the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
18 Mar 2021
18 Mar 2021
Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations
- 1Institute of Applied Physics & Oeschger Center for Climate Change Research, Microwave Physics, University of Bern, Switzerland
- 2Institute for Meteorology, Universität Leipzig, Leipzig, Germany
- 3Institute for Solar-Terrestrial Physics, German Aerospace Center (DLR), Neustrelitz, Germany
- 4Department of Earth and Planetary Science, Kyushu University, Japan
- 5High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA
- 6Max Planck Institute for Meteorology, Hamburg, Germany
- 7Fraunhofer Institute for Computer Graphics Research IGD, Rostock, Germany
- 8Dept. of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7
- 9Western Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, N6A 5B7, Canada
- 10ITM Physics Laboratory, Mail Code 675, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 11Australian Antarctic Division, Kingston, Tasmania, Australia
- 12Sodankyla Geophysical Observatory, University of Oulu, Finland
- 13University of Leicester, Leicester, UK
- 14Swedish Institute of Space Physics, Kiruna, Sweden
- 1Institute of Applied Physics & Oeschger Center for Climate Change Research, Microwave Physics, University of Bern, Switzerland
- 2Institute for Meteorology, Universität Leipzig, Leipzig, Germany
- 3Institute for Solar-Terrestrial Physics, German Aerospace Center (DLR), Neustrelitz, Germany
- 4Department of Earth and Planetary Science, Kyushu University, Japan
- 5High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA
- 6Max Planck Institute for Meteorology, Hamburg, Germany
- 7Fraunhofer Institute for Computer Graphics Research IGD, Rostock, Germany
- 8Dept. of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7
- 9Western Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, N6A 5B7, Canada
- 10ITM Physics Laboratory, Mail Code 675, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 11Australian Antarctic Division, Kingston, Tasmania, Australia
- 12Sodankyla Geophysical Observatory, University of Oulu, Finland
- 13University of Leicester, Leicester, UK
- 14Swedish Institute of Space Physics, Kiruna, Sweden
Abstract. Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable to compare climate models or long term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observations from six meteor radars at two conjugate latitudes to validate the corresponding mean winds and atmospheric diurnal and semidiurnal tides from three GCMs, namely Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Community Climate Model Extension (Specified Dynamics) (WACCM-X(SD)) and Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate that there are interhemispheric differences in the seasonal characteristics of the diurnal and semidiurnal tide. There also are some differences in the mean wind climatologies of the models and the observations. Our results indicate that GAIA shows a reasonable agreement with the meteor radar observations during the winter season, whereas WACCM-X(SD) shows a better agreement with the radars for the hemispheric zonal summer wind reversal, which is more consistent with the meteor radar observations. The free running UA-ICON tends to show similar winds and tides compared to WACCM-X(SD).
Gunter Stober et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2021-142', Anonymous Referee #1, 19 Apr 2021
This study compares model simulations with metero radar (MR) observations. it presents the first systematic investigation of interhemispheric differences of mean winds and atmospheric tides at conjugate latitudes from observations and comprehensive models applying a unified diagnostic. It is a much needed study. While I appreciate the heroic effort of the authors, I am troubled by the lack of similarity between the model simulations described here and the MR observations. Previous studies - as properly discussed in this manuscript - revealed a much closer match between MR data and NAVGEM-HA. I am troubled by how badly the models are doing here.
The authors discuss the different behavior of the gravity wave drag parameterization in these models, arguing that the mean circulation is different to partialy explain the differences, i believe. I don't disagree in general, however such discrepancies seems to point to a fundamental flaw in these models: the lack of observations at MLT altitudes. Isn't that the take-home-message of this study?
Moreover, some of the models use atmospheric specifications (like MERRA): what is the time cadence of these atmospheric specifications? Typically these data are provided 6-hourly, which would not resolve semdiurnal variability, and in such case the comparison is between observations and the model's own climatology. In the same spirit, what it the nudging time scale? A long time scale would prevent the model to be tightly associated with the atmospheric analysis.
Specific comments:
Page 3, bottom: Why McCormack et al. (2015). That's a QBO paper. I think you want to use McCormack et al. (2017) as in the rest of the manuscript.
