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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/angeo-2020-63
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-63
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  09 Oct 2020

09 Oct 2020

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This preprint is currently under review for the journal ANGEO.

Temperature decadal trends, and their relation to diurnal variations in the lower thermosphere, stratosphere, and mesosphere, based on measurements from SABER on TIMED

Frank T. Huang1, and Hans G. Mayr2, Frank T. Huang and Hans G. Mayr
  • 1University of Maryland, Baltimore County, MD 21250, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD 20771, US
  • retired

Abstract. We have derived the behavior of decadal temperature trends over the 24 hours of local time, based on zonal averages of SABER data, years 2012 to 2014, 20 to 100 km, within 48° of the equator. Similar results have not been available previously. We find that the temperature trends, based on zonal mean measurements at a fixed local time, can be different from those based on measurements made at a different fixed local time. The trends can vary significantly in local time, even from hour to hour. This agrees with some findings based on night-time lidar measurements. This knowledge is relevant because the large majority of temperature measurements, especially in the stratosphere, are made by instruments on sun-synchronous operational satellites which measure at only one or two fixed local times, for the duration of their missions. In these cases, the zonal mean trends derived from various satellite data are tied to the specific local times at which each instrument samples the data, and the trends are then also biased by the local time. Consequently, care is needed in comparing trends based on various measurements with each other, unless the data are all measured at the same local time. A similar caution is needed when comparing with models, since the zonal means from 3D models reflect averages over both longitude and the 24 hours of local time. Consideration is also needed in merging data from various sources to produce generic, continuous longer-term records. Diurnal variations of temperature themselves, in the form of thermal tides, are well known, and are due to absorption of solar radiation. We find that at least part of the reason that temperature trends are different for different local times is that the amplitudes and phases of the tides themselves follow trends over the same time span of the data. Much of past efforts have focused on the temperature values with local time when merging data from various sources, and on the effect of unintended satellite orbital drifts, which result in drifting local times at which the temperatures are measured. However, the effect of local time on trends has not been well researched. We also derive estimates of trends by simulating the drift of local time due to drifting orbits. Our comparisons with results found by others (AMSU, lidar) are favorable and informative. They may explain at least in part, the bridge between results based on daytime AMSU data and night time lidar measurements. However, these examples do not a pattern make, and more comparisons and study are needed.

Frank T. Huang and Hans G. Mayr

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Frank T. Huang and Hans G. Mayr

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