Research
I have worked with Dr. Nancy Chanover and Dr. Jim Murphy to study
zonal wind speeds in giant planet atmospheres.
We have imaged Jupiter and Saturn with the AO-Vis camera on the AEOS
3.63-meter telescope on Haleakala. The data were taken with tip/tilt
correction, enhancing the spatial resolution, and using a pair of filters
designed to probe different altitudes. One filter is centered on a
methane absorption band at 727 nm, while the other is centered on a
nearby continuum region at 751 nm.
In the absence of clouds, the filters would span an order of magnitude in
pressure sensitivity. With the presence of the uppermost cloud deck, assumed
to be composed of ammonia based on chemical equilibrium arguments, the two
filters effectively sound to the center and upper boundary of the tropospheric
cloud deck. Such a pair of filters provides vertical discrimination,
allowing for the search for variations in the cloud levels and the horizontal
(zonal) winds with height.
We have determined wind speeds for several different latitudes and known cloud
features on Jupiter and Saturn. While Jupiter's zonal wind jets are thought to
be relatively stable, recent reports of a decrease in Saturn's zonal winds at
cloud level near the equator suggest that differences between the two planets
exist. The stability of the zonal wind jets has important implications for the
modeling of global circulation and energy balance in the giant planet
atmospheres.
In related project, we have observed the nightside of Venus at 2.3 microns
using both IRTF on Mauna Kea and APO in New Mexico during the past two
inferior conjuctions. Using IRTF we observed over a ten day span for 3-hours
each day, which is sufficient to determine the major cloud motions. More
recently, by using both APO and IRTF we achieved a 5-hour temporal baseline
each day over six days of observation. We see the lower cloud deck of Venus
(48 - 52 km) backlit by 2.3 micron thermal radiation emanating from the
surface and the lower atmosphere. These observations have allowed us to
derive cloud-level wind speeds, and identify transient features in the
observed Venusian wind field.
Our observations typically consist of many (a few thousand) short exposures of
Venus during each twilight opportunity. These sequences lend themselves to
image restoration processing by iterative blind deconvolution. We present
restorations implemented using "IDAC" (Jefferies and Christou, ApJ, 415,
1993), a code that is distributed through the Center for Adaptive Optics at UC
Santa Cruz. The use of IDAC has significantly increased the resolution of our
ground based observations of Venus. This increases the accuracy of our wind
speed measurements to the point were we can look for meridional motion.
We have adapted feature-tracking algorithms from several terrestrial remote
sensing applications in order to track cloud movement. We are beginning to
model wind vector fields based on these algorithms, and to evaluate their
potential advantages and shortfalls.
Meetings
I presented a poster on A Sharper View of Venus: Strategies For Precise
Cloud Tracking of Venus' Lower Cloud Deck at the October 2006
Division of Planetary Sciences meeting in Pasadena.
I presented a poster on Vertical Discrimination in the Zonal Wind Speeds
of Jupiter and Saturn at the November 2004 Division of Planetary Sciences
meeting in Louisville.
