Advanced Regional Prediction System Model Research Articles

Atmospheric dispersion of hydrogen sulfide using a modified ARPS model: a case study.

Exposure to disgusting smells constitutes a type of atmospheric pollution from industrial and human activities. Complaints stemming from various sources of unpleasant odors have become a serious concern in both sparsely and densely populated countries. Hydrogen sulfide is a compound characterized by its disgusting odor. In this work, a new chemical reaction was incorporated to Advanced Regional Prediction System (ARPS) model, to calculate the H2S air concentrations. A turbulent boundary layer flow is computed using the LES code ARPS 4.5.2. A LES coupled with a Lagrangian stochastic model has been applied to the study of reactive scalar dispersion downwind of a localized source of H2S. The study case corresponds to the H2S emission of cellulose mill. Two bad odor event was evaluating in order to compare the result of the model with the measured concentrations. The results of this model application provides good description of the plumes for two event of bad odor records in the zone. The values resulting from the analysis of the air samples are within the concentration range estimated by the model. The model is a valid and useful tool to simulate atmospheric pollution episodes that involve non-conservative pollutants, that is, chemical species that, when in contact with the atmospheric components, react, and giving rise to the formation of secondary compounds. It is possible used the developed modeling system in cases of diagnosis and prognosis of real situations and even emergencies, with an appropriate level of precision for studies of this type.

A Coastal Bay Summer Breeze Study, Part 2: High-resolution Numerical Simulation of Sea-breeze Local Influences

We complete the analysis of the data obtained during the experimental campaign around the semi circular bay of Quiberon, France, during two weeks in June 2006 (see Part 1). A reanalysis of numerical simulations performed with the Advanced Regional Prediction System model is presented. Three nested computational domains with increasing horizontal resolution down to 100 m, and a vertical resolution of 10 m at the lowest level, are used to reproduce the local-scale variations of the breeze close to the water surface of the bay. The Weather Research and Forecasting mesoscale model is used to assimilate the meteorological data. Comparisons of the simulations with the experimental data obtained at three sites reveal a good agreement of the flow over the bay and around the Quiberon peninsula during the daytime periods of sea-breeze development and weakening. In conditions of offshore synoptic flow, the simulations demonstrate that the semi-circular shape of the bay induces a corresponding circular shape in the offshore zones of stagnant flow preceding the sea-breeze onset, which move further offshore thereafter. The higher-resolution simulations are successful in reproducing the small-scale impacts of the peninsula and local coasts (breeze deviations, wakes, flow divergences), and in demonstrating the complexity of the breeze fields close to the surface over the bay. Our reanalysis also provides guidance for numerical simulation strategies for analyzing the structure and evolution of the near-surface breeze over a semi-circular bay, and for forecasting important flow details for use in upcoming sailing competitions.

A quantitative comparison of precipitation forecasts between the storm-scale numerical weather prediction model and auto-nowcast system in Jiangsu, China

Extrapolation techniques and storm-scale Numerical Weather Prediction (NWP) models are two primary approaches for short-term precipitation forecasts. The primary objective of this study is to verify precipitation forecasts and compare the performances of two nowcasting schemes: a Beijing Auto-Nowcast system (BJ-ANC) based on extrapolation techniques and a storm-scale NWP model called the Advanced Regional Prediction System (ARPS). The verification and comparison takes into account six heavy precipitation events that occurred in the summer of 2014 and 2015 in Jiangsu, China. The forecast performances of the two schemes were evaluated for the next 6h at 1-h intervals using gridpoint-based measures of critical success index, bias, index of agreement, root mean square error, and using an object-based verification method called Structure-Amplitude-Location (SAL) score. Regarding gridpoint-based measures, BJ-ANC outperforms ARPS at first, but then the forecast accuracy decreases rapidly with lead time and performs worse than ARPS after 4–5h of the initial forecast. Regarding the object-based verification method, most forecasts produced by BJ-ANC focus on the center of the diagram at the 1-h lead time and indicate high-quality forecasts. As the lead time increases, BJ-ANC overestimates precipitation amount and produces widespread precipitation, especially at a 6-h lead time. The ARPS model overestimates precipitation at all lead times, particularly at first.

