scholarly journals Impact of the Desert dust on the summer monsoon system over Southwestern North America

2012 ◽  
Vol 12 (8) ◽  
pp. 3717-3731 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
L. R. Leung
Keyword(s):  
North America ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Lower Atmosphere ◽  
Shortwave Radiation ◽  
Western Slope ◽  
Monsoon Circulation ◽  
The North ◽  
Moisture Fluxes ◽  
June July

Abstract. The radiative forcing of dust emitted from the Southwest United States (US) deserts and its impact on monsoon circulation and precipitation over the North America monsoon (NAM) region are simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem) for 15 years (1995–2009). During the monsoon season, dust has a cooling effect (−0.90 W m−2) at the surface, a warming effect (0.40 W m−2) in the atmosphere, and a negative top-of-the-atmosphere (TOA) forcing (−0.50 W m−2) over the deserts on 24-h average. Most of the dust emitted from the deserts concentrates below 800 hPa and accumulates over the western slope of the Rocky Mountains and Mexican Plateau. The absorption of shortwave radiation by dust heats the lower atmosphere by up to 0.5 K day−1 over the western slope of the Mountains. Model sensitivity simulations with and without dust for 15 summers (June-July-August) show that dust heating of the lower atmosphere over the deserts strengthens the low-level southerly moisture fluxes on both sides of the Sierra Madre Occidental. It also results in an eastward migration of NAM-driven moisture convergence over the western slope of the Mountains. These monsoonal circulation changes lead to a statistically significant increase of precipitation by up to ~40 % over the eastern slope of the Mountains (Arizona-New~Mexico-Texas regions). This study highlights the interaction between dust and the NAM system and motivates further investigation of possible dust feedback on monsoon precipitation under climate change and the mega-drought conditions projected for the future.

scholarly journals The impact of Great Basin Desert dust on the summer monsoon system over southwestern North America

2011 ◽  
Vol 11 (12) ◽  
pp. 31735-31767 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
L. R. Leung
Keyword(s):  
North America ◽  
Great Basin ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Lower Atmosphere ◽  
Shortwave Radiation ◽  
Western Slope ◽  
Monsoon Circulation ◽  
Great Basin Desert ◽  
The Impact

Abstract. The radiative forcing of dust emitted from the Great Basin Desert (GBD) and its impact on monsoon circulation and precipitation over the North America monsoon (NAM) region are simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem) for 15 yr (1995–2009). During the monsoon season, dust has a cooling effect (−0.90 W m−2) at the surface, a warming effect (0.40 W m−2) in the atmosphere, and a negative top-of-the-atmosphere (TOA) forcing (−0.50 W m−2) over the GBD region on 24-h average. Most of the dust emitted from the GBD concentrates below 800 hPa and stacks over the western slope of the Rocky Mountains and Mexican Plateau. The absorption of shortwave radiation by dust heats the lower atmosphere by up to 0.5 K day−1 over the western slope of the Mountains. Model sensitivity simulations with and without dust for 15 summers (June-July-August) show that dust heating of the lower atmosphere over the GBD region remotely strengthens the low-level southerly moisture fluxes on both sides of the Sierra Madre Occidental. It also results in an eastward migration of NAM-driven moisture convergence over the western slope of the Mountains. These monsoonal circulation changes lead to a statistically significant increase of precipitation by up to ~40% over the eastern slope of the Mountains (Arizona-New Mexico-Texas regions). This study highlights the interaction between dust and the NAM system and motivates further investigation of possible dust feedback on monsoon precipitation under climate change and the mega-drought conditions projected for the future.

scholarly journals Warm Conveyor Belts and Their Role for Cloud Radiative Forcing in the Extratropical Storm Tracks

2019 ◽  
Vol 32 (16) ◽  
pp. 5325-5343 ◽  
Author(s):  
Hanna Joos
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Storm Tracks ◽  
Shortwave Radiation ◽  
Ice Clouds ◽  
Cloud Band ◽  
Cloud Radiative Forcing ◽  
The North ◽  
Conveyor Belts ◽  
Warm Conveyor Belts

