The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5 degrees and 148 degrees ). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H(2)O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO(3), aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.

The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.

[1] Recent research suggests that mineral dust plays an important role in terrestrial weather and climate, not only by altering the atmospheric radiation budget, but also by affecting cloud microphysics and optical properties. In addition, dust transport and related Aeolian processes have been substantially modifying the surface of Mars. Dusty convective plumes and dust devils are frequently observed in terrestrial deserts and are ubiquitous features of the Martian landscape. There is evidence that they are important sources of atmospheric dust on both planets. Many studies have shown that on a small scale, dust sourcing is sensitive to a large number of factors, such as soil cover, physical characteristics, composition, topography, and weather. We have been doing comparative studies of dust events on Earth and Mars in order to shed light on important physical processes of the weather and climate of both planets. Our 2002 field campaign showed that terrestrial dust devils produce heat and dust fluxes two and five orders of magnitude larger than their background values. It also showed that charge separation within terrestrial dust devils produces strong electric fields that might play a significant role in dust sourcing. Since Martian dust devils and dust storms are stronger and larger than terrestrial events, they probably produce even stronger fluxes and electric fields.

The Rayleigh lidar technique has been applied to observe temperature fluctuations induced by gravity waves within the upper stratosphere. Observations were carried out on a routine basis for 1 year (130 clear nights) at the campus of York University near Toronto (44°N, 80°W). The waves were on occasion observed to induce marginal convective instability while exhibiting no substantial vertical amplitude growth. In general, the vertical variation in the amplitude of fractional temperature perturbations and associated available potential energy density implied the waves were strongly dissipated. Dramatic changes in the distribution of spectral energy with respect to vertical wave number were observed over the course of a few hours. The total resolved available potential energy in the gravity wave field varied considerably from day to day and seasonally with a winter maximum and summer minimum.

Within the westerly jet the wind speed increases with height and its direction does not change substantially. We have been able to observe how the gravity wave activity changed in response to these distinct changes in the background dynamical conditions. ObservationsThe lidar at Eureka is able to measure profiles of temperature within the upper stratosphere and lower mesosphere. (Details of the measurement and analysis technique are described elsewhere [Whiteway and Carswell 1994, 1995].) The vertical resolution in the measurement is 300 m and for gravity wave studies we use half hour average profiles. Figure 2a shows a half hour average temperature profile that has been smoothed in the vertical with a

No abstract

Phoenix, the first Mars Scout mission, capitalizes on the large NASA investments in the Mars Polar Lander and the Mars Surveyor 2001 missions. On 4 August 2007, Phoenix was launched to Mars from Cape Canaveral, Florida, on a Delta 2 launch vehicle. The heritage derived from the canceled 2001 lander with a science payload inherited from MPL and 2001 instruments gives significant advantages. To manage, build, and test the spacecraft and its instruments, a partnership has been forged between the Jet Propulsion Laboratory, the University of Arizona (home institution of principal investigator P. H. Smith), and Lockheed Martin in Denver; instrument and scientific contributions from Canada and Europe have augmented the mission. The science mission focuses on providing the ground truth for the 2002 Odyssey discovery of massive ice deposits hidden under surface soils in the circumpolar regions. The science objectives, the instrument suite, and the measurements needed to meet the objectives are briefly described here with reference made to more complete instrument papers included in this special section. The choice of a landing site in the vicinity of 68°N and 233°E balances scientific value and landing safety. Phoenix will land on 25 May 2008 during a complex entry, descent, and landing sequence using pulsed thrusters as the final braking strategy. After a safe landing, twin fan‐like solar panels are unfurled and provide the energy needed for the mission. Throughout the 90‐sol primary mission, activities are planned on a tactical basis by the science team; their requests are passed to an uplink team of sequencing engineers for translation to spacecraft commands. Commands are transmitted each Martian morning through the Deep Space Network by way of a Mars orbiter to the spacecraft. Data are returned at the end of the Martian day by the same path. Satisfying the mission's goals requires digging and providing samples of interesting layers to three on‐deck instruments. By verifying that massive water ice is found near the surface and determining the history of the icy soil by studying the mineralogical, chemical, and microscopic properties of the soil grains, Phoenix will address questions concerning the effects of climate change in the northern plains. A conclusion that unfrozen water has modified the soil naturally leads to speculation as to the biological potential of the soil, another scientific objective of the mission.

A useful analytic model describing the response of a photon-counting (PC) system has been developed. The model describes the nonlinear count loss and apparent count gain arising from the overlap of photomultiplier tube (PMT) pulses, taking into account the distribution in amplitude of the PMT output pulses and the effect of the pulse-height discrimination threshold. Comparisons between the model and Monte Carlo simulations show excellent agreement. The model has been applied to a PC lidar system with favorable results. Application of the model has permitted us to extend the linear operating range of the PC system and to quantify accurately the response of the system in its nonlinear operating regime, thus increasing the useful dynamic range of the system by 1 order of magnitude.