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- Author or Editor: Roderick S. Quiroz x
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Abstract
Satellite-measured radiances offer the first opportunity for investigating the total structure of winter stratospheric warmings, a phenomenon whose cause is still unknown despite intensive study since 1952, Vertical temperature profiles inferred from Nimbus III and IV SIRS 15 μ infrared measurements do not appear to be ideally suited for monitoring sudden warmings above the 10-mb level because of increased dependence, in the upper stratosphere, of inverse solutions of the radiative transfer equation on the climatological or “first-guess” profiles employed. In this paper, a temperature model for stratospheric warmings is presented, from which radiance changes are calculated by direct solution of the integral radiative transfer equation. The model is based on a review of past warming events and its construction was guided by stated physical constraints. The radiance changes correspond to changes in the temperature structure from a pre-warming condition to an arbitrary phase of warming. Warmings by 20–90C centered at altitudes 20–45 km are considered. For a typical warm-layer thickness (20–25 km), it is shown that the central altitude and the amplitude of warming can be satisfactorily discriminated through the use of two simple parameters including the ratio of radiance change in SIRS channels 7 (∼678 cm−1) and 8 (∼669 cm−1). A nomogram is developed for specifying warming altitude and amplitude from observed radiance changes and is tested during a major warming which began in late December 1969 and which involved warming by more than 70C. Amplitudes and altitudes of warming were generally well specified, with rms departures from the observed values of 8C in amplitude and 2.4 km in altitude, if one unsuccessful specification for warming above 40 km is excluded. Possible explanations of this case are suggested.
Abstract
Satellite-measured radiances offer the first opportunity for investigating the total structure of winter stratospheric warmings, a phenomenon whose cause is still unknown despite intensive study since 1952, Vertical temperature profiles inferred from Nimbus III and IV SIRS 15 μ infrared measurements do not appear to be ideally suited for monitoring sudden warmings above the 10-mb level because of increased dependence, in the upper stratosphere, of inverse solutions of the radiative transfer equation on the climatological or “first-guess” profiles employed. In this paper, a temperature model for stratospheric warmings is presented, from which radiance changes are calculated by direct solution of the integral radiative transfer equation. The model is based on a review of past warming events and its construction was guided by stated physical constraints. The radiance changes correspond to changes in the temperature structure from a pre-warming condition to an arbitrary phase of warming. Warmings by 20–90C centered at altitudes 20–45 km are considered. For a typical warm-layer thickness (20–25 km), it is shown that the central altitude and the amplitude of warming can be satisfactorily discriminated through the use of two simple parameters including the ratio of radiance change in SIRS channels 7 (∼678 cm−1) and 8 (∼669 cm−1). A nomogram is developed for specifying warming altitude and amplitude from observed radiance changes and is tested during a major warming which began in late December 1969 and which involved warming by more than 70C. Amplitudes and altitudes of warming were generally well specified, with rms departures from the observed values of 8C in amplitude and 2.4 km in altitude, if one unsuccessful specification for warming above 40 km is excluded. Possible explanations of this case are suggested.
Abstract
Knowledge of the horizontal variation of density is required in a number of problems, such as the calculation of aerodynamic heating rates of lifting reentry vehicles in near-horizontal flight. On constant-pressure surfaces the density field is given by the isotherms; but since the pressure surfaces may have great inclination in the stratosphere and mesosphere, compared with the troposphere, constant-height analyses are needed for a direct measure of the horizontal density variations. With suitable assumptions, previously analyzed constant-pressure maps can be converted hydrostatically to yield accurate constant-height maps. A computerized procedure is described for obtaining such maps from high-level constant-pressure analyses of the National Meteorological Center. Examples of synoptic density maps obtained for 30 and 40 km are shown and are discussed in relation to standard atmosphere values of the density. Good agreement is found between average values based on the maps and 1966 Supplemental Atmosphere values for 30 and 60N. The synoptic variability, however, is considerable, with strong horizontal gradients a common feature in high latitudes in winter. The summer atmosphere at the heights examined is found to be nearly barotropic, with relatively weak density gradients. For a hypothetical reentry trajectory, sample data for a specific day in winter are used to calculate the density changes along the trajectory.
