James A. Whiteway

H2O at the Phoenix Landing Site

Phoenix Ascending The Phoenix mission landed on Mars in March 2008 with the goal of studying the ice-rich soil of the planets northern arctic region. Phoenix included a robotic arm, with a camera attached to it, with the capacity to excavate through the soil to the ice layer beneath it, scoop up soil and water ice samples, and deliver them to a combination of other instruments—including a wet chemistry lab and a high-temperature oven combined with a mass spectrometer—for chemical and geological analysis. Using this setup, Smith et al. (p. 58) found a layer of ice at depths of 5 to 15 centimeters, Boynton et al. (p. 61) found evidence for the presence of calcium carbonate in the soil, and Hecht et al. (p. 64) found that most of the soluble chlorine at the surface is in the form of perchlorate. Together these results suggest that the soil at the Phoenix landing site must have suffered alteration through the action of liquid water in geologically the recent past. The analysis revealed an alkaline environment, in contrast to that found by the Mars Exploration Rovers, indicating that many different environments have existed on Mars. Phoenix also carried a lidar, an instrument that sends laser light upward into the atmosphere and detects the light scattered back by clouds and dust. An analysis of the data by Whiteway et al. (p. 68) showed that clouds of ice crystals that precipitated back to the surface formed on a daily basis, providing a mechanism to place ice at the surface. A water ice layer was found 5 to 15 centimeters beneath the soil of the north polar region of Mars. 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° and 148°). 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; H2O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO3, aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.

Mars Water-Ice Clouds and Precipitation

Phoenix Ascending The Phoenix mission landed on Mars in March 2008 with the goal of studying the ice-rich soil of the planets northern arctic region. Phoenix included a robotic arm, with a camera attached to it, with the capacity to excavate through the soil to the ice layer beneath it, scoop up soil and water ice samples, and deliver them to a combination of other instruments—including a wet chemistry lab and a high-temperature oven combined with a mass spectrometer—for chemical and geological analysis. Using this setup, Smith et al. (p. 58) found a layer of ice at depths of 5 to 15 centimeters, Boynton et al. (p. 61) found evidence for the presence of calcium carbonate in the soil, and Hecht et al. (p. 64) found that most of the soluble chlorine at the surface is in the form of perchlorate. Together these results suggest that the soil at the Phoenix landing site must have suffered alteration through the action of liquid water in geologically the recent past. The analysis revealed an alkaline environment, in contrast to that found by the Mars Exploration Rovers, indicating that many different environments have existed on Mars. Phoenix also carried a lidar, an instrument that sends laser light upward into the atmosphere and detects the light scattered back by clouds and dust. An analysis of the data by Whiteway et al. (p. 68) showed that clouds of ice crystals that precipitated back to the surface formed on a daily basis, providing a mechanism to place ice at the surface. Laser remote sensing from Mars’ surface revealed water-ice clouds that formed during the day and precipitated at night. 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.

Rayleigh Lidar Observations of Thermal Structure and Gravity Wave Activity in the High Arctic during a Stratospheric Warming

Abstract During February and March 1993, Rayleigh lidar observations of temperature structure and gravity wave activity were carried out in the high Canadian Arctic at Eureka, Northwest Territories (80°N, 86°W). A sudden warming was observed first in the upper stratosphere during late February and then at lower levels in early March. The warming appeared to be part of a disturbance of the entire middle atmosphere with temperature changes in the mesosphere and lower stratosphere being opposite in sign to those in the upper stratosphere. Shorter time and length scale temperature fluctuations, observed in the upper stratosphere, are interpreted as being a result of atmospheric gravity waves. The wave amplitudes are shown to be capable of inducing convective instability. The rms perturbation and available potential energy density show substantial vertical and day-to-day variability in regions of conservative and dissipative growth rates. Vertical growth of the potential energy spectral density is seen to ceas...

Correction for nonlinear photon-counting effects in lidar systems

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.

Lidar observations of gravity wave activity in the upper stratosphere over Toronto

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.