Simulation of quasi-linear mesoscale convective systems in northern China: Lightning activities and storm structure

Two intense quasi-linear mesoscale convective systems (QLMCSs) in northern China were simulated using the WRF (Weather Research and Forecasting) model and the 3D-Var (three-dimensional variational) analysis system of the ARPS (Advanced Regional Prediction System) model. A new method in which the lightning density is calculated using both the precipitation and non-precipitation ice mass was developed to reveal the relationship between the lightning activities and QLMCS structures. Results indicate that, compared with calculating the results using two previous methods, the lightning density calculated using the new method presented in this study is in better accordance with observations. Based on the calculated lightning densities using the new method, it was found that most lightning activity was initiated on the right side and at the front of the QLMCSs, where the surface wind field converged intensely. The CAPE was much stronger ahead of the southeastward progressing QLMCS than to the back it, and their lightning events mainly occurred in regions with a large gradient of CAPE. Comparisons between lightning and non-lightning regions indicated that lightning regions featured more intense ascending motion than non-lightning regions; the vertical ranges of maximum reflectivity between lightning and non-lightning regions were very different; and the ice mixing ratio featured no significant differences between the lightning and non-lightning regions.

Isolating effects of terrain and soil moisture heterogeneity on the atmospheric boundary layer: Idealized simulations to diagnose land‐atmosphere feedbacks

AbstractThe effects of terrain, soil moisture heterogeneity, subsurface properties, and water table dynamics on the development and behavior of the atmospheric boundary layer are studied through a set of idealized numerical experiments. The mesoscale atmospheric model Advanced Regional Prediction System (ARPS) is used to isolate the effects of subsurface heterogeneity, terrain, and soil moisture initialization. The simulations are initialized with detailed soil moisture distributions obtained from offline spin‐ups using a coupled surface‐subsurface model (ParFlow‐CLM). In these idealized simulations, we observe that terrain effects dominate the planetary boundary layer (PBL) development during early morning hours, while the soil moisture signature overcomes that of terrain during the afternoon. Water table and subsurface properties produce a similar effect as that of soil moisture as their signatures (reflected in soil moisture profiles, energy fluxes, and evaporation at the land surface) can also overcome that of terrain during afternoon hours. This is mostly clear for land surface energy fluxes and evaporation at the land surface. We also observe the coupling between water table depth and planetary boundary layer depth in our cases is strongest within wet‐to‐dry transition zones. This extends the findings of previous studies which demonstrate the subsurface connection to surface energy fluxes is strongest in such transition zones. We investigate how this connection extends into the atmosphere and can affect the structure and development of the convective boundary layer.

Multiscale Simulation of a Prescribed Fire Event in the New Jersey Pine Barrens Using ARPS-CANOPY

AbstractSmoke prediction products are one of the tools used by land management personnel for decision making regarding prescribed fires. This study documents the application to a prescribed fire of a smoke prediction system that employs ARPS-CANOPY, a modified version of the Advanced Regional Prediction System (ARPS) model containing a canopy submodel, as the meteorological driver. In this paper, the performance of ARPS-CANOPY in simulating meteorological fields in the vicinity of a low-intensity fire is assessed using flux-tower data collected prior to and during a low-intensity prescribed fire in the New Jersey Pine Barrens in March 2011. A three-dimensional high-resolution plant area density dataset is utilized to define the characteristics of the canopy, and the fire is represented in ARPS-CANOPY as a heat flux to the atmosphere. The standard ARPS model is compared with reanalysis and upper-air data to establish that the model can simulate the observed synoptic-mesoscale and planetary boundary layer features that are salient to this study. ARPS-CANOPY profiles of mean turbulent kinetic energy, wind speed/direction, and temperature exhibit patterns that appear in the flux-tower observations during both the preburn phase of the experiment and the period of time the flux tower experienced perturbed atmospheric conditions due to the impinging fire. Last, the character and source of turbulence in and around the fire line are examined. These results are encouraging for smoke prediction efforts since transport of smoke from low-intensity fires is highly sensitive to the near-surface meteorological conditions and, in particular, turbulent flows.

