摘要:

Several recent developments have led to a strong upsurge of interest in the dynamics of the middle atmosphere, which is that portion of the atmosphere between the tropopause (8‐16 km) and 100 km altitude. One is the development of new theoretical insights and capabilities, notably the renewed interest in traveling planetary waves, and in the Lagrangian approach to atmospheric dynamics, with the demonstration that it provides illuminating insights into the interactions between waves and the mean flow. The number and scope of computer models has also grown rapidl

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09589

年代:1981

数据来源: WILEY

摘要:

The study of atmospheric dynamics in the Middle Atmosphere Program (MAP) will depend strongly on both the quality and quantity of wind measurements taken during the program. This paper presents a survey of the status of the many techniques which can be utilized to measure wind in the middle atmosphere. Most wind observations in the stratosphere and mesosphere have been made in situ by using balloons and rockets. These observations have been supplemented for many years by observations from ground‐based remote systems such as the meteor radar. In addition, geostrophic winds can be inferred from satellite radiance measurements. In recent years, several radar techniques have been developed that could add significantly to the data base of wind observations for MAP. These include the incoherent scatter radar method, the spaced antenna drift method, and the MST radar technique. The real problem for MAP is to obtain adequate wind data in the 30–80 km range. For this altitude range a variety of rocket techniques are used routinely (about once a week) at stations of the world‐wide Meteorological Rocket Network (MRN). While recent developments in radar measurements of the middle atmosphere raise the possibility of continuous remote wind measurement by using the MST radar and the spaced antenna drift method at a few locations, a truly global set of wind observations must await the development of new satellite techniques that will not be available for another 5–1

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09591

年代:1981

数据来源: WILEY

摘要:

Remote temperature measurements from satellites are currently validated by using rocketsonde and radiosonde data. The reliability of the validation is directly dependent upon how well these measurements and those from the satellites represent the atmosphere. Past experience indicates that remote and in situ mean temperatures usually agree within a few degrees, while agreement between individual observations is not as good. It has been suggested that this may be due to atmospheric variability observed by the rocketsonde and radiosonde techniques but unresolved by the satellite. This observed variability, especially when measurements are obtained close in time and space, is of particular concern since this raises the question whether the variability is due to natural atmospheric change or arises from instrumental instabilities. It is shown that the U.S. rocketsonde, the Super Loki Datasonde, provides reliable temperature measurements to about 1°C. A sample of measurements obtained close together in time is analyzed to provide this estimate. It is important that the Middle Atmosphere Program (MAP) take advantage of the rocketsonde's measurement capability not only to validate remote measurements but to obtain detailed measurements of localized phenomena in the middle atmosphere

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09599

年代:1981

数据来源: WILEY

摘要:

The Millstone Hill 440 MHz radar at Westford, Massachusetts, has been upgraded for studies of turbulence and winds in the troposphere and lower stratosphere. Useful data have been obtained up to 20 km altitude. The radar has been operated with a peak pulse power of 1–1.5 MW, a pulse length of 10 μs and a pulse repetition of 500 Hz. The 150‐foot diameter steerable antenna has been used differently in three types of experiments, (1) Antenna azimuth scans with fixed elevation, (2) elevation scan with fixed azimuth, and (3) fixed antenna. Azimuth scan experiments can obtain both the horizontal and the vertical wind components. Antenna elevation scans have been used to investigate the horizontal structure of turbulence. The fixed antenna experiments provide maximum time resolution and are useful for studying the occurrence of waves. Waves in both the velocity andCn2, the refractive index turbulence structure constant, have been frequently observed at heights near the tropopause and below. The waves have periods 10–20 min and have been interpreted as internal gravity waves. The largest amplitude waves have been found to occur (1–2 km) below the level of a velocity shear. Waves generally persist for several cycles. By using the antenna elevation scan method, the level of turbulence (as measured by theCn2value) has been measured at points separated by 10–20 km. Horizontal patches of turbulence have been found that appear to move wit

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09605

年代:1981

数据来源: WILEY

摘要:

Winds from a medium frequency (2.2 MHz) radar, operating as a partial reflection drifts system, have been obtained for four seasons of 1979/1980. Harmonic and spectral analyses have been used to provide monthly profiles of zonal and meridional winds, and the amplitudes and phases of 12 and 24 hour tides, at heights from 70 to 110 km. There are distinctive changes in tidal vertical wavelengths and phases between winter‐ and summer‐like months. Fluctuations of the mean daily wind and the tides during the stratwarm of February 1980 are documented. Oscillation of the wind, for all seasons, with periods from 2 to 30 days, are related to Rossby periods for atmospheric normal modes. Energy densities for oscillations appropriate to waves ranging in scale from gravity, through tidal, to planetary waves are evaluated by month and are compared with turbulence parameters for energy dissipation rates and vertical eddy diffusion coefficients. There are winter maxima and summer secondary maxima in both energy densities and turbulence parameters, which suggest a relationship between certain waves and the creation of turbule

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09615

年代:1981

数据来源: WILEY

摘要:

