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Abstract
An unbounded hyperbolic-tangent barotropic shear flow is assumed. The complex phase speeds and eigenfunction structure of unstable modes are studied numerically. A reversal of the planetary and shear vorticity gradient is required for these modes to exist. For sufficiently small wavenumber, the unstable modes, which can be associated with the modes of a discontinuous shear layer, are found on both sides of the neutral solution curve in wavenumber-shear parameter space. For sufficiently large wavenumbers, the unstable modes are contiguous to the neutral solution. For an intermediate range of wavenumbers, there are two sets of unstable modes (one contiguous to the neutral solution and one not); one set merges with the zero β unstable mode and one set vanishes for sufficiently small β (or large shear). Above some critical value of wavenumber, the set of modes at fixed wavenumber merging with the neutral solution is contiguous to the neutral boundary, whereas below the critical wavenumber value this set of modes extends beyond the neutral boundary, while the set of modes contiguous to the neutral boundary vanishes for sufficiently large shear. For shears comparable to or less than the neutral boundary shear and for values of wavenumber at least as small as those for which two modes are found, one set of unstable modes is essentially wavelike on the relatively westerly side of the shear zone. These waves can extract momentum from great distances beyond the region of shear. More generally, latitudinally propagating Rossby waves incident on a region of negative vorticity gradient with phase speed matching mean flow speed within this region should be over-reflected, with largest over-reflection occurring for phase speed near that of an unstable mode.
Abstract
An unbounded hyperbolic-tangent barotropic shear flow is assumed. The complex phase speeds and eigenfunction structure of unstable modes are studied numerically. A reversal of the planetary and shear vorticity gradient is required for these modes to exist. For sufficiently small wavenumber, the unstable modes, which can be associated with the modes of a discontinuous shear layer, are found on both sides of the neutral solution curve in wavenumber-shear parameter space. For sufficiently large wavenumbers, the unstable modes are contiguous to the neutral solution. For an intermediate range of wavenumbers, there are two sets of unstable modes (one contiguous to the neutral solution and one not); one set merges with the zero β unstable mode and one set vanishes for sufficiently small β (or large shear). Above some critical value of wavenumber, the set of modes at fixed wavenumber merging with the neutral solution is contiguous to the neutral boundary, whereas below the critical wavenumber value this set of modes extends beyond the neutral boundary, while the set of modes contiguous to the neutral boundary vanishes for sufficiently large shear. For shears comparable to or less than the neutral boundary shear and for values of wavenumber at least as small as those for which two modes are found, one set of unstable modes is essentially wavelike on the relatively westerly side of the shear zone. These waves can extract momentum from great distances beyond the region of shear. More generally, latitudinally propagating Rossby waves incident on a region of negative vorticity gradient with phase speed matching mean flow speed within this region should be over-reflected, with largest over-reflection occurring for phase speed near that of an unstable mode.
Abstract
The ability to detect subtle trends in upper stratospheric ozone places strict requirements on satellite-based Solar Backscatter Ultraviolet (SBUV) sensors intended for this purpose. Simulation of the long-term change in backscattered radiance indicates trends in the range 1.0–1.6% per decade depending on wavelength for an ozone depletion scenario based on chlorofluorocarbon (CFC) chemistry. The maximum percentage change in the measured quantity, as would be sensed by the Nimbus-7 SBUV experiment and future similar instruments, is roughly a factor of two less than the maximum percentage change in ozone, the quantity of geophysical interest. Furthermore, interannual variations, whose magnitude can be estimated from the SBUV data set, could obscure a CFC-related trend in radiance when viewed over a period less than a decade. Even when such atmospheric noise and possible solar cycle variations are neglected, the detection of an ozone trend of the magnitude predicted for CFC-related chemistry requires a set of radiance measurements that are internally consistent to 1% or better over a time span of a decade.
