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NASA NTRS1973

Radiative instability of a cloudy planetary atmosphere.

A cloudy planetary atmosphere at rest is shown to be unstable to disturbances of large horizontal scale. The energy source for the instability is the change in radiative heat flux associated with vertical displacement near the emitting level. A simple model is described in which the net heating rate in the cloud is proportional to the vertical displacement of the cloud. The constant of proportionality may be either positive or negative. Disturbances may take the form of either quasi-steady geostrophic motions or amplified inertia-gravity waves. The model is applied to Jupiter's zonal winds and to motions near the Venus cloud tops, and provides a possible explanation for many important features of these two flows.

Gierasch, P. J.↗

NASA NTRS1973

Estimation of bounds for the geopotential coefficients

A numerical analysis of zonal geopotential coefficients and the bounds on the tesseral coefficients is presented. Modifications designed to incorporate data on the earth's density distribution are developed. The nature of the modifications and the application are discussed.

Payne, M. H.↗

NASA NTRS1973

Mean meridional circulation in the Southern Hemisphere stratosphere during the polar night

Atmospheric structure derived from satellite, multichannel radiance data is used to calculate zonally averaged vertical motions in the wintertime stratosphere of both hemispheres. The Northern Hemisphere calculations confirm the two celled meridional circulation calculated by previous authors. The Southern Hemisphere results show a three celled structure with descending motion over the South Pole. The variability of the mean meridional circulation in the Southern Hemisphere in relation to the presence or absence of a minor midwinter warming is also discussed.

Adler, R. F.↗

NASA NTRS1974

Periodic variations in stratospheric meridional wind from 20-65 km, at 80 deg N to 8 deg S

The variability of stratospheric meridional winds is examined in both space and time. Height-latitude sections for January along 70 deg E and 90 deg W show a divergence zone above 50 km near 60 deg N and an intense convergence zone 40 km near 50 deg N over North America. This latter structure, with southward winds in the Arctic and northward winds at mid-latitudes over North America, persists from October through April. Tidal winds dominate all other circulation features in summer at all latitudes, and throughout the year at low latitudes. To help understand the observed patterns of variability, long-term periodic features are analyzed. The quasi-biennial oscillation, annual wave, and four-month wave have amplitudes of about 10, 20, and 10 m/sec respectively in the Arctic near 45 km. The phase of the annual wave changes by nearly 180 deg in a narrow zone near 45 deg N. The semiannual wave has an amplitude of 10 m/sec. 50 deg N above 50 km equinoctial phase dates in the region of maximum amplitude. This polar semiannual wave corresponds closely to that previously found in the zonal wind.

Nastrom, G. D.↗

NASA NTRS1973

Investigation of the responses of the general circulation at 700 mb to solar-geomagnetic disturbance

The Northern Hemisphere 700 mb contour heights from 20 N to 70 N for the period 1947-1970 are studied in conjunction with 272 key days, where the daily increase of the Ci index equals or exceeds 1.0. The superposed epoch method is applied from 33 days before to 66 days after the key day for a variety of zonal and meridional indices. It is shown that the 700 mb height difference between 20 N and 55 N increases significantly in winter 4 days following geomagnetic disturbance (in summer a less prominent but statistically significant increase is found 2 days earlier). The effect is most clear in winter in the quadrant 90-175 W and corresponds to a 7% increase in the mean geostrophic westerly flow. The statistical significance of the results is established by applying Student's t-test to the difference of each daily mean from the continuum.

Stolov, H. L.↗

NASA NTRS1973

Satellite-tracking and earth-dynamics research programs

The following activities in Smithsonian Astrophysical Observatory's (SAO) earth-dynamics programs are covered: (1) satellite-tracking network operations; (2) satellite geodesy and geophysics programs; (3) atmospheric research. Approximately 46,000 successful range measurements were acquired by the SAO laser stations in Peru, South Africa, Brazil, and Arizona. The Peole satellite-tracking campaign conducted in conjunction with the Centre National d'Etudes Spatiales was completed in August 1973. The SAO network obtained 4482 validated returns of 310 arcs of Peole. These data are of particular value for obtaining more accurate gravity-field and zonal-harmonics coefficients.

