The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Yi Wang - One of the best experts on this subject based on the ideXlab platform.
-
The early summertime Saharan heat low: sensitivity of the radiation budget and Atmospheric Heating to water vapour and dust aerosol
Atmospheric Chemistry and Physics, 2018Co-Authors: Netsanet K. Alamirew, Martin C. Todd, Claire L. Ryder, John M. Marsham, Yi WangAbstract:Abstract. The Saharan heat low (SHL) is a key component of the west African climate system and an important driver of the west African monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and Atmospheric Heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (21.4 ∘ N, 0.9 ∘ E), close to the SHL core for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top-of-atmosphere (TOA) radiation budget and therefore the column-integrated Heating over the SHL ( ∼ 7 W m −2 per standard deviation of dust aerosol optical depth – AOD). As such, we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface ( ∼ 11 W m −2 per standard deviation of dust AOD), presumably leading to reduced sensible heat flux in the boundary layer, which is more than compensated by direct radiative Heating from shortwave (SW) absorption by dust in the dusty boundary layer. In contrast, water vapour invokes a radiative warming at the surface of ∼ 6 W m −2 per standard deviation of column-integrated water vapour in kg m −2 . Net effects involve a pronounced net Atmospheric radiative convergence with Heating rates on average of 0.5 K day −1 and up to 6 K day −1 during synoptic/mesoscale dust events from monsoon surges and convective cold-pool outflows (“haboobs”). On this basis, we make inferences on the processes driving variability in the SHL associated with radiative and advective Heating/cooling. Depending on the synoptic context over the region, processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m −2 in column-integrated water vapour (equivalent to a change in 2.6 W m −2 TOA net flux) and typically lack variability in dust and thus are expected to poorly represent these couplings. An improved representation of dust and water vapour and quantification of associated radiative impact in models is thus imperative to further understand the SHL and related climate processes.
-
The summertime Saharan heat low: Sensitivity of the radiation budget and Atmospheric Heating to water vapor and dust aerosol
2017Co-Authors: Netsanet K. Alamirew, Martin C. Todd, Claire L. Ryder, John M. Marsham, Yi WangAbstract:Abstract. The Saharan heat low (SHL) is a key component of the West African climate system and an important driver of the West African Monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and Atmospheric Heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (0.9E, 21.4N), close to the SHL core, for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top of atmosphere (TOA) radiation budget and therefore the column integrated Heating over the SHL (~7 W m−2 per standard deviation of dust AOD). As such we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface (~11 W m−2 per standard deviation of dust AOD), presumably leading to reduced sensible heat flux into the boundary layer, which is more than compensated by direct radiative Heating from SW absorption by dust in the dusty boundary layer. In contrast water vapour invokes a longwave radiative warming of at the surface of ~6 W m−2 per standard deviation of column integrated water vapour in Kg m−2. Net effects involve a pronounced net Atmospheric radiative convergence with Heating rates on average of 0.5 K day−1 and up to 6 K day−1 during synoptic/meso-scale dust events from monsoon surges and convective cold pool outflows (‘haboobs’). On this basis we make inferences on the processes driving variability in the SHL associated with radiative and advective Heating/cooling. Depending on the synoptic context over the region processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m−2 in column integrated water vapour (equivalent to a change in 2.6 W m−2 TOA net flux) and typically lack variability in dust, and so are expected to poorly represent these couplings. An improved representation dust and water vapour and quantification of associated radiative impact is thus imperative in quest for the answer to what remains to be uncertain related with the climate system of the SHL region.
Song Yang - One of the best experts on this subject based on the ideXlab platform.
-
Role of Atmospheric Heating over the South China Sea and western Pacific regions in modulating Asian summer climate under the global warming background
Climate Dynamics, 2015Co-Authors: Song YangAbstract:The response of monsoon precipitation to global warming, which is one of the most significant climate change signals at the earth’s surface, exhibits very distinct regional features, especially over the South China Sea (SCS) and adjacent regions in boreal summer. To understand the possible Atmospheric dynamics in these specific regions under the global warming background, changes in Atmospheric Heating and their possible influences on Asian summer climate are investigated by both observational diagnosis and numerical simulations. Results indicate that Heating in the middle troposphere has intensified in the SCS and western Pacific regions in boreal summer, accompanied by increased precipitation, cloud cover, and lower-tropospheric convergence and decreased sea level pressure. Sensitivity experiments show that middle and upper tropospheric Heating causes an east–west feedback pattern between SCS and western Pacific and continental South Asia, which strengthens the South Asian High in the upper troposphere and moist convergence in the lower troposphere, consequently forcing a descending motion and adiabatic warming over continental South Asia. When air–sea interaction is considered, the simulation results are overall more similar to observations, and in particular the bias of precipitation over the Indian Ocean simulated by AGCMs has been reduced. The result highlights the important role of air–sea interaction in understanding the changes in Asian climate.