Abstract
The ability to detect subtle trends in upper stratospheric ozone places strict requirements on satellite-based Solar Backscatter Ultraviolet (SBUV) sensors intended for this purpose. Simulation of the long-term change in backscattered radiance indicates trends in the range 1.0–1.6% per decade depending on wavelength for an ozone depletion scenario based on chlorofluorocarbon (CFC) chemistry. The maximum percentage change in the measured quantity, as would be sensed by the Nimbus-7 SBUV experiment and future similar instruments, is roughly a factor of two less than the maximum percentage change in ozone, the quantity of geophysical interest. Furthermore, interannual variations, whose magnitude can be estimated from the SBUV data set, could obscure a CFC-related trend in radiance when viewed over a period less than a decade. Even when such atmospheric noise and possible solar cycle variations are neglected, the detection of an ozone trend of the magnitude predicted for CFC-related chemistry requires a set of radiance measurements that are internally consistent to 1% or better over a time span of a decade.
Abstract
Knowledge of the agronomic production of odd hydrogen in the dissociation of water vapor is limited by uncertainties in the penetration of solar irradiance in the Schumann-Rung bands of O2 and by incomplete information concerning the products of photolysis at Lyman alpha. Consideration of an error sources involved in computing the H2o dissociation rate in the wavelength region 175–200 nm leads to an estimated uncertainty of ±35% at an altitude of 90 km for an overhead sun. The uncertainty increases with decreasing altitude such that the true dissociation rate at 60 km for an overhead sun lies between 0.45 and 1.55 times the result computed using the best input parameters currently available. Calculations of the H2o dissociation rate by Lyman alpha should include the variation in O2 opacity across the solar line width. Neglect of this can lead to errors as large as 50% at altitudes where the process is the major source of odd hydrogen.
Abstract
Knowledge of the agronomic production of odd hydrogen in the dissociation of water vapor is limited by uncertainties in the penetration of solar irradiance in the Schumann-Rung bands of O2 and by incomplete information concerning the products of photolysis at Lyman alpha. Consideration of an error sources involved in computing the H2o dissociation rate in the wavelength region 175–200 nm leads to an estimated uncertainty of ±35% at an altitude of 90 km for an overhead sun. The uncertainty increases with decreasing altitude such that the true dissociation rate at 60 km for an overhead sun lies between 0.45 and 1.55 times the result computed using the best input parameters currently available. Calculations of the H2o dissociation rate by Lyman alpha should include the variation in O2 opacity across the solar line width. Neglect of this can lead to errors as large as 50% at altitudes where the process is the major source of odd hydrogen.
Abstract
Oscillator strengths and predissociation linewidths deduced in recent studies predict a dissociation rate for O2 in the Schumann-Runge bands which is significantly larger in the upper stratosphere and lower mesosphere than previously believed. Error bars on molecular parameters required in the cross-section calculation translate into uncertainties in the dissociation rate which are less than ±10% at all altitudes where the Schumann-Runge bands are agronomically significant.
Abstract
Oscillator strengths and predissociation linewidths deduced in recent studies predict a dissociation rate for O2 in the Schumann-Runge bands which is significantly larger in the upper stratosphere and lower mesosphere than previously believed. Error bars on molecular parameters required in the cross-section calculation translate into uncertainties in the dissociation rate which are less than ±10% at all altitudes where the Schumann-Runge bands are agronomically significant.
Abstract
Absorption of solar photons by nitric oxide in the wavelength ranges 181.3–183.5 and 189.4–191.6 nm leads to predissociation of the molecule in the mesosphere and upper stratosphere. Molecular oxygen controls the penetration of the required solar irradiance via absorption in the Schumann-Runge bands, while attenuation due to ozone becomes significant in the upper stratosphere. The calculation of the nitric oxide dissociation rate is complicated by the need to include all rotational fine structure in both the NO and O2 cross sections. The dissociation rate computed here for the upper mesosphere is a factor of 3.6 less than that reported in past work when currently accepted values of the oscillator strengths and solar irradiance are used. In addition, improved molecular parameters describing the O2 cross section predict less attenuation of the dissociation rate with decreasing altitude than results previously available.
Abstract
Absorption of solar photons by nitric oxide in the wavelength ranges 181.3–183.5 and 189.4–191.6 nm leads to predissociation of the molecule in the mesosphere and upper stratosphere. Molecular oxygen controls the penetration of the required solar irradiance via absorption in the Schumann-Runge bands, while attenuation due to ozone becomes significant in the upper stratosphere. The calculation of the nitric oxide dissociation rate is complicated by the need to include all rotational fine structure in both the NO and O2 cross sections. The dissociation rate computed here for the upper mesosphere is a factor of 3.6 less than that reported in past work when currently accepted values of the oscillator strengths and solar irradiance are used. In addition, improved molecular parameters describing the O2 cross section predict less attenuation of the dissociation rate with decreasing altitude than results previously available.
