Articles | Volume 37, issue 4
https://doi.org/10.5194/angeo-37-581-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/angeo-37-581-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Regular paper
| 
18 Jul 2019
Regular paper |
| 18 Jul 2019
| 18 Jul 2019
On the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere
Kathrin Baumgarten
CORRESPONDING AUTHOR
Leibniz-Institute of Atmospheric Physics at the University of Rostock, Kühlungsborn, Germany
Gunter Stober
Leibniz-Institute of Atmospheric Physics at the University of Rostock, Kühlungsborn, Germany
Institute of Applied Physics, Microwave Physics, University of Bern, Bern, Switzerland
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Gunter Stober, Diego Janches, Vivien Matthias, Dave Fritts, John Marino, Tracy Moffat-Griffin, Kathrin Baumgarten, Wonseok Lee, Damian Murphy, Yong Ha Kim, Nicholas Mitchell, and Scott Palo
Ann. Geophys., 39, 1–29, https://doi.org/10.5194/angeo-39-1-2021, https://doi.org/10.5194/angeo-39-1-2021, 2021
Gunter Stober, Kathrin Baumgarten, John P. McCormack, Peter Brown, and Jerry Czarnecki
Atmos. Chem. Phys., 20, 11979–12010, https://doi.org/10.5194/acp-20-11979-2020, https://doi.org/10.5194/acp-20-11979-2020, 2020
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This paper presents a first cross-comparison of meteor ground-based observations and a meteorological analysis (NAVGEM-HA) to compare a seasonal climatology of winds and temperatures at the mesosphere/lower thermosphere. The validation is insofar unique as we not only compare the mean state but also provide a detailed comparison of the short time variability of atmospheric tidal waves. Our analysis questions previous results claiming the importance of lunar tides.
Michael Gerding, Jochen Zöllner, Marius Zecha, Kathrin Baumgarten, Josef Höffner, Gunter Stober, and Franz-Josef Lübken
Atmos. Chem. Phys., 18, 15569–15580, https://doi.org/10.5194/acp-18-15569-2018, https://doi.org/10.5194/acp-18-15569-2018, 2018
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We describe the first comparative study of noctilucent clouds (NLCs) and mesospheric summer echoes at midlatitudes. Therefore, this study compares fresh clouds (small particles) with fully evolved clouds in the mesosphere, hinting at their evolution. It is shown that, in contrast to higher latitudes, here only a thin layer of fresh particles exist above the NLCs. This gives evidence that NLCs are not formed locally but are typically advected. This needs to be acknowledged in trend studies.
Kathrin Baumgarten, Michael Gerding, Gerd Baumgarten, and Franz-Josef Lübken
Atmos. Chem. Phys., 18, 371–384, https://doi.org/10.5194/acp-18-371-2018, https://doi.org/10.5194/acp-18-371-2018, 2018
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Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The temporal variation of these waves is studied using a record long 10-day continuous Rayleigh–Mie–Raman lidar sounding at midlatitudes. This data set shows a large variability of these waves on timescales of a few days and therefore provides new insights into wave intermittency phenomena, which can help to improve model simulations.
Michael Gerding, Maren Kopp, Josef Höffner, Kathrin Baumgarten, and Franz-Josef Lübken
Atmos. Meas. Tech., 9, 3707–3715, https://doi.org/10.5194/amt-9-3707-2016, https://doi.org/10.5194/amt-9-3707-2016, 2016
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Temperature soundings by lidar are an important tool for the understanding of the middle atmosphere, including gravity waves and tides. Though, mesospheric lidar soundings at daytime are rare. We describe a daylight-capable RMR lidar with optical bandwidths in the range of the Doppler broadened laser backscatter. We account for the systematic temperature error induced by the optical filter, and present examples of daylight-independent temperature sounding as well as tidal analysis.
Zishun Qiao, Alan Z. Liu, Gunter Stober, Javier Fuentes, Fabio Vargas, Christian L. Adami, and Iain M. Reid
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-126, https://doi.org/10.5194/amt-2024-126, 2024
Revised manuscript under review for AMT
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This paper describes the installation of the Chilean Observation Network De MeteOr Radars (CONDOR) and its initial results. The routine winds are point-to-point comparable to the co-located lidar winds. The retrievals of spatially resolved horizontal wind fields, vertical winds, and temperatures are also facilitated benefiting from the extensive meteor detections. The successful deployment and maintenance of CONDOR provide 24/7 and state-of-the-art wind measurements to the research community.
Guochun Shi, Witali Krochin, Eric Sauvageat, and Gunter Stober
Atmos. Chem. Phys., 24, 10187–10207, https://doi.org/10.5194/acp-24-10187-2024, https://doi.org/10.5194/acp-24-10187-2024, 2024
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Here we investigated ozone anomalies over polar regions during sudden stratospheric and final stratospheric warming with ground-based microwave radiometers at polar latitudes compared with reanalysis and satellite data. The underlying dynamical and chemical mechanisms are responsible for the observed ozone anomalies in both events. Our research sheds light on these processes, emphasizing the need for a deeper understanding of these processes for more accurate climate modeling and forecasting.
Florian Günzkofer, Gunter Stober, Johan Kero, David R. Themens, Njål Gulbrandsen, Masaki Tsutsumi, and Claudia Borries
EGUsphere, https://doi.org/10.5194/egusphere-2024-2708, https://doi.org/10.5194/egusphere-2024-2708, 2024
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The Earth’s magnetic field is not closed at high latitudes. Electrically charged particles can penetrate the Earth’s atmosphere, deposit their energy, and heat the local atmosphere-ionosphere. This presumably causes an upwelling of the neutral atmosphere which affects the atmosphere-ionosphere coupling. We apply a new analysis technique to infer the atmospheric density from incoherent scatter radar measurements. We show qualitatively how particle precipitation affects the neutral atmosphere.
