15 results on '"D'amato, T."'
Search Results
2. Downslope Winds and Dust Storms in the Salton Basin
- Author
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Evan, Amato T, Evan, Amato T, Evan, Amato T, and Evan, Amato T
- Abstract
The Salton basin is a closed, subsea level basin located in extreme southeastern California. At the center of the basin lies the Salton Sea, the state’s largest inland lake, which is surrounded by a desert landscape characterized by paleo lakebed surfaces, dry washes, alluvial fans, and interdunes. Dust storms are common occurrence in this region. However, despite the regularity of dust outbreaks here, little is known about the meteorological processes responsible for these storms. Here I use observations and output from reanalysis to elucidate the meteorological controls on dust emission events in the Salton basin during 2015–18. Analysis of surface and upper-air observations, satellite data, and reanalysis, suggest that the largest dust storms in the region are associated with an upper-level low centered near the coastline of western Canada, which directs a zonal low-level jet over the region. Flow blocking by a coastal mountain range results in isentropic drawdown of air in the lee of these mountains. Once surface warming at the floor of the Salton basin is sufficient such that the density of the descending air is greater than that of the ambient air at the surface, the downslope windstorm reaches the desert floor and initiates dust emission. This process may also be accompanied by a downwind propagating hydraulic jump. These processes appear to be similar to those responsible for the strongest dust events in the Owens Valley, and may represent the main mechanisms for emission from other closed basins. more...
- Published
- 2019
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3. A New Method to Characterize Changes in the Seasonal Cycle of Snowpack
- Author
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Evan, Amato T, Evan, Amato T, Evan, Amato T, and Evan, Amato T
- Abstract
In the western United States, water stored as mountain snowpack is a large percentage of the total water needed to meet the region’s demands, and it is likely that, as the planet continues to warm, mountain snowpack will decline. However, detecting such trends in the observational record is challenging because snowpack is highly variable in both space and time. Here, a method for characterizing mountain snowpack is developed that is based on fitting observed annual cycles of snow water equivalent (SWE) to a gamma-distribution probability density function. A new method for spatially interpolating the distribution’s fitting parameters to create a gridded climatology of SWE is also presented. Analysis of these data shows robust trends in the shape of the annual cycle of snowpack in the western United States. Over the 1982–2017 water years, the annual cycle of snowpack is becoming narrower and more Gaussian. A narrowing of the annual cycle corresponds to a shrinking of the length of the winter season, primarily because snowpack melting is commencing earlier in the water year. Because the annual cycle of snowpack at high elevations tends to be more skewed than at lower elevations, a more Gaussian shape suggests that snowpack is becoming more characteristic of that at lower elevations. Although no robust downward trends in annual-mean SWE are found, robust trends in the shape of the SWE annual cycle have implications for regional water resources. more...
- Published
- 2019
4. Downslope Winds and Dust Storms in the Salton Basin
- Author
-
Evan, Amato T, Evan, Amato T, Evan, Amato T, and Evan, Amato T
- Abstract
The Salton basin is a closed, subsea level basin located in extreme southeastern California. At the center of the basin lies the Salton Sea, the state’s largest inland lake, which is surrounded by a desert landscape characterized by paleo lakebed surfaces, dry washes, alluvial fans, and interdunes. Dust storms are common occurrence in this region. However, despite the regularity of dust outbreaks here, little is known about the meteorological processes responsible for these storms. Here I use observations and output from reanalysis to elucidate the meteorological controls on dust emission events in the Salton basin during 2015–18. Analysis of surface and upper-air observations, satellite data, and reanalysis, suggest that the largest dust storms in the region are associated with an upper-level low centered near the coastline of western Canada, which directs a zonal low-level jet over the region. Flow blocking by a coastal mountain range results in isentropic drawdown of air in the lee of these mountains. Once surface warming at the floor of the Salton basin is sufficient such that the density of the descending air is greater than that of the ambient air at the surface, the downslope windstorm reaches the desert floor and initiates dust emission. This process may also be accompanied by a downwind propagating hydraulic jump. These processes appear to be similar to those responsible for the strongest dust events in the Owens Valley, and may represent the main mechanisms for emission from other closed basins. more...
