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Global Characteristics of the Lunar Tidal Modulation of the Equatorial Electrojet Derived from Champ Observations : Volume 30, Issue 3 (08/03/2012)

By Lühr, H.

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Book Id: WPLBN0004002140
Format Type: PDF Article :
File Size: Pages 10
Reproduction Date: 2015

Title: Global Characteristics of the Lunar Tidal Modulation of the Equatorial Electrojet Derived from Champ Observations : Volume 30, Issue 3 (08/03/2012)  
Author: Lühr, H.
Volume: Vol. 30, Issue 3
Language: English
Subject: Science, Annales, Geophysicae
Collections: Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Historic
Publication Date:
2012
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Maus, S., Lühr, H., & Siddiqui, T. A. (2012). Global Characteristics of the Lunar Tidal Modulation of the Equatorial Electrojet Derived from Champ Observations : Volume 30, Issue 3 (08/03/2012). Retrieved from http://www.ebooklibrary.org/


Description
Description: Helmholtz Centre Potsdam, GFZ – German Research Centre for Geosciences, Potsdam, Germany. It has been known since many decades that lunar tide has an influence on the strength of the equatorial electrojet (EEJ). There has, however, never been a comprehensive study of the tidal effect on a global scale. Based on the continuous magnetic field measurements by the CHAMP satellite over 10 years it is possible to investigate the various aspects of lunar effects on the EEJ. The EEJ intensity is enhanced around times when the moon is overhead or at the antipode. This effect is particularly strong around noon, shortly after new and full moon. The lunar tide manifests itself as a semi-diurnal wave that precesses through all local times within one lunar month. The largest tidal amplitudes are observed around December solstice and smallest around June solstice. The tidal wave crest lags behind the moon phase. During December this amounts to about 4 days while it is around 2 days during other times of the year. We have not found significant longitudinal variations of the lunar influence on the EEJ. When comparing the average EEJ amplitude at high solar activity with that during periods of solar minimum conditions a solar cycle dependence can be found, but the ratio between tidal amplitude and EEJ intensity stays the same. Actually, tidal signatures standout clearer during times of low solar activity. We suggest that the tidal variations are caused by a current system added to the EEJ rather than by modulating the EEJ. Gravitational forcing of the lower atmosphere by the moon and the sun is assumed to be the driver of an upward propagating tidal wave. The larger tidal amplitudes around December solstice can be related to stratospheric warming events which seem to improve the conditions for upward propagation.

The results described here have to large extent been presented as a Julius-Bartels Medal Lecture during the General Assembly 2011 of the European Geosciences Union.


Summary
Global characteristics of the lunar tidal modulation of the equatorial electrojet derived from CHAMP observations

Excerpt
Alken, P. and Maus, S.: Spatio-temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC-C satellite measurements, J. Geophys. Res., 112, A09305, <a href=http://dx.doi.org/10.1029/2007JA012524>doi:10.1029/2007JA012524, 2007.; Bartels, J.: Aufschlüsse über die Ionosphäre aus der Analyse sonnen- und mond-tägiger erdmagnetischer Schwankungen, Z. Geophys., 12, 368–378, 1936.; Bartels, J. and Johnston, H. F.: Geomagnetic tides in horizontal intensity at Huancayo, Part I, terrestrial magnetism and atmospheric electricity, J. Geophys. Res., 45, 269–308, 1940.; Bartels, J. and Kertz, W.: Gezeitenartige Schwingungen der Atmosphäre, in: Landoldt-Börnstein, Astronomie und Geophysik, edited by: Bartel, J. and Ten Bruggencate, P., pp. 674–685, Springer, Berlin-Göttingen-Heidelberg, 1952.; Chapman, S. and Lindzen, R.: Atmospheric Tides, pp. 66–105, Reidel, Dordrecht, Holland, 1970.; Chau, J. L., Fejer, B. G., and Goncharenko, L. P.: Quiet variability of equatorial E-B drifts during a sudden stratospheric warming event, Geophys. Res. Lett., 36, L05101, <a href=http://dx.doi.org/10.1029/2008GL036785>doi:10.1029/2008GL036785, 2009.; England, S. L., Maus. S., Immel, T. L., and Mende, S. B.: Longitude variation of the E-region electric fields caused by atmospheric tides, Geophys. Res. Lett., 33, L21105, <a href=http://dx.doi.org/10.1029/2006GL027465>doi:10.1029/2006GL027465, 2006.; Fejer, B. G., Olson, M. E., Chau, J. L., Stolle, C., Lühr, H., Goncharenko, L. P., Yumoto, K., and Nagatsuma, T.: Lunar-dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings, J. Geophys. Res., 115, A00G03, <a href=http://dx.doi.org/10.1029/2010JA015273>doi:10.1029/2010JA015273, 2010.; 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., 107, 4754, <a href=http://dx.doi.org/10.1029/2001JD001236>doi:10.1029/2001JD001236, 2002.; Jadhav, G., Rajaram, M., and Rajaram, R.: A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations, J. Geophys. Res., 107, 1175, <a href=http://dx.doi.org/10.1029/2001JA000183>doi:10.1029/2001JA000183, 2002.; Lühr, H., Maus, S., and Rother, M.: The noon-time equatorial electrojet, its spatial features as determined by the CHAMP satellite, J. Geophys. Res., 109, A01306, <a href=http://dx.doi.org/10.1029/2002JA009656>doi:10.1029/2002JA009656, 2004.; Lühr, H., Rother, M., Häusler, K., Alken, P., and Maus, S.: The influence of nonmigrating tides on the longitudinal variation of the equatorial electrojet, J. Geophys. Res., 113, A08313, <a href=http://dx.doi.org/10.1029/2008JA013064>doi:10.1029/2008JA013064, 2008.; Lühr, H., Rother, M., Häusler, K., Fejer, B., and Alken, P.: Direct comparison of non-migrating tidal signatures in the electrojet, vertical plasma drift and equatorial ionization anomaly, J. Atmos. Solar-Terr. Phys., 75–76, 31–43, <a href=http://dx.doi.org/10.1016/j.jastp.2011.07.009>doi:10.1016/j.jastp.2011.07.009, 2011.; Manoj, C., Maus, S., Lühr, H., and Alken, P.: Penetration characteristics of the interplanetary electric field to the daytime equatorial ionosphere, J. Geophys. Res., 113, A12310, <a href=http://dx.doi.org/10.1029/2008JA013381>doi:10.1029/2008JA013381, 2008.; Maus, S., Rother, M., Stolle, C., Mai, W., Choi, S.-C., Lühr, H., Cooke, D., and Roth, C.: Third generation of the Potsdam Magnetic Model of the Earth (POMME), Geochem. Geophys. Geosyst., 7, Q07008, <a href=http://dx.doi.org/10.1029/2006GC001269>doi:10.1029/2006GC001269, 2006.; Maus, S., Alken, P., and Lühr, H.: Electric fields and zonal winds in the equatorial ionosphere inferred from CHAMP satellite magnetic measurements, Geophys. Res. Lett., 34, L23102, <a href=http://dx.doi.


 

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