Convection-Aerosol Interactions in the United Arab Emirates: A Sensitivity Study

Abstract. The Weather Research and Forecasting (WRF) model is used to investigate convection-aerosol interactions in the United Arab Emirates for a summertime convective event. Both an idealised and scaled versions of a 7-year climatological aerosol distribution are considered. The convection on 14 August 2013 was triggered by the low-level convergence of the circulation associated with the Arabian Heat Low (AHL) and the daytime sea-breeze circulation. The cold pools associated with the convective events, as well as the low-level wind convergence along the Intertropical Discontinuity (ITD) earlier in the day, explain the dustier environment, with Aerosol Optical Depths (AODs) in excess of two. Due to a colder surface and air temperature, the AHL is incorrectly represented in WRF, which leads to a mismatch between the observed and modelled clouds and precipitation. Employing interior nudging in the outermost grids of the three-nested simulation has a small but positive impact on the model predictions of the innermost nest. This is because the higher temperatures from more accurate boundary conditions are offset by colder temperatures from locally enhanced precipitation, the latter arising from a shift in the position of the AHL. Numerical experiments revealed a high sensitivity to the aerosol properties. In particular, replacing 20 % of the rural aerosols by carbonaceous particles has an impact on the surface radiative fluxes comparable to increasing the aerosol loading by a factor of 10, with a daily-averaged reduction in the UAE-averaged net shortwave radiation flux of ~90 W m−2 and an increase in the net longwave radiation flux of ~51 W m−2. However, in the former, WRF generates 20 % more precipitation than in the latter, due to a broader and weaker AHL. The surface downward and upward shortwave and upward longwave radiation fluxes are found to scale linearly with the aerosol loading, while the downward longwave radiation flux varies by less than ±12 W m−2 when the aerosol amount and/or properties are changed. An increase in the aerosol loading also leads to drier conditions due to a shift in the position of the AHL and rainfall occurring in a drier region, with a domain-wise decrease in the daily accumulated rainfall of 16 % when the aerosol loading is increased by a factor of 10. In addition, the onset of convection is also delayed.

Download Full-text

Sensitivity of Summertime Convection to Aerosol Loading and Properties in the United Arab Emirates

Atmosphere ◽

10.3390/atmos12121687 ◽

2021 ◽

Vol 12 (12) ◽

pp. 1687

Author(s):

Ricardo Fonseca ◽

Diana Francis ◽

Michael Weston ◽

Narendra Nelli ◽

Sufian Farah ◽

...

Keyword(s):

United Arab Emirates ◽

Wrf Model ◽

Longwave Radiation ◽

High Sensitivity ◽

Sea Breeze ◽

Aerosol Composition ◽

Onset Of Convection ◽

Carbonaceous Particles ◽

Aerosol Loading ◽

Rural Aerosols

The Weather Research and Forecasting (WRF) model is used to investigate convection–aerosol interactions in the United Arab Emirates (UAE) for a summertime convective event. Both an idealized and climatological aerosol distributions are considered. The convection on 14 August 2013 was triggered by the low-level convergence of the cyclonic circulation associated with the Arabian Heat Low (AHL) and the daytime sea-breeze circulation. Numerical experiments reveal a high sensitivity to aerosol properties. In particular, replacing 20% of the rural aerosols by carbonaceous particles has a comparable impact on the surface radiative fluxes to increasing the aerosol loading by a factor of 10. In both cases, the UAE-averaged net shortwave flux is reduced by ~90 W m−2 while the net longwave flux increases by ~51 W m−2. However, when the aerosol composition is changed, WRF generates 20% more precipitation than when the aerosol loading is increased, due to a broader and weaker AHL. The surface downward and upward shortwave and upward longwave radiation fluxes are found to scale linearly with the aerosol loading. An increase in the amount of aerosols also leads to drier conditions and a delay in the onset of convection due to changes in the AHL.

Download Full-text

Trends in surface radiation and cloud radiative effect at four Swiss sites for the 1996–2015 period

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-13227-2019 ◽

2019 ◽

Vol 19 (20) ◽

pp. 13227-13241 ◽

Cited By ~ 3

Author(s):

Stephan Nyeki ◽

Stefan Wacker ◽

Christine Aebi ◽

Julian Gröbner ◽

Giovanni Martucci ◽

...