Figure 3 and similar figures. The authors really need to add contours: the color palette has a very large dynamic range and for the reader it is impossible to discern contours, especially when the largerst values are at the edges of the panels and the vast majority of the figure is a bland uniform color. Also, I think would it help explaining the figures (and for us the readers, understanding it) if one hemisphere (say the SH) is rotate by 6 months, so that the same season is always in the middle.
Page 10, middle. Why is it expected that conjugate latitudes see almost the same behavior?
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AC1: 'Reply on RC1', Gunter Stober, 17 May 2021
We thank the reviewer for his comments on the paper. We will revise the paper in some paragraphs to put more emphasis on some aspects that are mentioned in the general comment. We are going to include some sentences pointing at the difference between the meteorological analysis NAVGEM-HA and the comprehensive GCMs (WACCM-X(SD), GAIA, and ICON) that were analyzed in this study. The NAVGEM-HA meteorological data shows a good agreement mainly due to the 4DVAR data assimilation up to the mesosphere, which is not comparable to the nudging of the comprehensive models such as WACCM-X(SD) and GAIA with reanalysis data up to the stratosphere. Our study confirms that the climatological fields at the mesosphere are more or less the result of the model physics rather than affected by the nudging.
WACCM-X(SD) is nudged to MERRA reanalysis fields every 3 hours with a soft forcing and a time scale of up to 50 hours. However, it has to be noted that the 3DVAR data assimilation in MERRA2 has a cadence of 6 hours, although MERRA2 provides data fields every 3 hours.
We revised all figures according to the reviewer's suggestions and shifted the time axis for all southern latitude systems by half a year. We added labeled contours for the tidal amplitude plots and also contour lines in the phase plots.
We expect at least some symmetry between both hemispheres due to the residual circulation between the summer and winter poles.
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AC1: 'Reply on RC1', Gunter Stober, 17 May 2021
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RC2: 'Comment on acp-2021-142', Anonymous Referee #2, 21 Apr 2021
The paper is a solid and well-founded comparison between northern and southern hemispheric MLT observations on the one hand and the comparison of the model output of three whole atmosphere GMCs with the observations on the other hand. The structure of the paper is logical and clear, but resembles more a technical report than a scientific paper.
The main presentation of the results is a mixture of contrasting observations from the two hemispheres for different locations and the same presentation for the model results (10 of 15 figures do this plus the five in the Appendix). As the technical methodology appears to be very sound, I only have two main remarks that might help modify the current manuscript and improve the presentation:
(a) I would suggest separating the physical comparison between the hemispherical observations from the comparision GCMs to the observations. This would allow the authors to formulate research questions that can be addressed and answered by the comparision. The comparision between the GCMs and the observations shouls constitute a second main part of the paper. Currently, it is a hudgepodge, hard to read and difficult to separate the individual results.(b) The authors go to great lengths to create a homogeneous data set consisting of both observations and model outputs on comparable altitude-time grids. I wonder why the results are presented and discussed only qualitatively (" ... agrees reasonably well ...", etc). Why don't the authors show differences of the climatological means MODEL vs. OBSERVATION? I admit that the authors use a lot of effort to turn the shocking disagreements into positive words (e.g. " .... shows a better agreement with the radars for the hemispheric zonal summer wind reversal ..." ) but for scientific usage a QUANTIFICATION of the differences would be really desirable!
Nevertheless, the study has its merits but really needs focus.
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AC2: 'Reply on RC2', Gunter Stober, 17 May 2021
The reviewer comments about our manuscript are appreciated. We are going to revise the manuscript putting more emphasis on the interhemispheric differences in the observations and separate these findings a bit more from the model results. However, we would like to keep the general layout of the figures in the main part. The seasonal morphology of mean winds and tides provides a better qualitative comparison for the model development. Although it would be desirable to obtain a good quantitative agreement to the observations of WACCM-X(SD), GAIA and ICON-UA, the first goal is to improve the qualitative seasonal pattern. However, as suggested by the reviewer, we will add the quantitative comparison in the appendix for the mean winds to include the best from both worlds in the paper.
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AC2: 'Reply on RC2', Gunter Stober, 17 May 2021
Gunter Stober et al.
Gunter Stober et al.
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