Some main results of experimental investigations of the dynamical regime of the lower thermosphere over east Siberia (85–95 km) are presented. Regular measurements of horizontal ionospheric drifts by the radio‐physical method of closely spaced receivers by using a long wavelength transmitter operating at a frequency of 200 kHz have been carried out near Irkutsk during 1975–1979. The seasonal and interannual variations of the prevailing wind (zonal and meridional), and amplitudes and phases of semidiurnal tides, are investigated. Planetary waves with periods of 1–30 days and internal gravity waves with periods of 20–80 min are found in the wind field. Comparison with results of analogous measurements in central Europe reveals a longitudinal effect on the dynamical regime of the mid‐latitude lower t

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09626

年代:1981

数据来源: WILEY

摘要:

A number of mechanisms involving interaction between radiation, photochemistry, and dynamics that may affect the thermal compositional or dynamical structure of the stratosphere are discussed. The effect of coupling between radiative transfer, photochemistry, and advection of ozone by stratospheric winds on the effective relaxation rate of temperature perturbations is illustrated through the use of four examples. It is shown that for the vertical structure typical of planetary waves, ozone fluctuations act to hasten the relaxation of temperature perturbations in the upper stratosphere and to slow the relaxation in the lower half of the stratosphere. Next, the coupling between chemical sources and sinks of ozone and advection of air by motions is discussed. A simple Lagrangian model is employed and related to results from Eulerian model studies. Emphasis is placed upon the large eddy transports produced at the transition level between dynamical and photochemical control of ozone and also upon the mean ozone increases which eddies can produce in regions where there are sharp gradients in both the equilibrium ozone mixing ratio and the relaxation time scale for ozone perturbations. Finally, the variations of the effective relaxation rate of temperature perturbations are shown to be potentially important in determining the mean structure of the stratosphere during the winter season. These variations in the relaxation of temperature perturbations result from ozone variations produced both by chemistry and motions. In particular, a rapid increase in the effective damping rate of planetary waves between the middle and upper stratosphere leads to a rapid increase with height of eddy heat transports produced by the coupling between radiation and dynamics. This in turn can produce a significant modification of the zonal mean structure of the upper stratosphere.

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09631

年代:1981

数据来源: WILEY

摘要:

A zonally averaged numerical model of the thermosphere is used to examine the coupling between neutral composition, including N2, O2, and O, temperature, and winds at solstice for solar minimum conditions. The meridional circulation forced by solar heating results in a summer‐to‐winter flow, with a winter enhancement in atomic oxygen density that is a factor of about 1.8 greater than the summer hemisphere at 160 km. The O2and N2densities are found to be higher in the summer hemisphere by factors of 2–3 at altitudes near 100 km. The O2and N2variations are associated with a latitudinal gradient in total number density, which is required to achieve pressure balance in the presence of large zonal jets. Latitudinal profiles of OI (5577 Å) green line emission intensity are calculated by using both Chapman and Barth mechanisms. Composition of the lower thermosphere is shown to be strongly influenced by circulation patterns initiated in the stratosphere and lower mesosphere, below the lower boundary used in the

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09641

年代:1981

数据来源: WILEY

摘要:

A recurrent, global‐scale, 2‐day oscillation, in the middle atmosphere is well documented in a variety of data sources: meteor wind, partial reflection, satellite, and rocketsonde. The observed period is almost invariably near 2.1 days, and the zonal structure has been established as a westward propagating, wave number 3 mode. Observations also indicate that the meridional wind component maximizes near the equator and dominates the wind field at low latitudes. These features suggest the disturbance's identification with the wave number 3 Rossby‐gravity normal mode of a windless, isothermal atmosphere. Such modes are found to exist largely independent of the mean fields. The eigenperiods are only modestly altered by mean wind variations on the lowest three scale heights, and the influence on the mode structure is local. The vertical growth of amplitude is enhanced in regions of weak westerly wind relative to the wave and equatorward temperature gradient, while the vertical growth rate is retarded and amplitudes may even decay in regions of strong westerlies or poleward temperature gradient. In realistic mean fields, the third Rossby‐gravity mode has magnified responses very near 2.25 days in both equinox and solstice conditions. The horizontal structure remains largely intact in the lowest levels. However, considerable asymmetry is introduced in the solstice upper stratosphere and mesosphere by the magnified vertical growth of amplitude in the summer hemisphere. The latter results from the moderate easterlies and equatorward temperature gradient characteristic of the region. As for the simple eigenstructure, the meridional wind component in this region maximizes near the equator and dominates the wind field up to mid‐

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09654

年代:1981

数据来源: WILEY

摘要:

Evidence is presented for the existence of a wave number 3, westward traveling 2‐day oscillation in the temperature measurements made by the Nimbus 5 SCR and Nimbus 6 PMR instruments. The wave has largest amplitude in the mesosphere at low latitudes of the summer hemisphere and has a markedly asymmetrical meridional structure. It is suggested that the wave may be a free wave similar to the 5‐day wave identified in Nimbus 5 SCR data by Rodgers (1976). The vertical structure shows little phase tilt and a slight indication of an increase in amplitude with hei

ISSN:0148-0227    

DOI:10.1029/JC086iC10p09661

年代:1981

数据来源: WILEY