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Abstract
Analysis of three cloud seeding experiments over areas of Australia suggests that results varied with cloud-top temperature; when cumulus and similar clouds had top temperatures ≲−10C rainfall was increased by seeding, but when the cloud tops were warmer rainfall was decreased.
Abstract
Analysis of three cloud seeding experiments over areas of Australia suggests that results varied with cloud-top temperature; when cumulus and similar clouds had top temperatures ≲−10C rainfall was increased by seeding, but when the cloud tops were warmer rainfall was decreased.
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No Abstract Available.
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An American Meteorological Society committee, working cooperatively with the U.S. Environmental Protection Agency (EPA), has sponsored a peer review and evaluation of 10 rural diffusion models that are now used in regulatory procedures or have been submitted to EPA for such use. This review revealed that none of the models can be considered up-to-date scientifically, and that there is no basis for choice among them in terms of predictive accuracy. Regardless of the scientific merit of any model, significant inaccuracy in the predictions would arise from the inherent uncertainty in the diffusion process and from inadequacies of the input data.
An American Meteorological Society committee, working cooperatively with the U.S. Environmental Protection Agency (EPA), has sponsored a peer review and evaluation of 10 rural diffusion models that are now used in regulatory procedures or have been submitted to EPA for such use. This review revealed that none of the models can be considered up-to-date scientifically, and that there is no basis for choice among them in terms of predictive accuracy. Regardless of the scientific merit of any model, significant inaccuracy in the predictions would arise from the inherent uncertainty in the diffusion process and from inadequacies of the input data.
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No Abstract Available.
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Abstract
To explore the vertical coherence of the vertical temperature structure in the atmosphere, an analysis is performed of the full three-dimensional spatial structure of the temperature field monthly mean anomalies from the 40-yr ECMWF Re-Analysis (ERA-40) for a core region of the Tropics from 30°N to 30°S, with results projected globally. The focus is on the first three empirical orthogonal functions (EOFs), two of which have primary relationships to El Niño–Southern Oscillation (ENSO) and feature rather different vertical structures. The second (EOF-2) also has a weak ENSO signature but a very complex vertical structure and reflects mainly nonlinear trends, some real but also some in large part spurious and associated with problems in assimilating satellite data. The dominant pattern (EOF-1) in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30°N to 30°S that increases in magnitude with height to 300 hPa, drops to zero about 100 hPa at the tropopause, and has reverse sign to 30 hPa with peak negative values at 70 hPa. Spatially at low levels it shows warmth throughout most of the Tropics although with weak or slightly opposite sign in the western tropical Pacific and a strong reversed sign in the Pacific subtropics. Coherent wave structures below 700 hPa at higher latitudes cancel out in the zonal mean. However, the structure becomes more zonal above about 700 hPa and features off-equatorial maxima straddling the equator in the eastern Pacific in the upper troposphere with opposite sign at 100 hPa, as a signature of a forced Rossby wave. The corresponding sea level pressure pattern is similar to but more focused in equatorial regions than the Southern Oscillation pattern. The time series highlights the 1997/98 El Niño along with those in 1982/83 and 1986/87, and the 1988/89 La Niña, and correlates strongly with global mean surface temperatures. Missing, however, is the prolonged sequence of three successive El Niño events in the early 1990s, which are highlighted in EOF-3 as part of a mainly lower-frequency decadal variation that features modest zonal mean warming below 700 hPa, cooling from 700 to 300 hPa, and warming above 300 hPa, peaking at 100 hPa and extending from 40°N to 50°S. Spatially at the surface this pattern is dominated by Southern Oscillation wave-1 structures throughout the Tropics and especially the subtropics. The regional temperature structures are coherent throughout the troposphere, with strongest values in the Pacific and extending well into the extratropics, with a sign reversal at and above 100 hPa. Strong Rossby wave signatures are featured in the troposphere with a distinctive quadrupole pattern that reverses at 100 hPa. The vertical coherence of all patterns suggests that they should be apparent in broad-layer satellite temperature records but that stratospheric anomalies are not independent. The quite different three-dimensional structure of these different patterns highlights the need to consider the full structure outside of the Pacific and at all vertical levels in accounting for impacts of ENSO, and how they relate to the global mean.