S. Platnick - One of the best experts on this subject based on the ideXlab platform.
-
Impact of tropospheric nitrogen dioxide on the regional radiation budget
Atmospheric Chemistry and Physics, 2009Co-Authors: A. P. Vasilkov, J. Joiner, L. Oreopoulos, J. F. Gleason, P. Veefkind, E. Bucsela, E. A. Celarier, Robert Spurr, S. PlatnickAbstract:Abstract. Following the launch of several satellite ultraviolet and visible spectrometers including the Ozone Monitoring Instrument (OMI), much has been learned about the global distribution of nitrogen dioxide (NO2). NO2, which is mostly anthropogenic in origin, absorbs solar radiation at ultraviolet and visible wavelengths. We parameterized NO2 absorption for fast radiative transfer calculations. Using this parameterization with cloud, surface, and NO2 information from different sensors in the NASA A-train constellation of satellites and NO2 profiles from the Global Modeling Initiative (GMI), we compute the global distribution of net Atmospheric Heating (NAH) due to tropospheric NO2 for January and July 2005. The globally-averaged NAH values due to tropospheric NO2 are very low: they are about 0.05 W/m2. While the impact of NO2 on the global radiative forcing is small, locally it can produce instantaneous net Atmospheric Heating of 2–4 W/m2 in heavily polluted areas. We assess the impact of clouds and find that they reduce the globally-averaged NAH values by 5–6% only. However, because most of NO2 is contained in the boundary layer in polluted regions, the cloud shielding effect can significantly reduce the net Atmospheric Heating due to tropospheric NO2 (up to 50%). We examine the effect of diurnal variations in NO2 emissions and chemistry on net Atmospheric Heating and find only a small impact of these on the daily-averaged Heating (11–14% at the most). We also examine the sensitivity of NO2 absorption to various geophysical conditions. Effects of the vertical distributions of cloud optical depth and NO2 on net Atmospheric Heating and downwelling radiance are simulated in detail for various scenarios including vertically-inhomogeneous convective clouds observed by CloudSat. The maximum effect of NO2 on downwelling radiance occurs when the NO2 is located in the middle part of the cloud where the optical extinction peaks.
-
Impact of tropospheric nitrogen dioxide on the regional radiation budget
2009Co-Authors: A. P. Vasilkov, J. Joiner, L. Oreopoulos, J. F. Gleason, P. Veefkind, E. Bucsela, E. A. Celarier, R. J. D. Spurr, S. PlatnickAbstract:Abstract. Following the launch of several satellite ultraviolet and visible spectrometers including the Ozone Monitoring Instrument (OMI), much has been learned about the global distribution of nitrogen dioxide (NO2). NO2, which is mostly anthropogenic in origin, absorbs solar radiation at ultraviolet and visible wavelengths. We parameterized NO2 absorption for fast radiative transfer calculations. Using this parameterization with cloud, surface, and NO2 information from different sensors in the NASA A-train constellation of satellites and NO2 profiles from the Global Modeling Initiative (GMI), we compute the global distribution of net Atmospheric Heating due to tropospheric NO2 for January and July 2005. We assess the impact of clouds and find that because most of N02 is contained in the boundary layer in polluted regions, the cloud shielding effect can significantly reduce the net Atmospheric Heating due to NO2. We examine the effect of diurnal variations in NO2 emissions and chemistry on net Atmospheric Heating and find only a small impact of these on the daily-averaged Heating. While the impact of NO2 on the global radiative forcing is small, locally it can produce instantaneous net Atmospheric Heating of 2–4 W/m2 in heavily polluted areas. We also examine the sensitivity of NO2 absorption to various geophysical conditions. Effects of the vertical distributions of cloud optical depth and NO2 on net Atmospheric Heating and downwelling radiance are simulated in detail for various scenarios including vertically-inhomogeneous convective clouds observed by CloudSat. The maximum effect of NO2 on downwelling radiance occurs when the NO2 is located in the middle part of the cloud where the optical extinction peaks.
Netsanet K. Alamirew - One of the best experts on this subject based on the ideXlab platform.