Keyword(s):

Longwave Radiation ◽

Ground Temperature ◽

Surface Radiation ◽

Specific Humidity ◽

Shortwave Radiation ◽

Radiative Effect ◽

Cloud Properties ◽

Cloud Radiative Effect ◽

Downward Longwave Radiation ◽

Integrated Water Vapour

Abstract. The trends of meteorological parameters and surface downward shortwave radiation (DSR) and downward longwave radiation (DLR) were analysed at four stations (between 370 and 3580 m a.s.l.) in Switzerland for the 1996–2015 period. Ground temperature, specific humidity, and atmospheric integrated water vapour (IWV) trends were positive during all-sky and cloud-free conditions. All-sky DSR and DLR trends were in the ranges of 0.6–4.3 W m−2 decade−1 and 0.9–4.3 W m−2 decade−1, respectively, while corresponding cloud-free trends were −2.9–3.3 W m−2 decade−1 and 2.9–5.4 W m−2 decade−1. Most trends were significant at the 90 % and 95 % confidence levels. The cloud radiative effect (CRE) was determined using radiative-transfer calculations for cloud-free DSR and an empirical scheme for cloud-free DLR. The CRE decreased in magnitude by 0.9–3.1 W m−2 decade−1 (only one trend significant at 90 % confidence level), which implies a change in macrophysical and/or microphysical cloud properties. Between 10 % and 70 % of the increase in DLR is explained by factors other than ground temperature and IWV. A more detailed, long-term quantification of cloud changes is crucial and will be possible in the future, as cloud cameras have been measuring reliably at two of the four stations since 2013.

Download Full-text

The influence of radiation flux in Northwest Pacific on the Western Pacific warm pools and typhoons over the past 170 years

Environmental Research Communications ◽

10.1088/2515-7620/ac3ef5 ◽

2021 ◽

Author(s):

Chai Boyu ◽

Feng Xu ◽

Jianjun Xu ◽

Han Li-guo ◽

CHEN Si-qi ◽

...

Keyword(s):

Radiation Flux ◽

Longwave Radiation ◽

Warm Pool ◽

Western Pacific ◽

Shortwave Radiation ◽

Northwest Pacific ◽

Western Pacific Warm Pool ◽

The Past ◽

Pacific Warm Pool ◽

The Western Pacific

Abstract Based on various statistical methods and empirical orthogonal function (EOF) analysis, this study analyzes the correlation of radiation flux of Northwest Pacific in the 100 years scale with the western Pacific warm pool and typhoon development. The key results are as follows. First, the surface downwelling longwave radiation (SDLR) received by key areas in Northwest Pacific significantly increased over the past 170 years. The surface downwelling shortwave radiation (SDSR) decreased, and TOA (Top of Atmosphere) incident shortwave radiation (TISR) slightly fluctuated and increased in the 11a (11 years) period. Second, there was the strongest correlation between the Western Pacific warm pool and SDLR, and both increased continuously. Third, since 1945, there has been a tendency of increasing after decreasing in the annual frequency and the share of severe typhoons, and the formation area distribution of typhoons has turned more even. Taking 1998 as a cut-off point, before 1998, there was no obvious correlation between the strong typhoon frequency and SDLR. However, such correction became stronger after 1998. They were affected by the changes of SDLR, SDSR, TISR, vapor, vorticity, vertical velocity, SST and h100 . Forth, the SDLR and TISR are major factors influencing the Western Pacific warm pool, typhoon motion and other varieties. While SDLR mainly increases in the tropical areas, TISR tends to fluctuate and increase slightly. Their changes are consistent with the change general characteristics of strengthening of typhoon.

Download Full-text

Evaluation of Surface Radiative Fluxes over the Tropical Oceans in AMIP Simulations

Atmosphere ◽

10.3390/atmos10100606 ◽

2019 ◽

Vol 10 (10) ◽

pp. 606 ◽

Cited By ~ 1

Author(s):

Xin Zhou ◽

Pallav Ray ◽

Kristine Boykin ◽

Bradford S. Barrett ◽

Pang-Chi Hsu

Keyword(s):