Abstract The link between cloud radiative forcing (CRF) and warm conveyor belts (WCBs), which are strongly ascending airstreams in extratropical cyclones, is investigated based on ERA-Interim reanalysis from 1979 to 2011. Clouds associated with WCBs can be liquid, mixed phase, or ice clouds. They interact with the longwave and shortwave radiation in different ways and thus strongly influence Earth’s radiative budget in the extratropical storm tracks in a complex way. In this study, WCBs are identified with a Lagrangian method, where WCBs are represented by trajectories that rise at least 600 hPa in 48 h in the vicinity of an extratropical cyclone, and CRF is traced along all WCB trajectories during the considered 30-yr period. The results show that due to the poleward ascent of WCBs, they exhibit negative net cloud forcing (NetCRF) in the southern part of the associated cloud band, whereas in their northern part, NetCRF gets positive due to the lack of sunlight in the winter months. This nonuniform CRF along WCBs from low to high latitudes increases the meridional NetCRF gradient. Furthermore, in their outflow regions in the North Atlantic, where WCBs are mainly associated with ice clouds, WCBs contribute up to 10 W m−2 to the global climatological NetCRF maximum in winter. The results highlight the importance of WCBs in modulating the radiative budget in the extratropics. Furthermore, the results emphasize the need for a correct representation of WCBs in climate models to correctly simulate the cloud–circulation coupling.

scholarly journals The vertical structure of cloud radiative heating over the Indian subcontinent during summer monsoon

2015 ◽  
Vol 15 (4) ◽  
pp. 5423-5459 ◽  
Author(s):  
E. Johansson ◽  
A. Devasthale ◽  
T. L'Ecuyer ◽  
A. M. L. Ekman ◽  
M. Tjernström
Keyword(s):  
Vertical Structure ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Deep Convection ◽  
Radiative Heating ◽  
Monsoon Circulation ◽  
Upper Troposphere ◽  
Tropical Tropopause ◽  
Stratiform Clouds ◽  
June July

Abstract. Every year the monsoonal circulation over the Indian subcontinent gives rise to a variety of cloud types that differ considerably in their ability to heat or cool the atmosphere. These clouds in turn affect monsoon dynamics via their radiative impacts, both at the surface and in the atmosphere. New generation of satellites carrying active radar and lidar sensors are allowing realistic quantification of cloud radiative heating (CRH) by resolving the vertical structure of the atmosphere in an unprecedented detail. Obtaining this information is a first step in closing the knowledge gap in our understanding of the role that different clouds play as regulators of the monsoon and vice versa. Here, we use collocated CloudSat-CALIPSO data sets to understand following aspects of cloud-radiation interactions associated with Indian monsoon circulation. (1) How does the vertical distribution of CRH evolve over the Indian continent throughout monsoon season? (2) What is the absolute contribution of different clouds types to the total CRH? (3) How do active and break periods of monsoon affect the distribution of CRH? And finally, (4) what are the net radiative effects of different cloud types on surface heating? In general, the vertical structure of CRH follows the northward migration and the retreat of monsoon from May to October. It is found that the alto- and nimbostratus clouds intensely warm the middle troposphere and equally strongly cool the upper troposphere. Their warming/cooling consistently exceeds ±0.2 K day−1 (after weighing by vertical cloud fraction) in monthly mean composites throughout the middle and upper troposphere respectively, with largest impact observed in June, July and August. Deep convective towers cause considerable warming in the middle and upper troposphere, but strongly cool the base and inside of the tropical tropopause layer (TTL). Such cooling is stronger during active (−1.23 K day−1) monsoon conditions compared to break periods (−0.36 K day−1). The contrasting warming effect of high clouds inside the TTL is found to be double in magnitude during active conditions compared to break periods. It is further shown that stratiform clouds (combining alto- and nimbostratus clouds) and deep convection significantly cool the surface with net radiative effect in the order of −100 and −400 W m−2, respectively, while warming the atmosphere in the order of 40 and 150 W m−2. While deep convection produces strong cooling at the surface during active periods of monsoon, the importance of stratiform clouds, on the other hand, increases during break periods. The contrasting CREs in the atmosphere and at surface, and during active and break conditions, have direct implications for monsoonal circulation.

Comparison of climate response to marine cloud brightening and ocean albedo modification: A model study

2021 ◽  
Author(s):  
Mengying Zhao ◽  
Long Cao ◽  
Lei Duan ◽  
Govindasamy Bala ◽  
Ken Caldeira
Keyword(s):  
Global Warming ◽  
Solar Radiation ◽  
Land Surface ◽  
Radiative Forcing ◽  
Hydrological Cycle ◽  
Lower Atmosphere ◽  
Shortwave Radiation ◽  
Climate Response ◽  
Tropical Ocean ◽  
Climate Effect