- Published
- 2019
5. A New Method to Characterize Changes in the Seasonal Cycle of Snowpack
- Author
-
Evan, Amato T, Evan, Amato T, Evan, Amato T, and Evan, Amato T
- Abstract
In the western United States, water stored as mountain snowpack is a large percentage of the total water needed to meet the region’s demands, and it is likely that, as the planet continues to warm, mountain snowpack will decline. However, detecting such trends in the observational record is challenging because snowpack is highly variable in both space and time. Here, a method for characterizing mountain snowpack is developed that is based on fitting observed annual cycles of snow water equivalent (SWE) to a gamma-distribution probability density function. A new method for spatially interpolating the distribution’s fitting parameters to create a gridded climatology of SWE is also presented. Analysis of these data shows robust trends in the shape of the annual cycle of snowpack in the western United States. Over the 1982–2017 water years, the annual cycle of snowpack is becoming narrower and more Gaussian. A narrowing of the annual cycle corresponds to a shrinking of the length of the winter season, primarily because snowpack melting is commencing earlier in the water year. Because the annual cycle of snowpack at high elevations tends to be more skewed than at lower elevations, a more Gaussian shape suggests that snowpack is becoming more characteristic of that at lower elevations. Although no robust downward trends in annual-mean SWE are found, robust trends in the shape of the SWE annual cycle have implications for regional water resources. more...
- Published
- 2019
6. A new satellite-based global climatology of dust aerosol optical depth A new satellite-based global climatology of dust aerosol optical depth
- Author
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Voss, Kara K, Voss, Kara K, Evan, Amato T, Voss, Kara K, Voss, Kara K, and Evan, Amato T
- Published
- 2020
7. Global and regional importance of the direct dust-climate feedback.
- Author
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Kok, Jasper F, Kok, Jasper F, Ward, Daniel S, Mahowald, Natalie M, Evan, Amato T, Kok, Jasper F, Kok, Jasper F, Ward, Daniel S, Mahowald, Natalie M, and Evan, Amato T
- Abstract
Feedbacks between the global dust cycle and the climate system might have amplified past climate changes. Yet, it remains unclear what role the dust-climate feedback will play in future anthropogenic climate change. Here, we estimate the direct dust-climate feedback, arising from changes in the dust direct radiative effect (DRE), using a simple theoretical framework that combines constraints on the dust DRE with a series of climate model results. We find that the direct dust-climate feedback is likely in the range of -0.04 to +0.02 Wm -2 K-1, such that it could account for a substantial fraction of the total aerosol feedbacks in the climate system. On a regional scale, the direct dust-climate feedback is enhanced by approximately an order of magnitude close to major source regions. This suggests that it could play an important role in shaping the future climates of Northern Africa, the Sahel, the Mediterranean region, the Middle East, and Central Asia. more...
- Published
- 2018
8. Global and regional importance of the direct dust-climate feedback.
- Author
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Kok, Jasper F, Kok, Jasper F, Ward, Daniel S, Mahowald, Natalie M, Evan, Amato T, Kok, Jasper F, Kok, Jasper F, Ward, Daniel S, Mahowald, Natalie M, and Evan, Amato T
- Abstract
Feedbacks between the global dust cycle and the climate system might have amplified past climate changes. Yet, it remains unclear what role the dust-climate feedback will play in future anthropogenic climate change. Here, we estimate the direct dust-climate feedback, arising from changes in the dust direct radiative effect (DRE), using a simple theoretical framework that combines constraints on the dust DRE with a series of climate model results. We find that the direct dust-climate feedback is likely in the range of -0.04 to +0.02 Wm -2 K-1, such that it could account for a substantial fraction of the total aerosol feedbacks in the climate system. On a regional scale, the direct dust-climate feedback is enhanced by approximately an order of magnitude close to major source regions. This suggests that it could play an important role in shaping the future climates of Northern Africa, the Sahel, the Mediterranean region, the Middle East, and Central Asia. more...
- Published
- 2018
9. On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low-forced winds.
- Author
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Wang, Weijie, Wang, Weijie, Evan, Amato T, Flamant, Cyrille, Lavaysse, Christophe, Wang, Weijie, Wang, Weijie, Evan, Amato T, Flamant, Cyrille, and Lavaysse, Christophe
- Abstract
A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous-year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. We reconcile this contradiction showing that interannual variability in Sahelian rainfall and surface wind speeds over the Sahara are the result of changes in lower tropospheric air temperatures over the Saharan heat low (SHL). As the SHL warms, an anomalous tropospheric circulation develops that reduces wind speeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust "hotspots" in the Sahara. Our results shed light on why climate models are, to date, unable to reproduce observed historical variability in dust emission and transport from this region. more...
- Published
- 2015
10. On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low-forced winds.
- Author
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Wang, Weijie, Wang, Weijie, Evan, Amato T, Flamant, Cyrille, Lavaysse, Christophe, Wang, Weijie, Wang, Weijie, Evan, Amato T, Flamant, Cyrille, and Lavaysse, Christophe
- Abstract
A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous-year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. We reconcile this contradiction showing that interannual variability in Sahelian rainfall and surface wind speeds over the Sahara are the result of changes in lower tropospheric air temperatures over the Saharan heat low (SHL). As the SHL warms, an anomalous tropospheric circulation develops that reduces wind speeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust "hotspots" in the Sahara. Our results shed light on why climate models are, to date, unable to reproduce observed historical variability in dust emission and transport from this region. more...
