Magnetic Ripples Observed by Low-altitude Satellites and their Relation to Micro-barometric and Ground Magnetic Variations

The `magnetic ripples' are small scale magnetic fluctuations observed in upper ionosphere by low altitude satellites such as CHAMP or Swarm, and they are spatial structure of field-aligned currents along satellite orbit. They are observed almost always in mid- and low-latitudes. From their geographical and seasonal characteristics, they are supposed to be caused by the atmospheric waves which propagates from lower atmosphere to the ionosphere. Although the global distribution and its local time or seasonal variation of the amplitude of magnetic ripples, or the correlation with meteorological phenomena such as typhoons strongly suggest the cumulus convection as the main origin, we need to clarify which mode of atmospheric waves, i.e., acoustic wave or internal gravity wave, mainly contributes to the magnetic ripples and what meteorological condition correspond them. For those purposes, we analyze ground based magnetic and micro-barometric variations. We try to make quantitative estimation of the contribution from both acoustic and internal mode of gravity waves, acoustic resonance, etc. by calculating PSD (power spectral density) of pressure and ground magnetic variations. In this paper, we present their basic characteristics and discuss the relation with magnetic ripples. [Acknowledgments]: The ground observations have been supported by many people including students at our graduate school and by the collaboration with other institutions.