Witali Krochin, Axel Murk, and Gunter Stober
Atmos. Meas. Tech., 17, 5015–5028, https://doi.org/10.5194/amt-17-5015-2024, https://doi.org/10.5194/amt-17-5015-2024, 2024
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Atmospheric tides are global-scale oscillations with periods of a fraction of a day. Their observation in the middle atmosphere is challenging and rare, as it requires continuous measurements with a high temporal resolution. In this paper, temperature time series of a ground-based microwave radiometer were analyzed with a spectral filter to derive thermal tide amplitudes and phases in an altitude range of 25–50 km at the geographical locations of Payerne and Bern (Switzerland).
Arthur Gauthier, Claudia Borries, Alexander Kozlovsky, Diego Janches, Peter Brown, Denis Vida, Christoph Jacobi, Damian Murphy, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Johan Kero, Nicholas Mitchell, Tracy Moffat-Griffin, and Gunter Stober
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2024-13, https://doi.org/10.5194/angeo-2024-13, 2024
Revised manuscript under review for ANGEO
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This study focuses on the TIMED Doppler Interferometer (TIDI)-Meteor Radar(MR) comparison of zonal and meridional winds and their dependence on local time and latitude. The correlation calculation between TIDI winds measurements and MR winds shows good agreement. A TIDI-MR seasonal comparison and the altitude-latitude dependence for winds is performed. TIDI reproduce the mean circulation well when compared with the MRs and might be useful as a lower boundary for general circulation models.
Alistair Bell, Eric Sauvageat, Gunter Stober, Klemens Hocke, and Axel Murk
EGUsphere, https://doi.org/10.5194/egusphere-2024-2474, https://doi.org/10.5194/egusphere-2024-2474, 2024
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Hardware and software developments have been made on a 22 GHz microwave radiometer for the measurement of middle atmosphere water vapour near Bern, Switzerland. Previous measurements dating back to 2010 have been re-calibrated and an improved optimal estimation retrieval performed on these measurements, giving a 13 year long dataset. Measurements made with new and improved instrumental hardware are used to correct previous measurements, which show better agreement than the non-corrected dataset.
Gunter Stober, Sharon L. Vadas, Erich Becker, Alan Liu, Alexander Kozlovsky, Diego Janches, Zishun Qiao, Witali Krochin, Guochun Shi, Wen Yi, Jie Zeng, Peter Brown, Denis Vida, Neil Hindley, Christoph Jacobi, Damian Murphy, Ricardo Buriti, Vania Andrioli, Paulo Batista, John Marino, Scott Palo, Denise Thorsen, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Kathrin Baumgarten, Johan Kero, Evgenia Belova, Nicholas Mitchell, Tracy Moffat-Griffin, and Na Li
Atmos. Chem. Phys., 24, 4851–4873, https://doi.org/10.5194/acp-24-4851-2024, https://doi.org/10.5194/acp-24-4851-2024, 2024
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On 15 January 2022, the Hunga Tonga-Hunga Ha‘apai volcano exploded in a vigorous eruption, causing many atmospheric phenomena reaching from the surface up to space. In this study, we investigate how the mesospheric winds were affected by the volcanogenic gravity waves and estimated their propagation direction and speed. The interplay between model and observations permits us to gain new insights into the vertical coupling through atmospheric gravity waves.
Florian Günzkofer, Gunter Stober, Dimitry Pokhotelov, Yasunobu Miyoshi, and Claudia Borries
Atmos. Meas. Tech., 16, 5897–5907, https://doi.org/10.5194/amt-16-5897-2023, https://doi.org/10.5194/amt-16-5897-2023, 2023
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Electric currents in the ionosphere can impact both satellite and ground-based infrastructure. These currents depend strongly on the collisions of ions and neutral particles. Measuring ion–neutral collisions is often only possible via certain assumptions. The direct measurement of ion–neutral collision frequencies is possible with multifrequency incoherent scatter radar measurements. This paper presents one analysis method of such measurements and discusses its advantages and disadvantages.
Florian Günzkofer, Dimitry Pokhotelov, Gunter Stober, Ingrid Mann, Sharon L. Vadas, Erich Becker, Anders Tjulin, Alexander Kozlovsky, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Evgenia Belova, Johan Kero, Nicholas J. Mitchell, and Claudia Borries
Ann. Geophys., 41, 409–428, https://doi.org/10.5194/angeo-41-409-2023, https://doi.org/10.5194/angeo-41-409-2023, 2023
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Gravity waves (GWs) are waves in Earth's atmosphere and can be observed as cloud ripples. Under certain conditions, these waves can propagate up into the ionosphere. Here, they can cause ripples in the ionosphere plasma, observable as oscillations of the plasma density. Therefore, GWs contribute to the ionospheric variability, making them relevant for space weather prediction. Additionally, the behavior of these waves allows us to draw conclusions about the atmosphere at these altitudes.
Guochun Shi, Witali Krochin, Eric Sauvageat, and Gunter Stober
Atmos. Chem. Phys., 23, 9137–9159, https://doi.org/10.5194/acp-23-9137-2023, https://doi.org/10.5194/acp-23-9137-2023, 2023
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We present the interannual and climatological behavior of ozone and water vapor from microwave radiometers in the Arctic.
By defining a virtual conjugate latitude station in the Southern Hemisphere, we investigate altitude-dependent interhemispheric differences and estimate the ascent and descent rates of water vapor in both hemispheres. Ozone and water vapor measurements will create a deeper understanding of the evolution of middle atmospheric ozone and water vapor.
Gunter Stober, Alan Liu, Alexander Kozlovsky, Zishun Qiao, Witali Krochin, Guochun Shi, Johan Kero, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Kathrin Baumgarten, Evgenia Belova, and Nicholas Mitchell
Ann. Geophys., 41, 197–208, https://doi.org/10.5194/angeo-41-197-2023, https://doi.org/10.5194/angeo-41-197-2023, 2023
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The Hunga Tonga–Hunga Ha‘apai volcanic eruption was one of the most vigorous volcanic explosions in the last centuries. The eruption launched many atmospheric waves traveling around the Earth. In this study, we identify these volcanic waves at the edge of space in the mesosphere/lower-thermosphere, leveraging wind observations conducted with multi-static meteor radars in northern Europe and with the Chilean Observation Network De Meteor Radars (CONDOR).
