Mary Jane Bartholomew

Mid‐infrared spectroscopy of Pahala ash palagonite and implications for remote sensing studies of Mars

Remote sensing of Mars at mid-infrared wavelengths could be used to identify different silicate rocks and minerals. Current knowledge suggests that the primary components of the surface of Mars are basaltlike rocks and a palagonitelike dust. To study the mid-infrared (7–20 μm) spectroscopy of this combination of materials, we examined the influence of Pahala ash palagonite on the biconical reflectance of quartzite and basalt. The reflectance of the palagonite is flat and low (1–2%), unlike the reflectance of quartzite and basalt. The reflectance of quartzite or basalt is significantly reduced by the addition of small amounts of the palagonite dust. A dusting of 1–20 μm palagonite particles and 20–250 μm particle clumps, covering 50% of the quartzite host, reduces the quartzite mid-infrared reflectance by 50%, as expected for an essentially black coating. Similar data were obtained for basalt. Even for extremely small amounts of palagonite (2–100 μm thickness, averaging 5 μm), the reflectance of the underlying rock is linearly related to exposed surface area. To confirm the opaque behavior of the Pahala ash palagonite coatings, we estimated the imaginary part (k) of the refractive index from transmission measurements. The strong absorption and low reflectance (high emissivity) of the palagonite at 8–11 μm and 17–25 μm explain its opaque behavior. Estimates of the extinction coefficient indicate that even a 5-μm thickness of Pahala ash palagonite is optically thick in these wavelength ranges where silicate rock identification is critical. Thus mid-infrared remote sensing of rocks on Mars will be practical only for dust-free areas.

Design, Operation, and Calibration of a Shipboard Fast-Rotating Shadowband Spectral Radiometer

This paper describes the design, calibration, and deployment of a fast-rotating shadowband radiometer (FRSR) that accurately decomposes downward shortwave (solar) irradiance into direct-beam and diffuse components from a moving platform, such as a ship on the ocean. The FRSR has seven channels, one broad-band silicone detector, and six 10-nm-wide channels at 415, 500, 610, 660, 860, and 940 nm. The shadowband technique produces estimates of the direct-beam normal irradiance, the diffuse irradiance (sky component), and the total irradiance. The direct-beam normal irradiances produce time series of aerosol optical thickness. A proven ability to derive meaningful at-sea estimates of aerosol optical depth from an economical, automated, and reliable instrument opens the way to a distributed network of such measurements from volunteer observing ships in all areas of the World Ocean. The processing algorithms are key to the instrument’s ability to derive direct-normal beam irradiance without gimbals and a gyro-stabilized table. At-sea Langley plots were produced during the Aerosols99 cruise of the R/V Ronald H. Brownfrom Norfolk, Virginia, to Cape Town, South Africa. A Langley calibration of the instrument at the Mauna Loa Observatory confirmed prior calibrations and demonstrated that the calibration was stable over the duration of the cruise. The standard deviation in all plots was of the order 2% for all channels.

Convective cloud vertical velocity and mass‐flux characteristics from radar wind profiler observations during GoAmazon2014/5

A radar wind profiler (RWP) dataset collected during the two-year DOE ARM Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign is used to estimate convective cloud vertical velocity, area fraction and mass flux profiles. Vertical velocity observations are presented using cumulative frequency histograms and weighted-mean profiles to provide insights in a manner suitable for GCM-model scale comparisons (spatial domains from 20 km to 60 km). Convective profile sensitivity to changes in environmental conditions and seasonal regime controls is also considered. Aggregate and ensemble average vertical velocity, convective area fraction and mass flux profiles, as well as magnitudes and relative profile behaviors, are found consistent with previous studies. Updrafts and downdrafts increase in magnitude with height to mid-levels (6 to 10 km), with updraft area also increasing with height. Updraft mass flux profiles similarly increase with height, showing a peak in magnitude near 8 km. Downdrafts are observed to be most frequent below the freezing level, with downdraft area monotonically decreasing with height. Updraft and downdraft profile behaviors are further stratified according to environmental controls. These results indicate stronger vertical velocity profile behaviors under higher CAPE and lower low-level moisture conditions. Sharp contrasts in convective area fraction and mass flux profiles are most pronounced when retrievals are segregated according to Amazonian wet and dry season conditions. During this deployment, wet season regimes favored higher domain mass flux profiles, attributed to more frequent convection that offsets weaker average convective cell vertical velocities.

A Summary of Precipitation Characteristics from the 2006–11 Northern Australian Wet Seasons as Revealed by ARM Disdrometer Research Facilities (Darwin, Australia)

AbstractThe variability of rainfall and drop size distributions (DSDs) as a function of large-scale atmospheric conditions and storm characteristics is investigated using measurements from the Atmospheric Radiation Measurement Program (ARM) facility at Darwin, Australia. Observations are obtained from an impact disdrometer with a near continuous record of operation over five consecutive wet seasons (2006–11). Bulk rainfall characteristics are partitioned according to diurnal accumulation, convective and stratiform precipitation classifications, objective monsoonal regime, and MJO phase. Findings support previous Darwin studies suggesting a significant diurnal and DSD parameter signal associated with both convective–stratiform and wet season monsoonal regime classification. Negligible MJO phase influence is determined for cumulative disdrometric statistics over the Darwin location.