Anatomy of cirrus clouds: Results from the Emerald airborne campaigns

The Emerald airborne measurement campaigns have provided a view of the anatomy of cirrus clouds in both the tropics and mid-latitudes. These experiments have involved two aircraft that combine remote sensing and in-situ measurements. Results are presented here from two separate flights: one in frontal cirrus above Adelaide, Australia, the other in the cirrus outflow from convection above Darwin. Recorded images of ice crystals are shown in relation to the cloud structure measured simultaneously by an airborne lidar. In mid-latitude frontal cirrus, columnar and irregular ice crystals were observed throughout the cloud while rosettes were found only at the top. The cirrus outflow from a tropical thunderstorm extended for hundreds of kilometres between the heights of 12.2 and 15.8 km. This was composed mainly of hexagonal plates, columns, and large crystal aggregates that originated from within the main core region of the convection. A small number of bullet rosettes were found at the top of the outflow cirrus and this is interpreted as an indication of in-situ crystal formation. It was found that the largest aggregates fell to the lower regions of the outflow cirrus cloud while the single crystals and small aggregates remained at the top.

Mesospheric temperature inversions with overlying nearly adiabatic lapse rate: An Indication of a well‐mixed turbulent layer

The Rayleigh lidar technique was applied to study the thermal structure of the middle atmosphere. Observations were carried out on a routine basis for one year (130 clear nights) at the main campus of York University near Toronto (44°N,80°W). Mesospheric temperature inversions were generally found to occur below a height of 70 km during winter and above during summer. The most interesting aspect of our observations was that the inversions were often associated with an overlying nearly adiabatic lapse rate which extended for several kilometres. We interpret this as being an indication (or signature) of a well-mixed turbulent layer. A one-dimensional numerical model was applied to demonstrate that a well-defined turbulent layer within the mesosphere can bring about a thermal structure quite similar to that which was commonly observed—an inversion with overlying nearly adiabatic lapse.

Observation of gravity wave generation and breaking in the lowermost stratosphere

Measurements with the Aberystwyth VHF radar have revealed a striking illustration of gravity wave generation and breaking in the lowermost stratosphere. Horizontal wind measurements show an inertia-gravity wave that was essentially monochromatic and persisted for longer than 5 days, with a maximum perturbation amplitude of approximately 10 ms−1. Radiosonde measurements show that this wave induced shear instability that led to intense turbulence close to the tropopause. The event was associated with a highly curved jet stream over Europe, suggesting that geostrophic adjustment was a likely source mechanism.

The Gravity Wave–Arctic Stratospheric Vortex Interaction

Abstract Four hundred and twenty-two nights of stratospheric gravity wave observations were obtained with a Rayleigh lidar in the High Arctic at Eureka (80°N, 86°W) during six wintertime measurement campaigns between 1992/93 and 1997/98. The measurements are grouped in positions relative to the arctic stratospheric vortex for comparison. Low gravity wave activity is found in the vortex core, outside of the vortex altogether, and in the vortex jet before mid-December. High gravity wave activity is only found in the vortex jet after late December, and is related to strengthening of the jet and decreased critical-level filtering. Calculations suggest that the drag induced by the late-December gravity wave energy increases drives a warming already observed in the vortex core, thereby reducing vortex-jet wind speeds. The gravity waves provide a feedback mechanism that regulates the strength of the arctic stratospheric vortex.

Modeling ozone laminae in ground‐based Arctic wintertime observations using trajectory calculations and satellite data

Reverse-trajectory calculations initialized with ozone observed by the Upper Atmosphere Research Satellite Microwave Limb Sounder (MLS) provide high-resolution ozone profiles for comparison with lidar and ozonesonde observations from the Arctic Stratospheric Observatory facility near Eureka in the Canadian Arctic (∼80°N, 86°W). By statistical measures, calculated profiles show a small average improvement over MLS profiles in the agreement of small-scale structure with that in ground-based observations throughout the stratosphere, and a larger (although still modest) and more consistent improvement in the lower stratosphere. Nearly all of the calculated profiles initialized with daily gridded MLS data show some improvement in the lower stratosphere. Even in cases where overall agreement between profiles is mediocre, there are frequently one or more individual features in the calculated profiles that strongly resemble laminae in the ground-based observations. Differential advection of ozone by the large-scale winds leads to lamination in three distinct ways. Filamentation results in lamination throughout the stratosphere, with comparable features arising from initializations with gridded MLS data and with potential vorticity/θ-space reconstructions of MLS data (reconstructed (RC) fields). Laminae also form in the middle and lower stratosphere in conjunction with intrusions into the vortex; while calculations initialized with RC fields produce laminae, the agreement of structure calculated using gridded MLS initialization data with ground-based observations is distinctly better. Inside the lower stratospheric vortex, laminae form by advection of local features in the MLS initialization fields; RC-initialized calculations fail to produce any significant features since these local ozone variations are not strongly correlated with potential vorticity. That local features observed by MLS are needed to produce laminae resembling those in independent ground-based observations at Eureka indicates that both datasets are capturing real atmospheric features.