Gunter Stober, Alan Liu, Alexander Kozlovsky, Zishun Qiao, Ales Kuchar, Christoph Jacobi, Chris Meek, Diego Janches, Guiping Liu, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Evgenia Belova, Johan Kero, and Nicholas Mitchell
Atmos. Meas. Tech., 15, 5769–5792, https://doi.org/10.5194/amt-15-5769-2022, https://doi.org/10.5194/amt-15-5769-2022, 2022
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Precise and accurate measurements of vertical winds at the mesosphere and lower thermosphere are rare. Although meteor radars have been used for decades to observe horizontal winds, their ability to derive reliable vertical wind measurements was always questioned. In this article, we provide mathematical concepts to retrieve mathematically and physically consistent solutions, which are compared to the state-of-the-art non-hydrostatic model UA-ICON.
Witali Krochin, Francisco Navas-Guzmán, David Kuhl, Axel Murk, and Gunter Stober
Atmos. Meas. Tech., 15, 2231–2249, https://doi.org/10.5194/amt-15-2231-2022, https://doi.org/10.5194/amt-15-2231-2022, 2022
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This study leverages atmospheric temperature measurements performed with a ground-based radiometer making use of data that was collected during a 4-year observational campaign applying a new retrieval algorithm that improves the maximal altitude range from 45 to 55 km. The measurements are validated against two independent data sets, MERRA2 reanalysis data and the meteorological analysis of NAVGEM-HA.
Sumanta Sarkhel, Gunter Stober, Jorge L. Chau, Steven M. Smith, Christoph Jacobi, Subarna Mondal, Martin G. Mlynczak, and James M. Russell III
Ann. Geophys., 40, 179–190, https://doi.org/10.5194/angeo-40-179-2022, https://doi.org/10.5194/angeo-40-179-2022, 2022
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A rare gravity wave event was observed on the night of 25 April 2017 over northern Germany. An all-sky airglow imager recorded an upward-propagating wave at different altitudes in mesosphere with a prominent wave front above 91 km and faintly observed below. Based on wind and satellite-borne temperature profiles close to the event location, we have found the presence of a leaky thermal duct layer in 85–91 km. The appearance of this duct layer caused the wave amplitudes to diminish below 91 km.
Christoph Jacobi, Friederike Lilienthal, Dmitry Korotyshkin, Evgeny Merzlyakov, and Gunter Stober
Adv. Radio Sci., 19, 185–193, https://doi.org/10.5194/ars-19-185-2021, https://doi.org/10.5194/ars-19-185-2021, 2021
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We compare winds and tidal amplitudes in the upper mesosphere/lower thermosphere region for cases with disturbed and undisturbed geomagnetic conditions. The zonal winds in both the mesosphere and lower thermosphere tend to be weaker during disturbed conditions. The summer equatorward meridional wind jet is weaker for disturbed geomagnetic conditions. The effect of geomagnetic variability on tidal amplitudes, except for the semidiurnal tide, is relatively small.
Gunter Stober, Alexander Kozlovsky, Alan Liu, Zishun Qiao, Masaki Tsutsumi, Chris Hall, Satonori Nozawa, Mark Lester, Evgenia Belova, Johan Kero, Patrick J. Espy, Robert E. Hibbins, and Nicholas Mitchell
Atmos. Meas. Tech., 14, 6509–6532, https://doi.org/10.5194/amt-14-6509-2021, https://doi.org/10.5194/amt-14-6509-2021, 2021
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Wind observations at the edge to space, 70–110 km altitude, are challenging. Meteor radars have become a widely used instrument to obtain mean wind profiles above an instrument for these heights. We describe an advanced mathematical concept and present a tomographic analysis using several meteor radars located in Finland, Sweden and Norway, as well as Chile, to derive the three-dimensional flow field. We show an example of a gravity wave decelerating the mean flow.
Gunter Stober, Ales Kuchar, Dimitry Pokhotelov, Huixin Liu, Han-Li Liu, Hauke Schmidt, Christoph Jacobi, Kathrin Baumgarten, Peter Brown, Diego Janches, Damian Murphy, Alexander Kozlovsky, Mark Lester, Evgenia Belova, Johan Kero, and Nicholas Mitchell
Atmos. Chem. Phys., 21, 13855–13902, https://doi.org/10.5194/acp-21-13855-2021, https://doi.org/10.5194/acp-21-13855-2021, 2021
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Little is known about the climate change of wind systems in the mesosphere and lower thermosphere at the edge of space at altitudes from 70–110 km. Meteor radars represent a well-accepted remote sensing technique to measure winds at these altitudes. Here we present a state-of-the-art climatological interhemispheric comparison using continuous and long-lasting observations from worldwide distributed meteor radars from the Arctic to the Antarctic and sophisticated general circulation models.
Gunter Stober, Diego Janches, Vivien Matthias, Dave Fritts, John Marino, Tracy Moffat-Griffin, Kathrin Baumgarten, Wonseok Lee, Damian Murphy, Yong Ha Kim, Nicholas Mitchell, and Scott Palo
Ann. Geophys., 39, 1–29, https://doi.org/10.5194/angeo-39-1-2021, https://doi.org/10.5194/angeo-39-1-2021, 2021
Gunter Stober, Kathrin Baumgarten, John P. McCormack, Peter Brown, and Jerry Czarnecki
Atmos. Chem. Phys., 20, 11979–12010, https://doi.org/10.5194/acp-20-11979-2020, https://doi.org/10.5194/acp-20-11979-2020, 2020
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This paper presents a first cross-comparison of meteor ground-based observations and a meteorological analysis (NAVGEM-HA) to compare a seasonal climatology of winds and temperatures at the mesosphere/lower thermosphere. The validation is insofar unique as we not only compare the mean state but also provide a detailed comparison of the short time variability of atmospheric tidal waves. Our analysis questions previous results claiming the importance of lunar tides.