- Published
- 2015
11. Derivation of an observation-based map of North African dust emission
- Author
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Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, Doherty, Owen, Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, and Doherty, Owen more...
- Abstract
Highlights: • North African dust emission and emission frequency from six models are examined. • There is a power law relationship between emission and emission event frequency. • The lognormal distribution of surface winds gives rise to this power law relation. • Annual North Africa dust emission is estimated via satellite retrievals of emission frequency. • We estimate that 82% of all North Africa dust emission is between 15° and 20°N. Abstract: Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodélé depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Aïr and Hoggar Mountains, making this area the second most important region of emission within North Africa. more...
- Published
- 2015
- Full Text
- View/download PDF
12. Derivation of an observation-based map of North African dust emission
- Author
-
Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, Doherty, Owen, Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, and Doherty, Owen more...
- Abstract
Highlights: • North African dust emission and emission frequency from six models are examined. • There is a power law relationship between emission and emission event frequency. • The lognormal distribution of surface winds gives rise to this power law relation. • Annual North Africa dust emission is estimated via satellite retrievals of emission frequency. • We estimate that 82% of all North Africa dust emission is between 15° and 20°N. Abstract: Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodélé depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Aïr and Hoggar Mountains, making this area the second most important region of emission within North Africa. more...
- Published
- 2015
- Full Text
- View/download PDF
13. Derivation of an observation-based map of North African dust emission
- Author
-
Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, Doherty, Owen, Evan, Amato T., Fiedler, Stephanie, Zhao, Chun, Menut, Laurent, Schepanski, Kerstin, Flamant, Cyrille, and Doherty, Owen more...
- Abstract
Highlights: • North African dust emission and emission frequency from six models are examined. • There is a power law relationship between emission and emission event frequency. • The lognormal distribution of surface winds gives rise to this power law relation. • Annual North Africa dust emission is estimated via satellite retrievals of emission frequency. • We estimate that 82% of all North Africa dust emission is between 15° and 20°N. Abstract: Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodélé depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Aïr and Hoggar Mountains, making this area the second most important region of emission within North Africa. more...
- Published
- 2015
- Full Text
- View/download PDF
14. An analysis of aeolian dust in climate models
- Author
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Evan, Amato T., Flamant, Cyrille, Fiedler, Stephanie, Doherty, Owen, Evan, Amato T., Flamant, Cyrille, Fiedler, Stephanie, and Doherty, Owen
- Abstract
Aeolian dust is a key aspect of the climate system. Dust can modify the Earth's energy budget, provide long-range transport of nutrients, and influence land surface processes via erosion. Consequently, effective modeling of the climate system, particularly at regional scales, requires a reasonably accurate representation of dust emission, transport, and deposition. Here we evaluate African dust in 23 state-of-the-art global climate models used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that all models fail to reproduce basic aspects of dust emission and transport over the second half of the twentieth century. The models systematically underestimate dust emission, transport, and optical depth, and year-to-year changes in these properties bear little resemblance to observations. These findings cast doubt on the ability of these models to simulate the regional climate and the response of African dust to future climate change. Key Points: - CMIP5 models underestimate African dust emission and transport - The dust size distribution is biased toward small particles in CMIP5 models - CMIP5 models do not represent coupled processes that involve African dust more...
- Published
- 2014
- Full Text
- View/download PDF
15. An analysis of aeolian dust in climate models
- Author
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Evan, Amato T., Flamant, Cyrille, Fiedler, Stephanie, Doherty, Owen, Evan, Amato T., Flamant, Cyrille, Fiedler, Stephanie, and Doherty, Owen
- Abstract
Aeolian dust is a key aspect of the climate system. Dust can modify the Earth's energy budget, provide long-range transport of nutrients, and influence land surface processes via erosion. Consequently, effective modeling of the climate system, particularly at regional scales, requires a reasonably accurate representation of dust emission, transport, and deposition. Here we evaluate African dust in 23 state-of-the-art global climate models used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that all models fail to reproduce basic aspects of dust emission and transport over the second half of the twentieth century. The models systematically underestimate dust emission, transport, and optical depth, and year-to-year changes in these properties bear little resemblance to observations. These findings cast doubt on the ability of these models to simulate the regional climate and the response of African dust to future climate change. Key Points: - CMIP5 models underestimate African dust emission and transport - The dust size distribution is biased toward small particles in CMIP5 models - CMIP5 models do not represent coupled processes that involve African dust more...
- Published
- 2014
- Full Text
- View/download PDF
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