Assessment of numerical model predictions of a severe weather in northern Iran: a case study

The capability of numerical models in simulating severe weather is related to the setting up of the parameters in the model, and the dynamical and physical schemes implemented in the model. Every model is not able to make accurate predictions in different time and locations. The Advanced Regional Prediction System (ARPS) was used with three different horizontal resolutions (30, 10, and 4 km) to simulate a severe snow storm in the south of the Caspian Sea, focusing primarily on the Tehran metropolitan area. This extratropical cyclone is selected due to its heavy precipitation (up to 3 m of snow in some regions) and a significant damage in terms of human and financial losses, as well as the variety forms of precipitation during its activity, including snow, rain, and hail. The ARPS model is used because the current operational numerical model, the Weather Research and Forecasting (WRF), at the national forecasting center of Iran does not predict well such an extreme event, particularly on the east coast of the Caspian Sea. Quantitatively speaking, our large-scale analyses show that there is a low bias in the simulated surface pressure, although the pressure patterns have generally admissible similarity with the observations. Geopotential height at 500 hPa is in reasonable agreement with the GFS reanalysis (here after observations). In terms of precipitation, the maximum values are simulated to be on the coasts of the Caspian Sea. In the innermost domain with 4-km horizontal resolution, precipitation values have been compared against the observations. The accumulative precipitation values in most of the weather stations are more than the actual values. Simulation results also indicate that in Mehrabad airport (center of Tehran) the model has successfully predicted vertical profiles of the considered variables.

Analyses and Numerical Modeling of Gravity Waves Generated by Flow over Nanling Mountains

Although there have been many observational and modeling studies of gravity waves excited by topograpghy, the detailed structure and its changes in real world are still poorly understood. The interaction of topography and background flow are described in details for a better understanding of the gravity waves observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery over Nanling Mountains. The evolutionary process and spatial structure of gravity waves were investigated by using almost all available observational data, including MODIS satellite imagery, the Final Analyses (FNL) data issued by National Centers for Environmental Prediction (NCEP), the aerosol backscattering signal data from Lidar, the surface observational data and the sounding data of Nanling mountain regions. In order to study its development mechanism, choosing the initial sounding of Jiangxi Gaizhou station located in the upstream of Nanling regions, and using the Advanced Regional Prediction System (ARPS), the numerical simulation was performed. It is shown that the ARPS model reproduced the main features of gravity waves reasonably well, where the gravity waves and turbulent mixed layer are consistent with the satellite image and the aerosol backscattering signal from Lidar observation. It is well-known that gravity wave-induced turbulence and thus turbulent mixing could affect the local composition of chemical species, which plays a significant role in the formation of low visibility and precipitation associated with local orography.

Implementation of a new cumulus parameterization scheme based on an explicit time-dependent tilting cloud model in ARPS model

A one-dimensional Explicit Time-dependent Tilting cloud Model (ETTM) that separates updraft and downdraft columns and takes into account the effect of cloud tilting on precipitation is introduced and incorporated into the Advanced Regional Prediction System (ARPS). Results of the stand-alone ETTM are compared with that of cloud resolving simulations using the ARPS mesoscale model. Inter-comparison is performed by qualitative examination of simulated parameters such as vertical distribution of fluxes of mass, heat, and moisture. Although there is a great degree of similarity between the vertical profiles, ETTM systematically underestimates magnitudes of all fluxes. Sensitivity tests carried with ETTM show that the effect of varying cloud radius and tilting angle is considerable on the simulated cloud behavior. Increasing the cloud radius, results in a corresponding increase in fluxes of mass, heat, and moisture, while increasing the cloud tilt angle has the opposite effect. Since ETTM showed promise as a suitable sub-grid cumulus parameterization scheme; it was incorporated into ARPS as an additional cumulus parameterization scheme (CPS) to be available for the wider community. Results of simulations using ETTM and other CPSs already available in ARPS were compared for 2, 4 and 10 km grid spacings to assess its utility. Simulation results of the 2 km grid showed that at this resolution, the simulated time series of updraft velocities using the new scheme (ETTM) compared well with the results of other schemes in the ARPS model. The simulations with horizontal resolution of 4 km that was compared with the convection resolving reference run (No-CPS-2KM) showed almost consistent results for all schemes except for one using KF scheme. The results of the simulation with the ETTM scheme and other schemes in the model with resolution of 10 km showed that at this resolution, there is not significant difference between the uses of these schemes.