Leonie Bernet, Elmar Brockmann, Thomas von Clarmann, Niklaus Kämpfer, Emmanuel Mahieu, Christian Mätzler, Gunter Stober, and Klemens Hocke
Atmos. Chem. Phys., 20, 11223–11244, https://doi.org/10.5194/acp-20-11223-2020, https://doi.org/10.5194/acp-20-11223-2020, 2020
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With global warming, water vapour increases in the atmosphere. Water vapour is an important gas because it is a natural greenhouse gas and affects the formation of clouds, rain and snow. How much water vapour increases can vary in different regions of the world. To verify if it increases as expected on a regional scale, we analysed water vapour measurements in Switzerland. We found that water vapour generally increases as expected from temperature changes, except in winter.
Franziska Schranz, Jonas Hagen, Gunter Stober, Klemens Hocke, Axel Murk, and Niklaus Kämpfer
Atmos. Chem. Phys., 20, 10791–10806, https://doi.org/10.5194/acp-20-10791-2020, https://doi.org/10.5194/acp-20-10791-2020, 2020
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We measured middle-atmospheric ozone, water vapour and zonal and meridional wind with two ground-based microwave radiometers which are located at Ny-Alesund, Svalbard, in the Arctic. In this article we present measurements of the small-scale horizontal ozone gradients during winter 2018/2019. We found a distinct seasonal variation of the ozone gradients which is linked to the planetary wave activity. We further present the signatures of the SSW in the ozone, water vapour and wind measurements.
Jonas Hagen, Klemens Hocke, Gunter Stober, Simon Pfreundschuh, Axel Murk, and Niklaus Kämpfer
Atmos. Chem. Phys., 20, 2367–2386, https://doi.org/10.5194/acp-20-2367-2020, https://doi.org/10.5194/acp-20-2367-2020, 2020
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The middle atmosphere (30 to 70 km altitude) is stratified and, despite very strong horizontal winds, there is less mixing between the horizontal layers. An important driver for the energy exchange between the layers in this regime is atmospheric tides, which are waves that are driven by the diurnal cycle of solar heating. We measure these tides in the wind field for the first time using a ground-based passive instrument. Ultimately, such measurements could be used to improve atmospheric models.
Sven Wilhelm, Gunter Stober, and Peter Brown
Ann. Geophys., 37, 851–875, https://doi.org/10.5194/angeo-37-851-2019, https://doi.org/10.5194/angeo-37-851-2019, 2019
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We report on long-term observations of atmospheric parameters in the mesosphere and lower thermosphere made over the last 2 decades for the northern-latitude locations of Andenes, Juliusruh, and Tavistock. The observations are based on meteor wind measurements and further include the long-term variability of winds, tides, and the kinetic energy of gravity waves and planetary waves. Furthermore, the influence on an 11-year oscillation on the winds and tides is presented.
Dimitry Pokhotelov, Gunter Stober, and Jorge Luis Chau
Atmos. Chem. Phys., 19, 5251–5258, https://doi.org/10.5194/acp-19-5251-2019, https://doi.org/10.5194/acp-19-5251-2019, 2019
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Twelve years of radar observations from a mid-latitude location in Kühlungsborn, Germany have been analysed to study characteristics of mesospheric summer echoes (MSEs). The statistical analysis shows that MSEs have a strong daytime preference and early summer seasonal preference. It is demonstrated that the meridional wind transport from polar regions is the important controlling factor for MSEs, while no clear connection to geomagnetic and solar activity is found.
Fazlul I. Laskar, Gunter Stober, Jens Fiedler, Meers M. Oppenheim, Jorge L. Chau, Duggirala Pallamraju, Nicholas M. Pedatella, Masaki Tsutsumi, and Toralf Renkwitz
Atmos. Chem. Phys., 19, 5259–5267, https://doi.org/10.5194/acp-19-5259-2019, https://doi.org/10.5194/acp-19-5259-2019, 2019
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Meteor radars are used to track and estimate the fading time of meteor trails. In this investigation, it is observed that the diffusion time estimated from such trail fading time is anomalously higher during noctilucent clouds (NLC) than that in its absence. We propose that NLC particles absorb background electrons and thus modify the background electrodynamics, leading to such an anomaly.
Nikoloz Gudadze, Gunter Stober, and Jorge L. Chau
Atmos. Chem. Phys., 19, 4485–4497, https://doi.org/10.5194/acp-19-4485-2019, https://doi.org/10.5194/acp-19-4485-2019, 2019
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We show a possibility of measuring mean vertical winds during the summer months using polar mesosphere summer echo (PMSE) observations. Middle Atmosphere Alomar Radar System observations of PMSE five-beam radial velocities are analysed to obtain the results. We found that sampling issues are the reason for bias in vertical wind measurements at the edges of PMSE altitudes. However, the PMSE is a good tracer for the mean vertical wind estimation at the central altitudes with its peak occurrence.
Sven Wilhelm, Gunter Stober, Vivien Matthias, Christoph Jacobi, and Damian J. Murphy
Ann. Geophys., 37, 1–14, https://doi.org/10.5194/angeo-37-1-2019, https://doi.org/10.5194/angeo-37-1-2019, 2019
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This study shows that the mesospheric winds are affected by an expansion–shrinking of the mesosphere and lower thermosphere that takes place due to changes in the intensity of the solar radiation, which affects the density within the atmosphere. On seasonal timescales, an increase in the neutral density occurs together with a decrease in the eastward-directed zonal wind. Further, even after removing the seasonal and the 11-year solar cycle variations, we show a connection between them.
Michael Gerding, Jochen Zöllner, Marius Zecha, Kathrin Baumgarten, Josef Höffner, Gunter Stober, and Franz-Josef Lübken
Atmos. Chem. Phys., 18, 15569–15580, https://doi.org/10.5194/acp-18-15569-2018, https://doi.org/10.5194/acp-18-15569-2018, 2018
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We describe the first comparative study of noctilucent clouds (NLCs) and mesospheric summer echoes at midlatitudes. Therefore, this study compares fresh clouds (small particles) with fully evolved clouds in the mesosphere, hinting at their evolution. It is shown that, in contrast to higher latitudes, here only a thin layer of fresh particles exist above the NLCs. This gives evidence that NLCs are not formed locally but are typically advected. This needs to be acknowledged in trend studies.