Abstract
Knowledge of the horizontal variation of density is required in a number of problems, such as the calculation of aerodynamic heating rates of lifting reentry vehicles in near-horizontal flight. On constant-pressure surfaces the density field is given by the isotherms; but since the pressure surfaces may have great inclination in the stratosphere and mesosphere, compared with the troposphere, constant-height analyses are needed for a direct measure of the horizontal density variations. With suitable assumptions, previously analyzed constant-pressure maps can be converted hydrostatically to yield accurate constant-height maps. A computerized procedure is described for obtaining such maps from high-level constant-pressure analyses of the National Meteorological Center. Examples of synoptic density maps obtained for 30 and 40 km are shown and are discussed in relation to standard atmosphere values of the density. Good agreement is found between average values based on the maps and 1966 Supplemental Atmosphere values for 30 and 60N. The synoptic variability, however, is considerable, with strong horizontal gradients a common feature in high latitudes in winter. The summer atmosphere at the heights examined is found to be nearly barotropic, with relatively weak density gradients. For a hypothetical reentry trajectory, sample data for a specific day in winter are used to calculate the density changes along the trajectory.
An inventory of Soviet meteorological rocket soundings, 1957–1966, is provided, along with a sample of the first detailed observational results published by the Central Aerological Observatory. A description is given of the basic observational technique, involving an assembly of pressure gages and resistance thermometers in a separated nose cone which descends by parachute. Observational accuracies are noted. Similarities and differences in United States and Soviet rocket programs are pointed out, and attention is called to Soviet emphasis on density derivation and on scientific scheduling of launchings for the study of special atmospheric features such as stratospheric warmings.
An inventory of Soviet meteorological rocket soundings, 1957–1966, is provided, along with a sample of the first detailed observational results published by the Central Aerological Observatory. A description is given of the basic observational technique, involving an assembly of pressure gages and resistance thermometers in a separated nose cone which descends by parachute. Observational accuracies are noted. Similarities and differences in United States and Soviet rocket programs are pointed out, and attention is called to Soviet emphasis on density derivation and on scientific scheduling of launchings for the study of special atmospheric features such as stratospheric warmings.
Abstract
In preference to the use of persistent height anomalies for determining the presence of blocking, new criteria were developed which take the observed flow conditions into account. These criteria were applied daily at 500 mb, using filtered Northern Hemisphere height maps retaining zonal waves 0–5, beginning in July 1981. Blocking statistics for the 3-yr period through June 1984 are in remarkably close agreement with the results from longer-period published data sets involving the use of a split-jet flow as a principal criterion. Thus this data set, albeit short, is deemed appropriate for investigating the long-wave properties of blocks.
During July 1981–June 1984, 47 blocks were observed; the long-wave composition of blocks lasting at least 10 days (24 cases) is examined in detail. Contrary to Austin's (1980) hypothesis that blocking should arise from the constructive interference of stationary long waves with enhanced amplitude but normal phase, it is found that traveling waves (predominantly retrogressive) played a significant role in 20 of the 24 cases. The long waves making up these blocks, in the zonal wavenumber domain 1–4, moreover had a phase behavior consistent with the wavenumber dependence in the Rossby wave dispersion equation.
A dramatic increase in Northern Hemisphere blocking activity within the sample, from 1982–83 to 1983–84, is shown to be due mainly to increases in the Pacific–North American (PNA) and North Soviet Union (NSU) sectors. A time–longitude diagram depicts the shifting of blocking activity from the main region of blocking, the Atlantic–west European area, to the PNA and NSU sectors. These regional shifts were substantially associated with the longitudinal phase pattern of travelling waves 1 in high latitudes.
