The structure and variability of the middle atmosphere of Venus (60 to 140 km) were studied from the Pioneer Venus orbiter by using an infrared remote sensing instrument developed from those on terrestrial weather satellites. The wavelengths observed were selected to allow the vertical temperature profile, the albedo, the cloud opacity profile, and the far infrared opacity due to water vapor to be inferred from the data. The measured temperature field has been used to model the dynamics of the region, and the thermal and solar fluxes have been used to compute the planetary radiation budget. The results for the diurnal variation of temperature at a given height show fairly small amplitudes up to an altitude of about 95 km, above which the day to night contrast increases rapidly with height. At the equator the dependence of temperature in the stratosphere (65 to 95 km) on solar longitude is dominated by a wave number 2 solar tide with an amplitude of about 10 K. Transient features including traveling waves are also present on a wide range of scales. The equator to pole gradients are larger than expected, and the stratosphere is typically 15 to 20 K warmer at the pole than at the equator. Nightside temperatures in the mesosphere (95 to 140 km) are generally low except for a local maximum near the antisolar point, and breakdown of local thermodynamic equilibrium is evident above about 120 km. The winds forced by the measured temperature field in a diagnostic circulation model show the ‘4‐day’ zonal wind decreasing rapidly with height above the clouds and becoming very small by 80 or 90 km. altitude. The mean meridional component reverses at about the same altitude and pole‐to‐equator winds as high as 100 m s−1 are produced above 100 km. The most significant discovery concerning the cloud morphology is a dramatic ‘dipole’ structure, consisting of two clearings in the cloud at locations straddling the pole and rotating around it every 2.7 days. The clearings are thought to be evidence for subsidence of the atmosphere at the center of a polar vortex. The absence of corresponding evidence for descending motions elsewhere suggests that a single large circulation cell may fill the northern hemisphere at levels near the cloud tops. A crescent‐shaped ‘collar’ region, consisting of anomalous and variable temperature and cloud structure, surrounds the pole at about 70°N and rises perhaps 15 km above the mean cloud top elevation; it has a solar‐fixed component and sometimes contains spiral streaks. This feature, and the double vortex eye, are large, persistent deviations from the mean circulation due to planetary‐scale waves of unknown origin. No explanation is offered at present for the dominance of wave number 2 structures at equatorial and polar latitudes, while the mid‐latitudes are dominated by a wave number 1 feature (the polar collar). A thin, ubiquitous haze is found covering the northern hemisphere, including the polar features. The far‐infrared opacity of the atmosphere is greater in the afternoon than at any other lo...

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Pioneer Venus has revealed important new features of the structure and the circulation of Venus' atmosphere. The temperature decreases from nearly 750 K at the surface to about 180 K at about 100 km. Above 100 km, there is a marked contrast between the day‐side and the night‐side thermal structures. On the day side there is a thermosphere in which temperatures increase with height to an exospheric temperature of about 300 K. On the night side there is a ‘cryosphere’ in which temperatures decrease with height to an exospheric temperature of about 100 K. The atmosphere is stably stratified from the highest altitudes down to about 28 km except for a layer in the clouds, between about 50 and 55 km, which is nearly adiabatic. Between about 20 and 28 km, the lapse rate is also nearly adiabatic while there is evidence for stable stratification between about 10 and 20 km. Horizontal thermal contrasts are of the order of 1–2% in the deep atmosphere and 100% in the upper atmosphere. At and below the clouds, temperatures generally decrease with latitude on constant pressure surfaces; above the clouds, between about 70 and 90 km, there is a reversed zonally averaged latitudinal temperature gradient. The dominant circulation of the atmosphere above the lowest one or two scale heights is a zonal retrograde motion with 100 m/s winds at 60 km altitude. There is also a superrotation of the atmosphere at altitudes of 150 km and above. Low latitude height profiles of the zonal wind have alternating layers of high and low shear which correlate with structure in the vertical profiles of static stability. Advection of heat by the large zonal winds helps maintain the relatively small longitudinal thermal contrasts throughout the atmosphere below the clouds. Latitudinal temperature and pressure contrasts are consistent with a zonally rotating atmosphere in approximate cyclostrophic balance. Meridional winds below 60 km vary in speed from a few to about 10 m/s; the winds are poleward at the cloud tops. A cloud level Hadley cell driven by solar heating combines with the zonal circulation to produce a cloud top polar vortex. Eddies in the form of convective cells, small‐scale gravity waves, and planetary scale waves are found throughout the atmosphere. Eddies, as well as mean meridional circulations, may be important in the transport of energy and momentum. Venus' atmospheric circulation is not steady despite the planet's small obliquity and nearly circular orbit.

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Abstract.The problem of creating synoptic maps from asynopticMly gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called "trajectory mapping." Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories.In particular, we have considered (1) calculational errors; (2) uncertainties in the values and locations of constituent measurements, (3) errors incurred by neglecting diabatic effects, and (4) sensitivity to differences in wind field analyses. These studies reveal that the global fields derived from the advection of large numbers of measurements are relatively insensitive to the errors in the individual trajectories. The trajectory mapping technique has been successfully apphed to a variety of problems. In this paper, the following two applications demonstrate the usefulness of the technique: an analysis of dynamical wave-breaking events and an examination of Upper Atmosphere Research Satellite data accuracy.