<p>Solar radiation modification (SRM), an artificial intervention to reduce the amount of solar radiation reaching the surface, has been proposed as a potential option to ameliorate some undesired consequences of global warming. Marine cloud brightening (MCB) and ocean albedo modification (OAM) are two proposed SRM approaches. MCB aims to cool the planet by increasing marine cloud albedo that might be achieved by injecting sea salt into low marine cloud.  OAM aims to cool the planet by increasing surface ocean albedo that might be achieved by using highly reflective microbubbles over ocean. There is speculation that climate effect of OAM and MCB would be similar as forcing is applied only over ocean in both cases.</p><p>In this study, we use NCAR CESM model to compare climate response in  these two SRM approaches under the framework of “fast versus slow response”. The term “fast” refers to climate adjustment that is associated with rapid adjustment of the atmosphere and land surface, and “slow” refers to climate feedbacks that are associated with the slow evolution of sea surface temperature.</p><p>In our simulation we find that to offset global warming from a doubling of atmospheric CO<sub>2</sub>, OAM requires a stronger negative effective radiative forcing than that of MCB, indicating MCB is more effective in producing cooling per unit of radiative forcing. This is mainly associated with differing fast climate adjustment between OAM and MCB forcing. OAM increases upward shortwave radiation from surface and heats the lower atmosphere, causing low-level clouds to dissipate. A reduction in low cloudiness allows more solar radiation to reach the surface, partly offsetting the negative radiative forcing from increase in ocean albedo. At equilibrium state, however, OAM and MCB produces similar pattern of change in temperature and hydrological cycle, but prominent differences in climate response is observed over the tropical ocean where OAM produces larger reduction in precipitation and evaporation than that of MCB. Our results indicate that there is similarity between climate response to marine cloud brightening and ocean albedo increase, but caution should be exercised when using climate response from one to infer the other. </p>

scholarly journals Radiative impact of mineral dust on monsoon precipitation variability over West Africa

2011 ◽  
Vol 11 (5) ◽  
pp. 1879-1893 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
L. Ruby Leung ◽  
S. Hagos
Keyword(s):  
West Africa ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Atmospheric Stability ◽  
Early Morning ◽  
Surface Energy Budget ◽  
Cooling Effect ◽  
Lower Atmosphere ◽  
Convective Precipitation ◽  
Monsoon Variability

Abstract. The radiative forcing of dust and its impact on precipitation over the West Africa monsoon (WAM) region is simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem). During the monsoon season, dust is a dominant contributor to aerosol optical depth (AOD) over West Africa. In the control simulation, on 24-h domain average, dust has a cooling effect (−6.11 W m−2) at the surface, a warming effect (6.94 W m−2) in the atmosphere, and a relatively small TOA forcing (0.83 W m−2). Dust modifies the surface energy budget and atmospheric diabatic heating. As a result, atmospheric stability is increased in the daytime and reduced in the nighttime, leading to a reduction of late afternoon precipitation by up to 0.14 mm/h (25%) and an increase of nocturnal and early morning precipitation by up to 0.04 mm/h (45%) over the WAM region. Dust-induced reduction of diurnal precipitation variation improves the simulated diurnal cycle of precipitation when compared to measurements. However, daily precipitation is only changed by a relatively small amount (−0.17 mm/day or −4%). The dust-induced change of WAM precipitation is not sensitive to interannual monsoon variability. On the other hand, sensitivity simulations with weaker to stronger absorbing dust (in order to represent the uncertainty in dust solar absorptivity) show that, at the lower atmosphere, dust longwave warming effect in the nighttime surpasses its shortwave cooling effect in the daytime; this leads to a less stable atmosphere associated with more convective precipitation in the nighttime. As a result, the dust-induced change of daily WAM precipitation varies from a significant reduction of −0.52 mm/day (−12%, weaker absorbing dust) to a small increase of 0.03 mm/day (1%, stronger absorbing dust). This variation originates from the competition between dust impact on daytime and nighttime precipitation, which depends on dust shortwave absorption. Dust reduces the diurnal variation of precipitation regardless of its absorptivity, but more reduction is associated with stronger absorbing dust.

Political orientation and moral foundations

2019 ◽  
Vol 118 (11) ◽  
pp. 365-371
Author(s):  
J Dorasamy ◽  
Mr Jirushlan Dorasamy
Keyword(s):  
South Africa ◽  
North America ◽  
American Studies ◽  
Political Orientation ◽  
The Political ◽  
Moral Foundations ◽  
Open Approach ◽  
Online Questionnaire ◽  
Moral Foundation ◽  
The North

Studies, especially in the North America, have shown a relationship between political orientation and moralfoundation. This study investigated whether moral judgements differ from the political orientation of participantsin South Africa moral judgment and the extent to which moral foundations are influenced by politicalorientation.Further, the study investigated the possibility of similar patterns with the North AmericanConservative-Liberal spectrum and the moral foundation. There were 300participants, 78 males and 222 females,who completed an online questionnaire relating to moral foundation and political orientation. The results partiallysupported the hypothesis relating to Liberal and Conservative orientation in South Africa. Further, this studypartially predicted the Liberal-Conservative orientation with patterns in the moral foundation, whilst showingsimilar findings to the North American studies. A growing rate of a neutral/moderate society is evidenced in SouthAfrica and abroad, thereby showing the emergence of a more open approach to both a political and generalstance.”””

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