The Accuracy of Marine Shadow-Band Sun Photometer Measurements of Aerosol Optical Thickness and Ångström Exponent

Abstract An analytical uncertainty propagation model is used in conjunction with laboratory and field data to quantify the uncertainty in measurements of the direct-normal irradiance, aerosol optical thickness, and Angstrom exponent made with a ship-mounted fast-rotating shadow-band radiometer (FRSR). Total uncertainties in FRSR measurements of aerosol optical thickness are found to be 0.02–0.03 at the 95% confidence level (two standard deviations). The “lever-arm” effect, a salient characteristic of the Langely technique in which uncertainties in aerosol optical thickness measurements are reduced as the solar zenith angle increases, is essentially offset by orientation uncertainty. Lack of a lever-arm effect precludes Langley calibration of FRSRs while at sea; they must be calibrated on land. Uncertainties in FRSR measurements of the two-wavelength Angstrom exponent are shown to depend strongly on the aerosol optical thickness, with the maximum uncertainty of 0.6 associated with clean, maritime air masses.

The Green Ocean: Precipitation Insights from the GoAmazon2014/5 Experiment

This study summarizes the precipitation properties collected during the GoAmazon2014/5 campaign near Manaus in central Amazonia, Brazil. Precipitation breakdowns, summary radar rainfall relationships and self-consistency concepts from a coupled disdrometer and radar wind profiler measurements are presented. The properties of Amazon cumulus and associated stratiform precipitation are discussed, including segregations according to seasonal (wet or dry regime) variability, cloud echo-top height and possible aerosol influences on the apparent oceanic characteristics of the precipitation drop size distributions. Overall, we observe that the Amazon precipitation straddles behaviors found during previous U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program tropical deployments, with distributions favoring higher concentrations of smaller drops than ARM continental examples. Oceanic-type precipitation characteristics are predominantly observed during the Amazon wet seasons. An exploration of the controls on wet season precipitation properties reveals that wind direction, compared with other standard radiosonde thermodynamic parameters or aerosol count/regime classifications performed at the ARM site, provides a good indicator for those wet season Amazon events having an oceanic character for their precipitation drop size distributions.

Design of a Shadowband Spectral Radiometer for the Retrieval of Thin Cloud Optical Depth, Liquid Water Path, and the Effective Radius

ThedesignandoperationofaThin-CloudRotatingShadowbandRadiometer(TCRSR)describedherewas used to measure the radiative intensity of the solar aureole and enable the simultaneous retrieval of cloud optical depth, drop effective radius, and liquid water path. The instrument consists of photodiode sensors positioned beneath two narrow metal bands that occult the sun by moving alternately from horizon to horizon. Measurements from the narrowband 415-nm channel were used to demonstrate a retrieval of the cloud properties of interest. With the proven operation of the relatively inexpensive TCRSR instrument, its usefulness for retrieving aerosol properties under cloud-free skies and for ship-based observations is discussed.

Analysis of shipboard aerosol optical thickness measurements from multiple sunphotometers aboard the R/V Ronald H. Brown during the Aerosol Characterization Experiment - Asia

Marine sunphotometer measurements collected aboard the R/V Ronald H. Brown during the Aerosol Characterization Experiment-Asia (ACE-Asia) are used to evaluate the ability of complementary instrumentation to obtain the best possible estimates of aerosol optical thickness and Angstrom exponent from ships at sea. A wide range of aerosol conditions, including clean maritime conditions and highly polluted coastal environments, were encountered during the ACE-Asia cruise. The results of this study suggest that shipboard hand-held sunphotometers and fast-rotating shadow-band radiometers (FRSRs) yield similar measurements and uncertainties if proper measurement protocols are used and if the instruments are properly calibrated. The automated FRSR has significantly better temporal resolution (2 min) than the hand-held sunphotometers when standard measurement protocols are used, so it more faithfully represents the variability of the local aerosol structure in polluted regions. Conversely, results suggest that the hand-held sunphotometers may perform better in clean, maritime air masses for unknown reasons. Results also show that the statistical distribution of the Angstrom exponent measurements is different when the distributions from hand-held sunphotometers are compared with those from the FRSR and that the differences may arise from a combination of factors.

ARM - Midlatitude Continental Convective Clouds

Convective processes play a critical role in the Earths energy balance through the redistribution of heat and moisture in the atmosphere and their link to the hydrological cycle. Accurate representation of convective processes in numerical models is vital towards improving current and future simulations of Earths climate system. Despite improvements in computing power, current operational weather and global climate models are unable to resolve the natural temporal and spatial scales important to convective processes and therefore must turn to parameterization schemes to represent these processes. In turn, parameterization schemes in cloud-resolving models need to be evaluated for their generality and application to a variety of atmospheric conditions. Data from field campaigns with appropriate forcing descriptors have been traditionally used by modelers for evaluating and improving parameterization schemes.