Weiffenbach, G. C.↗

NASA NTRS1973

Interhemispheric comparison of atmospheric circulation features as evaluated from Nimbus satellite data

Atmospheric structure derived from satellite, multichannel radiance data is used to calculate zonally averaged vertical motions in the wintertime stratosphere of both hemispheres using a heat budget approach. The Northern Hemisphere calculations based on the satellite data are shown to compare favorably with a computation carried out with conventional data, and with results of previous studies. The mean Southern Hemisphere pattern for the month of July 1969 indicates a two-celled structure with the high latitude cell centered at 60-65S. The axis of sinking motion in this cell is at approximately 50S, while the rising motion is centered at 70S. Thus the Antarctic stratospheric jet stream is associated with an indirect cell. Two individual ten-day periods from July 1969 are examined to compare the mean meridional circulation and eddy heat flux patterns in the Southern Hemisphere during a minor midwinter warming and during a quiet period.

Reiter, E. R.↗

NASA NTRS1974

The ROAD program

The philosophy, history, operation, calibration of and some analyses with the ROAD (Rapid Orbit Analysis and Determination) program are described. This semi-numeric trajectory program integrates and analyses mean element variations for earth orbits with great efficiency. Through it's use, extensive zonal, resonant harmonic and earth tidal determinations have been made at Goddard Space Flight Center since 1969.

Wagner, C. A.↗

NASA NTRS1974

The aurora as a source of planetary-scale waves in the middle atmosphere

Photographs of global scale auroral forms taken by scanning radiometers onboard weather satellites in 1972 show that auroral bands exhibit well organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well organized neutral wind fields in the 150- to 200-km region during the geomagnetic storm of May 27, 1967. Further, the horizontal scale size revealed by these observations are in agreement with that of high altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. Although there is, at present, no observation of substorm related waves of this scale size at mesospheric and stratospheric altitudes, the possible existence of a new source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.

Chiu, Y. T.↗

NASA NTRS1973

Transequatorial effects of sea-surface temperature anomalies in a global general circulation model

An effort is made to describe the development of the model atmosphere's response to the sea-surface temperature (SST) anomalies in terms of their effect on the pole-to-pole meridional profile of the zonal mean 600-mb surface, which represents approximately the middle level of the model. The initial effect of a positive SST anomaly located in extratropical latitudes of the Pacific Ocean is found to be an inflation of the isobaric surfaces, relative to a control run, within the latitude band of the warm pool. In experiments with a North Pacific warm pool, the inflation continued for about 3 weeks in both winter and summer.

Spar, J.↗

NASA NTRS1974

The GISS model of the global atmosphere

A description and numerical results are presented for a global atmospheric circulation model developed at the Goddard Institute for Space Studies (GISS). The model version described is a 9-level primitive-equation model in sigma coordinates. It includes a realistic distribution of continents, oceans and topography. Detailed calculations of energy transfer by solar and terrestrial radiation make use of cloud and water vapor fields calculated by the model. The model hydrologic cycle includes two precipitation mechanisms: large-scale supersaturation and a parameterization of subgrid-scale cumulus convection. Results are presented both from a comparison of the 13th to the 43rd days (January) of one integration with climatological statistics, and from five short-range forecasting experiments. In the extended integration, the near-equilibrium January-mean model atmosphere exhibits an energy cycle in good agreement with observational estimates, together with generally realistic zonal mean fields of winds, temperature, humidity, transports, diabatic heating, evaporation, precipitation, and cloud cover.

Somerville, R. C. J.↗

NASA NTRS1974

Periodic variation of atmospheric circulation at 14-16 days

By means of spectrum analysis of select components of the tropospheric and lower stratospheric energy cycle in the Northern Hemisphere (20 N to the pole), we are able to demonstrate the existence of a 14-16 day cycle in the atmosphere. The principal energy transfer of this cycle is the conversion from zonal available to eddy available potential energy in the troposphere. This is accompanied by an energy exchange from eddy available potential to eddy kinetic energy and thence by means of the pressure-work effect at the stratospheric boundary to the eddy kinetic energy in the stratosphere. The possible physical forcing functions of this cycle are discussed.

