A study of a fair weather boundary layer in TOGA-COARE: Parameterization of surface fluxes in large scale and regional models for light wind conditions

Abstract An approach is presented for the construction of linear response functions of a cumulus ensemble to large-scale temperature and moisture perturbations using a cloud system–resolving model (CSRM). A set of time-invariant, horizontally homogeneous, anomalous temperature and moisture tendencies is added, one at a time, to the forcing of the CSRM. By recording the departure of the equilibrium domain-averaged temperature and moisture profiles from those of a control experiment and through a matrix inversion, a sufficiently complete and accurate set of linear response functions is constructed for use as a parameterization of the cumulus ensemble around the reference mean state represented by the control experiment. This approach is applied to two different mean state conditions in which the CSRM, when coupled with 2D gravity waves, exhibits interestingly different behaviors. With a more strongly convecting mean state forced by the large-scale vertical velocity profile taken from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), spontaneous development of convectively coupled waves requires moisture variations above the boundary layer, whereas with a mean state of radiative–convective equilibrium (RCE) not forced by large-scale vertical advection, the development of convectively coupled waves is stronger and persists even when moisture variations above the boundary layer are removed. The linear response functions were able to reproduce these behaviors of the full CSRM with some quantitative accuracy. The linear response functions show that both temperature and moisture perturbations at a range of heights can regulate convective heating. The ability for convection to remove temperature anomalies, thus maintaining convective neutrality, decreases considerably from the lower troposphere to the middle and upper troposphere. It is also found that the response of convective heating to a lower tropospheric temperature anomaly is more top-heavy in the RCE case than in the TOGA COARE case. Comparing the linear response functions with the treatment of convection in an earlier simple model by the present author indicates general consistency, lending confidence that the instability mechanisms identified in that model provide the correct explanation to the instability seen in the CSRM simulations and the instability’s dependence on the mean state.

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Including Atmospheric Layers in Vegetation and Urban Offline Surface Schemes

Journal of Applied Meteorology and Climatology ◽

10.1175/2009jamc1866.1 ◽

2009 ◽

Vol 48 (7) ◽

pp. 1377-1397 ◽

Cited By ~ 64

Author(s):

Valéry Masson ◽

Yann Seity

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Single Layer ◽

Urban Canopy ◽

Atmospheric Model ◽

Surface Fluxes ◽

Surface Boundary ◽

Surface Cooling ◽

Stable Conditions ◽

Surface Scheme

Abstract A formulation to include prognostic atmospheric layers in offline surface schemes is derived from atmospheric equations. Whereas multilayer schemes developed previously need a complex coupling between atmospheric-model levels and surface-scheme levels, the coupling proposed here remains simple. This is possible because the atmospheric layers interacting with the surface scheme are independent of the atmospheric model that could be coupled above. The surface boundary layer (SBL; both inside and just above the canopy) is resolved prognostically, taking into account large-scale forcing, turbulence, and, if any, drag and canopy forces and surface fluxes. This formulation allows one to retrieve the logarithmic law in neutral conditions, and it has been validated when coupled to a 3D atmospheric model. Systematic comparisons with 2-m observations and 10-m wind have been made for 2 months. The SBL scheme is able to model the 2-m temperature accurately, as well as the 10-m wind, without any use of analytical interpolation. The largest improvement takes place during stable conditions (i.e., by night), during which analytical laws and interpolation methods are known to be less accurate, and in mountainous areas, in which nocturnal low-level flow is strongly influenced by surface cooling. The prognostic SBL scheme is shown to solve the nighttime physical disconnection problem between surface and atmosphere models. The inclusion of the SBL into the urban Town Energy Balance scheme is presented in a paper by Hamdi and Masson in which the ability of the method to simulate the profiles of both mean and turbulent quantities from above the building down to the road surface is shown using data from the Basel Urban Boundary Layer Experiment (BUBBLE). The proposed method will allow the inclusion of the detailed physics of the multilayer schemes (e.g., the interactions of the SBL flow with forest or urban canopy) into a single-layer scheme that is easily coupled with atmospheric models.

