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Various topics related to middle atmosphere research are discussed. Variability of the middle atmosphere during winter, climatology, gravity waves, atmospheric turbulence, transport processes of trace species and aerosols, and research in the Antarctic are among the topics covered.
Ozone observed by seven satellite instruments, the Atmospheric Trace Molecule Spectroscopy instrument (ATMOS), Stratospheric Aerosol and Gas Experiment (SAGE) II, Polar Ozone and Aerosol Measurement (POAM) II instrument, Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS), Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA), and Millimeter-wave Atmospheric Sounder (MAS), during early November 1994 is mapped in equivalent latitude/potential temperature (EqL/ theta )space to facilitate nearly global comparisons of measurements taken in similar air masses.
The evolution of wave energy, enstrophy, and wave motion for atmospheric Rossby waves in a variable mean flow are discussed from a theoretical and pedagogic standpoint. In the absence of mean flow gradients, the wave energy density satisfies a local conservation law, with the appropriate flow velocity being the group velocity. In the presence of mean flow variations, wave energy is not conserved, but wave action is, provided the mean flow is independent of longitude. Wave enstrophy is conserved for arbitrary variations of the mean flow. Connections with Eliassen-Palm flux are also discussed.
The evolution of wave energy, enstrophy, and wave motion for atmospheric Rossby waves in a variable mean flow are discussed from a theoretical and pedagogic standpoint. In the absence of mean flow gradients, the wave energy density satisfies a local conservation law, with the appropriate flow velocity being the group velocity. In the presence of mean flow variations, wave energy is not conserved, but wave action is, provided the mean flow is independent of longitude. Wave enstrophy is conserved for arbitrary variations of the mean flow. Connections with Eiiassen-Palm flux are also discussed.
Alfven wave propagation in a spherically symmetric isothermal and stratified stellar atmosphere are analzyed using a time-dependent MHD numerical model. Particular consideration is given to wave reflection and the resultant trapping of the wave due to a peak in the Alfven speed in the atmosphere. Resonance frequencies in the trapping region and the effect of trapping on Alfven wave pressure force and propagation are examined. The data reveal that Alfven wave trapping has a potentially important role in accelerating winds from cool stars.
Broad, tutorial coverage is given to the technical and scientific aspects of mesosphere stratosphere troposphere (MST) meteorological radar systems. Control issues, signal processing, atmospheric waves, the historical aspects of radar atmospheric dynamics, incoherent scatter radars, radar echoes, radar targets, and gravity waves are among the topics covered.
The Atmospheric Laboratory for Applications and Science-2 (ATLAS-2), was designed to collect data on the relationship between the sun's energy output and Earth's middle atmosphere and how these factors affect the ozone layer. The ATLAS-2 flew on the Space Shuttle Discovery's mission SST-56, launched on April 8, 1993. The videotape consists of an animated tour of the instruments that were included as part of the mission. The first half of the tape shows the various instruments, pointing to each in turn and identifying each by the associated initialisms. The instruments identified were: the Atmospheric Trace Molecule Spectroscopy (ATMOS), Millimeter Wave Atmospheric Sounder (MAS), Shuttle Solar Backscatter Ultraviolet/A (SSBUV/A) spectrometer, Solar Spectrum Measurement (SOLSPEC) instrument, Solar Ultraviolet Irradiance Monitor (SUSIM), Active Cavity Radiometer (ACR) and Solar Constant (SOLCON).) The second half of the animation shows the same tour without the pointing or the identification of the instruments.
A universal spectrum of atmospheric buoyancy waves is proposed based on data from radiosonde, Doppler navigation, not-wire anemometer and Jimsphere balloon. The possible existence of such a universal spectrum clearly will have significant impact on several areas in the study of the middle atmosphere dynamics such as the parameterization of sub-grid scale gravity waves in global circulation models; the transport of trace constituents and heat in the middle atmosphere, etc. Therefore, it is important to examine more global wind data with temporal and spatial resolutions suitable for the investigation of the wave spectra. Mesosphere-stratosphere-troposphere (MST) radar observations offer an excellent opportunity for such studies. It is important to realize that radar measures the line-of-sight velocity which, in general, contains the combination of the vertical and horizontal components of the wave-associated particle velocity. Starting from a general oblique radar observation configuration, applying the dispersion relation for the gravity waves, the spectrum for the observed fluctuations in the line-of-sight gravity-wave spectrum is investigated through a filter function. The consequence of the filter function on data analysis is discussed.
Atmospheric effects on millimeter wave earth-space communication channels
Numerous experiments on the detection of atmospheric waves in the frequency range from acoustic to planetary at meteor heights have revealed that important wave sources are meteorological processes in the troposphere (cyclones, atmospheric fronts, jet streams, etc.). A dynamical theory based on the others work include describing the adaptation of meteorological fields to the geostropic equilibrium state. According to this theory, wave motions appear as a result of constant competition between the maladjustment of the wind and pressure fields due to nonlinear effects and the tendency of the atmosphere to establish a quasi-geostrophic equilibrium of these fields. These meteorological fields are discussed.
The weakly nonlinear theory for internal solitary waves is reviewed, and theoretical results of the vertical and horizontal structure of temperature, vertical displacements, and vertical and horizontal perturbations to the wind field associated with steadily propagating solitary waves are presented in two idealized atmospheric configurations. One configuration is representative of solitary waves observed in the lower troposphere and the other of solitary waves that occupy the entire troposphere. The important results of the theory are presented in a form that can be readily used by observationalists. The results obtained are then analyzed using actual rawinsonde data for two well-documented observations of atmospheric solitary waves, which are analogous to the two idealized configurations. The importance and difficulties of properly identifying the waveguide within which the solitary wave is confined are discussed. The fundamental role of a critical level in ducting the disturbances and thus in defining the thickness of the waveguide is illustrated in the example dealing with the solitary wave occupying the entire troposphere. Together, these two examples illustrate the decisions and compromises that must be made in applying the theory to the real atmosphere.