-
The early summertime Saharan heat low: sensitivity of the radiation budget and Atmospheric Heating to water vapour and dust aerosol
Atmospheric Chemistry and Physics, 2018Co-Authors: Netsanet K. Alamirew, Martin C. Todd, Claire L. Ryder, John M. Marsham, Yi WangAbstract:Abstract. The Saharan heat low (SHL) is a key component of the west African climate system and an important driver of the west African monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and Atmospheric Heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (21.4 ∘ N, 0.9 ∘ E), close to the SHL core for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top-of-atmosphere (TOA) radiation budget and therefore the column-integrated Heating over the SHL ( ∼ 7 W m −2 per standard deviation of dust aerosol optical depth – AOD). As such, we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface ( ∼ 11 W m −2 per standard deviation of dust AOD), presumably leading to reduced sensible heat flux in the boundary layer, which is more than compensated by direct radiative Heating from shortwave (SW) absorption by dust in the dusty boundary layer. In contrast, water vapour invokes a radiative warming at the surface of ∼ 6 W m −2 per standard deviation of column-integrated water vapour in kg m −2 . Net effects involve a pronounced net Atmospheric radiative convergence with Heating rates on average of 0.5 K day −1 and up to 6 K day −1 during synoptic/mesoscale dust events from monsoon surges and convective cold-pool outflows (“haboobs”). On this basis, we make inferences on the processes driving variability in the SHL associated with radiative and advective Heating/cooling. Depending on the synoptic context over the region, processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m −2 in column-integrated water vapour (equivalent to a change in 2.6 W m −2 TOA net flux) and typically lack variability in dust and thus are expected to poorly represent these couplings. An improved representation of dust and water vapour and quantification of associated radiative impact in models is thus imperative to further understand the SHL and related climate processes.
-
The summertime Saharan heat low: Sensitivity of the radiation budget and Atmospheric Heating to water vapor and dust aerosol
2017Co-Authors: Netsanet K. Alamirew, Martin C. Todd, Claire L. Ryder, John M. Marsham, Yi WangAbstract:Abstract. The Saharan heat low (SHL) is a key component of the West African climate system and an important driver of the West African Monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and Atmospheric Heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (0.9E, 21.4N), close to the SHL core, for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top of atmosphere (TOA) radiation budget and therefore the column integrated Heating over the SHL (~7 W m−2 per standard deviation of dust AOD). As such we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface (~11 W m−2 per standard deviation of dust AOD), presumably leading to reduced sensible heat flux into the boundary layer, which is more than compensated by direct radiative Heating from SW absorption by dust in the dusty boundary layer. In contrast water vapour invokes a longwave radiative warming of at the surface of ~6 W m−2 per standard deviation of column integrated water vapour in Kg m−2. Net effects involve a pronounced net Atmospheric radiative convergence with Heating rates on average of 0.5 K day−1 and up to 6 K day−1 during synoptic/meso-scale dust events from monsoon surges and convective cold pool outflows (‘haboobs’). On this basis we make inferences on the processes driving variability in the SHL associated with radiative and advective Heating/cooling. Depending on the synoptic context over the region processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m−2 in column integrated water vapour (equivalent to a change in 2.6 W m−2 TOA net flux) and typically lack variability in dust, and so are expected to poorly represent these couplings. An improved representation dust and water vapour and quantification of associated radiative impact is thus imperative in quest for the answer to what remains to be uncertain related with the climate system of the SHL region.
Min Wen - One of the best experts on this subject based on the ideXlab platform.
-
The relationship between heavy precipitation in the eastern region of China and Atmospheric Heating anomalies over the Tibetan Plateau and its surrounding areas
Theoretical and Applied Climatology, 2019Co-Authors: Xiaohui Shi, Jinqiu Chen, Min WenAbstract:The relationships among heavy precipitation in the eastern region of China, the Atmospheric heat source over the Tibetan Plateau and its surrounding areas, and Atmospheric circulation in East Asia were investigated using the multi-variate empirical orthogonal function (MV-EOF) method and synthetic analysis on daily meteorological data from May through August 2010, which were compared with data from 2013. The MV-EOF decomposition results revealed that the Atmospheric Heating over the eastern region of the Tibetan Plateau and the Bay of Bengal exhibited opposite trends when heavy precipitation events occurred in South China, West China, and the middle and lower reaches of the Yangtze River. These results indicated that the land–sea thermal contrast between the eastern region of the Tibetan Plateau and the Bay of Bengal was likely one of the key factors leading to the occurrence of heavy precipitation events in the eastern region of China. The results of the synthetic analysis revealed a possible physical mechanism: When the Atmospheric Heating was weak over the Tibetan Plateau and strong over the Bay of Bengal, there was a strong ascending motion over the Bay of Bengal and its surrounding areas, which was conducive to maintaining the South Asian high and the western Pacific subtropical high (WPSH) in southerly positions. This also resulted in weak water vapor transport in the southwest, thus forming continuous heavy precipitation in South China. After the increase in Atmospheric Heating over the Tibetan Plateau, the convergence and ascending motion of the lower atmosphere were strengthened, and the South Asian high moved northward to the plateau, with a strengthened eastward extension. The WPSH then lifted northward, and the airflow around it conveyed more water vapor to West China and the middle and lower reaches of the Yangtze River, resulting in heavy precipitation in these regions.