scholarly journals Dust radiative effects on atmospheric thermodynamics and tropical cyclogenesis over the Atlantic Ocean using WRF-Chem coupled with an AOD data assimilation system

2017 ◽  
Vol 17 (12) ◽  
pp. 7917-7939 ◽  
Author(s):  
Dan Chen ◽  
Zhiquan Liu ◽  
Chris Davis ◽  
Yu Gu
Keyword(s):  
Boundary Layer ◽  
Data Assimilation ◽  
Atlantic Ocean ◽  
Saharan Dust ◽  
Tropical Cyclogenesis ◽  
Moist Convection ◽  
Radiative Effects ◽  
Modis Aod ◽  
Atmospheric Thermodynamics ◽  
Convective Inhibition

Abstract. This study investigated the dust radiative effects on atmospheric thermodynamics and tropical cyclogenesis over the Atlantic Ocean using the Weather Research and Forecasting Model with Chemistry (WRF-Chem) coupled with an aerosol data assimilation (DA) system. MODIS AOD (aerosol optical depth) data were assimilated with the Gridpoint Statistical Interpolation (GSI) three-dimensional variational (3DVAR) DA scheme to depict the Saharan dust outbreak events in the 2006 summer. Comparisons with Ozone Monitoring Instrument (OMI), AErosol RObotic NETwork (AERONET), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations showed that the system was capable of reproducing the dust distribution. Two sets of 180 h forecasts were conducted with the dust radiative effects activated (RE_ON) and inactivated (RE_OFF) respectively. Differences between the RE_ON and RE_OFF forecasts showed that low-altitude (high-altitude) dust inhibits (favors) convection owing to changes in convective inhibition (CIN). Heating in dust layers immediately above the boundary layer increases inhibition, whereas sufficiently elevated heating allows cooling above the boundary layer that reduces convective inhibition. Semi-direct effects in which clouds are altered by thermodynamic changes are also noted, which then alter cloud-radiative temperature (T) changes. The analysis of a tropical cyclone (TC) suppression case on 5 September shows evidence of enhanced convective inhibition by direct heating in dust, but it also suggests that the low-predictability dynamics of moist convection reduces the determinism of the effects of dust on timescales of TC development (days).

scholarly journals Dust Radiative Effects on Atmospheric Thermodynamics and Tropical Cyclogenesis over the Atlantic Ocean Using WRF/Chem Coupled with an AOD Data Assimilation System

2016 ◽  
Author(s):  
Dan Chen ◽  
Zhiquan Liu ◽  
Chris Davis ◽  
Yu Gu
Keyword(s):  
Boundary Layer ◽  
Data Assimilation ◽  
Atlantic Ocean ◽  
Saharan Dust ◽  
Tropical Cyclogenesis ◽  
Moist Convection ◽  
Radiative Effects ◽  
Modis Aod ◽  
Atmospheric Thermodynamics ◽  
Convective Inhibition

Abstract. This study investigated the dust radiative effects on atmospheric thermodynamics and tropical cyclogenesis over the Atlantic Ocean using WRF-Chem coupled with an aerosol data assimilation (DA) system. MODIS AOD data were assimilated with the Gridpoint Statistical Interpolation three-dimensional variational DA scheme to depict the Saharan dust outbreak events in 2006 summer. Comparisons with Ozone Monitoring Instrument (OMI), AErosol RObotic NETwork (AERONET) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations showed that the system was capable of reproducing the dust distribution. Two sets of 180-hr forecasts were conducted with the dust radiative effects activated (RE_ON) and inactivated (RE_OFF), respectively. Differences between the RE_ON and RE_OFF forecasts showed that low-altitude (high-altitude) dust inhibits (favors) convection owing to changes in convective inhibition. Heating in dust layers immediately above the boundary layer increases inhibition whereas sufficiently elevated heating allows cooling above the boundary layer that reduces convective inhibition. Semi-direct effects are also noted in which clouds are altered by thermodynamic changes, which then alter cloud-radiative temperature changes. The analysis of a tropical cyclone (TC) suppression case on Sep. 5 shows evidence of enhanced convective inhibition by direct heating in dust, but also suggests that the low-predictability dynamics of moist convection reduces the determinism of the effects of dust on time scales of TC development (days).

