Abstract
Abstract. There is evidence that the ozone and temperature responses to the solar cycle of ∼11 years depend on the local times of measurements. Here we present relevant results based on SABER data over a full diurnal cycle, which were not previously available. In this area, almost all satellite data used are measured at only one or two fixed local times, which can differ among various satellites. Consequently, estimates of responses can be different depending on the specific data set. Furthermore, over years, due to orbital drift, the local times of the measurements of some satellites have also drifted. In contrast, SABER makes measurements at various local times, providing the opportunity to estimate diurnal variations over 24 h. We can then also estimate responses to the solar cycle over both a diurnal cycle and at the fixed local times of specific satellite data for comparison. Responses derived in this study, based on zonal means of SABER measurements, agree favorably with previous studies based on data from the HALOE instrument, which only measured data at sunrise and sunset, thereby supporting the analysis of both studies. We find that for ozone above ∼40 km, zonal means reflecting specific local times (e.g., 6, 12, 18, 24 LST – local solar time) lead to different values of responses, and to different responses based on zonal means that are also averages over the 24 h local time period, as in 3-D models. For temperature, the effects of diurnal variations on the responses are not negligible even at ∼30 km and above. We also considered the consequences of local time variations due to orbital drifts of certain operational satellites, and, for both ozone and temperature, their effects can be significant above ∼30 km. Previous studies based on other satellite data do not describe the treatment, if any, of local times. Some studies also analyzed data merged from different sources, with measurements made at different local times. Generally, the results of these studies do not agree very well among themselves. Although responses are a function of diurnal variations, this is not to say that they are the major reason for the differences, as there are likely other data-related issues. The effects due to satellite orbital drift may explain some unexpected variations in the responses, especially above 40 km.
Highlights
The understanding of the response of atmospheric ozone and temperature to the solar cycle of ∼ 11 years is important for both scientific and practical reasons
We describe how we can estimate new results of zonal means corresponding to specific local times, and new results estimating the effects of orbital drift on diurnal variations
For the new results of this study, we focus on the following: 1. responses to the solar cycle at 6 and 18 LST – comparisons with responses based on Halogen Occultation Experiment (HALOE) data (Beig et al, 2012; Fadnavis and Beig, 2006), which measure only at sunrise and sunset; 2. responses based on zonal means at specific local times; 3. responses with local times changing due to satellite orbital drifts; www.ann-geophys.net/37/471/2019/
Summary
The understanding of the response of atmospheric ozone and temperature to the solar cycle of ∼ 11 years is important for both scientific and practical reasons. Used as is, responses based on zonal means of the above measurements reflect long-term variations at the fixed local times, and could be a source of differences among the various studies. In contrast to most other measurements, SABER provides additional information which allows us to estimate daily ozone and temperature diurnal variations, and, in turn, the dependence of their responses to the decadal solar cycle on local time. We focus on zonal means of ozone and temperature, either at various specific local times, or averaged over local times (as in a 3-D model), and the effects of their diurnal variations on their responses to solar variability over a solar cycle of ∼ 11 years (2002–2014), from 20 to 100 km.
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