference the half-hourly latent heat fluxes (LE) measured with a large weighing lysimeter (LELys), the eddy covariance (EC) method and two methods based on surface renewal (SR) analysis to estimate LE were tested over short fescue grass. One method combined SR with the flux-gradient (profile) relationship, SR-P method, and the other with the dissipation method, SR-D method. When LE was estimated using traces of air moisture, good performances were obtained using the EC and the SR-P methods for samples with IFFP higher than 85%. However, the closest LE estimates were obtained using the residual method. For IFFP higher than 50%, the residual method combined with the sensible heat flux estimates determined using the SR-P method performed close to LELys and using the SR-D method good estimates were obtained for accumulated LELys. To estimate the sensible heat flux, the SR-D method can be recommended for day-to-day use by farmers because it is friendly and affordable.

scholarly journals Energy fluxes and surface characteristics over a cultivated area in Benin: daily and seasonal dynamics

2014 ◽  
Vol 18 (3) ◽  
pp. 893-914 ◽  
Author(s):  
O. Mamadou ◽  
J. M. Cohard ◽  
S. Galle ◽  
C. N. Awanou ◽  
A. Diedhiou ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Latent Heat ◽  
Bare Soil ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Evaporative Fraction ◽  
Surface Conditions ◽  
African Monsoon

Abstract. Latent and sensible heat surface fluxes are key factors of the western African monsoon dynamics. However, few long-term observations of these land surface fluxes are available; these are needed to increase understanding of the underlying processes and assess their impacts on the energy and water cycles at the surface–atmosphere interface. This study analyzes turbulent fluxes of one full year, measured with the eddy covariance technique, over a cultivated area in northern Benin (western Africa). The study site is part of the long-term AMMA–CATCH (African Monsoon Multidisciplinary Analysis–Coupling of the Tropical Atmosphere and Hydrological Cycle) hydrological observatory. The flux partitioning was investigated through the evaporative fraction (EF) and the Bowen ratio (β) at both seasonal and daily scales. Finally, the surface conductance (Gs) and the decoupling coefficient (Ω) were calculated and compared with specific bare soil or canopy models. Four contrasting seasons were identified and characterized by their typical daily energy cycles. The results pointed out the contrasting seasonal variations of sensible and latent heat fluxes due to changing atmospheric and surface conditions. In the dry season, the sensible heat fluxes were largely dominant (β ~ 10) and a low but significant evapotranspiration was measured (EF = 0.08); this was attributed to a few neighboring bushes, possibly fed by the water table. During the wet season, after the monsoon onset, surface conditions barely affected the evaporative fraction (EF), which remained steady (EF = 0.75); the latent heat flux was dominant and the Bowen ration (β) was about 0.4. During the dry-to-wet and wet-to-dry transition seasons, both EF and β were highly variable, as they depended on the atmospheric forcing or the response to isolated rains. A complete surface–atmosphere decoupling was never observed in 2008 (0 < Ω < 0.6), which suggests a systematic mixing of the air within the canopy with the atmospheric surface layer, irrespective of the atmospheric conditions and the vegetation height. Modeling approaches showed a good agreement of soil resistance with the Sakaguchi bare soil model. Canopy conductance was also well reproduced with the Ball–Berry stomata model. We showed that the skin surface temperature had a large seasonal and daily amplitude, and played a major role in all the surface processes. Consequently, an accurate modeling of the surface temperature is crucial to represent correctly the energy and water budgets for this region.

New results of the Land Atmosphere Feedback Experiment (LAFE)

2021 ◽  
Author(s):  
Volker Wulfmeyer ◽  
David D. Turner
Keyword(s):  
Remote Sensing ◽  
Latent Heat ◽  
Land Surface ◽  
Transport Processes ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Model Verification ◽  
Sensing Systems ◽  
Remote Sensing Systems ◽  
The Impact

&lt;p&gt;The Land-Atmosphere Feedback Experiment (LAFE) deployed several state-of-the-art scanning lidar and remote sensing systems to the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SPG) site during August 2017. A novel synergy of remote sensing systems was applied for simultaneous measurements of land-surface fluxes and horizontal and vertical transport processes in the atmospheric boundary layer (ABL). The impact of spatial inhomogeneities of the soil-vegetation continuum on L-A feedback was studied using the scanning capability of the instrumentation as well as soil, vegetation, and surface flux measurements. Thus, both the variability of surface fluxes and ABL dynamics and thermodynamics over the SGP site was studied for the first time. The objectives of LAFE are as follows:&lt;/p&gt;&lt;p&gt;I. Determine turbulence profiles and investigate new relationships among&amp;#160; gradients, variances, and fluxes&lt;br&gt;II. Map surface momentum, sensible heat, and latent heat fluxes using a synergy of scanning wind, humidity, and temperature lidar systems&lt;br&gt;III. Characterize land-atmosphere feedback and the moisture budget at the SGP site via the new LAFE sensor synergy&lt;br&gt;IV: Verify large-eddy simulation model runs and improve turbulence representations in mesoscale models.&lt;/p&gt;&lt;p&gt;In this presentation, the status of LAFE research and recent achievements of the science objectives are presented and discussed. Concerning I., long-term profiling capabilities of turbulent properties have been developed and will be presented such as continuous measurements of latent heat flux profiles for a duration of one month. Concerning II., we present a combination of tower and remote sensing measurements to study surface layer profiles of wind, temperature, and humidity. A first evaluation of the results demonstrates significant deviations from Monin-Obukhov similarity theory. Concerning III., Convective Triggering Potential (CTP)-Humidity Index (HIlow) metrics are presented at the SGP site to characterize L-A feedback and a new technique for determination of water-vapor advection, as important part of its budget. Last but not least, concerning IV., we present an advanced ensemble model design with turbulence permitting resolution for case studies and model verification from the convection-permitting to the turbulent scales in a realistic mesoscale environment. Using this framework, we introduce a strategy to apply the observations for the test and development of turbulence parameterizations. These results confirm that LAFE will make significant contributions to process understanding and the parameterization of the next generation of high-resolution weather forecast, climate, and earth system models.&lt;/p&gt;

scholarly journals On the Influence of Sea Surface Temperature distributions on the Development of Extratropical Cyclones

