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NASA NTRS1984

Axisymmetric circulations forced by heat and momentum sources - A simple model applicable to the Venus atmosphere

A simple mechanistic model of a zonally averaged circulation forced by heat and momentum sources is developed and applied to the Venus atmosphere in the light of recent data. Basic equations for a steady-state axisymmetric circulation are discussed, and the parametric dependence of a nearly inviscid Hadley circulation in the absence of eddy forcing is examined and extended to a wide range of thermal Rossby numbers. The effect of diffusion is considered and found to be small for the Venus cloud region. The zonally averaged eddy sources and sinks required to support the zonal superrotation on Venus are determined.

Hou, A. Y.↗

NASA NTRS1985

Teleconnections in the Southern Hemisphere

Monthly anomalies from climatology of sea level pressure and 500 mb geopotential height are used to study teleconnection patterns in the Southern Hemisphere. The data and method used are described, and correlations between zonally averaged anomalies are given. The zonal wavenumber three patterns and teleconnection patterns are given, and the results of eigenvector analysis with teleconnection patterns at 500 mb are reported. The zonally averaged anomalies display two patterns of variability; an out-of-phase relation between high and low latitudes and a pattern in which anomalies in midlatitudes vary out of phase with anomalies in low and high latitudes. In winter, midlatitudes are dominated by three centers of positive correlations over the oceans while the negative correlations are found at high and low latitudes. The teleconnection pattern in summer at 500 mb shows an out-of-phase relation between heights over the subtropical continents and heights in the midlatitude oceans.

Mo, K. C.↗

NASA NTRS1983

Daily earth radiation budget results from the Nimbus-7 scanning radiometer

Nimbus-7 broadband narrow-field-of-view scanning-radiometer data obtained in the Earth Radiation Budget Experiment on three days in 1979 (one with a blocking situation over the Northern Hemisphere, one with normal zonal flow, and one with two mature hurricanes over the Caribbean), are presented graphically and discussed. Both blocking and hurricane situations are characterized by anomalies (relative to the zonal-flow condition) in the zonally averaged emitted flux and albedo, with decreased tropical and midlatitude gradients in the case of blocking.

Randel, D. L.↗

NASA NTRS1984

Structure and dynamics of Saturn's atmosphere

The large-scale structure and dynamics of Saturn's atmosphere, as revealed in the visible markings, wind patterns, and horizontal variation of temperature, are discussed. The large-scale thermal structure is addressed, including the mean vertical structure and the seasons and jets of the horizontal temperature structure. Earth-based and Voyager wind observations are used to discuss the internal rate of rotation, the zonal wind profile, the eddies, and the eddy transport. Dynamic models of the atmospheric circulation are reviewed, discussing the depth of the zonal flow, upwelling and downwelling, deep convection, eddy-mean flow interactions, long-lived ovals, and the zonal velocity profile.

Ingersoll, A. P.↗

NASA NTRS1985

Diagnostic requirements for the superrotation on Venus

The eddy source pattern required to maintain zonally averaged circulation in the solar heating and zonal wind profiles of the Venus atmosphere below 80 km has been calculated. The calculated residual meridional circulation in the cloud top region corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks, which may be due to thermal tides.

Hou, A. Y.↗

NASA NTRS1985

Persistent anomalies, blocking and variations in atmospheric predictability

The fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography, is the model used in the present consideration of low frequency variability regimes in large scale atmospheric dynamics. The solutions obtained are studied as a function of the nondimensional intensity of the forcing and dissipation. The number of modes retained in the analysis allows the multiple equilibria thus obtained, which exhibit blocked and zonal flow patterns very similar to synoptically defined zonal and blocked Northern Hemisphere midlatitude flows, to appear for realistic values of the forcing. The number of episodes of blocked or zonal flow decreases monotonically as their duration increases, in agreement with observations.