Abstract
In preference to the use of persistent height anomalies for determining the presence of blocking, new criteria were developed which take the observed flow conditions into account. These criteria were applied daily at 500 mb, using filtered Northern Hemisphere height maps retaining zonal waves 0–5, beginning in July 1981. Blocking statistics for the 3-yr period through June 1984 are in remarkably close agreement with the results from longer-period published data sets involving the use of a split-jet flow as a principal criterion. Thus this data set, albeit short, is deemed appropriate for investigating the long-wave properties of blocks.
During July 1981–June 1984, 47 blocks were observed; the long-wave composition of blocks lasting at least 10 days (24 cases) is examined in detail. Contrary to Austin's (1980) hypothesis that blocking should arise from the constructive interference of stationary long waves with enhanced amplitude but normal phase, it is found that traveling waves (predominantly retrogressive) played a significant role in 20 of the 24 cases. The long waves making up these blocks, in the zonal wavenumber domain 1–4, moreover had a phase behavior consistent with the wavenumber dependence in the Rossby wave dispersion equation.
A dramatic increase in Northern Hemisphere blocking activity within the sample, from 1982–83 to 1983–84, is shown to be due mainly to increases in the Pacific–North American (PNA) and North Soviet Union (NSU) sectors. A time–longitude diagram depicts the shifting of blocking activity from the main region of blocking, the Atlantic–west European area, to the PNA and NSU sectors. These regional shifts were substantially associated with the longitudinal phase pattern of travelling waves 1 in high latitudes.
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Abstract
Relationships among the high-latitude stratospheric zonal wind, the tropospheric zonal wind in the region of the subtropical jet and over the equator, the Southern Oscillation, and the stratospheric tropical quasi-biennial oscillation (QBO) were examined from monthly anomaly data for 13 years (1968–80). Patterns of correlation wore found which are broadly consistent with the theory on vertical and latitudinal Rossby wave propagation, with high correlations diminishing rapidly in association with easterly basic flow. Lag correlations as high as 0.8–0.9 were found for leads of ∼1–7 months, based on three-month average anomalies for successive months. The simplified lead path is from Southern Oscillation to equatorial winds to subtropical winds to stratospheric high-latitude winds. Relationships involving the QBO appear weak compared to those involving the extratropical flows, the tropospheric equatorial flow of the east Pacific, and the Southern Oscillation. Even so, the structure of correlation found between the stratospheric high-latitude winds (or height gradients) and the QBO is consistent with “compositing” results of Holton and Tan (1980, 1982); moreover, the correlations found between the stratospheric high-latitude flow and the Southern Oscillation are consistent with compositing results of van Loon et al. (1982). Spectra for the variables examined all show a quasi-biennial signal, but coherences involving the QBO at periods 20–30 months were found to be weak to moderate, whereas coherences involving other pairs of variables were moderate to strong.
Abstract
Relationships among the high-latitude stratospheric zonal wind, the tropospheric zonal wind in the region of the subtropical jet and over the equator, the Southern Oscillation, and the stratospheric tropical quasi-biennial oscillation (QBO) were examined from monthly anomaly data for 13 years (1968–80). Patterns of correlation wore found which are broadly consistent with the theory on vertical and latitudinal Rossby wave propagation, with high correlations diminishing rapidly in association with easterly basic flow. Lag correlations as high as 0.8–0.9 were found for leads of ∼1–7 months, based on three-month average anomalies for successive months. The simplified lead path is from Southern Oscillation to equatorial winds to subtropical winds to stratospheric high-latitude winds. Relationships involving the QBO appear weak compared to those involving the extratropical flows, the tropospheric equatorial flow of the east Pacific, and the Southern Oscillation. Even so, the structure of correlation found between the stratospheric high-latitude winds (or height gradients) and the QBO is consistent with “compositing” results of Holton and Tan (1980, 1982); moreover, the correlations found between the stratospheric high-latitude flow and the Southern Oscillation are consistent with compositing results of van Loon et al. (1982). Spectra for the variables examined all show a quasi-biennial signal, but coherences involving the QBO at periods 20–30 months were found to be weak to moderate, whereas coherences involving other pairs of variables were moderate to strong.