Gunter Stober, Jorge L. Chau, Juha Vierinen, Christoph Jacobi, and Sven Wilhelm
Atmos. Meas. Tech., 11, 4891–4907, https://doi.org/10.5194/amt-11-4891-2018, https://doi.org/10.5194/amt-11-4891-2018, 2018
J. Federico Conte, Jorge L. Chau, Fazlul I. Laskar, Gunter Stober, Hauke Schmidt, and Peter Brown
Ann. Geophys., 36, 999–1008, https://doi.org/10.5194/angeo-36-999-2018, https://doi.org/10.5194/angeo-36-999-2018, 2018
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Based on comparisons of meteor radar measurements with HAMMONIA model simulations, we show that the differences exhibited by the semidiurnal solar tide (S2) observed at middle and high latitudes of the Northern Hemisphere between equinox times are mainly due to distinct behaviors of the migrating semidiurnal (SW2) and the non-migrating westward-propagating wave number 1 semidiurnal (SW1) tidal components.
Dimitry Pokhotelov, Erich Becker, Gunter Stober, and Jorge L. Chau
Ann. Geophys., 36, 825–830, https://doi.org/10.5194/angeo-36-825-2018, https://doi.org/10.5194/angeo-36-825-2018, 2018
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Atmospheric tides are produced by solar heating of the lower atmosphere. The tides propagate to the upper atmosphere and ionosphere playing an important role in the vertical coupling. Ground radar measurements of the seasonal variability of tides are compared with global numerical simulations. The agreement with radar data and limitations of the numerical model are discussed. The work represents a first step in modelling the impact of tidal dynamics on the upper atmosphere and ionosphere.
Sabine Wüst, Thomas Offenwanger, Carsten Schmidt, Michael Bittner, Christoph Jacobi, Gunter Stober, Jeng-Hwa Yee, Martin G. Mlynczak, and James M. Russell III
Atmos. Meas. Tech., 11, 2937–2947, https://doi.org/10.5194/amt-11-2937-2018, https://doi.org/10.5194/amt-11-2937-2018, 2018
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OH*-spectrometer measurements allow the analysis of gravity wave ground-based periods, but spatial information cannot necessarily be deduced. We combine the approach of Wachter at al. (2015) in order to derive horizontal wavelengths (but based on only one OH* spectrometer) with additional information about wind and temperature and compute vertical wavelengths. Knowledge of these parameters is a precondition for the calculation of further information such as the wave group velocity.
Gunter Stober, Svenja Sommer, Carsten Schult, Ralph Latteck, and Jorge L. Chau
Atmos. Chem. Phys., 18, 6721–6732, https://doi.org/10.5194/acp-18-6721-2018, https://doi.org/10.5194/acp-18-6721-2018, 2018
Rolf Rüfenacht, Gerd Baumgarten, Jens Hildebrand, Franziska Schranz, Vivien Matthias, Gunter Stober, Franz-Josef Lübken, and Niklaus Kämpfer
Atmos. Meas. Tech., 11, 1971–1987, https://doi.org/10.5194/amt-11-1971-2018, https://doi.org/10.5194/amt-11-1971-2018, 2018
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Wind information throughout the middle-atmosphere is crucial for the understanding of atmospheric dynamics but became available only recently, thanks to developments in remote sensing and modelling approaches. We present the first thorough assessment of the quality of the wind estimates by comparing co-located observations from lidar and microwave radiometry and opposing them to the major atmospheric models. Moreover we evaluated a new approach for measuring mesopause region wind by radiometry.
Qiang Li, Markus Rapp, Gunter Stober, and Ralph Latteck
Ann. Geophys., 36, 577–586, https://doi.org/10.5194/angeo-36-577-2018, https://doi.org/10.5194/angeo-36-577-2018, 2018
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With the powerful MAARSY radar, we detected 3D wind fields and the vertical winds show a non-Gaussian distribution. We further obtained the frequency spectrum of vertical wind. The distribution of the spectral slopes under different wind conditions is derived and their comparisons with the background horizontal winds show that the spectra become steeper with increasing wind velocities under quiet conditions, approach a slope of −5/3 at 10 m/s and then maintain this slope for even stronger winds.
Kathrin Baumgarten, Michael Gerding, Gerd Baumgarten, and Franz-Josef Lübken
Atmos. Chem. Phys., 18, 371–384, https://doi.org/10.5194/acp-18-371-2018, https://doi.org/10.5194/acp-18-371-2018, 2018
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Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The temporal variation of these waves is studied using a record long 10-day continuous Rayleigh–Mie–Raman lidar sounding at midlatitudes. This data set shows a large variability of these waves on timescales of a few days and therefore provides new insights into wave intermittency phenomena, which can help to improve model simulations.
Sven Wilhelm, Gunter Stober, and Jorge L. Chau
Ann. Geophys., 35, 893–906, https://doi.org/10.5194/angeo-35-893-2017, https://doi.org/10.5194/angeo-35-893-2017, 2017
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A comparison between winds and tides in the mesosphere and lower thermosphere based on measurements from a meteor radar (MR) and a medium-frequency radar in northern Norway was done to estimate potential biases between the two systems. Our results indicate reasonable agreement for the zonal and meridional wind components between 78 and 92 km. Based on these findings, we have taken the MR data as a reference and thus construct a consistent and homogenous wind from approximately 60 to 110 km.
Gunter Stober, Vivien Matthias, Christoph Jacobi, Sven Wilhelm, Josef Höffner, and Jorge L. Chau
Ann. Geophys., 35, 711–720, https://doi.org/10.5194/angeo-35-711-2017, https://doi.org/10.5194/angeo-35-711-2017, 2017
Qiang Li, Markus Rapp, Anne Schrön, Andreas Schneider, and Gunter Stober
Ann. Geophys., 34, 1209–1229, https://doi.org/10.5194/angeo-34-1209-2016, https://doi.org/10.5194/angeo-34-1209-2016, 2016
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Turbulence is an essential process in the atmosphere and ocean. Clear-air turbulence is a well-known threat for the safety of aviation. Using a powerful MST radar, we detected turbulence and compared it with the results from radiosondes. The correlation between turbulence and background conditions, e.g., Richardson number and wind shears, is determined. There is a nearly negative correlation between turbulence and Richardson number independent of the length scale over which it was calculated.
