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- Author or Editor: Leslie R. Lait x
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Abstract
A form of potential vorticity is described that has conservation properties similar to those of Ertel's potential vorticity (EPV) but removes the exponential variation with height displayed by EPV. This form is thus more suitable for inspecting vertical cross sections of potential vorticity and for use (with potential temperature) as a quasi-conserved coordinate in the analysis of chemical constituent data.
Abstract
A form of potential vorticity is described that has conservation properties similar to those of Ertel's potential vorticity (EPV) but removes the exponential variation with height displayed by EPV. This form is thus more suitable for inspecting vertical cross sections of potential vorticity and for use (with potential temperature) as a quasi-conserved coordinate in the analysis of chemical constituent data.
Abstract
The space-time Fourier analysis technique proposed by Salby for asynoptic satellite data has been applied to brightness temperatures derived from Stratospheric Sounding Unit radiances from three months during the Southern Hemisphere winter. A series of peaks are observed in the spectra for wavenumbers 1 through 4 which travel eastward with the same phase speed. The wave 1, 4-day, and wave 2, 1.8-day, features observed have been described previously in the literature, and the existence of a wave 3, 1.2-day oscillation has also been reported. The current analyses provide corroborating evidence for these, using a different dataset and analysis technique, in addition to reporting a previously undetected wave 4,0.8 day, feature. Twice-daily synoptic maps reconstructed from the transforms reveal, consistent with the findings of Prata, that these waves are components of one or more warm pools circling the pole with a period of about 3.8 days. These features exhibit sizable temperature perturbations (≈5 K) and long lifetimes in the upper stratosphere. One such pool retains its identity for at least seven complete revolutions around the pole.
Abstract
The space-time Fourier analysis technique proposed by Salby for asynoptic satellite data has been applied to brightness temperatures derived from Stratospheric Sounding Unit radiances from three months during the Southern Hemisphere winter. A series of peaks are observed in the spectra for wavenumbers 1 through 4 which travel eastward with the same phase speed. The wave 1, 4-day, and wave 2, 1.8-day, features observed have been described previously in the literature, and the existence of a wave 3, 1.2-day oscillation has also been reported. The current analyses provide corroborating evidence for these, using a different dataset and analysis technique, in addition to reporting a previously undetected wave 4,0.8 day, feature. Twice-daily synoptic maps reconstructed from the transforms reveal, consistent with the findings of Prata, that these waves are components of one or more warm pools circling the pole with a period of about 3.8 days. These features exhibit sizable temperature perturbations (≈5 K) and long lifetimes in the upper stratosphere. One such pool retains its identity for at least seven complete revolutions around the pole.
Abstract
A method proposed by Salby for computing the zonal space-time Fourier transform of asynoptically acquired satellite data has been tested and applied to soundings of brightness temperature taken by polar-orbiting satellites. The technique, which yields the exact transform of the data with no distortions of fast-moving waves, is found to be robust under reasonable conditions of randomly varying signals, sampling errors and missing data points. In addition, when applied to measurements from instruments with multiple-scan tracks, a large number of latitudinally closely spaced spectra results, which enables one to average over latitude instead of or in addition to conventional frequency averaging to achieve greater statistical reliability and better signal-to-noise ratio. Some results of applying the method to real data are presented. Several well-known waves are identified, as well as two previously unreported small-amplitude spectral peaks corresponding to waves in the Southern summer stratosphere having wavenumber 7 and a period of 2.09–2.97 d westward, and wavenumber 6 with a period of 4.17–5.90 d eastward.
Abstract
A method proposed by Salby for computing the zonal space-time Fourier transform of asynoptically acquired satellite data has been tested and applied to soundings of brightness temperature taken by polar-orbiting satellites. The technique, which yields the exact transform of the data with no distortions of fast-moving waves, is found to be robust under reasonable conditions of randomly varying signals, sampling errors and missing data points. In addition, when applied to measurements from instruments with multiple-scan tracks, a large number of latitudinally closely spaced spectra results, which enables one to average over latitude instead of or in addition to conventional frequency averaging to achieve greater statistical reliability and better signal-to-noise ratio. Some results of applying the method to real data are presented. Several well-known waves are identified, as well as two previously unreported small-amplitude spectral peaks corresponding to waves in the Southern summer stratosphere having wavenumber 7 and a period of 2.09–2.97 d westward, and wavenumber 6 with a period of 4.17–5.90 d eastward.
Abstract
Dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere is investigated using horizontal wind and temperature data. These were derived from synoptic maps of satellite-measured brightness temperatures, which were generated using the fast Fourier synoptic mapping technique of Salby. Circulation statistics from these data are compared to those from the National Meteorological Center (NMC) operational stratospheric analyses, demonstrating improvements afforded by detailed treatment of asynoptic sampling effects. The 4-day wave is isolated using temporally filtered data. Several events of wave growth and decay are observed in the upper stratosphere during August 1980. Derived zonal-mean and eddy statistics suggest that the 4-day wave results from an instability of the zonal-mean flow near 55°–60°S, at and above 1 mb. Inspection of climatological data suggests the source of the instability to be the “double-jet” structure in the upper stratosphere and mesosphere (the subtropical mesospheric jet near 30°S and the high-latitude extension of the polar night jet near 70°S). Contribution of the 4-day wave to the general circulation of the stratosphere is discussed: one feature attributable to the 4-day wave is a region of positive EP flux divergence in the upper stratosphere near 50°–60°S.
Abstract
Dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere is investigated using horizontal wind and temperature data. These were derived from synoptic maps of satellite-measured brightness temperatures, which were generated using the fast Fourier synoptic mapping technique of Salby. Circulation statistics from these data are compared to those from the National Meteorological Center (NMC) operational stratospheric analyses, demonstrating improvements afforded by detailed treatment of asynoptic sampling effects. The 4-day wave is isolated using temporally filtered data. Several events of wave growth and decay are observed in the upper stratosphere during August 1980. Derived zonal-mean and eddy statistics suggest that the 4-day wave results from an instability of the zonal-mean flow near 55°–60°S, at and above 1 mb. Inspection of climatological data suggests the source of the instability to be the “double-jet” structure in the upper stratosphere and mesosphere (the subtropical mesospheric jet near 30°S and the high-latitude extension of the polar night jet near 70°S). Contribution of the 4-day wave to the general circulation of the stratosphere is discussed: one feature attributable to the 4-day wave is a region of positive EP flux divergence in the upper stratosphere near 50°–60°S.
Abstract
A significant disruption of the quasi-biennial oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015/16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here this disruptive event is examined using global reanalysis winds and temperatures from 1980 to 2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015/16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40-hPa level. Two additional NH winters, 1987/88 and 2010/11, were also found to have large tropical lower-stratospheric momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases.
Abstract
A significant disruption of the quasi-biennial oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015/16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here this disruptive event is examined using global reanalysis winds and temperatures from 1980 to 2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015/16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40-hPa level. Two additional NH winters, 1987/88 and 2010/11, were also found to have large tropical lower-stratospheric momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases.
Abstract
The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).
Abstract
The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).
Abstract
This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.
Abstract
This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.