Gravity wave momentum flux in directional shear flows over three‐dimensional mountains: Linear and nonlinear numerical solutions as compared to linear analytical solutions

Gravity waves forced by circular bell‐shaped mountains are simulated using the Advanced Regional Prediction System model for four directionally sheared wind profiles W1, W2, W2a, and W2b. W1 is eastward at the surface, while the latter three are southeastward. With the vertical shear directed northward, W1 shows an increasing speed with height, whereas W2, W2a, and W2b are first decelerated in the bottom layer (beneath different heights). Gravity wave momentum flux (WMF) and its vertical divergence at four different Froude numbers (Fr) are investigated. At a large Froude number Fr = 80 where the waves are essentially linear, the simulated WMF and WMF divergence agree well with their linear analytic counterparts, thus providing a numerical validation for the analytical solutions of Xu et al. For moderately nonlinear waves at Fr = 1.6, the simulated WMFs are qualitatively similar to the analytical values but are amplified due to nonlinear effect. For more nonlinear waves at lower Froude numbers, an enhanced drag is found at the lower Fr = 0.4 in W1, W2a, and W2b, and a low drag is found at higher Fr = 0.8 in W2, in contrast to the corresponding constant‐flow solutions. Analyses on the mountain flow structure show that the height variation of the ambient wind speed has an important influence on the airflow behavior (e.g., flow over versus flow around a mountain), which in turn affects the drag. Thus, unlike the constant‐flow case, the wave drag state in turning flows cannot be determined from the surface‐based Froude number alone, and new wave drag parameterization schemes would be needed to properly account for directional shear effects. Additionally, directional wind shear can also introduce asymmetric development in the wake flow to trigger lee vortex shedding, which is observed in W2 at Fr = 0.4.

Analysis and Forecast of a Tornadic Thunderstorm Using Multiple Doppler Radar Data, 3DVAR, and ARPS Model

A three-dimensional variational (3DVAR) assimilation technique developed for a convective-scale NWP model—advanced regional prediction system (ARPS)—is used to analyze the 8 May 2003, Moore/Midwest City, Oklahoma tornadic supercell thunderstorm. Previous studies on this case used only one or two radars that are very close to this storm. However, three other radars observed the upper-level part of the storm. Because these three radars are located far away from the targeted storm, they were overlooked by previous studies. High-frequency intermittent 3DVAR analyses are performed using the data from five radars that together provide a more complete picture of this storm. The analyses capture a well-defined mesocyclone in the midlevels and the wind circulation associated with a hook-shaped echo. The analyses produced through this technique are used as initial conditions for a 40-minute storm-scale forecast. The impact of multiple radars on a short-term NWP forecast is most evident when compared to forecasts using data from only one and two radars. The use of all radars provides the best forecast in which a strong low-level mesocyclone develops and tracks in close proximity to the actual tornado damage path.

The Influence of Topography and Ambient Stability on the Characteristics of Cold-Air Pools: A Numerical Investigation

AbstractA high-resolution numerical investigation of a cold-air pooling process (under quiescent conditions) is carried out that systematically highlights the relations between the characteristics of the cold-air pools (e.g., slope winds, vertical temperature and wind structure, and cooling rate) and the characteristics of the topography (e.g., basin size and slope angle) under different ambient stabilities. The Advanced Regional Prediction System model is used to simulate 40 different scenarios at 100-m (10 m) horizontal (vertical) resolution. Results are within the range of similar observed phenomena. The main physical process governing the cooling process near the basin floor (<200 m in height) was found to be longwave radiative flux divergence, whereas vertical advection of temperature dominated the cooling process for the upper-basin areas. The maximum downslope wind speed is linearly correlated with both basin size and slope angle, with stronger wind corresponding to larger basin and lower slope angle. As the basin size increases, the influence of slope angle on maximum downslope wind decreases and the maximum is located farther down the slope. These relationships do not appear to be sensitive to stability, but weaker stability produces more cooling in the basin atmosphere by allowing stronger rising motion and adiabatic cooling. Insight gained from this study helps to improve the understanding of the cold-air pooling process within the investigated settings.

