An analysis of the Venus thermal infrared temperature maps

Abstract

We have performed a detailed analysis of the published Venus IR maps and have obtained a number of new results. The global contour map of the average temperature variations in the vicinity of 6120 km reveals the existence of saddle points along the equator at dawn, at noon, and just before sunset. The hot spots observed at 4:30–4:40 A.M. at 65°–68°S latitude appear to be in the vicinity of the coldest region from which the 8‐ to 14‐µm emissions originate. At large earth zenith angles the limb darkening curves show a hump which is attributed primarily to a single patchy haze layer in the vicinity of 6123 km and with a thickness of the order of 3 km. We obtain an average IR source region temperature of 250°K at the equator. At the poles the same altitude region is 8°K cooler.

The character of the thermal emission from Venus

“…Near the equator the maximum observed emission from the night side of Venus occurs near 9 P.M., as has been previously reported by several groups. Although Ainsworth and Herman [1978] This minimum corresponds to that given by Ainsworth and Herman, but it was not reported by Diner and Westphal [1978], perhaps a result of daily fluctuations among their seven observations. Poleward of 30 ø latitude the 9 P.M. maximum disappears; it becomes, in fact, a relative minimum.…”

Global Structure of Thermal Tides in the Upper Cloud Layer of Venus Revealed by LIR on Board Akatsuki

“…Thermal tides excited in the cloud layer has been considered one of the main acceleration sources that maintain the atmospheric superrotation of Venus (e.g., Fels & Lindzen, ; Hou et al, ; Plumb, ; Newman & Leovy, ; Takagi & Matsuda, ), in which the zonal wind speed of the atmosphere at the cloud top (~70 km) is more than 60 times faster than the rotation speed of the solid body of Venus. The structures of the thermal tides have been confirmed in a temperature field from space‐ and ground‐based observations (e.g., Ainsworth & Herman, ; Apt et al, ; Migliorini et al, ; Taylor et al, ; Zasova et al, ) and in zonal and meridional wind fields at the cloud top level by tracking cloud motions (e.g., Horinouchi et al, ; Kouyama et al, ; Limaye & Suomi, ; Moissl et al, ; Rossow et al, ; Sánchez‐Lavega et al, ). However, despite the importance of thermal tides in the Venusian atmosphere, the global feature of thermal tides across all local times and latitudes has not been obtained due to the limited data coverage of previous observations (e.g., a ground‐based observation did not cover the subsolar region, Apt et al, ; cloud tracking was limited to only dayside, and only one hemisphere was observable by spacecraft with a polar orbit, Migliorini et al, ; Taylor et al, ).…”

“…Global structure of thermal tides in the upper cloud layer of Venus revealed by LIR on board Akatsuki. Geophysical Research Letters, 46, 9457-9465. https://doi.org/10.1029/ 2019GL083820 based observations by Ainsworth and Herman (1978) covered the northern and southern hemispheres simultaneously, but the observational dates were quite limited, resulting in large data gaps in the high latitudes. Since the tidal amplitude at middle to high latitudes from their results is much greater than those obtained by space-borne observations, verification is needed.…”

“…However, despite the importance of thermal tides in the Venusian atmosphere, the global feature of thermal tides across all local times and latitudes has not been obtained due to the limited data coverage of previous observations (e.g., a ground‐based observation did not cover the subsolar region, Apt et al, ; cloud tracking was limited to only dayside, and only one hemisphere was observable by spacecraft with a polar orbit, Migliorini et al, ; Taylor et al, ). Ground‐based observations by Ainsworth and Herman () covered the northern and southern hemispheres simultaneously, but the observational dates were quite limited, resulting in large data gaps in the high latitudes. Since the tidal amplitude at middle to high latitudes from their results is much greater than those obtained by space‐borne observations, verification is needed.…”

Anomalous features in thermal radiance maps of Venus

“…Brown and Goody [1978] worked before conjunction and observed no difference between polar and equatorial behavior. The compilations of Ingersoll and Orton [1974] and Ainsworth and Herman [ 1978] both show low polar radiance between midnight and dawn but much less of an effect between sunset and midnight.…”