2021 ◽  
Author(s):  
Hai BUI ◽  
Thomas Spengler
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Minor Role ◽  
Extratropical Cyclones ◽  
The Absolute ◽  
Sst Gradient

AbstractThe sea surface temperature (SST) distribution can modulate the development of extratropical cyclones through sensible and latent heat fluxes. However, the direct and indirect effects of these surface fluxes, and thus the SST, are still not well understood. This study tackles this problem using idealized channel simulations of moist baroclinic development under the influence of surface fluxes. The model is initialized with a zonal wind field resembling the midlatitude jet and a different SST distribution for each experiment, where the absolute SST, the SST gradient, and the meridional position of the SST front are varied.The surface latent heat flux associated with the absolute SST plays a key role in enhancing the moist baroclinic development, while the sensible heat fluxes associated with the SST gradient play a minor role that can be detrimental for the development of the cyclone. The additional moisture provided by the latent heat fluxes originates from about 1000 km ahead of the cyclone a day prior to the time of the most rapid deepening. When the SST in this region is higher than 16°C, the additional latent heat is conducive for explosive cyclone development. For SSTs above 20°C, the cyclones feature characteristics of hybrid cyclones with latent heat release close to their core, maintaining their intensity for a longer period due to continuous and extensive moisture supply from the surface. A high absolute SST with a weak SST gradient, however, can lead to a delay of the deepening stage, because of unorganized convection at early stages reducing environmental baroclinicity.

Validating the Land-Atmosphere Coupling Behavior in Weather and Climate Models Using Observationally-Based Global Products

2021 ◽  
Author(s):  
Abedeh Abdolghafoorian ◽  
Paul A. Dirmeyer
Keyword(s):  
Heat Flux ◽  
Climate Models ◽  
Heat Waves ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Data Sets ◽  
Observational Uncertainty ◽  
Weather And Climate ◽  
The Impact

AbstractThe interactions between land and atmosphere (with terrestrial and atmospheric coupling segments) play a significant role in weather and climate. A predominant segment of land-atmosphere (L-A) feedbacks is the coupling between soil moisture (SM) and surface heat fluxes, the terrestrial coupling leg. The lack of high-quality long-term globally distributed observations, however, has hindered a robust, realistic identification of the terrestrial leg strength on a global scale. This exploratory study provides insight into how SM signals are translated into surface flux signals through the construction of a global depiction of the terrestrial leg from several recently developed global, gridded, observationally- and satellite-based data sets. The feasibility of producing global gridded estimates of L-A coupling metrics is explored. Five weather and climate models used for subseasonal to seasonal forecasting are confronted with the observational estimates to discern discrepancies that may affect their ability to predict phenomena related to L-A feedbacks, such as drought or heat waves. The terrestrial feedback leg from observations corroborates the “hot spots” of L-A coupling found in modeling studies, but the variances in daily time series of surface fluxes differ markedly. Better agreement and generally higher confidence are seen in metrics using latent heat flux than sensible heat flux. Observational metrics allow for clear stratification of model fidelity that is consistent across seasons, despite observational uncertainty. The results highlight the impact of SM on partitioning available surface energy and illustrate the potential of global observationally-based data sets for the assessment of such relationships in weather and climate models.

scholarly journals Coupling soil-vegetationatmosphere- transfer model with energy balance model for estimating energy and water vapor fluxes over an olive grove in a semi-arid region

2012 ◽  
Vol 1 (1) ◽  
pp. 1 ◽  
Author(s):  
Jamal Ezzahar ◽  
Salah Er-Raki ◽  
Hamid Marah ◽  
Said Khabba ◽  
Noureddine Amenzou ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Temperature ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Olive Grove ◽  
Sensible Heat ◽  
Conservation Of Energy

Simple soil-vegetation-transfer (SVAT) and energy balance models were used to estimate the surface turbulent fluxes (<em>i.e. </em>sensible and latent heat fluxes) over a complex olive grove using thermal infra-red surface temperature (TIRST). This approach used a dual source SVAT model to calculate the sensible heat fluxes from radiometric surface temperature. These fluxes were then used together with the estimates of the available energy also derived from TIRST to estimate the latent heat flux by applying the first law of thermodynamics <em>i.e.</em> the conservation of energy principle. The data used to validate this approach were collected over an irrigated olive grove site located in central Morocco near Marrakech. Mass and energy fluxes, as well as micrometeorological parameters, were continuously measured during the year 2003. The comparison between estimated and measured daily sensible heat fluxes yielded an acceptable agreement in spite of the complexity of the study surface with a correlation coefficient (R<sup>2</sup>=0.86) and root mean square error (RMSE) of 28 Wm<sup>-2</sup>. For the latent heat fluxes, the statistical result for the comparison between estimated and measured daily values showed a larger scatter than that revealed for the sensible heat fluxes (R<sup>2</sup>=0.75; RMSE=31.42 Wm<sup>-2</sup>). However, the correspondence is to be considered acceptable given the difficulty in estimating latent heat flux over such a complex field. Therefore, it can be concluded that, in spite of the simplicity of the proposed approach, it can be considered a suitable tool for estimating the turbulent fluxes using TIRST over complex surfaces.

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