Abstract
Analysis of temperature measurements obtained over an eight-year period in the vicinity of the low-latitude tropopause confirms the existence of longitude regions which are consistently colder by approximately 2–3 K than elsewhere in the tropics. These temperature differences, however, are confined to a layer of thickness 3–5 km centered on the tropopause. The lowest monthly mean temperatures observed at the colder stations yield saturation mixing ratios that are consistent with the range of measured stratospheric water vapor. Examination of the daily variations in temperature at a given station reveals a more complex pattern than indicated by the monthly averages. On many days temperatures at the colder longitudes correspond to water vapor abundances that are less than observed in the stratosphere despite the favorable comparison of the monthly means. The results point to the need for a series of water vapor soundings at selected longitudes and times in order to define the extent to which the tropical tropopause controls the stratospheric water vapor abundance.
Abstract
Analysis of temperature measurements obtained over an eight-year period in the vicinity of the low-latitude tropopause confirms the existence of longitude regions which are consistently colder by approximately 2–3 K than elsewhere in the tropics. These temperature differences, however, are confined to a layer of thickness 3–5 km centered on the tropopause. The lowest monthly mean temperatures observed at the colder stations yield saturation mixing ratios that are consistent with the range of measured stratospheric water vapor. Examination of the daily variations in temperature at a given station reveals a more complex pattern than indicated by the monthly averages. On many days temperatures at the colder longitudes correspond to water vapor abundances that are less than observed in the stratosphere despite the favorable comparison of the monthly means. The results point to the need for a series of water vapor soundings at selected longitudes and times in order to define the extent to which the tropical tropopause controls the stratospheric water vapor abundance.
Abstract
Analysis of backscattered ultraviolet radiances observed at tropical latitudes by the Atmosphere Explorer-E satellite reveals both annual and semiannual cycles in upper stratospheric ozone. The annual variation dominates the signal at wavelengths which sense ozone primarily above 45 km while below this, to the lowest altitude sensed, 35 km, the semiannual component has comparable amplitude. Comparison of radiance measurements taken with the same instrument at solar minimum during 1976 and solar maximum in 1979 show no significant differences. This suggests that variations in upper stratospheric ozone over the solar cycle are small, although the data presently available do not allow a definite conclusion.
Abstract
Analysis of backscattered ultraviolet radiances observed at tropical latitudes by the Atmosphere Explorer-E satellite reveals both annual and semiannual cycles in upper stratospheric ozone. The annual variation dominates the signal at wavelengths which sense ozone primarily above 45 km while below this, to the lowest altitude sensed, 35 km, the semiannual component has comparable amplitude. Comparison of radiance measurements taken with the same instrument at solar minimum during 1976 and solar maximum in 1979 show no significant differences. This suggests that variations in upper stratospheric ozone over the solar cycle are small, although the data presently available do not allow a definite conclusion.
Abstract
Under the auspices of the Commission for Instruments and Methods of Observation of the World Meteorological Organization, meteorological rocketsonde intercomparisons took place at Wallops Island in March 1972 and at the Guiana Space Center, French Guiana, in September 1973. France, Japan and the United States participated in the Wallops tests, and France, the United Kingdom, the Union of Soviet Socialist Republics and the United States participated in the Guiana tests. Measurements were made during the day as well as at night.
Comparisons ire presented of temperature and wind data obtained by the different rocketsonde systems over the. altitude region from 25 to 80 km. Results indicate generally good compatibility among temperatures obtained below approximately 50 km. Above that level, biases increasing with height are evident. Temperature adjustments are derived, which, when applied to operational rocketsonde data, would in the mean achieve compatibility for synoptic analyses and other uses. Comparisons among wind observations indicate generally good agreement below approximately 60 km. However, some significant problem areas are pointed out and discussed.
The Guiana series of observations also provided valuable information on the diurnal temperature change at stratospheric and mesospheric levels. An evaluation of this aspect is presented, and results are compared with those predicted by tidal theory.