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Land surface spinup for episodic modeling

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-8165-2014 ◽

2014 ◽

Vol 14 (15) ◽

pp. 8165-8172 ◽

Cited By ~ 26

Author(s):

W. M. Angevine ◽

E. Bazile ◽

D. Legain ◽

D. Pino

Keyword(s):

Boundary Layer ◽

Soil Moisture ◽

Spatial Variability ◽

Land Surface ◽

Large Scale ◽

Layer Structure ◽

Numerical Models ◽

Surface Fluxes ◽

Boundary Layer Structure ◽

Soil Variables

Abstract. Soil moisture strongly controls the surface fluxes in mesoscale numerical models, and thereby influences the boundary layer structure. Proper initialization of soil moisture is therefore critical for faithful simulations. In many applications, such as air quality or process studies, the model is run for short, discrete periods (a day to a month). This paper describes one method for soil initialization in these cases – self-spinup. In self-spinup, the model is initialized with a coarse-resolution operational model or reanalysis output, and run for a month, cycling its own soil variables. This allows the soil variables to develop appropriate spatial variability, and may improve the actual values. The month (or other period) can be run more than once if needed. The case shown is for the Boundary Layer Late Afternoon and Sunset Turbulence experiment, conducted in France in 2011. Self-spinup adds spatial variability, which improves the representation of soil moisture patterns around the experiment location, which is quite near the Pyrenees Mountains. The self-spinup also corrects a wet bias in the large-scale analysis. The overall result is a much-improved simulation of boundary layer structure, evaluated by comparison with soundings from the field site. Self-spinup is not recommended as a substitute for multi-year spinup with an offline land data assimilation system in circumstances where the data sets required for such spinup are available at the required resolution. Self-spinup may fail if the modeled precipitation is poorly simulated. It is an expedient for cases when resources are not available to allow a better method to be used.

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Boundary Layer Quasi-Equilibrium Limits Convective Intensity Enhancement from the Diurnal Cycle in Surface Heating

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0346.1 ◽

2019 ◽

Vol 77 (1) ◽

pp. 217-237

Author(s):

Zachary R. Hansen ◽

Larissa E. Back ◽

Peigen Zhou

Keyword(s):

Boundary Layer ◽

Diurnal Cycle ◽

Large Scale ◽

Deep Convection ◽

Reanalysis Data ◽

Surface Fluxes ◽

Quasi Equilibrium ◽

The Impact ◽

Precipitation Enhancement ◽

High Percentile

Abstract A combination of cloud-permitting model (CPM) simulations, satellite, and reanalysis data are used to test whether the diurnal cycle in surface temperature has a significant impact on the intensity of deep convection as measured by high-percentile updraft velocities, lightning, and CAPE. The land–ocean contrast in lightning activity shows that convective intensity varies between land and ocean independently from convective quantity. Thus, a mechanism that explains the land–ocean contrast must be able to do so even after controlling for precipitation variations. Motivated by the land–ocean contrast, we use idealized CPM simulations to test the impact of the diurnal cycle on high-percentile updrafts. In simulations, updrafts are somewhat enhanced due to large-scale precipitation enhancement by the diurnal cycle. To control for large-scale precipitation, we use statistical sampling techniques. After controlling for precipitation enhancement, the diurnal cycle does not affect convective intensities. To explain why sampled updrafts are not enhanced, we note that CAPE is also not increased, likely due to boundary layer quasi equilibrium (BLQE) occurring over our land area. Analysis of BLQE in terms of net positive and negative mass flux finds that boundary layer entrainment, and even more importantly downdrafts, account for most of the moist static energy (MSE) sink that is balancing surface fluxes. Using ERA-Interim data, we also find qualitative evidence for BLQE over land in the real world, as high percentiles of CAPE are not greater over land than over ocean.