Characteristic plane harmonic free internal neutral atmospheric wave oblique propagation through horizontally stratified quiet atmosphere for various thermospheric parameters
An investigation is presented of coupled ocean-atmosphere models' behavior in an environment where atmospheric wave speeds are substantially reduced from dry atmospheric values by such processes as condensation-moisture convergence. Modes are calculated for zonally periodic, unbounded ocean-atmosphere systems, emphasizing the importance of an inclusion of prognostic atmosphere equations in simple coupled ocean-atmosphere models with a view to simulations of intraseasonal variability and its possible interaction with interannual variability. The dynamics of low and high frequency modes are compared; both classes are sensitive to the degree to which surface wind anomalies are able to affect the evaporation rate.
This study focuses on ocean surface fluxes, mainly the latent heat flux, and their impact on MJO propagation and associated precipitation structures over the Indian Ocean and Maritime Continent. The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model is used to simulate two MJO events during the 2017-2018 season: the December 10 - January 20, 2017 case, which maintained its strong precipitation signal over the Maritime Continent, and the March 1 - 20, 2018 case, which was weaker and did not propagate through the Maritime Continent. Both simulated MJO events show positive biases in surface rainfall compared with GPM IMERG data. During the MJO suppressed phase, the simulations rain more often than the observations. During the active phase, the westward propagating precipitation structures are more organized and much stronger compared with the observations, sometimes forming westward propagating cyclones that weakened the eastward precipitation signals. Two aspects of the surface flux interactions are investigated: the impact of the domain mean surface fluxes, and the impact of storm scale circulations and their interactions with local surface fluxes. Both aspects affect water vapor budget, atmosphere instability and mean flow, through which convection initiation, organization, and propagation are influenced. Model sensitivity tests with different radiation, microphysics, PBL schemes and nudging schemes indicate that in the control simulations, higher SST and surface fluxes, especially during the suppressed period, are the main reason of rainfall overestimation compared with IMERG data. The strong westward propagating signals are caused by both increased atmosphere instability and reduced mean wind shear. Unfortunately, the small differences in mean SST and surface fluxes between different model sensitivity tests are all within the satellite observation error margin, and cannot be directly corroborated by observations. One of the advantages of CYGNSS satellites is that they observe ocean surface wind and heat fluxes underneath strong rainfall events such as the convective systems associated with MJO active phases. Currently we are comparing CYGNSS level 2 surface fluxes retrievals and the model simulations in order to better understand the second aspect of the MJO and surface fluxes interactions, and how this affects MJO strengths and propagations. The interactive atmosphere-ocean-wave model also provides cases that directly comparing satellite observables (the bistatic radar cross section) and the model simulations (through CYGNSS satellite simulator). These discrepancies are more prominent in coupled ocean simulations, mainly due to higher SST and enhanced surface fluxes.
Gravity waves are ubiquitous throughout the atmosphere of Mars. Their propagation and dissipation influence the circulation and thermal structure of the middle and upper atmosphere. Yet there have been few studies of gravity wave characteristics in the middle atmosphere, a region that is critical for their propagation from generation in the lower atmosphere to dissipation and associated exchanges of momentum and energy in the upper atmosphere. There have been few studies because few atmospheric profiles span the middle atmosphere with the kilometer-scale or smaller vertical resolution that is Required to characterize gravity waves. Here we report the characterization of gravity waves in the middle atmosphere using 12 high-resolution atmospheric density profiles. Four of these were acquired from a ground-based stellar occultation from 1976 that yielded immersion and emersion profiles on opposite sides of the planet, and the remaining eight were measured during atmospheric entry by landers and rovers. Predominant wavelengths were 3–14 km, and amplitudes were generally 0.8%–2.5%. Where static stability is large and positive, gravity waves grow efficiently. In other instances, static stability is not large and positive over a wide altitude range, and gravity wave amplitudes do not behave as neatly. These observations of gravity waves in the middle atmosphere of Mars can be used to test gravity wave parameterizations in large-scale general circulation models and to investigate predictions for how gravity wave propagation and dissipation influence the circulation and thermal structure of the middle and upper atmosphere.
Previously collected data on atmospheric pressure, density, temperature and winds between 25 and 200 km from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others were analyzed by a daily-difference method, and results on the magnitude of atmospheric perturbations interpreted as gravity waves and planetary waves are presented. Traveling planetary-wave contributions in the 25-85 km range were found to have significant height and latitudinal variation. It was found that observed gravity-wave density perturbations and wind are related to one another in the manner predicted by gravity-wave theory. It was determined that, on the average, gravity-wave energy deposition or reflection occurs at all altitudes except the 55-75 km region of the mesosphere.
Decimeter and centimeter radio wave propagation in atmosphere of Venus
Observed wave-like cloud features on Venus, which at times form a Y-like structure which encircles the planet, were modelled numerically. Linearized primitive equations for a shallow, hydrostatic atmosphere are defined, along with upper boundary layer conditions for the 4-6 day periods detected in the atmospheric response to forcing. The basic state of the Venus atmosphere was considered to display variations in static stability and the mean zonal wind as a function of altitude. Forcing was introduced over a wide range of frequencies in order to produce the target oscillation modes. Combination of a midlatitude Rossby wave and an equatorial Kelvin wave was found to yield the observed Y-shape, which could be preserved with nonlinear coupling.