Convective distribution of dust over the Arabian Peninsula: the impact of model resolution

Abstract. Along the coasts of the Arabian Peninsula, convective dust storms are a considerable source of mineral dust to the atmosphere. Reliable predictions of convective dust events are necessary to determine their effects on air quality, visibility, and the radiation budget. In this study, the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) is used to simulate a 2016 summertime dust event over the Arabian Peninsula and examine the variability in dust fields and associated vertical transport due to the choice of convective parameterization and convection-permitting versus parameterized convection. Simulations are run at 45 and 15 km grid spacing with multiple cumulus parameterizations, and are compared to a 3 km simulation that permits explicit dry and moist convective processes. Five separate cumulus parameterizations at 15 km grid spacing were tested to quantify the spread across different parameterizations. Finally, the impact these variations have on radiation, specifically aerosol heating rates is also investigated. On average, in these simulations the convection-permitting case produces higher quantities of dust than the parameterized cases in terms of dust uplift potential, vertical dust concentrations, and vertical dust fluxes. Major drivers of this discrepancy between the simulations stem from the convection-permitting case exhibiting higher surface wind speeds during convective activity; lower dust emission wind threshold velocities due to drier soil; and more frequent, stronger vertical velocities which transport dust aloft and increase the atmospheric lifetime of these particles. For aerosol heating rates in the lowest levels, the shortwave effect prevails in the convection-permitting case with a net cooling effect, whereas a longwave net warming effect is present in the parameterized cases. The spread in dust concentrations across cumulus parameterizations at the same grid resolution (15 km) is an order of magnitude lower than the impact of moving from parameterized towards explicit convection. We conclude that tuning dust emissions in coarse-resolution simulations can only improve the results to first-order and cannot fully rectify the discrepancies originating from disparities in the representation of convective dust transport.

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Convective distribution of dust over the Arabian Peninsula: the impact of model resolution

10.5194/acp-2019-197 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jennie Bukowski ◽

Susan C. van den Heever

Keyword(s):

Arabian Peninsula ◽

Dust Emission ◽

Dust Storms ◽

Radiation Budget ◽

Grid Spacing ◽

Heating Rates ◽

Dust Transport ◽

Order Of Magnitude ◽

The Impact ◽

Cumulus Parameterizations

Abstract. Along the coasts of the Arabian Peninsula, convective dust storms are a considerable source of mineral dust to the atmosphere. Reliable predictions of convective dust events are necessary to determine their effects on air quality, visibility, and the radiation budget. In this study, the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) is used to simulate a 2016 summertime dust event over the Arabian Peninsula and examine the variability in dust fields and associated vertical transport due to the choice of convective parameterization and explicit versus parameterized convection. Simulations are run at 45 km and 15 km grid spacing with multiple cumulus parameterizations, and are compared to a 3 km simulation that permits explicit convective processes. Five separate cumulus parameterizations at 15 km grid spacing were tested to quantify the spread across different parameterizations. Finally, the impact these variations have on radiation, specifically aerosol heating rates is also investigated. On average, in these simulations the explicit case produces higher quantities of dust than the parameterized cases in terms of dust uplift potential, vertical dust concentrations, and vertical dust fluxes. Major drivers of this discrepancy between the simulations stem from the explicit case exhibiting higher surface windspeeds during convective activity, lower dust emission wind threshold velocities due to drier soil, and more frequent, stronger vertical velocities which transport dust aloft and increase the atmospheric lifetime of these particles. For aerosol heating rates in the lowest levels, the shortwave effect prevails in the explicit case with a net cooling effect, whereas a longwave net warming effect is present in the parameterized cases. The spread in dust concentrations across cumulus parameterizations at the same grid resolution (15 km) is an order of magnitude lower than the impact of moving from parameterized to explicit convection. We conclude that tuning dust emissions in coarse resolution simulations can only improve the results to first-order and cannot fully rectify the discrepancies originating from disparities in the representation of convective dust transport.

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Sea Surface Wind Correction Using HF Ocean Radar and Its Impact on Coastal Wave Prediction

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0249.1 ◽

2017 ◽

Vol 34 (9) ◽

pp. 2001-2020 ◽

Cited By ~ 3

Author(s):

Yukiharu Hisaki

Keyword(s):

