Simulated Long-term Evolution of the Thermosphere during the Holocene: 2. Circulation and Solar Tides
Abstract. On timescales longer than the solar cycle, long-term changes in CO2 concentration and geomagnetic field have the potential to affect thermospheric dynamics. In this paper, we investigate the thermospheric dynamical response to these two factors during the Holocene, using two sets of ~12,000-yr control runs by the coupled thermosphere-ionosphere model, GCITEM-IGGCAS. The main results indicate that increased/decreased CO2 will enhance/weaken the thermospheric circulation throughout the Holocene, but this effect is nonlinear. The cooling effect of CO2 in the thermosphere further provides plausible conditions for atmospheric tidal propagation and increases the thermospheric tidal amplitude. Geomagnetic variations induce hemispheric asymmetrical responses in the thermospheric circulation. Large changes in the circulation occur at high latitudes in the hemisphere with distant magnetic poles drift, inferring a crucial role of geomagnetic non-dipole variations in circulation changes. A positive correlation between the diurnal migrating tide (DW1) and geomagnetic dipole moment is revealed for the first time. The amplitude of DW1 in temperature will increase by ~1–3 K for each 1×1022 Am2 increase in dipole moment.
Xu Zhou et al.
Status: open (until 29 Mar 2023)
- RC1: 'Comment on egusphere-2023-234', Anonymous Referee #1, 22 Feb 2023 reply
Xu Zhou et al.
Xu Zhou et al.
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This work presents new and very interesting results regarding the paleo-thermosphere, linked to a previous work of the authors (Simulated Long‐Term Evolution of the Ionosphere During the Holocene). The research considering the Earth’s magnetic field of internal origin and the CO2 levels variation along the Holocene is important for long-term trend studies linked to climatic changes in the whole atmosphere, and also for short term analysis since the background thermosphere is key to understanding variabilities at any timescale.
I have only some minor comments to be considered by the authors:
* In Figure 2: Why is it opposite the changes in V between the northern and the southern hemisphere? Maybe I am missing something here.
* Figure 6: Why average between +30 and -30? That is the region enclosing the magentic equator, so there can be different variations in each hemisphere, so they will eventually cancel.
* What about the variation of the magnetic equator (or geomagnetic equator) along the holocene. Because I understand that you are considering an almost dipolar field, but not axial. So the changes in its tilt (and displacement form the center in addition) would contribute to the equator shifts.
Very minor corrections:
* Line 34: I think that in “since the Holocene”, it may should be “since the beginning of the Holocene”, or something like this.
* Line 56: in “The geomagnetic tiled angle ...” I think tiled has a typo error. I think it may be “tilt” or linked to this ?
* Line 111: in “the thermospheric dynamical response..” there are two dots at the end. Delete one.
* Line 118: in “equatorial meridional winds winds” delete one “winds”
* Line 136: About the fluctuations. Why one pair of values have minus-plus (+-) and the other just minus (-)?
* Line 166: “The circulation change in the northern hemisphere is much larger in the southern hemisphere, regardless during March or June.” I do not understand this sentence. Maybe you want to say that the circulation change was larger in the northen than in the southern hemisphere? And what about “regardsless during March or June? You mean that in the two months it is observed this relative difference between north and south?
* Caption of Figure 1: “Thermospheric circulation is illustrated by contours (zonal) and arrays (meridional and vertical)”. What do you mean by “arrays”? Maybe you mean “arrows”?
* Figure 9. Something is wrong with the values in the colorbar of the left figurre. Shouldn’t they be between 1 and -1?