Ch. Jacobi, N. Samtleben, and G. Stober
Adv. Radio Sci., 14, 169–174, https://doi.org/10.5194/ars-14-169-2016, https://doi.org/10.5194/ars-14-169-2016, 2016
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VHF meteor radar observations of mesosphere/lower thermosphere daily temperatures have been performed at Collm, Germany. The data have been analyzed with respect to long-period oscillations at time scales of 2 to 30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The results are comparable with analyses from radar wind measurements.
Michael Gerding, Maren Kopp, Josef Höffner, Kathrin Baumgarten, and Franz-Josef Lübken
Atmos. Meas. Tech., 9, 3707–3715, https://doi.org/10.5194/amt-9-3707-2016, https://doi.org/10.5194/amt-9-3707-2016, 2016
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Temperature soundings by lidar are an important tool for the understanding of the middle atmosphere, including gravity waves and tides. Though, mesospheric lidar soundings at daytime are rare. We describe a daylight-capable RMR lidar with optical bandwidths in the range of the Doppler broadened laser backscatter. We account for the systematic temperature error induced by the optical filter, and present examples of daylight-independent temperature sounding as well as tidal analysis.
Juha Vierinen, Jorge L. Chau, Nico Pfeffer, Matthias Clahsen, and Gunter Stober
Atmos. Meas. Tech., 9, 829–839, https://doi.org/10.5194/amt-9-829-2016, https://doi.org/10.5194/amt-9-829-2016, 2016
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This paper describes the use of pseudorandom coded continuous wave radar transmissions for meteor radar. This avoids range-aliased echoes, maximizes pulse compression gain, is less susceptible to RFI, allows time resolution to be changed flexibly, and enables multiple transmitters to operate on the same frequency without interfering each other. These features make the radar well suited for multi-static meteor radar networks. We show results from a measurement campaign to demonstrate the method.
T. Renkwitz, C. Schult, R. Latteck, and G. Stober
Adv. Radio Sci., 13, 41–48, https://doi.org/10.5194/ars-13-41-2015, https://doi.org/10.5194/ars-13-41-2015, 2015
S. Sommer, G. Stober, J. L. Chau, and R. Latteck
Adv. Radio Sci., 12, 197–203, https://doi.org/10.5194/ars-12-197-2014, https://doi.org/10.5194/ars-12-197-2014, 2014
G. Stober, S. Sommer, M. Rapp, and R. Latteck
Atmos. Meas. Tech., 6, 2893–2905, https://doi.org/10.5194/amt-6-2893-2013, https://doi.org/10.5194/amt-6-2893-2013, 2013
C. Schult, G. Stober, J. L. Chau, and R. Latteck
Ann. Geophys., 31, 1843–1851, https://doi.org/10.5194/angeo-31-1843-2013, https://doi.org/10.5194/angeo-31-1843-2013, 2013
V. Matthias, P. Hoffmann, A. Manson, C. Meek, G. Stober, P. Brown, and M. Rapp
Ann. Geophys., 31, 1397–1415, https://doi.org/10.5194/angeo-31-1397-2013, https://doi.org/10.5194/angeo-31-1397-2013, 2013
G. Stober, C. Schult, C. Baumann, R. Latteck, and M. Rapp
Ann. Geophys., 31, 473–487, https://doi.org/10.5194/angeo-31-473-2013, https://doi.org/10.5194/angeo-31-473-2013, 2013
T. Dunker, U.-P. Hoppe, G. Stober, and M. Rapp
Ann. Geophys., 31, 61–73, https://doi.org/10.5194/angeo-31-61-2013, https://doi.org/10.5194/angeo-31-61-2013, 2013
M. Rapp, J. M. C. Plane, B. Strelnikov, G. Stober, S. Ernst, J. Hedin, M. Friedrich, and U.-P. Hoppe
Ann. Geophys., 30, 1661–1673, https://doi.org/10.5194/angeo-30-1661-2012, https://doi.org/10.5194/angeo-30-1661-2012, 2012
Related subject area
Subject: Terrestrial atmosphere and its relation to the sun | Keywords: Waves and tides
Benchmarking microbarom radiation and propagation model against infrasound recordings: a vespagram-based approach
Evanescent acoustic-gravity modes in the isothermal atmosphere: systematization and applications to the Earth and solar atmospheres
Ekaterina Vorobeva, Marine De Carlo, Alexis Le Pichon, Patrick Joseph Espy, and Sven Peter Näsholm
Ann. Geophys., 39, 515–531, https://doi.org/10.5194/angeo-39-515-2021, https://doi.org/10.5194/angeo-39-515-2021, 2021
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Our approach compares infrasound data and simulated microbarom soundscapes in multiple directions. Data recorded during 2014–2019 at Infrasound Station 37 in Norway were processed and compared to model results in different aspects (directional distribution, signal amplitude, and ability to track atmospheric changes during extreme events). The results reveal good agreement between the model and data. The approach has potential for near-real-time atmospheric and microbarom diagnostics.
Oleg K. Cheremnykh, Alla K. Fedorenko, Evgen I. Kryuchkov, and Yuriy A. Selivanov
Ann. Geophys., 37, 405–415, https://doi.org/10.5194/angeo-37-405-2019, https://doi.org/10.5194/angeo-37-405-2019, 2019
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The fundamental mode of oscillations of the solar atmosphere, f-mode, plays an important role in solar physics. At an early stage of observation, it was found that its frequency is related to the wavelength by a ratio characteristic of waves on the surface of deep water. Subsequent observations revealed its inaccuracy. We derived waves with a different frequency–wavelength ratio and compared them with other possible waves of this type in both the solar and terrestrial atmosphere.