Assimilating remotely sensed cloud optical thickness into a mesoscale model

Abstract. The Advanced Regional Prediction System, a mesoscale atmospheric model, is applied to simulate the month of June 2006 with a focus on the near surface air temperatures around Paris. To improve the simulated temperatures which show errors up to 10 K during a day on which a cold front passed Paris, a data assimilation procedure to calculate 3-D analysis fields of specific cloud liquid and ice water content is presented. The method is based on the assimilation of observed cloud optical thickness fields into the Advanced Regional Prediction System model and operates on 1-D vertical columns, assuming that the horizontal background error covariance is infinite, i.e. an independent pixel approximation. The rationale behind it is to find vertical profiles of cloud liquid and ice water content that yield the observed cloud optical thickness values and are consistent with the simulated profile. Afterwards, a latent heat adjustment is applied to the temperature in the vertical column. Data from several meteorological stations in the study area are used to verify the model simulations. The results show that the presented assimilation procedure is able to improve the simulated 2 m air temperatures and incoming shortwave radiation significantly during cloudy days. The scheme is able to alter the position of the cloud fields significantly and brings the simulated cloud pattern closer to the observations. As the scheme is rather simple and computationally inexpensive, it is a promising new technique to improve the surface fields of retrospective model simulations for variables that are affected by the position of the clouds.

Location-specific weather predictions for Sriharikota (13.72°N, 80.22°E) through numerical atmospheric models during satellite launch campaigns

Accurate knowledge of different meteorological parameters over a launch site is very crucial for efficient management of satellite launch operations. Local weather over the Indian satellite launch site located at Sriharikota High Altitude Range (SHAR: 13.72°N, 80.22°E) is very much dependent on the atmospheric circulation prevailing over the Bay of Bengal oceanic region and topography-induced convective activities. With a view to providing severe weather threat prediction in terms of launch commit criteria (LCC), two numerical atmospheric models namely high-resolution regional model (HRM) and advanced regional prediction system (ARPS) are made operational over SHAR in a synoptic and mesoscale domain, respectively. In the present research article, two launch campaigns through Polar Satellite Launch Vehicle (PSLV-C11 and PSLV-C12) when contrasting weather conditions prevailed over the launch site are chosen for demonstration of potential of two models in providing location-specific short-to-medium-range weather predictions meeting the needs of LCC. In the case of PSLV-C11 campaign, when the launch site underwent frequent thundershower-associated rainfall, ARPS model–derived meteorological fields were effectively used in prediction of probability of the wet spells. On the other hand, Bay of Bengal underwent severe cyclonic storm during PSLV-C12 campaign, and its formation was reasonable captured through HRM simulations. It is concluded that a combination of HRM and ARPS provide reliable short-to-medium-range weather prediction over SHAR, which has got profound importance in launch-related activities.

The Urban Heat Island Intensity of Paris: A Case Study Based on a Simple Urban Surface Parametrization

We explore the ability of a simple urban surface parametrization, embedded in a mesoscale meteorological model, to correctly reproduce observed values of the urban heat island (UHI) intensity, which is defined as the urban-rural surface air temperature difference. To do so, a simple urban scheme was incorporated into the Advanced Regional Prediction System (ARPS). Subsequently, a simulation was performed with the coupled model over the wider area of Paris, for a 12-day period in June 2006 that was characterised by conditions prone to UHI development. Simulated 2-m air temperature was compared with observed values for urban and rural stations, yielding mean errors of 1.4 and 1.5 K, respectively. More importantly, it was found that the model also displayed an overall good capability of reproducing the observed temperature differences. In particular, the magnitude (up to 6 K) and timing of the diurnal cycle of the UHI intensity was simulated well, the model exhibiting a mean error of 1.15 K. As a result, our conclusion is that the ARPS model, extended with simple urban surface physics, is able to capture observed urban-rural air temperature differences well, at least for the domain and period studied.

Understanding snow-transport processes shaping the mountain snow-cover

Abstract. Mountain snow-cover is normally heterogeneously distributed due to wind and precipitation interacting with the snow cover on various scales. The aim of this study was to investigate snow deposition and wind-induced snow-transport processes on different scales and to analyze some major drift events caused by north-west storms during two consecutive accumulation periods. In particular, we distinguish between the individual processes that cause specific drifts using a physically based model approach. Very high resolution wind fields (5 m) were computed with the atmospheric model Advanced Regional Prediction System (ARPS) and used as input for a model of snow-surface processes (Alpine3D) to calculate saltation, suspension and preferential deposition of precipitation. Several flow features during north-west storms were identified with input from a high-density network of permanent and mobile weather stations and indirect estimations of wind directions from snow-surface structures, such as snow dunes and sastrugis. We also used Terrestrial and Airborne Laser Scanning measurements to investigate snow-deposition patterns and to validate the model. The model results suggest that the in-slope deposition patterns, particularly two huge cross-slope cornice-like drifts, developed only when the prevailing wind direction was northwesterly and were formed mainly due to snow redistribution processes (saltation-driven). In contrast, more homogeneous deposition patterns on a ridge scale were formed during the same periods mainly due to preferential deposition of precipitation. The numerical analysis showed that snow-transport processes were sensitive to the changing topography due to the smoothing effect of the snow cover.