Abstract
The period of the stratospheric quasi-biennial oscillation (QBO) in zonal wind is studied with the aid of rocket observations at Kwaialein (9°N, 168°N) for altitudes 25–35 km and rawinsonde observations for Balboa (9°N, 80°W) for pressure levels 50–10 mb, the latter for 1951–79. Since 1951, the period has varied between 21 and 34 months, with an average value near 28 months (2.3 years) at any height, but with slightly greater variability in the lower stratosphere. While the expected downward propagation of easterly and westerly phase was clearly observed, a downward propagation of period is not evident, consistent with the variable structure of the phase descent rates. A systematic modulation of QBO period occurred approximately and inversely in accord with the level of solar activity. Physical mechanisms that might account for the observed variation in QBO period are identified, within the context of assumed dynamical forcing by tropospheric waves. Comprehensive insight into the actual process accounting for the observed period modulation would be gained from improved observational data, including observations of solar ultraviolet behavior.
Abstract
The period of the stratospheric quasi-biennial oscillation (QBO) in zonal wind is studied with the aid of rocket observations at Kwaialein (9°N, 168°N) for altitudes 25–35 km and rawinsonde observations for Balboa (9°N, 80°W) for pressure levels 50–10 mb, the latter for 1951–79. Since 1951, the period has varied between 21 and 34 months, with an average value near 28 months (2.3 years) at any height, but with slightly greater variability in the lower stratosphere. While the expected downward propagation of easterly and westerly phase was clearly observed, a downward propagation of period is not evident, consistent with the variable structure of the phase descent rates. A systematic modulation of QBO period occurred approximately and inversely in accord with the level of solar activity. Physical mechanisms that might account for the observed variation in QBO period are identified, within the context of assumed dynamical forcing by tropospheric waves. Comprehensive insight into the actual process accounting for the observed period modulation would be gained from improved observational data, including observations of solar ultraviolet behavior.
Abstract
A major warming above the 10-mb level in February 1966 is described with the aid of rocket data from high-latitude stations at Heiss Island (81° N.) and Churchill (59° N.), together with high-level radiosonde reports from Berlin, Germany. At Heiss Island a temperature increase of 85°C is deduced at an altitude of 32 km, preceded by a record wind of nearly 400 kt (at 39 km), verified through thermal wind computations. Extraordinary vertical motions reaching 60 cm sec−1 are calculated from the thermodynamic equation. The warming is shown to have been similar to major warmings of the lower stratosphere in several respects, including the occurrence of 1) high winds related to pressure-gradient intensification several days before the peak temperature and 2) upward vertical motion in high latitudes in response to strong horizontal advection. Rocket soundings extending to the mesopause indicate the occurrence of warming to a height of at least 70 km. The mesospheric data further suggest that prior to warming events the upper polar mesosphere is characteristically cold, in accord with radiative calculations for winter. However, the mesospheric analysis is hampered by poor sampling, and an improved program of observation is needed to clarify the full structure of “stratospheric” warmings.
Abstract
A major warming above the 10-mb level in February 1966 is described with the aid of rocket data from high-latitude stations at Heiss Island (81° N.) and Churchill (59° N.), together with high-level radiosonde reports from Berlin, Germany. At Heiss Island a temperature increase of 85°C is deduced at an altitude of 32 km, preceded by a record wind of nearly 400 kt (at 39 km), verified through thermal wind computations. Extraordinary vertical motions reaching 60 cm sec−1 are calculated from the thermodynamic equation. The warming is shown to have been similar to major warmings of the lower stratosphere in several respects, including the occurrence of 1) high winds related to pressure-gradient intensification several days before the peak temperature and 2) upward vertical motion in high latitudes in response to strong horizontal advection. Rocket soundings extending to the mesopause indicate the occurrence of warming to a height of at least 70 km. The mesospheric data further suggest that prior to warming events the upper polar mesosphere is characteristically cold, in accord with radiative calculations for winter. However, the mesospheric analysis is hampered by poor sampling, and an improved program of observation is needed to clarify the full structure of “stratospheric” warmings.