Abstract
Under the auspices of the Commission for Instruments and Methods of Observation of the World Meteorological Organization, meteorological rocketsonde intercomparisons took place at Wallops Island in March 1972 and at the Guiana Space Center, French Guiana, in September 1973. France, Japan and the United States participated in the Wallops tests, and France, the United Kingdom, the Union of Soviet Socialist Republics and the United States participated in the Guiana tests. Measurements were made during the day as well as at night.
Comparisons ire presented of temperature and wind data obtained by the different rocketsonde systems over the. altitude region from 25 to 80 km. Results indicate generally good compatibility among temperatures obtained below approximately 50 km. Above that level, biases increasing with height are evident. Temperature adjustments are derived, which, when applied to operational rocketsonde data, would in the mean achieve compatibility for synoptic analyses and other uses. Comparisons among wind observations indicate generally good agreement below approximately 60 km. However, some significant problem areas are pointed out and discussed.
The Guiana series of observations also provided valuable information on the diurnal temperature change at stratospheric and mesospheric levels. An evaluation of this aspect is presented, and results are compared with those predicted by tidal theory.
Abstract
Backscatter ultraviolet data obtained by the Explorer E satellite imply very large ozone column abundances above 56 km in the tropics during mid-day. The number of molecules in a vertical column decays by a factor of 2–3 after the solar zenith angle exceeds 75° in the evening. An increase of similar magnitude occurs after sunrise. Such behavior implies the presence of a greater source of odd oxygen than is included in current photochemical theories. Ozone profiles deduced between altitudes of 50 and 62 km when the solar zenith angle exceeds 80° are in reasonable agreement with past rocket results.
Abstract
Backscatter ultraviolet data obtained by the Explorer E satellite imply very large ozone column abundances above 56 km in the tropics during mid-day. The number of molecules in a vertical column decays by a factor of 2–3 after the solar zenith angle exceeds 75° in the evening. An increase of similar magnitude occurs after sunrise. Such behavior implies the presence of a greater source of odd oxygen than is included in current photochemical theories. Ozone profiles deduced between altitudes of 50 and 62 km when the solar zenith angle exceeds 80° are in reasonable agreement with past rocket results.
Abstract
Localized Aviation MOS Program (LAMP) convection and lightning probability and “potential” guidance forecasts for the conterminous United States, developed by the Meteorological Development Laboratory (MDL), have been produced operationally and made available to aviation and other users through the National Digital Guidance Database (NDGD) since April 2014. In response to user requests for improved skill and resolution of these forecasts, MDL has recently made extensive upgrades, and a switch to the new LAMP guidance was made in January 2018. Upgrades include improved spatial and temporal resolution of the predictands, which were enabled by first time LAMP use of finescale radar reflectivity products from the Multi-Radar Multi-Sensor (MRMS) system, total lightning observations from a ground-based lightning sensing system, and finescale model output from the High Resolution Rapid Refresh (HRRR) model. This article describes how these new data inputs are applied in the LAMP model to obtain improved skill and sharpness of the convection and total lightning probability forecasts. Strengths and limitations in LAMP performance are shown through verification statistics and example verification maps for a selected intense convective storm case.
Abstract
Localized Aviation MOS Program (LAMP) convection and lightning probability and “potential” guidance forecasts for the conterminous United States, developed by the Meteorological Development Laboratory (MDL), have been produced operationally and made available to aviation and other users through the National Digital Guidance Database (NDGD) since April 2014. In response to user requests for improved skill and resolution of these forecasts, MDL has recently made extensive upgrades, and a switch to the new LAMP guidance was made in January 2018. Upgrades include improved spatial and temporal resolution of the predictands, which were enabled by first time LAMP use of finescale radar reflectivity products from the Multi-Radar Multi-Sensor (MRMS) system, total lightning observations from a ground-based lightning sensing system, and finescale model output from the High Resolution Rapid Refresh (HRRR) model. This article describes how these new data inputs are applied in the LAMP model to obtain improved skill and sharpness of the convection and total lightning probability forecasts. Strengths and limitations in LAMP performance are shown through verification statistics and example verification maps for a selected intense convective storm case.