A Study of Atmospheric Boundary Layer Spatial Changes over Heterogeneous Surface in Baiyangdian Area

AbstractA three‐dimensional non‐hydrostatic meso‐scale model ARPS (the Advanced Regional Prediction System) is used to study the atmospheric boundary layer structure over heterogeneous underlying surface in Baiyangdian Area. The results showed that, in sunny weak background, the situation that the specific humidity (SH) over land is larger than that over water is universal, and it appears at surface layer first, extends to the upper air later. For the different surface characteristics, the sensible and latent fluxes over water are smaller and stable all day, but over land, both of them are much more in day, and latent flux is much bigger than sensible flux specially. The turbulent motion in surface layer over land is very different from that over lake, so the turbulent transmissions have clearly effect on the spatial changes of SH. The local circulation also has impact on the spatial changes of vapor, and the upward and downward movements influence the turbulent development, as well as the vertical transmission of vapor. The vapor over land comes mainly from the evapotranspiration of soil and vegetation, while a small part of them from the water area.

Meteorological Modeling of Very High-Resolution Wind Fields and Snow Deposition for Mountains

Abstract The inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface. During major snowfall events, preferential deposition of snow and transport of previously deposited snow often takes place simultaneously. Both processes, however, are driven by the local wind field, which is influenced by the local topography. In this study, the meteorological model Advanced Regional Prediction System (ARPS) was used to compute mean flow fields of 50-m, 25-m-, 10-m-, and 5-m grid spacing to investigate snow deposition patterns resulting from two snowfall events on a mountain ridge in the Swiss Alps. Only the initial adaptation of the flow field to the topography is calculated with artificial boundary conditions. The flow fields then drive the snow deposition and transport module of Alpine3D, a model of mountain surface processes. The authors compare the simulations with partly new measurements of snow deposition on the Gaudergrat ridge. On the basis of these four grid resolutions, it was possible to investigate the effects of numerical resolution in the calculation of wind fields and in the calculation of the associated snow deposition. The most realistic wind field and deposition patterns were obtained with the highest resolution of 5 m. These high-resolution simulations confirm the earlier hypothesis that preferential deposition is active at the ridge scale and true redistribution—mainly via saltation—forms smaller-scale deposition patterns, such as dunes and cornices.

Fine‐scale modeling of the boundary layer wind field over steep topography

This paper describes the adaptation of wind fields to steep and complex terrain using fine‐scale numerical modeling. The work is motivated by the need of high‐resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes. Applying the nonhydrostatic and compressible atmospheric prediction model Advanced Regional Prediction System (ARPS) to steep alpine topography, the boundary layer flow was simulated and evaluated against measurements. The adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated. The topography used in our study has a length scale of 500 m, a typical height of 150 m, and maximum slopes of 45°. Numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration. This analysis indicates that a high‐resolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small‐scale flow features such as speed‐up, separation, and recirculation. The onset of flow separation is highly sensitive to initial and boundary conditions, slope angle, and surface roughness. The results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced. The simulated wind fields have been used to drive a numerical three‐dimensional snow drift model, which is presented in a companion paper by Lehning et al. (2008).

Modeling the energy balance in Marseille: Sensitivity to roughness length parameterizations and thermal admittance

During the ESCOMPTE campaign (Experience sur Site pour COntraindre les Modeles de Pollution atmospherique et de Transport d'Emissions), a 4‐day intensive observation period was selected to evaluate the Advanced Regional Prediction System (ARPS), a nonhydrostatic meteorological mesoscale model that was optimized with a parameterization for thermal roughness length to better represent urban surfaces. The evaluation shows that the ARPS model is able to correctly reproduce temperature, wind speed, and direction for one urban and two rural measurements stations. Furthermore, simulated heat fluxes show good agreement compared to the observations, although simulated sensible heat fluxes were initially too low for the urban stations. In order to improve the latter, different roughness length parameterization schemes were tested, combined with various thermal admittance values. This sensitivity study showed that the Zilitinkevich scheme combined with and intermediate value of thermal admittance performs best.