Legras, B.↗

NASA NTRS1985

The causation and sensitivity of the northern winter planetary waves

High-resolution calculations of the wintertime stationary atmospheric response to planetary scale topographic and thermal forcings have been made using a numerical model that solves the spherical primitive equations linearized about observed zonal wind and temperature fields. The model equations are presented and their numerical implementation is discussed. The model inputs and parameters are presented and the model's response to relativistic forcing is analyzed. In middle latitudes the response to topographic forcing strongly dominates the response to thermal forcing. In the midlatitude troposphere, the topographic response is insensitive to changes in the zonal wind. In the stratosphere, both the variance and mean are dominated by the topographic response. In general, the sensitivity of the planetary waves to changes in the zonal wind is found to be much smaller than other recent calculations have indicated.

Jacqmin, D.↗

NASA NTRS1985

Variability simulations with a steady, linearized primitive equations model

Solutions of the steady, primitive equations on a sphere, linearized about a zonally symmetric basic state are computed for the purpose of simulating monthly mean variability in the troposphere. The basic states are observed, winter monthly mean, zonal means of zontal and meridional velocities, temperatures and surface pressures computed from the 15 year NMC time series. A least squares fit to a series of Legendre polynomials is used to compute the basic states between 20 H and the equator, and the hemispheres are assumed symmetric. The model is spectral in the zonal direction, and centered differences are employed in the meridional and vertical directions. Since the model is steady and linear, the solution is obtained by inversion of a block, pente-diagonal matrix. The model simulates the climatology of the GFDL nine level, spectral general circulation model quite closely, particularly in middle latitudes above the boundary layer. This experiment is an extension of that simulation to examine variability of the steady, linear solution.

Kinter, J. L., III↗

NASA NTRS1985

Mesospheric Winds at Jicamaraca, Peru (12 Deg S, 77 Deg SW), November 19-21, 1981

The altitude of mean zonal wind in the mesosphere during the whole daytime observations is given. Positive value refers to eastward. At around 70 km, wind corresponds to summer easterly, and changes to westerly with increasing altitude above about 77 km. These are fairly compatible with known features of zonal wind at this latitude. Contour plot shows local time variations of zonal wind with daytime mean subtracted and averaged over three days. Shaded area designated westward wind with contour level of 2 m/s. The daily variation is almost in phase with altitude in the 65 to 80 km region. Thus the semidiurnal tide with long vertical wavelength is inferred to exist. Above 80 km, phase tilt occurs which indicates the contribution of the propagating diurnal component. Here the combination of dc and 12-hr component is fitted to the data below 80 km. The altitude profiles of the amplitude and phase of this semidiurnal component are shown.

Aso, T.↗

NASA NTRS1985

On the interaction between the quasi-2-day wave and the mean flow

Studies of the quasi-2-day wave show that it is a summertime phenomenon. Long-term measurement of the winds in the 60 to 100 km height range at Adelaide show that the wave appears in the late December but that the peak amplitudes are not reached until mid-January. In the summer of 1983 to 1984 the main phase of the wave appeared as a pulse in mid-January which lasted about 7 cycles (14 days). Little or no amplification with height was observed; peak amplitudes were about 60 m/s for the meridional and 20 m/s for the zonal component. Coincident with the onset of the pulse, a temporary but substantial change occurred throughout a deep layer of the upper mesosphere over a period of about 3 days. A change of more than 10 m/s occurred in the northward flow while the change in the zonal flow (about 30 m/s westward) actually caused a reversal of the prevailing zonal circulation.

Craig, R. L.↗

NASA NTRS1986

Equatorial thermospheric measurements of temperatures and winds at Arequipa, Peru

Enhancement of FPI temperatures above quiet levels was observed a few hours after the start of magnetic activity. Magnitude of this enhancement is about 300 degrees. This is followed by relaxation to prestorm levels. Apparent average offset of RPI temperatures from mass spectrometer incoherent scatter radar by 100 to 200 degrees for relatively quiet times is also observed. There was a definite suggestion of a midnight thermal enhancement for April and August data, with a magnitude of about 100 degrees, seen in both 1983 and 1984 observations. There was a definite enhancement of 6300A surface brightness in the south as compared with other directions, probably connected to the tropical airglow arcs. Meridional winds were small (less than 25 m/s) throughout night. Indication of northward migration of the observed 6300A enhancement in the evening hours as observations approach local winter solstice. This is probably related to the observed poleward (to the south) meridional wind (of magnitude 50 m/s) in this period. Zonal component of winds always eastward, but speed approaches zero sooner near equinox than at summer solstice. Typical magnitude at peak is of order 100 to 150 m/s. Suggestion of zonal wind increase after twilight and recovery of 6300A emission for April data. Origin not clear but may be related to midnight thermal enhancement. Meridional wind virtually zero for equinox in 1983; shows evening flow towards winter hemisphere in early evening for solstice data. Suggestion of post-midnight surge in April 1984 data. No major effects associated with magnetic storm activity, but a suggestion of decrease in zonal component below nominal levels.