Longwave Radiation ◽

Atmospheric Model ◽

Surface Radiation ◽

Shortwave Radiation ◽

Systematic Bias ◽

Model Ensemble ◽

Low Level ◽

Tropical Oceans ◽

Ensemble Mean ◽

Better Than

The performance of 20 models from the Atmospheric Model Intercomparison Project (AMIP) was evaluated concerning surface radiation over the tropical oceans (30° S–30° N) from 1979 to 2000. The model ensemble mean of the net surface shortwave radiation (QSW) was underestimated compared to the International Satellite Cloud Climatology Project (ISCCP) data by 4 W m−2. On the other hand, net longwave radiation (QLW) was overestimated by 4 W m−2, leading to an underestimation of the net surface radiation (Qrad) by 8 W m−2. The most prominent bias in the Qrad appears to be over regions of low-level clouds in the off-equatorial eastern Pacific, eastern Atlantic, and the south-eastern Indian Ocean. The root means squared error of QLW was larger than that of QSW in 17 out of 20 AMIP models. Overestimation of the total cloud cover and atmospheric humidity contributed to the underestimation of Qrad. In general, models with higher horizontal resolutions performed slightly better than those with coarser horizontal resolutions, although some systematic bias persists in all models and in all seasons, in particular, in regions of low-level clouds for QLW, and high-level clouds for QSW. The ensemble mean performed better than most models, but two high-resolution models (GFDL-HIRAM-C180 and GFDL-HIRAM-C360) outperform the model ensemble.

Download Full-text

Analysis of the Radiation Fluxes over Complex Surfaces on the Tibetan Plateau

Water ◽

10.3390/w13213084 ◽

2021 ◽

Vol 13 (21) ◽

pp. 3084

Author(s):

Chunxiao Wang ◽

Yaoming Ma ◽

Binbin Wang ◽

Weiqiang Ma ◽

Xuelong Chen ◽

...

Keyword(s):

Tibetan Plateau ◽

Surface Temperature ◽

Air Temperature ◽

Surface Albedo ◽

Longwave Radiation ◽

Heat Fluxes ◽

Shortwave Radiation ◽

The Tibetan Plateau ◽

Downward Shortwave Radiation ◽

Downward Longwave Radiation

Analysis of long-term, ground-based observation data on the Tibetan Plateau help to enhance our understanding of land-atmosphere interactions and their influence on weather and climate in this region. In this paper, the daily, monthly, and annual averages of radiative fluxes, surface albedo, surface temperature, and air temperature were calculated for the period of 2006 to 2019 at six research stations on the Tibetan Plateau. The surface energy balance characteristics of these six stations, which include alpine meadow, alpine desert, and alpine steppe, were then compared. The downward shortwave radiation at stations BJ, QOMS, and NAMORS was found to decrease during the study period, due to increasing cloudiness. Meanwhile, the upward shortwave radiation and surface albedo at all stations were found to have decreased overall. Downward longwave radiation, upward longwave radiation, net radiation, surface temperature, and air temperature showed increasing trends on inter-annual time scales at most stations. Downward shortwave radiation was maximum in spring at BJ, QOMS, NADORS, and NAMORS, due to the influence of the summer monsoon. Upward shortwave radiation peaked in October and November due to the greater snow cover. BJ, QOMS, NADORS, and NAMORS showed strong sensible heat fluxes in the spring while MAWORS showed strong sensible heat fluxes in the summer. The monthly and diurnal variations of surface albedo at each station were “U” shaped. The diurnal variability of downward longwave radiation at each station was small, ranging from 220 to 295 W·m−2.The diurnal variation in surface temperature at each station slightly lagged behind changes in downward shortwave radiation, and the air temperature, in turn, slightly lagged behind the surface temperature.

Download Full-text

Revising short and longwave radiation archives in view of possible revisions of the WSG and WISG reference scales: Methods and implications

10.5194/amt-2017-41 ◽

2017 ◽

Author(s):

Stephan Nyeki ◽

Stefan Wacker ◽

Julian Gröbner ◽

Wolfgang Finsterle ◽

Martin Wild

Keyword(s):

Time Series ◽

Longwave Radiation ◽

Surface Radiation ◽

Shortwave Radiation ◽

Standard Group ◽

Water Vapour Content ◽

Data Archives ◽

Downward Longwave Radiation ◽

Integrated Water Vapour ◽

A Minor

Abstract. A large number of radiometers are traceable to the World Standard Group (WSG) for shortwave radiation and the interim World Infra-red Standard Group (WISG) for longwave radiation, hosted by the Physikalisch Meteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC, Davos, Switzerland). The WSG and WISG have recently been found to over- and underestimate radiation values, respectively (Fehlmann et al., 2012; Gröbner et al., 2014), although research is still ongoing. In view of a possible revision of the reference scales of both standard groups, this study discusses the methods involved, and the implications on existing archives of radiation time-series, such as the Baseline Surface Radiation Network (BSRN). Based on PMOD/WRC calibration archives and BSRN data archives, the downward longwave radiation (DLR) time-series over the 2006–2015 periods were analysed at four stations (polar and mid-latitude locations). DLR was found to increase by up to 3.5 and 5.4 W m−2, respectively, after applying a WISG reference scale correction and a minor correction for the dependence of pyrgeometer sensitivity on atmospheric integrated water vapour content. Similar increases in DLR may be expected at other BSRN stations. Based on our analysis, a number of recommendations are made for future studies.