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Land surface spinup for episodic modeling

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-4723-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 4723-4744 ◽

Cited By ~ 2

Author(s):

W. M. Angevine ◽

E. Bazile ◽

D. Legain ◽

D. Pino

Keyword(s):

Boundary Layer ◽

Soil Moisture ◽

Spatial Variability ◽

Land Surface ◽

Large Scale ◽

Layer Structure ◽

Numerical Models ◽

Surface Fluxes ◽

Boundary Layer Structure ◽

Soil Variables

Abstract. Soil moisture strongly controls the surface fluxes in mesoscale numerical models, and thereby influences the boundary layer structure. Proper initialization of soil moisture is therefore critical for faithful simulations. In many applications, such as air quality or process studies, the model is run for short, discrete periods (a day to a month). This paper describes one method for soil initialization in these cases, self-spinup. In self-spinup, the model is initialized with a coarse-resolution operational model or reanalysis output, and run for a month, cycling its own soil variables. This allows the soil variables to develop appropriate spatial variability, and may improve the actual values. The month (or other period) can be run more than once if needed. The case shown is for the Boundary Layer Late Afternoon and Sunset Turbulence experiment, conducted in France in 2011. Self-spinup adds spatial variability, which improves the representation of soil moisture patterns around the experiment location, which is quite near the Pyrenees Mountains. The self-spinup also corrects a wet bias in the large-scale analysis. The overall result is a much-improved simulation of boundary layer structure, evaluated by comparison with soundings from the field site. Self-spinup is not recommended as a substitute for multi-year spinup with an offline land data assimilation system in circumstances where the data sets required for such spinup are available at the required resolution. Self-spinup may fail if the modeled precipitation is poorly simulated. It is an expedient for cases when resources are not available to allow a better method to be used.

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The Impact of Large-scale Flow Direction on the Formation of a Glacier Boundary Layer: Two LES Case Studies

10.5194/egusphere-egu21-2620 ◽

2021 ◽

Author(s):

Brigitta Goger ◽

Ivana Stiperski ◽

Keyword(s):

Boundary Layer ◽

Case Studies ◽

Flow Structure ◽

Large Scale ◽

Surface Fluxes ◽

Horizontal Wind ◽

Glacier Surface ◽

Ice Surface ◽

Large Scale Flow ◽

The Impact

The mass balance of mountain glaciers needs correct assessment for several applications, e. g. sea level rise estimates, catchment hydrology, and natural hazard warnings. It results, at any point on a glacier, from energy, mass, and momentum fluxes at the glacier-atmosphere interface. However, surface fluxes on glaciers are highly heterogeneous in space and time. To learn more about the processes leading to the spatial surface flux structure over a glacier surface, we employ large-eddy simulations with the WRF model at a horizontal grid mesh size of 48 m over the Hintereisferner, an approximately 6 km long valley glacier in the Austrian Alps. For model evaluation purposes, we use, besides our permanent measurement framework, four turbulence flux towers located on along- and across-glacier transects which were maintained in August 2018 on the glacier surface. Simulations were conducted for two case studies, namely one day with synoptic flow from the South-West (SW), and a day with synoptic flow from the North-West (NW). Comparison with the observations suggests that the model is able to reproduce the larger-scale flow structure and the local processes over the ice surface. On the SW day, thermally-induced flows dominate the near-surface wind patterns and a stable boundary layer forms above the ice surface due to the alignment of the katabatic glacier wind with the larger-scale flow. Under these conditions, the glacier surface is exposed to horizontal cold-air advection. However, on the NW day, the local terrain leads to the formation of a gravity wave with severe turbulence. The resulting cross-glacier flow erodes the glacier boundary layer, and the glacier ice experiences horizontal warm-air advection. In both cases, the model simulates the complex flow structure on different length scales that affect the vertical and horizontal exchange processes over the glacier surface and the local heat advection during the daytime. The spatial sensible heat flux pattern is strongly connected to the horizontal wind speed, wind direction, and TKE. The experiment suggests a major impact of the large-scale flow structure and the flow modification by the underlying terrain. Our model setup is able to resolve the relevant scales and is therefore a valuable tool to gain insight on the surface fluxes over truly complex, heterogeneous terrain.

