Lunar magnetic anomalies in the solar wind: Possible existence of mini-magnetosphere

It has been suggested that lunar magnetic anomaly fields are interacted with the solar wind plasma to form the mini-magnetosphere on the lunar surface. From the Lunar Prospector (LP) observations of magnetic fields, Lin et al.(1998) pointed out that a mini-magnetosphere was formed in the solar wind downstream of the strong magnetic anomaly in Imbrium antipode region. Harnett et al.(2000, 2002) demonstrated the presence of lunar mini-magnetospheres with MHD and particle simulations. If the mini-magnetosphere exists on the lunar surface and deflects solar wind particles, its role of barrier could produce a high-albedo region around the magnetic anomaly. In this study, we mainly investigate magnetic anomaly fields in the solar wind using the LP MAG low-altitude (15-40 km) data of level1. We detected lunar magnetic anomalies after preprocessing of the level1 data, using Hood's (1981) technique. In the present study, magnetic anomalies were mapped from the data sets in the tail lobe, the moon wake and the solar wind, and were compared with each other. We preliminarily analyzed three typical anomaly regions (Crisium antipode region, Descartes region, and Reiner Gamma region), and all of these three regions show clear magnetic anomalies even in the solar wind. We further carried out the detailed analysis of Reiner Gamma region. Its contour pattern of magnetic field intensities in the tail lobe or the wake is almost symmetrical with respect to the north-south line. However, such symmetry is obviously distorted in the solar wind to show some elongation toward the downstream of the solar wind. Also, the form of distortion seems to be changed when the solar wind conditions (dynamic pressure, the angle of incidence, and so on) are different. These results may support existence of the mini-magnetosphere in Reiner Gamma region. We will discuss the possible mini-magnetosphere comparing the LP MAG data with the ACE data of the solar wind.