Wind Direction ◽

Surface Wind ◽

Hf Radar ◽

Sea Surface ◽

Wave Parameter ◽

Simple Method ◽

Wind Speeds ◽

Wave Prediction ◽

Sea Surface Wind ◽

The Impact

AbstractBoth wind speeds and wind directions are important for predicting wave heights near complex coastal areas, such as small islands, because the fetch is sensitive to the wind direction. High-frequency (HF) radar can be used to estimate sea surface wind directions from first-order scattering. A simple method is proposed to correct sea surface wind vectors from reanalysis data using the wind directions estimated from HF radar. The constraints for wind speed corrections are that the corrections are small and that the corrections of horizontal divergences are small. A simple algorithm for solving the solution that minimizes the weighted sum of the constraints is developed. Another simple method is proposed to correct sea surface wind vectors. The constraints of the method are that corrections of wind vectors and horizontal divergences from the reanalysis wind vectors are small and that the projection of the corrected wind vectors to the direction orthogonal to the HF radar–estimated wind direction is small. The impact of wind correction on wave parameter prediction is large in the area in which the fetch is sensitive to wind direction. The accuracy of the wave prediction is improved by correcting the wind in that area, where correction of wind direction is more important than correction of wind speeds for the improvement. This method could be used for near-real-time wave monitoring by correcting forecast winds using HF radar data.

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The role of aerosol–radiation–cloud interactions in linking anthropogenic pollution over southern west Africa and dust emission over the Sahara

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-14657-2019 ◽

2019 ◽

Vol 19 (23) ◽

pp. 14657-14676 ◽

Cited By ~ 3

Author(s):

Laurent Menut ◽

Paolo Tuccella ◽

Cyrille Flamant ◽

Adrien Deroubaix ◽

Marco Gaetani

Keyword(s):

West Africa ◽

Mineral Dust ◽

Surface Wind ◽

Dust Emission ◽

Longwave Radiation ◽

Atmospheric Composition ◽

Anthropogenic Emissions ◽

Dust Emissions ◽

Aerosol Cloud ◽

The Impact

Abstract. The aerosol direct and indirect effects are studied over west Africa in the summer of 2016 using the coupled WRF-CHIMERE regional model including aerosol–cloud interaction parameterization. First, a reference simulation is performed and compared with observations acquired during the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) field campaign which took place in June and July 2016. Sensitivity experiments are also designed to gain insights into the impact of the aerosols dominating the atmospheric composition in southern west Africa (one simulation with halved anthropogenic emissions and one with halved mineral dust emissions). The most important effect of aerosol–cloud interactions is found for the mineral dust scenario, and it is shown that halving the emissions of mineral dust decreases the 2 m temperature by 0.5 K and the boundary layer height by 25 m on a monthly average (July 2016) and over the Saharan region. The presence of dust aerosols also increases (decreases) the shortwave (longwave) radiation at the surface by 25 W m−2. It is also shown that the decrease of anthropogenic emissions along the coast has an impact on the mineral dust load over west Africa by increasing their emissions in the Saharan region. It is due to a mechanism where particulate matter concentrations are decreased along the coast, imposing a latitudinal shift of the monsoonal precipitation and, in turn, an increase of the surface wind speed over arid areas, inducing more mineral dust emissions.

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Summertime dust storms over the Arabian Peninsula and impacts on radiation and atmospheric circulation.

10.5194/egusphere-egu21-439 ◽

2021 ◽

Author(s):

Diana Francis ◽

Jean-Pierre Chaboureau ◽

Narendra Nelli ◽

Juan Cuesta ◽

Noor Alshamsi

Keyword(s):

Dust Storm ◽

Radiative Forcing ◽

Arabian Peninsula ◽

Source Region ◽

Dust Storms ◽

Dimensional Structure ◽

Climate Projections ◽

Air Quality Forecast ◽

The Impact ◽

First Time

This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations.We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW.Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections.These results were published in November 2020 in the journal Atmospheric Research doi.org/10.1016/j.atmosres.2020.105364.

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On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low–forced winds

Science Advances ◽

10.1126/sciadv.1500646 ◽

2015 ◽

Vol 1 (9) ◽

pp. e1500646 ◽

Cited By ~ 21

Author(s):

Weijie Wang ◽

Amato T. Evan ◽

Cyrille Flamant ◽

Christophe Lavaysse

Keyword(s):

Interannual Variability ◽

Climate Models ◽

Surface Wind ◽

Large Body ◽

Dust Emission ◽

Wind Speeds ◽

African Dust ◽

Decadal Scale ◽

Sahelian Rainfall ◽

Heat Low

A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous-year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. We reconcile this contradiction showing that interannual variability in Sahelian rainfall and surface wind speeds over the Sahara are the result of changes in lower tropospheric air temperatures over the Saharan heat low (SHL). As the SHL warms, an anomalous tropospheric circulation develops that reduces wind speeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust “hotspots” in the Sahara. Our results shed light on why climate models are, to date, unable to reproduce observed historical variability in dust emission and transport from this region.