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An Evaluation of WRF Simulations of Clouds over the Southern Ocean with A-Train Observations

Monthly Weather Review ◽

10.1175/mwr-d-13-00128.1 ◽

2014 ◽

Vol 142 (2) ◽

pp. 647-667 ◽

Cited By ~ 19

Author(s):

Yi Huang ◽

Steven T. Siems ◽

Michael J. Manton ◽

Gregory Thompson

Keyword(s):

Boundary Layer ◽

Southern Ocean ◽

Large Scale ◽

Marine Boundary Layer ◽

Cloud Condensation Nuclei ◽

Surface Fluxes ◽

Shortwave Radiation ◽

Microphysical Properties ◽

Formidable Challenge ◽

Weak Surface

Abstract The representation of the marine boundary layer (BL) clouds remains a formidable challenge for state-of-the-art simulations. A recent study by Bodas-Salcedo et al. using the Met Office Unified Model highlights that the underprediction of the low/midlevel postfrontal clouds contributes to the largest bias of the surface downwelling shortwave radiation over the Southern Ocean (SO). A-Train observations and limited in situ measurements have been used to evaluate the Weather Research and Forecasting Model, version 3.3.1 (WRFV3.3.1), in simulating the postfrontal clouds over Tasmania and the SO. The simulated cloud macro/microphysical properties are compared against the observations. Experiments are also undertaken to test the sensitivity of model resolution, microphysical (MP) schemes, planetary boundary layer (PBL) schemes, and cloud condensation nuclei (CCN) concentration. The simulations demonstrate a considerable level of skill in representing the clouds during the frontal passages and, to a lesser extent, in the postfrontal environment. The simulations, however, have great difficulties in portraying the widespread marine BL clouds that are not immediately associated with fronts. This shortcoming is persistent to the changes of model configuration and physical parameterization. The representation of large-scale conditions and their connections with the BL clouds are discussed. A lack of BL moisture is the most obvious explanation for the shortcoming, which may be a consequence of either strong entrainment or weak surface fluxes. It is speculated that the BL wind shear/turbulence may be an issue over the SO. More comprehensive observations are necessary to fully investigate the deficiency of the simulations.

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Surface Fluxes and Boundary Layer Recovery in TOGA COARE: Sensitivity to Convective Organization

Journal of the Atmospheric Sciences ◽

10.1175/1520-0469(1998)055<2763:sfablr>2.0.co;2 ◽

1998 ◽

Vol 55 (17) ◽

pp. 2763-2781 ◽

Cited By ~ 36

Author(s):

Thomas R. Saxen ◽

Steven A. Rutledge

Keyword(s):

Boundary Layer ◽

Surface Fluxes ◽

Toga Coare ◽

Convective Organization

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A Study of the Response of Deep Tropical Clouds to Large-Scale Thermodynamic Forcings. Part II: Sensitivities to Microphysics, Radiation, and Surface Fluxes

Journal of the Atmospheric Sciences ◽

10.1175/jas3846.1 ◽

2007 ◽

Vol 64 (3) ◽

pp. 869-886 ◽

Cited By ~ 16

Author(s):

D. E. Johnson ◽

W-K. Tao ◽

J. Simpson

Keyword(s):

