QUESTION:
I would like to know more information about the cyclone on Mars.

ANSWER from Jim Bell on June 28, 1999:
Here is a copy of the press release that I wrote on the Martian cyclone.
Check the images at http://oposite.stsci.edu/pubinfo/pr/1999/22/index.html I
hope this provides you the information you were looking for. You can also
check out related news stories at:

http://abcnews.go.com/wire/Politics/Reuters19990519_1323.html
http://www.cnn.com/TECH/space/9905/19/mars.storm/
http://www.msnbc.com/news/271111.asp
http://www.cbs.com/prd1/now/template.display?p_story=154407&p_who=network

Press release text:

Astronomers using the Hubble Space Telescope to observe the planet Mars have
discovered an enormous cyclonic storm system raging in the planet's northern
polar regions. The storm was detected using the HST's Wide Field Planetary
Camera-2 by a team of astronomers observing Mars near its closest approach
to Earth in nearly eight years.

Detected most prominently in blue to ultraviolet images, the storm is not
one of the famous Martian dust storms, but is instead composed of water ice
clouds like storm systems on Earth. In form, the storm system is similar to
so-called "spiral" storms observed more than 20 years ago by NASA's Viking
Orbiter spacecraft, but it is nearly 3 times as large as the largest
previously-detected Martian spiral storm system. The storm is highly
organized, consisting of at least three, and perhaps more, bands of clouds
organized into a spiral structure and wrapped counterclockwise around a
hollow central core or "eye". The storm is nearly 1100 miles east-west and
900 miles north-south, and the eye of the storm is nearly 200 miles in
diameter. The system is larger than the planet's residual north polar ice
cap, and is comparable in size to similarly-shaped terrestrial hurricanes.

The image was obtained near the middle of the Martian northern hemisphere's
summer season, after the planet's seasonal CO2 polar cap has completely
sublimated away, leaving only the underlying residual water ice cap. The
smaller spiral storms seen previously by Viking were also detected during
the northern summer season, and also at high northern latitudes. Apparently,
this type of cyclonic circulation, though rare on Mars, must be related to
specific climatic circumstances unique to the planet's northern polar
regions at this season. Interestingly, similar storms, some comparable in
size to the Martian storm, have been seen in Earth's polar regions. On
Earth, these polar cyclones appear to be low pressure systems fueled by
strong contrasts in oceanic vs. atmospheric temperatures. In some cases,
winds within Earth's polar cyclones can reach hurricane force. The general
appearance of the Martian storm seems consistent with an intense low
pressure vortex with ascending motion causing cloud formation, possibly with
a small core that is cloud-free, like the eye of a hurricane.  The storm may
have been initiated by an unstable frontal system, and then amplified by the
strong temperature contrast between the relatively warm high latitude
Martian dark regions and the much colder and stable polar atmosphere.

It has not yet been possible to derive wind speeds, cloud heights, or a
"storm track" for this hurricane-like storm on Mars.  When first imaged by
HST on April 27, it was located near 65 deg. N latitude and 85 deg. W
longitude. When next imaged about 6 hours later, the storm appeared to have
moved only slightly eastward, but seemed to be in the process of
dissipating.  The storm has not been seen again in subsequent images, but
these have been centered on the opposite side of the planet. The storm may
have been a short-lived phenomenon, then, which would be consistent with the
short lifetimes (several days) observed for smaller spiral storms by Viking.

Because of problems with its main communications antenna, NASA's Mars Global
Surveyor spacecraft, currently orbiting the red planet, did not have any
instruments operating at the same time the storm was detected by HST. MGS
instruments were turned on a short time later, however, and they may provide
additional data with which to characterize the nature, extent, and duration
of this and other polar storm systems.

The team of astronomers obtaining and analyzing these HST images includes
Jim Bell (Cornell University, Principal Investigator), Michael Wolff and R.
Todd Clancy (Space Sciences Institute), Steven Lee (University of Colorado),
Philip James (University of Toledo), and Michael Ravine (Malin Space Science
Systems, Inc.).

accompanying image mosaic:

left: 410 nm discovery image of the Martian polar storm. The storm is
located near 65 deg. N latitude and 85 deg. W longitude, and is more than
1000 miles across. The residual north polar water ice cap is at top. A belt
of clouds like that seen in previous telescopic data during this Martian
season can also be seen in the planet's equatorial regions, standing out
prominently along the morning and evening equatorial limbs due to the
increased atmospheric path length.  Additional clouds can also be seen in
the southern polar regions, associated with the formation of the seasonal
southern winter polar CO2 ice cap.

upper right: Color polar stereographic view of the north polar region,
showing the location of the storm relative to the classical albedo features
in this area. Color composite of 410, 502, and 673 nm filter data. The color
data indicate that the storm is fairly dust-free and therefore likely
composed mostly of water ice clouds. The bright surface region beneath the
eye of the storm can be seen clearly.

lower right: Enhanced orthographic view of the storm centered on 65N, 85W.
The image has been processed to bring out additional detail in the storm's
spiral cloud structures.