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Influence of Assimilating CYGNSS Ocean Surface Wind Data on Tropical Cyclone Analyses and Predictions

10.5194/egusphere-egu2020-20553 ◽

2020 ◽

Author(s):

Bachir Annane ◽

Mark Leidner ◽

Ross Hoffman ◽

Feixiong Huang ◽

James Garrisson

Keyword(s):

Tropical Cyclones ◽

Surface Wind ◽

Ocean Surface ◽

Convective Precipitation ◽

Weather Research And Forecasting ◽

Wind Speeds ◽

Ocean Surface Winds ◽

Ocean Surface Wind ◽

The Impact ◽

Hwrf Model

<div> <div>For the analysis and forecasting of tropical cyclones, the main benefits of data from the CYGNSS constellation of satellites are the increased revisit frequency compared with polar-orbiting satellites and the ability to provide ocean surface wind observations through convective precipitation. Consequently, CYGNSS delivers an improved capability to observe the structure and evolution of ocean surface winds in and around tropical cyclones. This study quantifies the impact of assimilating CYGNSS delay-Doppler maps, CYGNSS retrieved wind speeds and derived CYGNSS wind vectors on 6-hourly analyses and 5-day forecasts of developing tropical cyclones, using the 2019 version of NOAA's operational Hurricane Weather Research and Forecasting (HWRF) model.</div> </div>

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The impact of ecosystem change on dust emission in North America

10.5194/egusphere-egu2020-21883 ◽

2020 ◽

Author(s):

Mark Hennen ◽

Nicholas Webb ◽

Adrian Chappell

Keyword(s):

North America ◽

North American ◽

Surface Wind ◽

Dust Emission ◽

Soil Surface ◽

Ecosystem Change ◽

Management Options ◽

Subjective Analysis ◽

Disturbance Regimes ◽

The Impact

An estimated 50 Mt yr-1 of dust is emitted from North American landscapes, with profound regional impacts (Shao et al., 2011). Dust emission flux in North America is controlled by wind speed and land surface (aerodynamic) roughness that are variable in both space and time. Vegetation growth, form and spatial distribution characterise different ecosystem regimes and protect the soil surface from the shearing stress of the wind. In the dry western US, diverse land use and management drivers create disturbance regimes that produce diverse ecosystem responses that could be drastically impacting rates of wind erosion and dust emission (Ravi et al., 2010). Resolving the impacts of ecosystem change on aeolian processes is needed to quantify anthropogenic-induced dust loads and identify management options as environmental solutions (Webb and Pierre, 2018).Currently, erosion surfaces in North America are derived from satellite imagery, either by spatial analysis of mean aerosol optical depth concentrations (e.g. Ginoux et al., 2012) or point source identification through subjective analysis of individual daily multispectral images (e.g. Lee et al., 2012; Kandakji et al., 2020). In either approach, the results are subjected to spatial and temporal bias caused by a lag in emission-to-observation period and loss of data during cloudy (dust and meteorological) periods. To complement these approaches we produced the first moderate (500 m) resolution daily maps of dust emission across the dry western United States. These maps were based on estimates of soil surface wind friction velocity (us*) derived from MODIS albedo data (Chappell and Webb 2016) using a commonly applied model (Marticorena and Bergammetti, 1995).The North American dust emission climatology from 2001-2018 was compared with the us* data volume to identify the spatio-temporal occurrence of three key disturbance regimes: i) land clearing for energy infrastructure, ii) invasion of shrublands by exotic annual grasses that alter fire regimes, and iii) replacement of grasslands by invasive shrub species. Against this background we examine the state and transition of ecosystem change across these landscapes to understand the impact on current dust emission. We use these findings to comment on the implications for future dust emission and to encourage the development of this modelling approach in Earth System Models. &#160;&#160;&#160;

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Tornado-Resolving Ensemble and Probabilistic Predictions of the 20 May 2013 Newcastle–Moore EF5 Tornado

Monthly Weather Review ◽

10.1175/mwr-d-18-0236.1 ◽

2019 ◽

Vol 147 (4) ◽

pp. 1215-1235 ◽

Cited By ~ 4

Author(s):

Nathan Snook ◽

Ming Xue ◽

Youngsun Jung

Keyword(s):