scholarly journals Effects of Saharan Dust on African Easterly Waves: The Impact of Aerosol-Affected Satellite Radiances on Data Assimilation

2021 ◽  
Author(s):  
Dustin Francis Phillip Grogan ◽  
Cheng-Hsuan Lu ◽  
Shih-Wei Wei ◽  
Sheng-Po Chen
Keyword(s):  
Data Assimilation ◽  
Large Scale ◽  
West African Monsoon ◽  
Forecast Model ◽  
Saharan Dust ◽  
African Easterly Waves ◽  
Radiative Effects ◽  
Easterly Waves ◽  
Brightness Temperatures ◽  
The Impact

Abstract. This study incorporates time-varying aerosols into satellite radiance calculations within the Global Data Assimilation System (GDAS) to investigate its impact on African easterly waves (AEWs) and their environment. Comparison of analysis fields from the aerosol-aware experiment and an aerosol-blind control during August 2017 showed that the aerosol-affected radiances accelerated the African easterly jet and West African monsoon flow; warmed the Saharan boundary layer; and modified the AEW vorticity structure, with increases in the northern circulation and decreases in the southern circulation. Analysis fields from each experiment were used in the Global Forecast System (GFS) to examine differences in forecasting two AEW cases that developed hurricanes over the Atlantic, but were structurally different over North Africa. The aerosol-aware experiment reduced errors in forecasting the AEW case whose northern circulation interacted with a large-scale Saharan dust plume; neutral improvement was found for the other AEW, which did not contain a northern circulation nor interacted with a dust plume. The changes to the analysis fields by the aerosol-aware assimilation are reminiscent of dust radiative effects that operate on AEWs and their environment. That is, the aerosol-affected radiances produce corrections to the brightness temperatures that modify the analysis fields like dust aerosols that are radiatively coupled to the atmospheric variables in the forecast model. We show qualitatively that dust radiative effects are captured by the aerosol-affected radiances for the AEW case that interacted with a dust plume, which served to improve forecasts of the wave downstream.

Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles

Tellus B ◽  
2009 ◽  
Vol 61 (1) ◽  
Author(s):  
Sebastian Otto ◽  
Eike Bierwirth ◽  
Bernadett Weinzierl ◽  
Konrad Kandler ◽  
Michael Esselborn ◽  
...  
Keyword(s):  
Saharan Dust ◽  
Radiative Effects ◽  
Spheroidal Model

Radiative Effects on Boundary-Layer Flow of a Nanofluid on a Continuously Moving or Fixed Permeable Surface

2012 ◽  
Vol 5 (3) ◽  
pp. 176-183 ◽  
Author(s):  
Ali J. Chamkha ◽  
Mohamed Modather ◽  
Saber M.M. EL-Kabeir ◽  
Ahmed M. Rashad
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Permeable Surface ◽  
Radiative Effects ◽  
Layer Flow

scholarly journals New developments in the representation of Saharan dust sources in the aerosol–climate model ECHAM6-HAM2

2016 ◽  
Vol 9 (2) ◽  
pp. 765-777 ◽  
Author(s):  
Bernd Heinold ◽  
Ina Tegen ◽  
Kerstin Schepanski ◽  
Jamie R. Banks
Keyword(s):  
Climate Model ◽  
Dust Emission ◽  
Source Area ◽  
Saharan Dust ◽  
Moist Convection ◽  
Dust Source ◽  
New Developments ◽  
Infrared Imager ◽  
Dust Sources ◽  
Dust Events