Download Full-text

Characterizing energy budget variability at a Sahelian site: a test of NWP model behaviour

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-15095-2017 ◽

2017 ◽

Vol 17 (24) ◽

pp. 15095-15119 ◽

Cited By ~ 1

Author(s):

Anna Mackie ◽

Paul I. Palmer ◽

Helen Brindley

Keyword(s):

Energy Budget ◽

Radiation Flux ◽

Linear Models ◽

Longwave Radiation ◽

Surface Radiation ◽

Radiation Budget ◽

Shortwave Radiation ◽

Daily Average ◽

Radiation Fluxes ◽

Nwp Model

Abstract. We use observations of surface and top-of-the-atmosphere (TOA) broadband radiation fluxes determined from the Atmospheric Radiation Measurement programme mobile facility, the Geostationary Earth Radiation Budget (GERB) and Spinning Enhanced Visible and Infrared Imager (SEVIRI) instruments and a range of meteorological variables at a site in the Sahel to test the ability of the ECMWF Integrated Forecasting System cycle 43r1 to describe energy budget variability. The model has daily average biases of −12 and 18 W m−2 for outgoing longwave and reflected shortwave TOA radiation fluxes, respectively. At the surface, the daily average bias is 12(13) W m−2 for the longwave downwelling (upwelling) radiation flux and −21(−13) W m−2 for the shortwave downwelling (upwelling) radiation flux. Using multivariate linear models of observation–model differences, we attribute radiation flux discrepancies to physical processes, and link surface and TOA fluxes. We find that model biases in surface radiation fluxes are mainly due to a low bias in ice water path (IWP), poor description of surface albedo and model–observation differences in surface temperature. We also attribute observed discrepancies in the radiation fluxes, particularly during the dry season, to the misrepresentation of aerosol fields in the model from use of a climatology instead of a dynamic approach. At the TOA, the low IWP impacts the amount of reflected shortwave radiation while biases in outgoing longwave radiation are additionally coupled to discrepancies in the surface upwelling longwave flux and atmospheric humidity.

Download Full-text

Revising shortwave and longwave radiation archives in view of possible revisions of the WSG and WISG reference scales: methods and implications

Atmospheric Measurement Techniques ◽

10.5194/amt-10-3057-2017 ◽

2017 ◽

Vol 10 (8) ◽

pp. 3057-3071 ◽

Cited By ~ 6

Author(s):

Stephan Nyeki ◽

Stefan Wacker ◽

Julian Gröbner ◽

Wolfgang Finsterle ◽

Martin Wild

Keyword(s):

Time Series ◽

Longwave Radiation ◽

Surface Radiation ◽

Shortwave Radiation ◽

Standard Group ◽

Water Vapour Content ◽

Data Archives ◽

Downward Longwave Radiation ◽

Integrated Water Vapour ◽

A Minor

Abstract. A large number of radiometers are traceable to the World Standard Group (WSG) for shortwave radiation and the interim World Infrared Standard Group (WISG) for longwave radiation, hosted by the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC, Davos, Switzerland). The WSG and WISG have recently been found to over- and underestimate radiation values, respectively (Fehlmann et al., 2012; Gröbner et al., 2014), although research is still ongoing. In view of a possible revision of the reference scales of both standard groups, this study discusses the methods involved and the implications on existing archives of radiation time series, such as the Baseline Surface Radiation Network (BSRN). Based on PMOD/WRC calibration archives and BSRN data archives, the downward longwave radiation (DLR) time series over the 2006–2015 period were analysed at four stations (polar and mid-latitude locations). DLR was found to increase by up to 3.5 and 5.4 W m−2 for all-sky and clear-sky conditions, respectively, after applying a WISG reference scale correction and a minor correction for the dependence of pyrgeometer sensitivity on atmospheric integrated water vapour content. Similar increases in DLR may be expected at other BSRN stations. Based on our analysis, a number of recommendations are made for future studies.

