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Do surface and air temperatures contain similar imprints of evaporative conditions?

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Panwar,  Annu
Research Group Biospheric Theory and Modelling, Dr. A. Kleidon, Max Planck Institute for Biogeochemistry, Max Planck Society;
IMPRS International Max Planck Research School for Global Biogeochemical Cycles, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Kleidon,  Axel
Research Group Biospheric Theory and Modelling, Dr. A. Kleidon, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Renner,  Maik
Research Group Biospheric Theory and Modelling, Dr. A. Kleidon, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Citation

Panwar, A., Kleidon, A., & Renner, M. (2019). Do surface and air temperatures contain similar imprints of evaporative conditions? Geophysical Research Letters, 46(7), 3802-3809. doi:10.1029/2019GL082248.


Cite as: http://hdl.handle.net/21.11116/0000-0003-37A5-5
Abstract
Generally, surface and air temperatures seem closely related but we show that they respond differently to evaporative conditions. We evaluate the temperature increase in response to solar radiation for different evaporative fractions, using observations from the Southern Great Plains. The warming rate of air temperature decreases only by 1.7 × 10−3 K/(Wm−2) from dry to moist conditions compared to a stronger reduction by 14 × 10−3 K/(W m−2) for surface temperature. The weaker response of air temperature to evaporative fraction is explained by the larger growth of boundary layer on drier days, which suppresses the warming of air. Estimates based on this explanation reproduce the warming rate of air temperature in observations. Our results show that diurnal variations of surface temperatures contain imprints of evapotranspiration while air temperatures do not. These findings appear important to be considered when using, analyzing, or interpreting temperature data in studies dealing with climate change, hydrology, or land‐atmosphere interactions. Surface and air temperatures are measured just 2m apart, so it might seem that they carry the same information. Here we show that these temperature measurements respond rather differently to whether the surface evaporates or not. To show this, we use data from a well‐equipped measurement site in the Central United States and calculate the rates by which the surface and the air warm in response to solar radiation. We found that the surface temperature responds about 8 times stronger to evaporation than air temperature. We explain this weaker response of air temperature by the stronger growth of the boundary layer without evaporation. This results in a deeper, well‐mixed boundary layer that does not warm as strongly. What our results imply is that evaporation may be inferred from surface temperatures, but not from air temperatures.