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- Author or Editor: J. L. Stanford x
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Abstract
Large-amplitude planetary waves in the southern winter stratosphere are observed to occur episodically, the result of episodic tropospheric forcing. This work is an observational study of the dynamics of the planetary waves, focusing on the evolution through a typical life cycle. Time lag correlations of wave amplitude with the Eliassen-Palm flux vector reveal the characteristic heat and momentum flux patterns associated with wave evolution. Energetic studies clearly show that the stratospheric waves can be understood in terms of a life cycle of vertical propagation from the troposphere, followed by decay from barotropic interactions with the zonal mean flow. Although usually of secondary importance baroclinic decay of stratospheric wave energy is also observed, resulting from equatorward heat flux in the lower stratosphere. Good agreement in the energy balances discounts in situ instability in the stratosphere as a source of wave activity. An average or composite over several clearly propagating cases reveals the wave structure and evolution, and suggests a source of planetary wave activity in the upper tropospheric.
Abstract
Large-amplitude planetary waves in the southern winter stratosphere are observed to occur episodically, the result of episodic tropospheric forcing. This work is an observational study of the dynamics of the planetary waves, focusing on the evolution through a typical life cycle. Time lag correlations of wave amplitude with the Eliassen-Palm flux vector reveal the characteristic heat and momentum flux patterns associated with wave evolution. Energetic studies clearly show that the stratospheric waves can be understood in terms of a life cycle of vertical propagation from the troposphere, followed by decay from barotropic interactions with the zonal mean flow. Although usually of secondary importance baroclinic decay of stratospheric wave energy is also observed, resulting from equatorward heat flux in the lower stratosphere. Good agreement in the energy balances discounts in situ instability in the stratosphere as a source of wave activity. An average or composite over several clearly propagating cases reveals the wave structure and evolution, and suggests a source of planetary wave activity in the upper tropospheric.
Abstract
Thunderstorm radio noise measurements at several frequencies in the range 0.01–74 MHz have been made with specially designed remote recording stations in Iowa. The data were recorded during the spring and summer of 1974 when a series of severe storm systems produced a great number of large hail and tornado reports in Iowa. Computer analyses were made of nearly a billion bits of data, corresponding to 170 h of real-time recordings. Careful compilations of surface severe weather reports, hail damage information from insurance companies, and studies on the Des Moines WSR-57 radar echoes were compared with the analyzed radio noise data. The results include the following:
1) In agreement with earlier work, large‐amplitude radio noise impulse rates were found to he generally good indicators of thunderstorm severity. Although the majority of the radio energy radiated from major lightning strokes occurs in the 0.01 MHz range, this frequency was found to be a poor indicator of storm severity; the higher frequencies (megahertz range) were considerably better. The character of the noise appears similar at 2.5 and 74 MHz.
2) In at least five cases, tornadic events correlated in time with radio noise count rate peaks. One funnel cloud was reported equidistant at 60 km from two recording stations and coincident with count rate peaks at both stations, lending credence to the idea that the peak was associated with the storm occurrence, rather than with corona or other local effects.
3) No unusual radio noise was recorded during the lifetime of a small, verified tornado at 19 km range. In addition, the count rates for its parent thunderstorm would not have indicated severity.
In spite of inherent atmospheric variableness, the radio noise technique is a useful complementary indicator of storm severity.
Abstract
Thunderstorm radio noise measurements at several frequencies in the range 0.01–74 MHz have been made with specially designed remote recording stations in Iowa. The data were recorded during the spring and summer of 1974 when a series of severe storm systems produced a great number of large hail and tornado reports in Iowa. Computer analyses were made of nearly a billion bits of data, corresponding to 170 h of real-time recordings. Careful compilations of surface severe weather reports, hail damage information from insurance companies, and studies on the Des Moines WSR-57 radar echoes were compared with the analyzed radio noise data. The results include the following:
1) In agreement with earlier work, large‐amplitude radio noise impulse rates were found to he generally good indicators of thunderstorm severity. Although the majority of the radio energy radiated from major lightning strokes occurs in the 0.01 MHz range, this frequency was found to be a poor indicator of storm severity; the higher frequencies (megahertz range) were considerably better. The character of the noise appears similar at 2.5 and 74 MHz.
2) In at least five cases, tornadic events correlated in time with radio noise count rate peaks. One funnel cloud was reported equidistant at 60 km from two recording stations and coincident with count rate peaks at both stations, lending credence to the idea that the peak was associated with the storm occurrence, rather than with corona or other local effects.
3) No unusual radio noise was recorded during the lifetime of a small, verified tornado at 19 km range. In addition, the count rates for its parent thunderstorm would not have indicated severity.
In spite of inherent atmospheric variableness, the radio noise technique is a useful complementary indicator of storm severity.
Abstract
The purpose of this note is to show that not all tornadic storms yield the same radio-frequency noise behavior. One funnel cloud observed gave significant radio noise over a frequency range from 2.5 to 144 MHz.
Abstract
The purpose of this note is to show that not all tornadic storms yield the same radio-frequency noise behavior. One funnel cloud observed gave significant radio noise over a frequency range from 2.5 to 144 MHz.