Abstract. In the aerosol–climate model ECHAM6-HAM2, dust source activation (DSA) observations from Meteosat Second Generation (MSG) satellite are proposed to replace the original source area parameterization over the Sahara Desert. The new setup is tested in nudged simulations for the period 2007 to 2008. The evaluation is based on comparisons to dust emission events inferred from MSG dust index imagery, Aerosol Robotic Network (AERONET) sun photometer observations, and satellite retrievals of aerosol optical thickness (AOT).The model results agree well with AERONET measurements especially in terms of seasonal variability, and a good spatial correlation was found between model results and MSG-SEVIRI (Spinning-Enhanced Visible and InfraRed Imager) dust AOT as well as Multi-angle Imaging SpectroRadiometer (MISR) AOT. ECHAM6-HAM2 computes a more realistic geographical distribution and up to 20 % higher annual Saharan dust emissions, using the MSG-based source map. The representation of dust AOT is partly improved in the southern Sahara and Sahel. In addition, the spatial variability is increased towards a better agreement with observations depending on the season. Thus, using the MSG DSA map can help to circumvent the issue of uncertain soil input parameters.An important issue remains the need to improve the model representation of moist convection and stable nighttime conditions. Compared to sub-daily DSA information from MSG-SEVIRI and results from a regional model, ECHAM6-HAM2 notably underestimates the important fraction of morning dust events by the breakdown of the nocturnal low-level jet, while a major contribution is from afternoon-to-evening emissions.

scholarly journals On the Impact of Unmanned Aerial System Observations on Numerical Weather Prediction in the Coastal Zone

2018 ◽  
Vol 146 (2) ◽  
pp. 599-622 ◽  
Author(s):  
David D. Flagg ◽  
James D. Doyle ◽  
Teddy R. Holt ◽  
Daniel P. Tyndall ◽  
Clark M. Amerault ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Data Assimilation ◽  
Numerical Weather Prediction ◽  
Research Laboratory ◽  
Weather Prediction ◽  
Ocean Model ◽  
Naval Research ◽  
Unmanned Aerial System ◽  
Numerical Weather ◽  
The Impact

Abstract The Trident Warrior observational field campaign conducted off the U.S. mid-Atlantic coast in July 2013 included the deployment of an unmanned aerial system (UAS) with several payloads on board for atmospheric and oceanic observation. These UAS observations, spanning seven flights over 5 days in the lowest 1550 m above mean sea level, were assimilated into a three-dimensional variational data assimilation (DA) system [the Naval Research Laboratory Atmospheric Variational Data Assimilation System (NAVDAS)] used to generate analyses for a numerical weather prediction model [the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)] with a coupled ocean model [the Naval Research Laboratory Navy Coastal Ocean Model (NCOM)]. The impact of the assimilated UAS observations on short-term atmospheric prediction performance is evaluated and quantified. Observations collected from 50 radiosonde launches during the campaign adjacent to the UAS flight paths serve as model forecast verification. Experiments reveal a substantial reduction of model bias in forecast temperature and moisture profiles consistently throughout the campaign period due to the assimilation of UAS observations. The model error reduction is most substantial in the vicinity of the inversion at the top of the model-estimated boundary layer. Investigations reveal a consistent improvement to prediction of the vertical position, strength, and depth of the boundary layer inversion. The relative impact of UAS observations is explored further with experiments of systematic denial of data streams from the NAVDAS DA system and removal of individual measurement sources on the UAS platform.

scholarly journals Parameter Estimation Using Ensemble-Based Data Assimilation in the Presence of Model Error

2015 ◽  
Vol 143 (5) ◽  
pp. 1568-1582 ◽  
Author(s):  
Juan Ruiz ◽  
Manuel Pulido
Keyword(s):  
Parameter Estimation ◽  
Data Assimilation ◽  
Model Error ◽  
Forecast Skill ◽  
Moist Convection ◽  
Treatment Techniques ◽  
Correction Technique ◽  
Error Treatment ◽  
Data Assimilation System ◽  
Assimilation System