Cited articles
Baumgarten, K., Gerding, M., and Lübken, F.-J.: Seasonal variation of
gravity wave parameters using different filter methods with daylight lidar
measurements at mid-latitudes, J. Geophys. Res.-Atmos., 122, 2683–2695,
https://doi.org/10.1002/2016JD025916, 2017. a, b
Baumgarten, K., Gerding, M., Baumgarten, G., and Lübken, F.-J.: Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding, Atmos. Chem. Phys., 18, 371-384, https://doi.org/10.5194/acp-18-371-2018, 2018. a, b
Becker, E.: Mean-Flow Effects of Thermal Tides in the Mesosphere and Lower
Thermosphere, J. Atmos. Sci., 74, 2043–2063,
https://doi.org/10.1175/JAS-D-16-0194.1, 2017. a, b, c
Chapman, S. and Lindzen, R. S.: Atmospheric tides: Thermal and
Gravitational, Gordon and Breach, New York, 1970. a
Ehard, B., Kaifler, B., Kaifler, N., and Rapp, M.: Evaluation of methods for gravity wave extraction from middle-atmospheric lidar temperature measurements, Atmos. Meas. Tech., 8, 4645–4655, https://doi.org/10.5194/amt-8-4645-2015, 2015. a
Fleming, E. L., Chandra, S., Barnett, J. J., and Corney, M.: Zonal mean
temperature, pressure, zonal wind, and geopotential height as functions of
latitude, Adv. Space Res., 10, 11–59, 1990. a
Fong, W., Lu, X., Chu, X., Fuller-Rowell, T. J., Yu, Z., Roberts, B. R., Chen,
C., Gardner, C. S., and McDonald, A. J.: Winter temperature tides from 30 to
110 km at McMurdo (77.8∘ S, 166.7∘ E), Antarctica:
Lidar observations and comparisons with WAM, J. Geophys. Res.-Atmos., 119,
2846–2863, https://doi.org/10.1002/2013JD020784,
2014. a
Forbes, J. M.: Tidal and Planetary Waves, 67–87, Geophysical Monograph Series, American Geophysical
Union, https://doi.org/10.1029/GM087p0067, 1995. a
Forbes, J. M. and Garrett, H. B.: Theoretical studies of atmospheric tides,
Rev. Geophys., 17, 1951–1981, https://doi.org/10.1029/RG017i008p01951, 1979. a, b
Forbes, J. M. and Hagan, M. E.: Diurnal propagating tide in the presence of
mean winds and dissipation: a numerical investigation, Planet. Space
Sci., 36, 579–590, https://doi.org/10.1016/0032-0633(88)90027-X,
1988. a
Forbes, J. M. and Wu, D.: Solar Tides as Revealed by Measurements of Mesosphere
Temperature by the MLS Experiment on UARS, J. Atmos. Sci., 63,
1776–1797, https://doi.org/10.1175/JAS3724.1, 2006. a
Fritts, D. C. and Alexander, M. J.: Gravity wave dynamics and effects in the
middle atmosphere, Rev. Geophys., 41, 1003,
https://doi.org/10.1029/2001RG000106, 2003. a
Gelaro, R., McCarty, W., Suárez, M. J., Todling, R., Molod, A., Takacs, L.,
Randles, C. A., Darmenov, A., Bosilovich, M. G., Reichle, R., Wargan, K.,
Coy, L., Cullather, R., Draper, C., Akella, S., Buchard, V., Conaty, A.,
da Silva, A. M., Gu, W., Kim, G.-K., Koster, R., Lucchesi, R., Merkova, D.,
Nielsen, J. E., Partyka, G., Pawson, S., Putman, W., Rienecker, M., Schubert,
S. D., Sienkiewicz, M., and Zhao, B.: The Modern-Era Retrospective
Analysis for Research and Applications, Version 2 (MERRA-2),
J. Climate, 30, 5419–5454, https://doi.org/10.1175/JCLI-D-16-0758.1, 2017. a, b
Gerding, M., Kopp, M., Höffner, J., Baumgarten, K., and Lübken, F.-J.: Mesospheric temperature soundings with the new, daylight-capable IAP RMR lidar, Atmos. Meas. Tech., 9, 3707–3715, https://doi.org/10.5194/amt-9-3707-2016, 2016. a
Hagan, M. E. and Forbes, J. M.: Migrating and nonmigrating diurnal tides in the
middle and upper atmosphere excited by tropospheric latent heat release, J. Geophys. Res.-Atmos., 107, ACL 6-1–ACL 6-15, https://doi.org/10.1029/2001JD001236,
2002. a
Hauchecorne, A. and Chanin, M. L.: Density and Temperature Profiles obtained by
Lidar between 35 and 70 km, Geophys. Res. Lett., 7, 565–568, 1980. a
Hoffmann, P., Becker, E., Singer, W., and Placke, M.: Seasonal variation of
mesospheric waves at northern middle and high latitudes, J. Atmos. Sol.-Terr.
Phy., 72, 1068–1079, https://doi.org/10.1016/j.jastp.2010.07.002, 2010. a
Holton, J. R.: An introduction to dynamic meteorology, International
Geophysics Series, Elsevier Academic Press, Burlington, MA, 4th Edn., 2004. a
Hu, X., Liu, A. Z., Gardner, C. S., and Swenson, G. R.: Characteristics of
quasi-monochromatic gravity waves observed with Na lidar in the mesopause
region at Starfire Optical Range, NM, Geophys. Res. Lett., 29,
22-1–22-4, https://doi.org/10.1029/2002GL014975,
2002. a
Jacobi, C.: 6 year mean prevailing winds and tides measured by VHF meteor
radar over Collm (51.3∘ N, 13.0∘ E), J. Atmos. Sol.-Terr.
Phy., 78–79, 8–18, https://doi.org/10.1016/j.jastp.2011.04.010, 2012. a
Kopp, M., Gerding, M., Höffner, J., and Lübken, F.-J.: Tidal
signatures in temperatures derived from daylight lidar soundings above
Kühlungsborn (54∘ N, 12∘ E), J. Atmos. Sol.-Terr.