Large Scale ◽

Longwave Radiation ◽

Surface Fluxes ◽

Tropical Ocean ◽

Surface Precipitation ◽

Mass Fluxes ◽

Toga Coare ◽

The Mean ◽

Thermodynamics And Dynamics ◽

Microphysical Processes

Abstract The Goddard Cumulus Ensemble (GCE) model is used to examine the sensitivities of multiday 2D simulations of deep tropical convection to surface fluxes, interactive radiation, and ice microphysical processes. The simulations incorporate large-scale temperature, moisture, and momentum forcings, from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) for the period 19–27 December 1992. This study shows that, when surface fluxes are eliminated, the mean simulated atmosphere is much cooler and drier, convection and CAPE are much weaker, precipitation is less, and low-level to midlevel cloudiness is much greater. Surface fluxes using the TOGA COARE flux algorithm are weaker than with the aerodynamic formulation, but closer to the observed fluxes. In addition, trends similar to those noted above for the case without surface fluxes are produced for the TOGA COARE flux case, albeit to a much lesser extent. The elimination of shortwave and longwave radiation is found to have only minimal effects on the mean thermodynamics, convection, and precipitation. However, exclusion of radiation in the model does have a significant impact on cloud temperatures and structure above 200 mb. The removal of ice microphysical processes produces major changes in the structure of the clouds. Much of the liquid water is transported to the upper levels of the troposphere and evaporates, resulting in less mean total surface precipitation. The precipitation primarily occurs in regions of narrow, but intense, convective rainfall bands. The elimination of melting processes (diabatic cooling and conversions to rain) leads to greater (ice) hydrometeor mass below the 0°C level and reduced latent cooling. This, along with weaker vertical cloud mass fluxes, produces a much warmer and moister boundary layer, and a greater mean CAPE. Finally, the elimination of the graupel species has only a small impact on mean total precipitation, thermodynamics, and dynamics of the simulation, but does produce much greater snow mass just above the melting layer.

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The role of air-sea ice-ocean interaction processes for Arctic-midlatitude linkages

10.5194/egusphere-egu2020-15116 ◽

2020 ◽

Author(s):

Sara Khosravi ◽

Annette Rinke ◽

Wolfgang Dorn ◽

Christof Lüpkes ◽

Vladimir Gryanik ◽

...

Keyword(s):

Boundary Layer ◽

Sea Ice ◽

Large Scale ◽

Climate Models ◽

Arctic Sea Ice ◽

Surface Fluxes ◽

The Arctic ◽

Russian Science ◽

Large Scale Circulation ◽

The Impact

Climate models have deficits in reproducing Arctic circulation and sea ice development. The air-sea ice-ocean interaction parametrizations could be a potential reason of this shortcoming. In most climate models air-sea ice-ocean interaction are parametrized based on mid-latitude conditions which is not appropriate for polar region. The POLEX project, funded by Helmholtz Association and Russian Science Foundation, is studying the impact of improved representation of Arctic air-sea ice-ocean interaction on changes in Arctic atmospheric circulation and Arctic-midlatitude linkages. We have used a new suite of parametrizations, which are easily applicable for climate simulations and have been developed based on SHEBA expedition data by Gryanik and L&#252;pkes (2018). We implemented the new parametrizations in the global atmospheric model (ECHAM6) in the framework of POLEX to estimate its effect on regional Arctic and large-scale circulation changes. Several steps have been defined for implementing the new parameterization to be able to distinguish and understand better the impact of its parameters. Roughness length and stability functions for stable stratification have been modified. Here the initial results of ECHAM6 sensitivity runs for different steps of the parameterization will be presented. We will present first results from process-oriented evaluation over the Arctic sea ice, e.g. how is the impact on the simulation of the two states of the Arctic boundary layer in winter. Furthermore, we will show that the large-scale circulation reacts to the new parametrization in different months and years differently. Reference: Gryanik, V.M. and C. L&#252;pkes (2018) An efficient non-iterative bulk parametrization of surface fluxes for stable atmospheric conditions over polar sea-ice, Boundary-Layer Meteorol., 166, 301-325

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