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

Abstract

Abstract. We have derived the behavior of decadal temperature trends over the 24 h of local time, based on zonal averages of SABER data, for the years 2012 to 2014, from 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 nighttime 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. Similar caution is needed when comparing with models, since the zonal means from 3D models reflect averages over both longitude and the 24 h 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. Many of the 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 (Advanced Microwave Sounding Unit, AMSU; lidar) are favorable and informative. They may explain, at least in part, the bridge between results based on daytime AMSU data and nighttime lidar measurements. However, these examples do not form a pattern, and more comparisons and study are needed.

Climatology and Long-Term Trends in the Stratospheric Temperature and Wind Using ERA5

“…The negative temperature trends around −0.2 to −0.3 degrees per decade in the lower stratosphere are confirmed by [3] based on the MERRA2 and ERA5 reanalysis data for 1980-2019. The temperature changes in the higher parts of the middle atmosphere are discussed in more detail in many studies, e.g., [4,5], confirming the cooling of the stratosphere and mesosphere. Chemistry-climate models can also be used to analyze temperature trends, with the possibility of simulations of different radiative forcing and ozone-depleting substances emissions, e.g., [6,7].…”

Progress in investigating long-term trends in the mesosphere, thermosphere, and ionosphere

“…The general pattern is cooling, particularly in the mesosphere, but various observations are only mostly but not fully consistent, maybe partially due to insufficient length of the data series used; She et al ( 2019) claim that data sets longer than two solar cycles are necessary to obtain a reliable long-term trend. Huang and Mayr (2021) found that trends might significantly vary with local time and height in the whole height range of 30-110 km, but they studied data series that are only 13 years long. Also model simulations provide general cooling, even though the WACCM simulations by Qian et al (2019) indicate that the temperature trend becomes near-zero or even slightly positive in the summer upper mesosphere, likely due to dynamic effects (winds and atmospheric wave activity).…”

“…The most studied parameter was temperature. Huang and Mayr (2021) found that trends might significantly vary with local time and height in the whole height range of 30-110 km, but they studied data series that were only 13 years long. However, She et al ( 2019) claim that data sets longer than two solar cycles are necessary to obtain a re-liable long-term temperature trend.…”

Progress in investigating long-term trends in the mesosphere, thermosphere and ionosphere

“…The most studied parameter was temperature. Huang and Mayr (2021) found that trends might significantly vary with local time and height in the whole height range of 30-110 km but they studied data series only 13 years long. However, She et al (2019) Meteor radar wind data from high/middle latitudes revealed no significant trend in diurnal tides and changes of semidiurnal tide, which differ according to altitude and latitude.…”

“…consistent, partially maybe due to insufficient length of data series used; She et al (2019) claim that data sets longer than two solar cycles are necessary to obtain reliable long-term trend. Huang and Mayr (2021) found that trends might significantly vary with local time and height in the whole height range of 30-110 km but they studied data series only 13 years long.…”