Variability of Total Latent Heating Rate over Three Climatic Zones in West Africa

Abstract. The radiative forcing due to mineral dust over West Africa is investigated using the radiative code STREAMER, as well as remote sensing and in situ observations gathered during the African Monsoon Multidisciplinary Analysis Special Observing Period (AMMA SOP). We focus on two days (13 and 14 June 2006) of an intense and long-lasting episode of dust being lifted in remote sources in Chad and Sudan and transported across West Africa in the African easterly jet region, during which airborne operations were conducted at the regional scale, from the southern fringes of the Sahara to the Gulf of Guinea. Profiles of heating rates are computed from airborne LEANDRE 2 and space-borne CALIOP lidar observations using two mineral dust model constrained by airborne in situ data and ground-based sunphotometer obtained during the campaign. Complementary space-borne observations (from MODIS) and in-situ observations such as dropsondes are also used to take into account a realistic infrared contribution of the water vapour. We investigate the variability of the heating rate on the vertical within a dust plume, as well as the contribution of longwave radiation to the heating rate and the radiative forcing of dust during the nighttime. The sensitivity of the so-derived heating rate is also analyzed for some key variables for which the associated uncertainties are quite large. During daytime, the warming associated with the presence of dust was found to be between 1.5 K day−1 and 4 K day−1, on average, depending on altitude and latitude. Strong warming (i.e. heating rates as high as 8 K day−1) was also observed locally in some limited part of the dust plumes. Obviously, during nighttime much smaller values of heating/cooling are retrieved (less than ±1 K day−1) but large enough to modify the low tropospheric equilibrium. Furthermore, cooling is observed as the result of the longwave forcing in the dust layer, while warming is observed below the dust layer, in the monsoon layer.

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Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-7143-2009 ◽

2009 ◽

Vol 9 (18) ◽

pp. 7143-7160 ◽

Cited By ~ 82

Author(s):

M. Mallet ◽

P. Tulet ◽

D. Serça ◽

F. Solmon ◽

O. Dubovik ◽

...

Keyword(s):

West Africa ◽

Surface Temperature ◽

Heating Rate ◽

Mineral Dust ◽

Convective Available Potential Energy ◽

Atmospheric Model ◽

Heat Fluxes ◽

Convective Activity ◽

Sensible Heat ◽

Dust Aerosols

Abstract. The present work analyses the effect of dust aerosols on the surface and top of atmosphere radiative budget, surface temperature, sensible heat fluxes, atmospheric heating rate and convective activity over West Africa. The study is focused on the regional impact of a major dust event over the period of 7–14 March 2006 through numerical simulations performed with the mesoscale, nonhydrostatic atmospheric model MesoNH. Due to its importance on radiative budgets, a specific attention has been paid to the representation of dust single scattering albedo (SSA) in MesoNH by using inversions of the AErosol RObotic NETwork (AERONET). The radiative impacts are estimated using two parallel simulations, one including radiative effects of dust and the other without them. The simulations of dust aerosol impacts on the radiative budget indicate remarkable instantaneous (at midday) decrease of surface shortwave (SW) radiations over land, with regional (9°–17° N, 10° W–20° E) mean of −137 W/m2 during the 9 to 12 March period. The surface dimming resulting from the presence of dust is shown to cause important reduction of both surface temperature (up to 4°C) and sensible heat fluxes (up to 100 W/m2), which is consistent with experimental observations. At the top of the atmosphere, the SW cooling (regional mean of −12.0 W/m2) induced by mineral dust is shown to dominate the total net (shortwave + longwave) effect. The maximum SW heating occurs within the dusty layer with values comprised between 4 and 7° K by day and LW effect results in a cooling of −0.10/−0.20° K by day. Finally, the simulations suggest the decrease of the convective available potential energy (CAPE) over the region in the presence of mineral dust.

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Radiative Cooling, Latent Heating, and Cloud Ice in the Tropical Upper Troposphere

Journal of Climate ◽

10.1175/jcli-d-21-0444.1 ◽

2021 ◽

pp. 1-39

Keyword(s):

Heating Rate ◽

Radiative Cooling ◽

Convective Heating ◽

Tropospheric Temperature ◽

Latent Heating ◽

Upper Troposphere ◽

Eddy Heat Flux ◽

Cloud Ice ◽

The Impact ◽

Tropical Upper Troposphere

Abstract The radiative cooling rate in the tropical upper troposphere is expected to increase as climate warms. Since the tropics are approximately in radiative-convective equilibrium (RCE), this implies an increase in the convective heating rate, which is the sum of the latent heating rate and the eddy heat flux convergence. We examine the impact of these changes on the vertical profile of cloud ice amount in cloud-resolving simulations of RCE. Three simulations are conducted: a control run, a warming run, and an experimental run in which there is no warming but a temperature forcing is imposed to mimic the warming-induced increase in radiative cooling. Surface warming causes a reduction in cloud fraction at all upper tropospheric temperature levels but an increase in the ice mixing ratio within deep convective cores. The experimental run has more cloud ice than the warming run at fixed temperature despite the fact that their latent heating rates are equal, which suggests that the efficiency of latent heating by cloud ice increases with warming. An analytic expression relating the ice-related latent heating rate to a number of other factors is derived and used to understand the model results. This reveals that the increase in latent heating efficiency is driven mostly by 1) the migration of isotherms to lower pressure and 2) a slight warming of the top of the convective layer. These physically robust changes act to reduce the residence time of ice along at any particular temperature level, which tempers the response of the mean cloud ice profile to warming.

