L. S. Elson

Overview of VEGA Venus Balloon in Situ Meteorological Measurements

The VEGA balloons made in situ measurements of pressure, temperature, vertical wind velocity, ambient light, frequency of lightning, and cloud particle backscatter. Both balloons encountered highly variable atmospheric conditions, with periods of intense vertical winds occurring sporadically throughout their flights. Downward winds as large as 3.5 meters per second occasionally forced the balloons to descend as much as 2.5 kilometers below their equilibrium float altitudes. Large variations, in pressure, temperature, ambient light level, and cloud particle backscatter (VEGA-1 only) correlated well during these excursions, indicating that these properties were strong functions of altitude in those parts of the middle cloud layer sampled by the balloons.

VEGA Balloon Dynamics and Vertical Winds in the Venus Middle Cloud Region.

The VEGA balloons provided a long-term record of vertical wind fluctuations in a planetary atmosphere other than Earths. The vertical winds were calculated from the observed displacement of the balloon relative to its equilibrium float altitude. The winds were intermittent; a large burst lasted several hours, and the peak velocity was 3 meters per second.

Implications of the Vega balloon results for Venus atmospheric dynamics

Both VEGA balloons encountered vertical winds with typical velocities of 1 to 2 meters per second. These values are consistent with those estimated from mixing length theory of thermal convection. However, small-scale temperature fluctuations for each balloon were sometimes larger than predicted. The approximate 6.5-kelvin difference in temperature consistently seen between VEGA-1 and VEGA-2 is probably due to synoptic or planetary-scale nonaxisymmetric disturbances that propagate westward with respect to the planet. There is also evidence from Doppler data for the existence of solar-fixed nonaxisymmetric motions that may be thermal tides. Surface topography may influence atmospheric motions experienced by the VEGA-2 balloon.

VEGA Balloon System and Instrumentation.

The VEGA Venus balloon radio transmissions received on Earth were used to measure the motion of the balloons and to obtain the data recorded by onboard sensors measuring atmospheric characteristics. Thus the balloons themselves, the gondolas, the onboard sensors, and the radio transmission system were all components of the experiment. A description of these elements is given, and a few details of data sampling and formatting are discussed.

Thermal structure of the venus atmosphere in the middle cloud layer.

Thermal structure measurements obtained by the two VEGA balloons show the Venus middle cloud layer to be generally adiabatic. Temperatures measured by the two balloons at locations roughly symmetric about the equator differed by about 6.5 kelvins at a given pressure. The VEGA-2 temperatures were about 2.5 kelvins cooler and those of VEGA-1 about 4 kelvins warmer than temperatures measured by the Pioneer Venus Large Probe at these levels. Data taken by the VEGA-2 lander as it passed through the middle cloud agreed with those of the VEGA-2 balloon. Study of individual frames of the balloon data suggests the presence of multiple discrete air masses that are internally adiabatic but lie on slightly different adiabats. These adiabats, for a given balloon, can differ in temperature by as much as 1 kelvin at a given pressure.

Infrared remote sounding of the middle atmosphere of venus from the pioneer orbiter.

Orbiter infrared measurements of the Venus atmosphere in the 60- to 140-kilometer region show very small diurnal temperature differences near the cloud tops, increasing somewhat at higher levels. The seasonal (that is, equator to pole) contrasts are an order of magnitude larger, and the temperatures unexpectedly increase with increasing latitude below 80 kilometers. An isothermal layer at least two scale heights in vertical extent is found near the 100-kilometer altitude, where the temperature is about 175 K. Structure is present in the cloud temperature maps on a range of spatial scales. The most striking is at high latitude, where contrasts of nearly 50 K are observed between a cold circumpolar band and the region near the pole itself.

Infrared Remote Sensing of the Atmosphere of Venus from the Pioneer 12 Orbiter

The Pioneer 12 spacecraft, which was placed into orbit about Venus on 4 December 1978, carried a multispectral radiometer designed to investigate the structure and meteorological properties of the middle atmosphere (60 to 140 km). This paper reviews the experiment concept, the design, implementation and calibration of the hardware, and the preliminary scientific results from data obtained through 14 February 1979.