Download Full-text

Simulation of Late Summer Arctic Clouds during ASCOS with Polar WRF

Monthly Weather Review ◽

10.1175/mwr-d-16-0079.1 ◽

2017 ◽

Vol 145 (2) ◽

pp. 521-541 ◽

Cited By ~ 22

Author(s):

Keith M. Hines ◽

David H. Bromwich

Keyword(s):

Liquid Water ◽

Climate Models ◽

Longwave Radiation ◽

Late Summer ◽

Shortwave Radiation ◽

The Arctic ◽

Microphysics Scheme ◽

Cloud Liquid Water ◽

Low Level ◽

Outer Domain

Low-level clouds are extensive in the Arctic and contribute to inadequately understood feedbacks within the changing regional climate. The simulation of low-level clouds, including mixed-phase clouds, over the Arctic Ocean during summer and autumn remains a challenge for both real-time weather forecasts and climate models. Here, improved cloud representations are sought with high-resolution mesoscale simulations of the August–September 2008 Arctic Summer Cloud Ocean Study (ASCOS) with the latest polar-optimized version (3.7.1) of the Weather Research and Forecasting (Polar WRF) Model with the advanced two-moment Morrison microphysics scheme. Simulations across several synoptic regimes for 10 August–3 September 2008 are performed with three domains including an outer domain at 27-km grid spacing and nested domains at 9- and 3-km spacing. These are realistic horizontal grid spacings for common mesoscale applications. The control simulation produces excessive cloud liquid water in low clouds resulting in a large deficit in modeled incident shortwave radiation at the surface. Incident longwave radiation is less sensitive. A change in the sea ice albedo toward the larger observed values during ASCOS resulted in somewhat more realistic simulations. More importantly, sensitivity tests show that a reduction in specified liquid cloud droplet number to very pristine conditions increases liquid precipitation, greatly reduces the excess in simulated low-level cloud liquid water, and improves the simulated incident shortwave and longwave radiation at the surface.

Download Full-text

Characteristics of Turbulence and Aerosol Optical and Radiative Properties during Haze–Fog Episodes in Shenyang, Northeast China

Atmosphere ◽

10.3390/atmos12121658 ◽

2021 ◽

Vol 12 (12) ◽

pp. 1658

Author(s):

Xiaolan Li ◽

Yanjun Ma ◽

Yangfeng Wang ◽

Shuo Lu ◽

Hujia Zhao ◽

...

Keyword(s):

Northeast China ◽

Longwave Radiation ◽

Dynamic Structure ◽

Radiative Properties ◽

Shortwave Radiation ◽

Aerosol Layer ◽

Mixed Episode ◽

Downward Longwave Radiation ◽

Haze Episode ◽

Pm2.5 Concentration

The characteristics of turbulence in the planetary boundary layer (PBL) and the aerosol optical and radiative properties during haze and haze–fog mixed episodes on 22–27 January 2021, in Shenyang, a provincial city in Northeast China, were analyzed using meteorological and aerosol observations. During the haze episode, the hourly mean PM2.5 concentration reached a maximum of 337 µg m−3 and visibility decreased to 1.6 km. The PM2.5 concentration decreased gradually during the haze–fog mixed episode as a result of the scavenging effects of fog, but visibility mostly remained below 1 km owing to high ambient relative humidity (>90%). During the haze–fog mixed episode, an increasing proportion of PM2.5 led to a higher ratio of the backward to the total scattering coefficient. As fog occurred, downward shortwave radiation arriving at the surface was significantly reduced, and upward longwave radiation increased and almost equaled the downward longwave radiation, which can be used as a good indicator for distinguishing haze and fog. Mechanical turbulence was weak during both episodes, and latent heat flux varied within a wider range during the haze–fog mixed episode. The PBL dynamic structure affected the vertical distribution of aerosols/fog droplets. Aerosol-rich layers appeared at altitudes below 0.5 km and above 0.6 km during the haze episode. The elevated aerosol layer was related to the aerosol transport from upstream polluted areas caused by strong upper-level turbulence, and it began to mix vertically after sunrise because of convective turbulence. Aerosols and fog droplets were mostly trapped in a shallower PBL with a height of 0.2–0.4 km during the haze–fog mixed episode because of weaker turbulence.

Download Full-text