Meriwether, J. W., Jr.↗

NASA NTRS1986

Optical interferometric measurements of nighttime equatorial thermospheric winds at Arequipa, Peru

Nighttime measurements of equatorial thermospheric wind dynamics were obtained at Arequipa, Peru, with an automated field-widened Fabry-Perot interferometer between April 1983 and August 1983 and reduced data from 62 nights. Significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed. Near the equinox, between 2000 and 2300 LT, the zonal wind component is eastward with an amplitude between 100 and 150 m/s that gradually ebbs to zero by dawn. The meridional component is generally small throughout the night. In the winter months (May to August) and at the winter solstice, the zonal wind persists eastward throughout the night with speeds between 50 and 150 m/s. The meridional component is directed poleward (southward) toward the winter hemisphere with a speed of 50-75 m/s that decays to zero by midnight. Interferometric measurements of the 630.0-nm intensity at equinox showed a major reduction of the emission listing 1 or 2 hours in all directions but south shortly after evening twilight; this decrease was not observed during winter.

Meriwether, J. W., Jr.↗

NASA NTRS1986

Mesoscale waves as a probe of Jupiter's deep atmosphere

Images from the Voyager north/south mapping sequences were searched for waves. A remarkable class of mesoscale waves was identified, with the following features: (1) the wavetrains are usually aligned zonally, i.e., wavecrests are north-south; (2) the average wavelength is 300 km with a standard deviation of only 20%; (3) the wavetrains are long; (4) the waves occur within 25 degrees of the equator, the bulk being at the equator itself; (5) the waves are centered at the extrema (in latitude) of the zonal flow; and (6) the meridional extent of the waves is typically 1 degree of latitude. These observations are interpreted as evidence of gravity waves propagating vertically within a leaky duct. A three-level model is assumed composed of a stable duct which extends up to the base of the NH3 cloud deck near 600 mb. Above this is a thin wave-trapping region characterized by a Richardson number Ri less than 1/4 and containing a critical level, where the local value of the zonal flow velocity equals the phase speed of the wave. This in turn is overlain by a stable region, representing the tropopause region and stratosphere.

Flaser, F. M.↗

NASA NTRS1986

Dynamic characteristics of observed sudden warmings

The planetary wave dynamics of stratospheric sudden warmings in the Northern Hemisphere for a large number of observed events that occurred during winters from 1970 to 1975 and 1978 to 1981 are investigated. The analysis describes wave propagation and zonal flow interaction from the troposphere upwards to near 50 km, and in some years to near 80 km. Three primary topics are covered here: (1) the interaction of zonally propagating and quasi-stationary planetary waves during warming events; (2) planetary wave influence on zonal flow near the stratopause; and (3) planetary wave propagation to near 80 km as seen from Stratospheric and Mesospheric Sounder (SAMS) data.

Dartt, D. G.↗

NASA NTRS1986

The morphology of Antarctic total ozone as seen by TOMS

A more detailed examination of the TOMS observations reveals a number of important aspects of the Antarctic ozone depletion. First, it is noted that the presence of large scale disturbances around the edge of the ozone hole can lead to highly variable station observations. Second, an examination of the zonal mean total ozone for the seven Octobers shows that the large systematic decline is not simply confined to the polar region but exists at midlatitudes as well. Integrations of the total ozone from the South Pole northwards show that a portion of the systematic trend of decreasing Antarctic total ozone (prior to 1985) seems to be due to a redistribution of total ozone to subpolar and midlatitude regions. That is, decreases at high latitudes are compensated by increases at lower latitudes. The correlation between zonal mean total ozone and 70 mb zonal mean temperatures from polar to midlatitudes shows that the systematic decreases in total ozone is well correlated with a systematic decrease in stratospheric temperatures.