Abstract
The “4-day wave” is an eastward moving quasi-nondispersive feature with period near 4 days occurring near the winter polar stratopause. This paper presents evidence of the 4-day feature in Microwave Limb Sounder (MLS) temperature, geopotential height, and ozone data from the late southern winters of 1992 and 1993. Space–time spectral analyses reveal a double-peaked temperature structure consisting of one peak near the stratopause and another in the lower mesosphere, with an out-of-phase relationship between the two peaks. This double-peaked structure is reminiscent of recent three-dimensional barotropic/baroclinic instability model predictions and is observed here for the first time. The height variation of the 4-day ozone signal is shown to compare well with a linear advective–photochemical tracer model. Negative regions of quasigeostrophic potential vorticity (PV) gradient and positive Eliassen–Palm flux divergence are shown to occur, consistent with instability dynamics playing a role in wave forcing. Spectral analyses of PV derived from MLS geopotential height fields reveal a 4-day signal peaking near the polar stratopause. The three-dimensional structure of the 4-day wave resembles the potential vorticity “charge” concept, wherein a PV anomaly in the atmosphere (analogous to an electrical charge in a dielectric material) induces a geopotential field, a vertically oriented temperature dipole, and circulation about the vertical axis.
Abstract
The “4-day wave” is an eastward moving quasi-nondispersive feature with period near 4 days occurring near the winter polar stratopause. This paper presents evidence of the 4-day feature in Microwave Limb Sounder (MLS) temperature, geopotential height, and ozone data from the late southern winters of 1992 and 1993. Space–time spectral analyses reveal a double-peaked temperature structure consisting of one peak near the stratopause and another in the lower mesosphere, with an out-of-phase relationship between the two peaks. This double-peaked structure is reminiscent of recent three-dimensional barotropic/baroclinic instability model predictions and is observed here for the first time. The height variation of the 4-day ozone signal is shown to compare well with a linear advective–photochemical tracer model. Negative regions of quasigeostrophic potential vorticity (PV) gradient and positive Eliassen–Palm flux divergence are shown to occur, consistent with instability dynamics playing a role in wave forcing. Spectral analyses of PV derived from MLS geopotential height fields reveal a 4-day signal peaking near the polar stratopause. The three-dimensional structure of the 4-day wave resembles the potential vorticity “charge” concept, wherein a PV anomaly in the atmosphere (analogous to an electrical charge in a dielectric material) induces a geopotential field, a vertically oriented temperature dipole, and circulation about the vertical axis.
Abstract
Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10–0.03 hPa) are studied for the early northern winter 1991/92 using the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) measurements. The study is aided by data from a 6-week parameterized-chemistry run of the Goddard Space Flight Center 3D Chemistry and Transport Model (CTM), initialized on 8 December 1991.
Generally, CO mixing ratios increase with height due to the increasing source contribution from CO2 photolysis. In the tropical upper stratosphere, however, a local maximum in CO mixing ratio occurs. A simple photochemical model is used to show that this feature results largely from methane oxidation.
In the extratropics the photochemical lifetime of CO is long, and therefore its evolution is dictated by large-scale motion of air, evidenced by strong correlation with Ertel potential vorticity. This makes CO one of the few useful observable tracers at the stratopause level and above. Thus CO maps are used to study the synoptic evolution of the polar vortex in early January 1992.
Modified Lagrangian mean mixing diagnostics are applied to ISAMS and CTM data to examine the strength of the mixing barrier at the polar vortex edge. It is demonstrated that planetary wave activity weakens the barrier, promoting vortex erosion. The vortex erosion first appears in the lower mesosphere and subsequently descends through the upper stratosphere, and is attributed to effects of planetary wave dissipation.
Agreement between ISAMS and CTM is good in the horizontal distribution of CO throughout the examined period, but vertical CO gradients in the CTM weaken with time relative to the ISAMS observations.
Abstract
Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10–0.03 hPa) are studied for the early northern winter 1991/92 using the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) measurements. The study is aided by data from a 6-week parameterized-chemistry run of the Goddard Space Flight Center 3D Chemistry and Transport Model (CTM), initialized on 8 December 1991.
Generally, CO mixing ratios increase with height due to the increasing source contribution from CO2 photolysis. In the tropical upper stratosphere, however, a local maximum in CO mixing ratio occurs. A simple photochemical model is used to show that this feature results largely from methane oxidation.
In the extratropics the photochemical lifetime of CO is long, and therefore its evolution is dictated by large-scale motion of air, evidenced by strong correlation with Ertel potential vorticity. This makes CO one of the few useful observable tracers at the stratopause level and above. Thus CO maps are used to study the synoptic evolution of the polar vortex in early January 1992.
Modified Lagrangian mean mixing diagnostics are applied to ISAMS and CTM data to examine the strength of the mixing barrier at the polar vortex edge. It is demonstrated that planetary wave activity weakens the barrier, promoting vortex erosion. The vortex erosion first appears in the lower mesosphere and subsequently descends through the upper stratosphere, and is attributed to effects of planetary wave dissipation.
Agreement between ISAMS and CTM is good in the horizontal distribution of CO throughout the examined period, but vertical CO gradients in the CTM weaken with time relative to the ISAMS observations.