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A Simplified Algorithm to Estimate Latent Heating Rate Using Vertical Rainfall Profiles Over the Tibetan Plateau

Journal of Geophysical Research Atmospheres ◽

10.1029/2018jd029297 ◽

2019 ◽

Vol 124 (2) ◽

pp. 942-963 ◽

Cited By ~ 3

Author(s):

Rui Li ◽

Wencheng Shao ◽

Jingchao Guo ◽

Yunfei Fu ◽

Yu Wang ◽

...

Keyword(s):

Tibetan Plateau ◽

Heating Rate ◽

The Tibetan Plateau ◽

Latent Heating ◽

Simplified Algorithm

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Radiative heating rates profiles associated with a springtime case of Bodélé and Sudan dust transport over West Africa

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-8131-2010 ◽

2010 ◽

Vol 10 (17) ◽

pp. 8131-8150 ◽

Cited By ~ 42

Author(s):

C. Lemaître ◽

C. Flamant ◽

J. Cuesta ◽

J.-C. Raut ◽

P. Chazette ◽

...

Keyword(s):

West Africa ◽

Heating Rate ◽

Mineral Dust ◽

Regional Scale ◽

Longwave Radiation ◽

Radiative Heating ◽

Heating Rates ◽

Dust Layer ◽

In Situ Observations

Abstract. The radiative heating rate due to mineral dust over West Africa is investigated using the radiative code STREAMER, as well as remote sensing and in situ observations gathered during the African Monsoon Multidisciplinary Analysis Special Observing Period (AMMA SOP). We focus on two days (13 and 14 June 2006) of an intense and long lasting episode of dust being lifted in remote sources in Chad and Sudan and transported across West Africa in the African easterly jet region, during which airborne operations were conducted at the regional scale, from the southern fringes of the Sahara to the Gulf of Guinea. Profiles of heating rates are computed from airborne LEANDRE 2 (Lidar Embarqué pour l'étude de l'Atmosphère: Nuages Dynamique, Rayonnement et cycle de l'Eau) and space-borne CALIOP (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) lidar observations using two mineral dust model constrained by airborne in situ data and ground-based sunphotometer obtained during the campaign. Complementary spaceborne observations (from the Moderate-resolution Imaging Spectroradiometer-MODIS) and in-situ observations such as dropsondes are also used to take into account the infrared contribution of the water vapour. We investigate the variability of the heating rate on the vertical within a dust plume, as well as the contribution of both shortwave and longwave radiation to the heating rate and the radiative heating rate profiles of dust during daytime and nighttime. The sensitivity of the so-derived heating rate is also analyzed for some key variables for which the associated uncertainties may be large. During daytime, the warming associated with the presence of dust was found to be between 1.5 K day−1 and 4 K day−1, on average, depending on altitude and latitude. Strong warming (i.e. heating rates as high as 8 K day−1) was also observed locally in some limited part of the dust plumes. The uncertainty on the heating rate retrievals in the optically thickest part of the dust plume was estimated to be between 0.5 and 1.4 K day−1. During nighttime much smaller values of heating/cooling are retrieved (less than ±1 K day−1). Furthermore, cooling is observed as the result of the longwave forcing in the dust layer, while warming is observed below the dust layer, in the monsoon layer.

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IMPETUS West Africa An Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa — Case Studies for Selected River Catchments in Different Climatic Zones

Water in the Middle East and in North Africa ◽

10.1007/978-3-662-10866-6_23 ◽

2004 ◽

pp. 275-286 ◽

Cited By ~ 1

Author(s):

P. Speth ◽

M. Christoph

Keyword(s):

Water Resources ◽

West Africa ◽

Case Studies ◽

Integrated Approach ◽

Climatic Zones ◽

Efficient Management ◽

Scarce Water ◽

River Catchments

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Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-2967-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 2967-3006 ◽

Cited By ~ 6

Author(s):

M. Mallet ◽

P. Tulet ◽

D. Serça ◽

F. Solmon ◽

O. Dubovik ◽

...

Keyword(s):

West Africa ◽

Surface Temperature ◽

Heating Rate ◽

Mineral Dust ◽

Cloud Microphysics ◽

Heat Fluxes ◽

Radiative Properties ◽

Convective Activity ◽

Sensible Heat ◽

Dust Aerosols

Abstract. The present work analyzes the effect of dust aerosols on the surface and top of atmosphere radiative budget, surface temperature, sensible heat fluxes, atmospheric heating rate and convective activity over West Africa. The study is focused on the regional impact of a major dust event over the period of 9–13 March. Numerical simulations have been performed with the MesoNH model in which full interactions between radiation and dynamics are introduced, through various components representing size-resolved aerosol and cloud microphysics, radiative properties of particles and clouds, dynamics, and a surface model. Due to its importance on radiative budgets, a specific attention has been paid to the representation of dust SSA in MesoNH by using AERONET inversions. The radiative impacts are estimated using two parallel simulations, one including radiative effects of dust and the other without them. The simulations of dust aerosol impacts on the radiative budget indicate remarkable instantaneous decrease of shortwave (SW) radiations, with regional (09°–17° N, 10° W–20° E) mean of −160 W/m2 during the 9 to 13 March period. The surface dimming resulting from the presence of dust is shown to cause important reduction of both surface temperature (up to 4°C over regions where high AODs occur) and sensible heat fluxes (up to 100 W/m2), which is consistent with experimental observations performed over the same region. At the top of the atmosphere, the SW cooling (regional mean of −13.5 W/m2) induced by mineral dust, although moderated by the longwave (LW) warming (regional mean of +5 W/m2), dominates the total net (shortwave + longwave) effect. The maximum SW heating occurs within the dusty layer with values comprised between 4 and 7°K by day and LW effect results in strong cooling (−6 to −16°K by day) below the dust layer. Finally, the simulations suggest the decrease of the convective available potential energy (CAPE) over the region in the presence of mineral dust.

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