Martian limb-viewing clouds: A study based on MCC, MCS and MARCI observations

摘要

MCC captured more than 30 images of Cloud and Dust layer appear over Martian limb during the operational period from September 24, 2014 to December 13, 2014. In the present analysis, we considered all the images of high altitude limb-viewing clouds. Projected heights of the limb viewing cloud are varying from 43 +/- 3-91 +/- 5 km above the Martian surface with a horizontal spreading varies from 400 +/- 12 km to 1200 +/- 21 km. We estimated the reflectance at the Top of the Atmosphere (TOA) or the insolation at TOA and accordingly calculated alpha value for the high altitude limb clouds to report the characteristics of the particle. The reflectance value is 0.18-0.41 for the red channel and 0.31 to 0.51 for the blue channel. The reflectance value indicates that the detached layer is formed of water ice particles, whereas the continuous haze is formed of both water ice and dust particle. A single event shows high altitude CO2 cloud having maximum reflectance in the green channel. Angstrom exponent (alpha) value varies from 0.8 to 1.88, indicates the presence of coarse mode, as well as fine mode particle with an effective radius, ranges from 0.4 mu m to 1.2 mu m for the dust particle whereas for water ice particle effective radius varies from 0.6 to 3.2 mu m. To estimate the physical properties like mixing ratio, extinction value, and effective radius, we analysed MRO-MCS data. We consulted MARCI daily global map and weather report to locate a dust event. We compare our results with GCM (MCD) to validate our information regarding dust and water ice in high altitude clouds. Our present work follows three possible reasons for the formation of the high altitude cloud, (i) interplanetary dust contribution, (ii) Solar wind contribution, and (iii) Local/regional dust storm on Mars. The third possible reason firmly explains the cloud events and shows that during dust storm and post dust storm period high altitude cloud appears at the limb. Deep convection, Hadley circulation, and other mechanism contribute to the lifting process of the dust and water ice particle to a height of similar to 50-80 km. Moreover, variation of CBL height and AOD concretizes the third possible reason i.e., the dust storm and complimenting the formation of water ice cloud.