Phy., 127, 37–50, https://doi.org/10.1016/j.jastp.2014.09.002, 2015. a, b, c
Lieberman, R. S., Riggin, D. M., Ortland, D. A., Oberheide, J., and Siskind,
D. E.: Global observations and modeling of nonmigrating diurnal tides
generated by tide-planetary wave interactions, J. Geophys. Res.-Atmos., 120,
11419–11437, https://doi.org/10.1002/2015JD023739, 2015. a, b
Lindzen, R. S.: Thermally driven diurnal tide in the atmosphere, Q. J. Roy.
Meteor. Soc., 93, 18–42, https://doi.org/10.1002/qj.49709339503, 1967. a
McLandress, C., Shepherd, G. G., and Solheim, B. H.: Satellite observations of
thermospheric tides: Results from the Wind Imaging Interferometer on UARS,
J. Geophys. Res.-Atmos., 101, 4093–4114,
https://doi.org/10.1029/95JD03359,
1996. a
Mukhtarov, P., Pancheva, D., and Andonov, B.: Global structure and seasonal and
interannual variability of the migrating diurnal tide seen in the SABER/TIMED
temperatures between 20 and 120 km, J. Geophys. Res.-Space, 114, A02309, https://doi.org/10.1029/2008JA013759, 2009. a, b
Oberheide, J., Hagan, M. E., Roble, R. G., and Offermann, D.: Sources of
nonmigrating tides in the tropical middle atmosphere, J. Geophys. Res.-Atmos., 107, ACL 6-1–ACL 6-14, https://doi.org/10.1029/2002JD002220,
2002. a, b
Oberheide, J., Hagan, M., Richmond, A., and Forbes, J.: DYNAMICAL METEOROLOGY,
Atmospheric Tides, in: Encyclopedia of Atmospheric Sciences,
edited by: North, G. R., Pyle, J., and Zhang, F., 287–297, Academic
Press, Oxford, 2nd Edn.,
https://doi.org/10.1016/B978-0-12-382225-3.00409-6, 2015. a
Pancheva, D., Mukhtarov, P., and Smith, A. K.: Climatology of the migrating
terdiurnal tide (TW3) in SABER/TIMED temperatures, J. Geophys. Res.-Space, 118, 1755–1767, https://doi.org/10.1002/jgra.50207, 2013. a
Pedatella, N. M., Oberheide, J., Sutton, E. K., Liu, H.-L., Anderson, J. L.,
and Raeder, K.: Short-term nonmigrating tide variability in the mesosphere,
thermosphere, and ionosphere, J. Geophys. Res.-Space, 121,
3621–3633, https://doi.org/10.1002/2016JA022528, 2016.
a
Pokhotelov, D., Becker, E., Stober, G., and Chau, J. L.: Seasonal variability of atmospheric tides in the mesosphere and lower thermosphere: meteor radar data and simulations, Ann. Geophys., 36, 825–830, https://doi.org/10.5194/angeo-36-825-2018, 2018. a, b
Sakazaki, T., Fujiwara, M., Zhang, X., Hagan, M. E., and Forbes, J. M.: Diurnal
tides from the troposphere to the lower mesosphere as deduced from
TIMED/SABER satellite data and six global reanalysis data sets, J. Geophys. Res.-Atmos., 117, d13108, https://doi.org/10.1029/2011JD017117,
2012. a, b
Sakazaki, T., Sato, K., Kawatani, Y., and Watanabe, S.: Three-dimensional
structures of tropical nonmigrating tides in a high-vertical-resolution
general circulation model, J. Geophys. Res.-Atmos., 120,
1759–1775, https://doi.org/10.1002/2014JD022464,
2015. a
Sakazaki, T., Fujiwara, M., and Shiotani, M.: Representation of solar tides in the stratosphere and lower mesosphere in state-of-the-art reanalyses and in satellite observations, Atmos. Chem. Phys., 18, 1437–1456, https://doi.org/10.5194/acp-18-1437-2018, 2018. a, b
Smith, A. K.: Global Dynamics of the MLT, Surv. Geophys., 33,
1177–1230, https://doi.org/10.1007/s10712-012-9196-9, 2012. a
Stober, G., Matthias, V., Jacobi, C., Wilhelm, S., Höffner, J., and Chau, J. L.: Exceptionally strong summer-like zonal wind reversal in the upper mesosphere during winter 2015/16, Ann. Geophys., 35, 711–720, https://doi.org/10.5194/angeo-35-711-2017, 2017. a
Wilhelm, S., Stober, G., and Chau, J. L.: A comparison of 11-year mesospheric and lower thermospheric winds determined by meteor and MF radar at 69∘ N, Ann. Geophys., 35, 893–906, https://doi.org/10.5194/angeo-35-893-2017, 2017. a
Yuan, T., She, C.-Y., Krueger, D., Reising, S. C., Zhang, X., and Forbes,
J. M.: A collaborative study on temperature diurnal tide in the midlatitude
mesopause region (41∘ N, 105∘ W) with Na lidar and
TIMED/SABER observations, J. Atmos. Sol.-Terr. Phy., 72, 541–549,
https://doi.org/10.1016/j.jastp.2010.02.007,
2010. a
Zhang, X., Forbes, J. M., Hagan, M. E., Russell, J. M., Palo, S. E., Mertens,
C. J., and Mlynczak, M. G.: Monthly tidal temperatures 20–120 km from
TIMED/SABER, J. Geophys. Res.-Space, 111, A10S08,
https://doi.org/10.1029/2005JA011504,
2006. a
Zhou, X., Wan, W., Yu, Y., Ning, B., Hu, L., and Yue, X.: New Approach to
Estimate Tidal Climatology From Ground- and Space-Based Observations, J.
Geophys. Res.-Space, 123, 5087–5101, https://doi.org/10.1029/2017JA024967,
2018. a, b
Short summary
The paper presents the variability in thermal tides in the middle atmosphere from temperature observations as well as from horizontal wind data using a new diagnostic approach which takes into account a possible intermittency of tides. The data are analyzed from a local as well as from a global perspective to distinguish between different tidal modes. Surprisingly, there are dominating tidal modes, which are seen in the local data, and a phase relation between temperature and winds is evaluated.
The paper presents the variability in thermal tides in the middle atmosphere from temperature...
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