P51A-0201
Equatorial Clouds and Haze before, during, and after Jupiter's Global Upheaval
HST/WFPC2 images of Jupiter from 2000, before the current upheaval, showed thick and nearly complete cloud coverage in the equatorial zone. Images from 2006/2007 show a decrease in cloud cover; most remaining clouds are associated with plumes extending from the northern and southern boundaries of the equatorial zone. The decreased cloudiness corresponds to a 20-30% decrease in the 953-nm continuum I/F within ± 5° of the equator, between 2000 and 2007. A preliminary comparison with 892-nm methane band images from both epochs suggests that the tropospheric haze, located just above the upper cloud sheet and just below the tropopause, is unchanged. The fine aerosols composing this haze may be composed of condensed hydrazine (a product of ammonia photolysis at the altitude of the haze layer) mixed with smaller amounts of hydrocarbon and other photochemical products drifting down from the stratosphere (Atreya et al., Icarus 31, 1977; Atreya et al., Plan. Sp. Sci. 53, 2005). Cloud particles from deeper in the troposphere may also be lofted into the haze region (West et al., Icarus 65, 1986), where particles with radii < 1 {μ}m precipitate on a timescale of about a year (Rossow, Icarus 36, 1978). Due to the large energies needed to penetrate into the stably stratified haze region, particle compositions may include NH4HS and H2O as well as NH3. If the clearing of equatorial clouds associated with the upheaval persists for several years, it will provide an opportunity to compare the contributions of the two haze formation mechanisms. The observed reduction in equatorial cloud cover implies a drop in the upward transport of fine particles, which would lead to a reduction of tropospheric haze within 1-3 years, as the small particles gradually fall out of the upper troposphere. Hydrazine haze should be in a steady state balance between photochemical production and loss through particle growth, precipitation, and evaporation. The reduced equatorial cloud opacity will lead to warming in the haze layer, with changes apparent in about 5 years according to estimates of the radiative timescale (Conrath et al., Icarus 83, 1990). Monitoring Jupiter's haze and cloud opacity over the next few years may therefore constrain the origin of the upper tropospheric haze, with rapid changes implying a significant source from deeper tropospheric condensation clouds. http://astro.berkeley.edu/~mikewong/#agu07
P51A-0202
Zonal jets as transport barriers in planetary atmospheres
Recent theoretical and numerical work has shown that a stable - and apparently preferred - mean flow pattern at midlatitudes on rapidly rotating large planets is a sequence of alternating narrow eastward and broad westward zonal jets. The corresponding potential vorticity (PV) distribution is characterized by a PV-staircase with PV-steps at the latitudes of the cores of the eastward jets. Numerically simulated solutions to the quasigeostrophic equation in a perturbed PV-staircase flow are presented. These simulations reveal that both eastward and westward zonal jets serve as robust meridional transport barriers. A theoretical explanation of the underlying barrier mechanism is provided. Consistent with these results, observations of Jupiter, whose weather layer mean flow pattern has the qualitative features of a PV-staircase flow, suggest that both eastward and westward zonal jets serve as robust meridional transport barriers. An alternative explanation of the mechanism by which zonal jets act as meridional barriers, based on the notion of a PV-barrier, correctly predicts that eastward jets act as transport barriers but incorrectly predicts that westward jets do not.
P51A-0203
Jupiter Stratospheric Jet Simulations
High resolution temperature maps of Jupiter's stratosphere, derived from observations made in late 2000 and early 2001 with the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft, revealed the existence of a 140 m/s zonal jet that is centered near 4 mbar. The existence of such an intense high-altitude jet was not previously known and its nature remains unclear. In order to explore the interplay that radiative and mechanical forcing mechanisms have on the onset of a jet like the one observed by Cassini, we use the EPIC general circulation model to perform spin-up experiments of Jupiter's stratosphere under the effect of different radiative and mechanical forcing terms. In our experiments we use radiative heating and cooling rates derived from measurements of temperature profiles, composition and aerosol distributions obtained from observations made with Galileo and Cassini. Different wave perturbations are used as mechanical forcing terms. We present the results of these experiments and analyze the effects that the different forcing terms have in the development of a jet like the one observed.
P51A-0204
Dust Measurements On-board the New Horizons Mission
The Venetia Burney Student Dust Counter (VSDC) on the New Horizons spacecraft was successfully commissioned on March 3, 2006 (DOY 2006/061). VSDC is a dust impact detector designed to map the dust distribution along the trajectory of the New Horizons spacecraft as it traverses our solar system. VSDC is the first student built instrument on a deep space mission and it is currently operated by a small group of undergraduate and graduate students at the Laboratory of Atmospheric and Space Physics (LASP), University of Colorado. By the time of this meeting (12/2007), VSDC will have operated for about 330 days, covering an approximate distance from 1.21 to 10 AU. VSDC is based on permanently polarized thin plastic film sensors that generate an electrical signal when an impacting dust particle penetrates them. The total surface area is about 0.1 square meters, and the detection threshold is about a micron in particle radius. In this talk we will briefly review the VSDC instrument. The in-flight tests and calibrations, as well as our initial science results will be discussed. We will report on the measured spatial and size distribution of interplanetary dust particles before and after the encounter with Jupiter. These measurements will be compared with earlier measurements by Ulysses, Galileo, and Cassini. http://lasp.colorado.edu/sdc/
P51A-0205
Magnetic Field Modulated Dust Streams From Jupiter in Interplanetary Space
The Ulysses (1992), Galileo (1995) and Cassini (2000) spacecrafts have confirmed the existence of high velocity (>200 km/s) collimated streams of charged (~5V) dust grains escaping from the Jovian magnetosphere to the Interplanetary space, whose dynamics is mainly dominated by the interplanetary Magnetic field (IMF). With Cassini, a similar phenomenon was observed at Saturn as well. There is strong evidence that these Jovian dust streams are closely related to the solar wind and particularly to compression regions, either Corotating interaction regions (CIRs) or –to a minor extent - Coronal mass ejections (CMEs). Actually dust streams seem ultimately to be generated by those strong enough events (B>~2nT).
