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Peter J. Gierasch
and
Richard M. Goody

Abstract

We have computed radiative decay times for thermal disturbances near the cloud tops of Jupiter and conclude that they are much larger than probable dynamical time constants. Under these circumstances radiative equilibrium calculations are of little significance.

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Arthur Y. Hou
and
Richard M. Goody

Abstract

For the solar heating and zonal wind profiles observed in the Venus atmosphere (below 80 km) we have calculated the eddy source pattern required to maintain the zonally averaged circulation.

In the cloud-top region (45-75 km) the calculated residual meridional circulation corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. For the amount of small-scale diffusion suggested by in situ measurements, the circulation is close to the nearly inviscid limit, and advections by the mean circulation must be balanced by eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks (i.e., Eliassen-Palm flux divergences or convergences), which may possibly be caused by thermal tides.

Below the cloud decks, the effect of meridional motions is small, and eddy sources are required to balance diffusion (if diffusion is as large as measurements indicate). Near the lower model boundary, differential solar heating forces a shallow Hadley cell which controls surface winds and ensures that the net surface torque vanishes in a steady state.

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Arthur Y. Hou
and
Richard M. Goody

Abstract

We have extended our previous calculations of zonally averaged temperature, circulation, and eddy source requirements for the Venus atmosphere to include the region from the surface to 95 km, using a Curtis matrix method for the radiation calculation. We conclude: (i) The cloud top circulation is not significantly changed from our previous calculations based on a radiative-relaxation method, but large differences occur in the lower atmosphere. (ii) The physical and dynamical states of the atmospheric regions above and below the cloud base are effectively independent and are equally important for accounting for the 4-day circulation at the cloud tops. (iii) Above the cloud base, the circulation is effectively inviscid and the eddy source requirements at the low latitudes are consistent with the mean-flow forcing by the semidiurnal tide. (iv) The circulation below the clouds is important compared to viscous dissipation above the lowest scale height. We discuss possible mechanisms for satisfying the tropical eddy source requirements in the lower atmosphere.

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Peter J. Gierasch
and
Richard M. Goody

Abstract

No abstract available.

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Arthur Y. Hou
,
Stephen B. Fels
, and
Richard M. Goody

Abstract

We have calculated the equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base. The results show that the tidal mechanism proposed by Fels and Lindzen can account for a substantial fraction—and possibly all—of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.

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Daniel B. Kirk-Davidoff
,
Richard M. Goody
, and
James G. Anderson

Abstract

Sampling retrievals of high-accuracy first-moment statistics constitute a central concern for climate research. Considered here is the important case of brightness temperature retrievals from a selection of possible orbits. Three-hourly global satellite brightness temperature data are used to predict the sampling error of monthly to annual mean brightness temperature retrieved by one or more satellites in low earth orbits. A true polar orbit is found to offer substantial advantages over a sun-synchronous orbit in the retrieval of annual mean brightness temperature, since the rotation of the local time of observation through two full diurnal cycles greatly reduces the error due to imperfect sampling of diurnal variations. Thus, a single polar orbiting satellite can produce annual mean, zonal mean brightness temperatures with typical sampling errors of less than 0.1 K, while even three sun-synchronous orbiters have high-latitude errors of up to 0.4 K. The error in retrievals of the annual mean diurnal cycle of brightness temperature is also discussed. In this case, high accuracy (<0.1 K) requires three cross-track scanning satellites in precessing orbits, or else a very large number (∼10) of nadir-viewing satellites in precessing orbits. The large sampling errors of sun-synchronous satellites are highly correlated from year to year, so that if equator-crossing times are held fixed, sampling errors in year-to-year differences of annual means are similar for sun-synchronous and precessing orbits.

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