Abstract
To explore the vertical coherence of the vertical temperature structure in the atmosphere, an analysis is performed of the full three-dimensional spatial structure of the temperature field monthly mean anomalies from the 40-yr ECMWF Re-Analysis (ERA-40) for a core region of the Tropics from 30°N to 30°S, with results projected globally. The focus is on the first three empirical orthogonal functions (EOFs), two of which have primary relationships to El Niño–Southern Oscillation (ENSO) and feature rather different vertical structures. The second (EOF-2) also has a weak ENSO signature but a very complex vertical structure and reflects mainly nonlinear trends, some real but also some in large part spurious and associated with problems in assimilating satellite data. The dominant pattern (EOF-1) in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30°N to 30°S that increases in magnitude with height to 300 hPa, drops to zero about 100 hPa at the tropopause, and has reverse sign to 30 hPa with peak negative values at 70 hPa. Spatially at low levels it shows warmth throughout most of the Tropics although with weak or slightly opposite sign in the western tropical Pacific and a strong reversed sign in the Pacific subtropics. Coherent wave structures below 700 hPa at higher latitudes cancel out in the zonal mean. However, the structure becomes more zonal above about 700 hPa and features off-equatorial maxima straddling the equator in the eastern Pacific in the upper troposphere with opposite sign at 100 hPa, as a signature of a forced Rossby wave. The corresponding sea level pressure pattern is similar to but more focused in equatorial regions than the Southern Oscillation pattern. The time series highlights the 1997/98 El Niño along with those in 1982/83 and 1986/87, and the 1988/89 La Niña, and correlates strongly with global mean surface temperatures. Missing, however, is the prolonged sequence of three successive El Niño events in the early 1990s, which are highlighted in EOF-3 as part of a mainly lower-frequency decadal variation that features modest zonal mean warming below 700 hPa, cooling from 700 to 300 hPa, and warming above 300 hPa, peaking at 100 hPa and extending from 40°N to 50°S. Spatially at the surface this pattern is dominated by Southern Oscillation wave-1 structures throughout the Tropics and especially the subtropics. The regional temperature structures are coherent throughout the troposphere, with strongest values in the Pacific and extending well into the extratropics, with a sign reversal at and above 100 hPa. Strong Rossby wave signatures are featured in the troposphere with a distinctive quadrupole pattern that reverses at 100 hPa. The vertical coherence of all patterns suggests that they should be apparent in broad-layer satellite temperature records but that stratospheric anomalies are not independent. The quite different three-dimensional structure of these different patterns highlights the need to consider the full structure outside of the Pacific and at all vertical levels in accounting for impacts of ENSO, and how they relate to the global mean.
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No Abstract Available.
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Abstract
Two rather different flavors of El Niño are revealed when the full three-dimensional spatial structure of the temperature field and atmospheric circulation monthly mean anomalies is analyzed using the Japanese Reanalysis (JRA-25) temperatures from 1979 through 2004 for a core region of the tropics from 30°N to 30°S, with results projected globally onto various other fields. The first two empirical orthogonal functions (EOFs) both have primary relationships to El Niño–Southern Oscillation (ENSO) but feature rather different vertical and spatial structures. By construction the two patterns are orthogonal, but their signatures in sea level pressure, precipitation, outgoing longwave radiation (OLR), and tropospheric diabatic heating are quite similar. Moreover, they are significantly related, with EOF-2 leading EOF-1 by about 4–6 months, indicating that they play complementary roles in the evolution of ENSO events, and with each mode playing greater or lesser roles in different events and seasons.
The dominant pattern (EOF-1) in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30°N to 30°S that increases in magnitude with height to 200 hPa, drops to zero about 100 hPa at the tropopause, and has reverse sign to 30 hPa with peak values at 70 hPa. It correlates strongly with global mean surface temperatures. EOF-2 emphasizes off-equatorial centers of action and strong Rossby wave temperature signatures that are coherent throughout the troposphere, with the strongest values in the Pacific that extend into the extratropics and a sign reversal at and above 150 hPa. Near the surface, both patterns feature boomerang-shaped opposite temperatures in the western tropical and subtropical Pacific, with similar sea level pressure patterns, but with EOF-1 more focused in equatorial regions. Both patterns are strongest during the boreal winter half-year when anomalous precipitation in the tropics and associated latent heating drive teleconnections throughout the world. For El Niño in northern winter EOF-1 has more precipitation in the eastern tropical Pacific, while EOF-2 has much drier conditions over northern Australia and the Indian Ocean. In northern summer, the main differences are in the South Pacific and Indian Ocean. Differences in teleconnections suggest great sensitivity to small changes in forcings in association with seasonal variations in the mean state.
Abstract
Two rather different flavors of El Niño are revealed when the full three-dimensional spatial structure of the temperature field and atmospheric circulation monthly mean anomalies is analyzed using the Japanese Reanalysis (JRA-25) temperatures from 1979 through 2004 for a core region of the tropics from 30°N to 30°S, with results projected globally onto various other fields. The first two empirical orthogonal functions (EOFs) both have primary relationships to El Niño–Southern Oscillation (ENSO) but feature rather different vertical and spatial structures. By construction the two patterns are orthogonal, but their signatures in sea level pressure, precipitation, outgoing longwave radiation (OLR), and tropospheric diabatic heating are quite similar. Moreover, they are significantly related, with EOF-2 leading EOF-1 by about 4–6 months, indicating that they play complementary roles in the evolution of ENSO events, and with each mode playing greater or lesser roles in different events and seasons.
The dominant pattern (EOF-1) in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30°N to 30°S that increases in magnitude with height to 200 hPa, drops to zero about 100 hPa at the tropopause, and has reverse sign to 30 hPa with peak values at 70 hPa. It correlates strongly with global mean surface temperatures. EOF-2 emphasizes off-equatorial centers of action and strong Rossby wave temperature signatures that are coherent throughout the troposphere, with the strongest values in the Pacific that extend into the extratropics and a sign reversal at and above 150 hPa. Near the surface, both patterns feature boomerang-shaped opposite temperatures in the western tropical and subtropical Pacific, with similar sea level pressure patterns, but with EOF-1 more focused in equatorial regions. Both patterns are strongest during the boreal winter half-year when anomalous precipitation in the tropics and associated latent heating drive teleconnections throughout the world. For El Niño in northern winter EOF-1 has more precipitation in the eastern tropical Pacific, while EOF-2 has much drier conditions over northern Australia and the Indian Ocean. In northern summer, the main differences are in the South Pacific and Indian Ocean. Differences in teleconnections suggest great sensitivity to small changes in forcings in association with seasonal variations in the mean state.
