LtE in CMO #278

From Johan WARELL


. . . . . . . .Sent: Friday, August 29, 2003 4:01 PM

Subject: Mars August 28


Dear all,


Sending you here the most recent batch of Mars images from last night. A visual drawing will following as it is scanned.


The preceding and southern limb hazes are substantially more yellow in character than the northern and following. There is a white tuft of cloud extending Nf the NPC, rotating with the disk over almost 2 h of time.


Now it has cleared up, time again for Mars!


Best wishes,


. . . . . . . .Sent: Sunday, August 31, 2003 3:45 AM

Subject: Mars August 30




Some new Mars images with the webcam, I was too tired to make any drawing last night. Though the SPC is thinning ever more, no sign of localized dust or major cloud activity.




. . . . . . . Sent: Friday, September 05, 2003 3:29 AM

Subject: Mars September 3


Dear Dan, Richard and Masami,


I send you here two Mars images from Sep 3 obtained with the webcam and the 25 cm SCT.


There is one interesting aspect of this data set. Note the appearance of thin white cloud streaks longitudinally across Mare Acidalium and equatorially across N Aurorae and Margaritifer Sinus, parallel with the edge of the NPH. I have not found other images from these longitudes and dates to compare with.


At first they struck me as processing artifacts due to their linear nature and arrangement. However, they are apparent also on different stacked-only versions of this image which have not been subjected to frequency filtering. On such images they are naturally of subdued sharpness and contrast, but their presence seems to verify their existence. The equatorial streak emanates from the morning cloud which obscures all of Solis Lacus north to Niliacus Lacus.


The filtration process thus unfortunately to effectively affect the contrast and optical depth of cloud structures in an unwanted fashion, which is serious enough to warrant consideration. High-frequency information is exaggerated in terms of contrast, low frequency is subdued which means that such cloud streaks appear brighter in filtered data and regional clouds (such as extended mo, ev clouds) are drastically reduced in visibility.


Therefore, in terms of studies of atmospheric phenomena, it may be of great value to publish unfiltered (but histogram intensity level adjusted) blue channel disk images in parallel with the filtered data set. Though softer than unfiltered images, less processing retains the natural aspect better and is more easily comparable to visual observations. I will try to take a further look into this problem and show you the result.


It appears that the monsoon has ended early here in Tucson, thus drier conditions with fewer low clouds are to be expected. I am doubtful however that the poor seeing conditions will improve until it cools down sufficiently during the day which might not happen before October.


Best regards,


Johan WARELL (Lunar and Planetary Laboratory, Tucson, Arizona, USA)

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