Characteristic Curve ◽

Surface Wind ◽

Horizontal Wind ◽

Grid Spacing ◽

Ensemble Forecasts ◽

Relative Operating Characteristic ◽

Near Surface ◽

Pressure Drops ◽

Wind Speeds ◽

Horizontal Grid

Abstract An ensemble of 10 forecasts is produced for the 20 May 2013 Newcastle–Moore EF5 tornado and its parent supercell using a horizontal grid spacing of 50 m, nested within ensemble forecasts with 500-m horizontal grid spacing initialized via ensemble Kalman filter data assimilation of surface and radar observations. Tornadic circulations are predicted in all members, though the intensity, track, and longevity of the predicted tornado vary substantially among members. Overall, tornadoes in the ensemble forecasts persisted longer and moved to the northeast faster than the observed tornado. In total, 8 of the 10 ensemble members produce tornadoes with winds corresponding to EF2 intensity or greater, with maximum instantaneous near-surface horizontal wind speeds of up to 130 m s−1 and pressure drops of up to 120 hPa; values similar to those reported in observational studies of intense tornadoes. The predicted intense tornadoes all acquire well-defined two-cell vortex structure, and exhibit features common in observed tornadic storms, including a weak-echo notch and low reflectivity within the mesocyclone. Ensemble-based probabilistic tornado forecasts based upon near-surface wind and/or vorticity fields at 10 m above the surface produce skillful forecasts of the tornado in terms of area under the relative operating characteristic curve, with probability swaths extending along and to the northeast of the observed tornado path. When probabilistic swaths of 0–3- and 2–5-km updraft helicity are compared to the swath of wind at 10 m above the surface exceeding 29 m s−1, a slight northwestward bias is present, although the pathlength, orientation, and the placement of minima and maxima show very strong agreement.

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The impact of Pacific Decadal Oscillation on springtime dust activity in Syria

10.5194/acp-2016-592 ◽

2016 ◽

Author(s):

Bing Pu ◽

Paul Ginoux

Keyword(s):

Middle East ◽

Optical Depth ◽

North Africa ◽

Pacific Decadal Oscillation ◽

Large Scale ◽

Arabian Peninsula ◽

Dust Storms ◽

Near Surface ◽

Deep Blue ◽

The Impact

Abstract. The increasing trend of aerosol optical depth in the Middle East and a recent severe dust storm in Syria have raised questions as whether dust storms will increase and promoted investigations on the dust activities driven by the natural climate variability underlying the ongoing human perturbations such as the Syrian civil war. This study examined the influences of the Pacific decadal oscillation (PDO) on dust activities in Syria using an innovative dust optical depth (DOD) dataset derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products. A significantly negative correlation is found between the Syrian DOD and the PDO in spring from 2003–2015. High DOD in spring is associated with lower geopotential height over the Middle East, Europe, and North Africa, accompanied by near surface anomalous westerly winds over the Mediterranean basin and southerly winds over the eastern Arabian Peninsula. These large-scale patterns promote the formation of the cyclones over the Middle East to trigger dust storms and also facilitate the transport of dust from North Africa, Iraq, and Saudi Arabian to Syria, where the transported dust dominates the seasonal mean DOD in spring. A negative PDO not only creates circulation anomalies favorable to high DOD in Syria but also suppresses precipitation in dust source regions over the eastern and southern Arabian Peninsula and northeastern Africa. On the daily scale, in addition to the favorable large-scale condition associated with a negative PDO, enhanced atmospheric instability in Syria associated with increased precipitation in Turkey and northern Syria is also critical for the development of strong springtime dust storms in Syria.

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Improving surface representation and consequences in NWP forecast

10.5194/ems2021-479 ◽

2021 ◽

Author(s):

Martina Tudor ◽

Stjepan Ivatek-Šahdan

Keyword(s):

Surface Roughness ◽

Surface Wind ◽

Surface Characteristics ◽

Model Forecast ◽

Grid Spacing ◽

Substantial Impact ◽

Wind Speeds ◽

Nwp Model ◽

Surface Fields

The fields that describe surface properties, from terrain height to vegetation types can have substantial impact on NWP model forecast, especially on the model variables close to the surface. These fields can be computed from different databases. Higher resolution of the terrain height database and higher quality of input data leads to a better representation of the terrain height and other surface fields, especially as NWP models move to a higher resolution. Here we use ALARO configuration of the ALADIN System with TOUCANS turbulence scheme (prognostic TKE) with nonhydrostatic dynamics in 2km resolution over Croatia. The model domain contains Dinaric Alps mountains and Adriatic sea.&#160; The existing operational NWP application uses fields from an old database that is insufficient to properly describe the surface in 2km grid spacing. The fields describing topography, such as terrain height, land sea mask, subgrid terrain variability including surface roughness are computed from a new database in substantially higher resolution. The new fields describing the surface characteristics are more realistic, but also substantially different from the fields used before.&#160; However, the model, including the turbulence parametrisation, was tuned using the old database. Therefore, the subsequent model forecast was not automatically improved when the fields from the new database were used. Tuning only one parameter in a scheme is substantial work, but tuning the whole model with a large number of tuning parametres is daunting. Therefore, the computation of surface roughness and other parameters was tuned in order to improve the 10m wind forecast. Decreased surface roughness does not always lead to higher surface wind speeds and vice versa.

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