Venus temperature range
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Temperature Range on Venus: An Overview
Venus Upper Mesosphere and Lower Thermosphere Temperatures
Ground-Based Spectroscopy Observations
Ground-based high-resolution infrared spectroscopy has provided valuable insights into the temperature range of Venus' upper mesosphere and lower thermosphere. Measurements from 1990 and 1991 using the NASA GSFC Infrared Heterodyne Spectrometer (IRHS) indicated temperatures ranging from approximately 200 to 240 K at around 110 km altitude . Similar measurements in 2009 using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) showed slightly lower temperatures, about 10-20 K cooler . These findings are consistent with more recent data from the SOIR instrument on Venus Express, although there is significant day-to-day and long-term variability due to atmospheric dynamics and solar activity .
Long-Term Observations at the Terminator
Between 2009 and 2015, long-term observations at the morning and evening terminators of Venus revealed temperatures ranging from 140 K to 240 K at around 110 km altitude . The mean temperatures were approximately 199 K ± 17 K for the morning side and 195 K ± 19 K for the evening side, with no significant difference between the two . These observations also showed no strong latitudinal dependency and no consistent long-term temperature trend, although variability in the order of tens of Kelvin was noted .
Mid-Atmosphere Temperatures
Galileo-NIMS Spectra Analysis
Analysis of thermal profiles from the Galileo-NIMS spectra, focusing on the night side of Venus between 70 and 90 km altitude, showed temperatures at 91 km to be about 10 K higher than earlier observations from the Pioneer Venus mission, while temperatures between 74 and 83 km were about 3.6 K colder . This study also found an equator-to-pole warming at constant pressure levels, which has implications for the zonal wind profiles .
O2 Airglow Observations
Near-infrared spectroscopic observations of the Venus nightside using the Infrared Imager and Spectrograph 2 (IRIS2) derived temperature maps for the mesosphere at around 95 km altitude. The temperatures ranged from about 181 to 196 K, typically 15-30 K higher than those expected from the Venus International Reference Atmosphere (VIRA) profile . These temperatures are similar to, but slightly lower than, those obtained from stellar occultation measurements with SPICAV on Venus Express .
Hydroxyl Airglow Emission
Temperatures on the night side of Venus at about 95 km altitude, determined using spectral features of the hydroxyl airglow emission, varied from 145.5 to about 198.1 K, with an average value of 176.3 K ± 14.3 K . These values are consistent with previous ground-based and space observations, showing a minimum at equatorial latitudes and increasing towards mid-latitudes .
Exospheric Temperatures
Day-to-Night Variation
The exospheric temperature of Venus shows significant variation from the dayside to the nightside. Measurements from the Venera 9 space probe indicated temperatures at 250 km altitude ranging from 500 K on the dayside to 200 K on the nightside . This large variation is attributed to the heating of the upper atmosphere by solar radiation and results in the transport of hydrogen from the dayside to the nightside .
Solar Cycle Influence
Calculations have shown that the exospheric temperature of Venus can vary significantly with the solar cycle, ranging from 450 K to 850 K . This variation is driven by changes in the extreme ultraviolet solar radiation, which affects the upper atmosphere's thermal structure .
Conclusion
The temperature range on Venus varies significantly across different altitudes and times of day. In the upper mesosphere and lower thermosphere, temperatures range from 140 K to 240 K, with notable variability due to atmospheric dynamics and solar activity. Mid-atmosphere temperatures show an equator-to-pole warming trend, while exospheric temperatures exhibit substantial day-to-night variation and are influenced by the solar cycle. These findings highlight the complex and dynamic nature of Venus' atmospheric thermal structure.
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