2003 Mars Report from Cooperative Observation Networks. I. Pre-Opposition

Abstract

We have two networks for cooperative Mars observations in Japan: Nishi-Harima Astronomical Observatory Mars Cooperative Observation and Association of Lunar and Planetary Observers in Japan. This paper is a summary of 3515 images collected by the two networks during the first half of the last apparition from 2002 October 18 through 2003 August 31, corresponding to the period of $L_{\mathrm{s}} \sim {83{}^{\mathrm {\circ }}} \hbox{--} {252{}^{\mathrm {\circ }}}$ ($L_{\mathrm{s}}$ is the areocentric longitude of the Sun). During this period, many interesting phenomena were observed. (1) Two local dust storms appeared about $L_{\mathrm{s}} = {214{}^{\mathrm {\circ }}}$ and $L_{\mathrm{s}} = {231{}^{\mathrm {\circ }}}$. (2) Hellas was obscured just before the occurrence of the first dust storm. This may be relevant to the dust storm. (3) Blue clearings were observed. The phenomena in this apparition may be attributed to the optical properties of the ground for the scattering of light. (4) Dark markings in the south polar cap (SPC) developed as the SPC receded in mid-spring of the southern hemisphere. Also, some bright spots appeared on the SPC. (5) The south polar hood receded polewards and SPC began to be observed at about $L_{\mathrm{s}} \sim {185{}^{\mathrm {\circ }}}$ (mid-May). (6) The north polar hood was not detected until $L_{\mathrm{s}} \sim {180{}^{\mathrm {\circ }}}$ in this apparition. (7) The low-latitude cloud belt had been observed until mid-May. In the dissipation phase, a less cloud area appeared in longitudes of 170${{}^{\mathrm {\circ }}}$-200${{}^{\mathrm {\circ }}}$ W.