Miller, A. J.↗

NASA NTRS1974

The differential rotation of the solar surface

The large-scale flow in the solar convection zone is discussed. The objective is to deduce from observation the principal physical balances in the governing equations. The simplest set of equations that seem potentially realistic are utilized. It is assumed that magnetic fields are negligible, that mixing-length theory gives an accurate representation of the mean structure, and that rigid-body rotation exists at the base. It is deduced that the zonal glow is geostrophic, the meridional flow is controlled by friction, and diffusive heating balances advective cooling due to vertical motion. Next, a detailed calculation of the latitude profile of surface angular velocity is performed, based on approximate equations containing only the principal balances, and agrees well with observation. Finally, it is demonstrated that the amplitude of the flow may be determined by the constraint that the net equatorward angular momentum flux vanish. The conclusions are consistent with the hypothesis that the flow is primarily a single large axisymmetric convection cell in each hemisphere.

Gierasch, P. J.↗

NASA NTRS1974

Analytical satellite theories based on a new set of canonical elements

A new analytical satellite theory is presented. Instead of the 6 classical elements of Delaunay, a set of 8 canonical elements is used. Whereas the time is the independent variable in classical theory, the true anomaly is the independent variable in the new theory. The new approach has four features: (1) The amount of formulas in the solution is reduced considerably. (2) The first order results are almost as accurate as second order results in classical theory. (3) The theory is easier to understand from a didactical point of view. (4) The problems connected with the inaccuracy of the mean motion that are typical for classical satellite theory are no longer present. The new elements are applied to analytical solutions of the zonal oblateness problem and to the problem of the 24 hour satellite.

Scheifele, G.↗

NASA NTRS1974

Effects of mean winds and horizontal temperature gradients on solar and lunar semidiurnal tides in the atmosphere

A description is given of specifications of mean seasonal zonal winds and temperatures. Equations for tidal perturbations of the basic states are discussed along with a numerical scheme which is, essentially, the scheme described by Lindzen and Kuo (1969). Results for the solar semidiurnal tide are considered along with an investigation of the lunar semidiurnal tide.

Lindzen, R. S.↗

NASA NTRS1974

Gravity results from Pioneer 10 Doppler data

Two-way Doppler data received from Pioneer 10 during its encounter with Jupiter have been analyzed, and preliminary results have been obtained on the mass and the gravity field of Jupiter and on the masses of the four Galilean satellites. The ratios of the masses of the satellites to the mass of Jupiter are approximately 0.00004696 for Io, 0.00002565 for Europa, 0.00007845 for Ganymede, and 0.00005603 for Callisto (all error estimates presented in this paper are standard errors; those for Pioneer 10 represent our evaluation of the real errors as distinguished from formal errors). The ratio of the mass of the sun to the mass of the Jupiter system is about 1047.342, which is in good agreement with recent determinations from the motions of asteroids. The second- and fourth-degree zonal harmonic coefficients in the gravity field of Jupiter are 0.014720 and -0.00065, respectively, based on an equatorial planetary radius of 71,400 km, and the derived dynamical oblateness is 0.0647 at the same radius. The Pioneer 10 data are consistent with the assumption that Jupiter is in hydrostatic equilibrium at all levels.

Anderson, J. D.↗

NASA NTRS1974

Assessment of ERTS-1 imagery as a tool for regional geological analysis in New York State

The author has identified the following significant results. Linear anomalies dominate the new geological information derived from ERTS-1 imagery, total lengths now exceeding 26,500 km. Maxima on rose diagrams for ERTS-1 anomalies correspond well with those for mapped faults and topographic lineaments. Multi-scale analysis of linears shows that single topographic linears at 1:2,500,000 may become dashed linears at 1:1,000,000 aligned zones of shorter parallel, en echelon, or conjugate linears at 1:5000,000, and shorter linears lacking any conspicuous zonal alignment at 1:250,000. Field work in the Catskills suggests that the prominent new NNE lineaments may be surface manifestations of dip slip faulting in the basement, and that it may become possible to map major joint sets over extensive plateau regions directly on the imagery. Most circular features found were explained away by U-2 airfoto analysis but several remain as anomalies. Visible glacial features include individual drumlins, drumlinoids, eskers, ice-marginal drainage channels, glacial lake shorelines, sand plains, and end moraines.

Isachsen, Y. W.↗

NASA NTRS1975

Solar activity and the motions of the upper atmosphere

A possible mechanism for the action of solar radiation on the motion of the upper atmosphere is considered that includes the time dependent interplanetary field contour line and its effect on zonal wind velocity. A strong correlation is reported between this induction mechanism and those indices of solar activity that characterize the magnetic fields of the solar plasma.

Dmitriyev, A. A.↗