Towards Turbulence and Wind Shear Models for the Venus Atmosphere

The design of in-situ missions such as the DAVINCI probe requires quantitative models of turbulence and wind shear in order to assess their effects on the vehicle motion which in turn can influence radio link performance or camera image blur. Some first-principles estimates can be derived from large-scale wind shears and convective fluxes . Experience with the Huygens probe at Titan also showed that the buoyancy frequency gives an informative guide to wind shear :  the large-scale vertical shear at Venus is typically 2-3 m/s/km : the strong stability just below and above the clouds may permit shears up to 10 m/s/km, these values being a little below and above the maximum seen by Huygens. 10 m/s/km is  considered the upper end of 'light turbulence' in terrestrial aviation.  I also present the limited information we have from Pioneer Venus accelerometer measurements, Doppler tracking (Venera, VEGA and Pioneer Venus) and wind measurements (VEGA balloons). For example, in the middle-cloud convective region, a characteristic turbulence amplitude is ~1.5 m/s over a length scale of about 700m, and some  localized shear reaches ~ 20 m/s/km.  A simple 'random-walk' model for the turbulent wind profile appears to describe the Venera data well. I present the model for the low latitudes to be visited by DAVINCI, and discuss considerations for extending the model to high latitude.