P51A-0206
Dust Structures Formation Near Jupiter
The dust particles dynamics in the outer Solar System has been a subject of study in the last decades, particularly in Jupiter where the space exploration has provided many interesting results that have been used to create several models related to the formation of dust structures, as the streams escaping from the Jovian magnetosphere or the tenuous rings via the capture of small rocky bodies. In this work a model is presented in order to analyze the dynamical behavior of captured micrometeoroids as part of the formation of tenuous annular structures around Jupiter or as part of the rocky material that can escape from the planetary magnetosphere. The model includes several forces that modulate the dynamics of these tiny bodies once they have been caught by the Jovian system. The results show that there are two preferential sizes of micrometeorites to be captured, these tiny dust particles remain around this planet, at least 5 years, describing a butterfly-like distribution located inside a latitudinal belt.
P51A-0207
Effects of a Nonlinear Treatment of Io's Interaction With the Jovian Magnetosphere
Io's interaction with the corotating plasma torus excites Alfvén waves which propagate through Jupiter's magnetosphere. They are partly reflected at density gradients and a complicated wave field develops downstream of Io. The Io-related auroral emission which serves as a screen for this wave field sometimes shows multiple footprints with variable distances as evidence of reflection processes. Therefore recent Hubble Space Telescope observations of the Io footprint morphology during the New Horizons flyby provide valuable constraints for the nature of the Io-Jupiter interrelation as well as for the reflection geometry. Here, we present nonlinear 3D-MHD simulations of this interaction with an improved magnetospheric model. We compare our findings to measured data and show the importance of including nonlinear effects especially for the description of MHD wave reflection. Moreover, we provide a possible explanation for the discrepancy between expected and measured inter-spot distances for different positions of Io in the plasma torus as well as the disappearance of multiple spots when Io is located in the torus center. Our results are also applicable to other moon- magnetosphere interactions, in particular to the Saturnian moon Enceladus.
P51A-0208
JIRAM, the Jupiter Infrared Auroral Mapper on Juno
JIRAM, the Jovian InfraRed Auroral Mapper, is part of the payload of the NASA New Frontiers mission Juno to Jupiter to be launched in August 2011. JIRAM scientific goals are: the exploration of the dynamics and the chemistry of Jovian auroral regions by high contrast imaging and spectroscopy, the study of the hot spots through the Jupiter troposphere in order to determine their vertical structure and hence test their formation mechanisms and, eventually, the sounding of the Jupiter atmosphere to map water moist convection and determine the water abundance and other constituents at depths corresponding to the water clouds. The JIRAM heritage comes from Italian Visual-InfraRed Imaging Spectrometers dedicated to planetary exploration like Cassini /VIMS-V, Rosetta and Venus Express /VIRTIS, and Dawn /VIR-MS. However, Juno presents more technological challenges due to the harsh radiative environment generated by the Jupiter powerful magnetic field, the spinning spacecraft, its speed in respect to the target to be observed ( which is more than 50 km/s at the Jupiter closest approach) and the shortness of the mission which impose a very tight observation schedule. JIRAM shares a single telescope, between an infrared camera and a spectrometer to allow a large observational flexibility in obtaining at the same time simultaneous images in a field of view of 5.9x1.7 deg and in the L ( 3.4 m) and M ( 5 m) bands. JIRAM will also perform measurements of spectral radiance over the central zone of the M image. It will also be able to compose spectral images of the planet between 1.85 and 5.2 m with a spectral resolution better than 10 nm.
P51A-0209
Planetary atmospheric science realized by space telescope mission, TOPS
The planetary space telescope mission named TOPS, telescope observatory for planets on small-satellite, will be launched in 2012 as a new small satellite mission series of JAXA. TOPS will be on 200kg-class satellite bus and consist of two 30-cm reflecting telescopes, which cover the wavelength range of 60-1100 nm. The precise pointing technique realizes spatial resolution less than about 0.6 arcsec in the visible wavelength range. Continuous measurements from the earth orbit enable us to monitor meso-scale atmospheric dynamics on planets in the solar system as well as the dynamics of exospheric plasma and ultraviolet auroras. Making use of complementary aspects of in-situ mission and TOPS, ground-based and balloon-born telescopes are the important strategy for planetary atmospheric science. In this presentation scientific application to the monitoring of planetary atmosphere, especially for Jupiter, Saturn and Venus will be introduced, adding to the brief outline of the mission.