Abstract This work explores the potential of online parameter estimation as a technique for model error treatment under an imperfect model scenario, in an ensemble-based data assimilation system, using a simple atmospheric general circulation model, and an observing system simulation experiment (OSSE) approach. Model error is introduced in the imperfect model scenario by changing the value of the parameters associated with different schemes. The parameters of the moist convection scheme are the only ones to be estimated in the data assimilation system. In this work, parameter estimation is compared and combined with techniques that account for the lack of ensemble spread and for the systematic model error. The OSSEs show that when parameter estimation is combined with model error treatment techniques, multiplicative and additive inflation or a bias correction technique, parameter estimation produces a further improvement of analysis quality and medium-range forecast skill with respect to the OSSEs with model error treatment techniques without parameter estimation. The improvement produced by parameter estimation is mainly a consequence of the optimization of the parameter values. The estimated parameters do not converge to the value used to generate the observations in the imperfect model scenario; however, the analysis error is reduced and the forecast skill is improved.

scholarly journals Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

2015 ◽  
Vol 15 (14) ◽  
pp. 8147-8163 ◽  
Author(s):  
M. Schäfer ◽  
E. Bierwirth ◽  
A. Ehrlich ◽  
E. Jäkel ◽  
M. Wendisch
Keyword(s):  
Boundary Layer ◽  
Radiative Transfer ◽  
Sea Ice ◽  
Three Dimensional ◽  
Open Water ◽  
Radiative Effects ◽  
Arctic Boundary Layer ◽  
Boundary Layer Clouds ◽  
Ice Edge ◽  
Ice Floes

Abstract. Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γλ measurements in the visible spectral range. In cloudy cases the transition of γλ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γλ above bright surfaces in the vicinity of open water, while γλ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of αwater = 0.042 and a sea-ice albedo of αice = 0.91 at 645 nm wavelength). The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0–200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI) in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L; for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500–1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field). The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500–1000 m cloud altitude), which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge results in uncertainties of up to 90 and 30 % in retrievals of τ and effective radius reff, respectively. With the help of Δ L, an estimate of the distance to the ice edge is given, where the retrieval uncertainties due to 3-D radiative effects are negligible.

scholarly journals Observations of the Relationship between 700-mb Temperatures and Severe Weather Reports across the Contiguous United States

2010 ◽  
Vol 25 (2) ◽  
pp. 799-814 ◽  
Author(s):  
Matthew J. Bunkers ◽  
John R. Wetenkamp ◽  
Jeffrey J. Schild ◽  
Anthony Fischer
Keyword(s):  
United States ◽  
Geographic Location ◽  
Careful Examination ◽  
Moist Convection ◽  
Severe Storm ◽  
Convective Inhibition ◽  
Deep Moist Convection ◽  
Time Of Year ◽  
Using Data ◽  
The Relationship

Abstract The relationship between 700-mb temperatures and convective severe storm reports is examined using data from 1993 to 2006 for the contiguous United States. Severe storm reports are used as a rough “proxy” for the occurrence of deep moist convection, and spatial and temporal distributions of 700-mb temperatures associated with these reports are analyzed. Secondarily, the distributions are assessed by individual severe storm report type, and convective inhibition also is evaluated. The motivation for this study is derived from the occasionally used 10°–12°C at 700 mb rule of thumb for estimating the extent and strength of the capping inversion. Whereas there is a semblance of merit for using this rule at times, its utility is shown to be strongly dependent on 1) geographic location, particularly with respect to surface elevation and the frequency of elevated mixed layers, and 2) the time of year. Calculation of convective inhibition, careful examination of the sounding, and assessment of lifting mechanisms likely are more valuable than 700-mb temperatures when forecasting the potential for deep moist convection and severe storms.

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