Schoeberl, Mark R.↗

NASA NTRS1986

Mesoscale waves as a probe of Jupiter's deep atmosphere

Search of the Voyager images of Jupiter reveals a class of mesoscale waves occurring near the extrema of the zonal velocity profile between latitudes 30 deg S and 30 deg N. The average horizontal wavelength is 300 km, compared to an atmospheric scale height of 20 km; the standard deviation about the mean is only 20 percent. The alignment of most wave trains is nearly zonal, i.e., wave crests are north-south. A typical wave packet is 20 wave crests in length and 1300 km wide. Modeling shows that the waves propagate in a duct below the ammonia condensation level (the visible clouds). For selection of one dominant mode, the Richardson number in the duct must be of order unity; this is the first quantitative determination that has ever been made of the stability of Jupiter's atmosphere below its clouds. The duct is topped by a trapping layer, the ammonia clouds, where the Richardson number is less than 0.25. Meridional trapping of the wave packets is due to the shear in the zonal wind. It is speculated that the period of the waves is diurnal and that they do not propagate poleward of latitudes + or - 30 deg because the Coriolis frequency exceeds the duct Brunt frequency. The waves might be excited by diurnal variations of moist convective activity in the ammonia clouds.

Flasar, F. M.↗

NASA NTRS1986

Effects of eddy initial conditions on nonlinear forcing of planetary scale waves by amplifying baroclinic eddies

The previous study of Young and Villere concerning growth of planetary scale waves forced by wave-wave interactions of amplifying intermediate scale baroclinic eddies is extended to investigate effects of different eddy initial conditions. A global, spectral, primitive equation model is used for the calculations. For every set of eddy initial conditions considered, growth rates of planetary modes are considerably greater than growth rates computed from linear instability theory for a fixed zonally independent basic state. However, values of growth rates ranged over a factor of 3 depending on the particular set of eddy initial conditions used. Nonlinear forcing of planetary modes via wave-wave coupling becomes more important than baroclinic growth on the basic state at small values of the intermediate-scale modal amplitudes. The relative importance of direct transfer of kinetic energy from intermediate scales of motion to a planetary mode, compared to baroclinic conversion of available potential energy to kinetic energy within that planetary mode, depends on the individual case. In all cases, however, the transfer of either kinetic or available potential energy to the planetary modes was accomplished principally by wave-wave transfer from intermediate scale eddies, rather than from the zonally averaged state. The zonal wavenumber 2 planetary mode was prominent in all solutions, even in those for which eddy initial conditions were such that a different planetary mode was selectively forced at the start. General characteristics of the structural evolution of the planetary wave components of total heat and momentum flux, and modal structures themselves, were relatively insensitive to variations in eddy initial conditions, even though quantitative details varied from case to case.

Young, Richard E.↗

NASA NTRS1987

Global atmospheric circulation statistics: Four year averages

Four year averages of the monthly mean global structure of the general circulation of the atmosphere are presented in the form of latitude-altitude, time-altitude, and time-latitude cross sections. The numerical values are given in tables. Basic parameters utilized include daily global maps of temperature and geopotential height for 18 pressure levels between 1000 and 0.4 mb for the period December 1, 1978 through November 30, 1982 supplied by NOAA/NMC. Geopotential heights and geostrophic winds are constructed using hydrostatic and geostrophic formulae. Meridional and vertical velocities are calculated using thermodynamic and continuity equations. Fields presented in this report are zonally averaged temperature, zonal, meridional, and vertical winds, and amplitude of the planetary waves in geopotential height with zonal wave numbers 1-3. The northward fluxes of sensible heat and eastward momentum by the standing and transient eddies along with their wavenumber decomposition and Eliassen-Palm flux propagation vectors and divergences by the standing and transient eddies along with their wavenumber decomposition are also given. Large interhemispheric differences and year-to-year variations are found to originate in the changes in the planetary wave activity.

Wu, M. F.↗