A43D-1557
A novel application of median filters and Fourier transforms for eddy covariance data
Eddy covariance (EC) is the standard for measuring trace gas fluxes between the atmosphere and the plant- and soil-covered terrestrial surface. Because EC fluxes are based on concepts of transport by turbulent atmospheric motions they require lengthy, computer-driven, intensively sampled data streams. But as the data stream becomes more machine-driven, the more important it is to be able to objectively identify, and possibly correct for, outliers, such as data spikes, drifts, and discontinuities, any of which if undetected can significantly impact the EC flux estimates and reduce their reliability and value. This study describes a novel use of the median filter and the Fourier transform to identify spikes, drifts, and discontinuities in high-frequency eddy covariance data streams and in the associated, but less intensively sampled, ambient meteorological data. For either application, the median filter is used to separate the data stream into a time dependent mean, M(ti), and a time dependent deviation from that mean, σ(t_i). In general, the advantage of the median filter is that it is not as influenced by bad data as the running mean filter or other linear filters. For the high-frequency EC data stream the median filter is combined with an often used turbulence despiker [Hojstrup 1993: 'A statistical data screening procedure'; Measurement Science and Technology 4, 153-157]. The resulting algorithm is considerably more robust and efficient. For the supporting ambient meteorological data the median filter cleanly removes the trends associated with sensor drift and data discontinuities. Data spikes are then removed by combining a second median filter with the Fourier transform, which are used in tandem to construct an ideal deviation time series [a σ(ti) that would occur if the data were not contaminated by noise, spikes, etc]. The ideal σ(ti) is then compared with the observed σ(ti) to develop objective criteria for spike detection. The spike detection algorithms for both high- frequency EC data and the ambient meteorological data allow for the seasonal variability in the data stream and the associated noise detection thresholds.
A43D-1558
Attenuation of trace gas fluctuations associated with turbulent flow in tubes: application to closed-path eddy covariance systems
Eddy covariance (EC) is the standard for measuring trace gas fluxes between the atmosphere and the terrestrial (vegetation/soil) surface. Nevertheless, the quality and reliability of fluxes measured with EC technology depend heavily on the unavoidable filtering effects associated with sensor design and sampling methods. Both open- and closed-path trace gas EC sensors can sample the atmospheric trace gas fluctuations fast enough to make reasonably reliable flux measurements. But closed-path sensors, which usually require long intake tubes, attenuate high frequency fluctuations more strongly than open-path sensors. On the other hand, closed-path sensors are the only available option for some trace gases (e.g., ozone) and often they can be used under conditions that preclude the use of open-path sensors (e.g., carbon dioxide and water vapor flux measurements during rain or snow events). Therefore, studies of tube attenuation effects should aid in the development of EC sensor technology and improve the reliability of and reduce the uncertainty inherent in EC trace gas fluxes. Here we report the results of a study to develop a physically-based model of the attenuation of atmospheric water vapor fluctuations on the inside walls of closed-path EC sampling tubes during turbulent tube flow for application to the measurement of water vapor (or evapotranspiration) fluxes. The specific goal of this study is to derive a mathematically-simple physically-based transfer function that can be used to correct closed-path EC fluxes for tube attenuation effects. We begin by reviewing observational studies of the attenuation of water vapor fluctuations during turbulent tube flow. We then outline the mathematical statement of this problem and we compare some new models, which we have developed for this study, with previous models. We close with a discussion and formulation of the model boundary conditions at the inside tube wall. This boundary condition, which is based on the adsorptive-desorptive fluxes to the tube wall, is critical to obtaining the desired transfer function because the transfer function is obtained directly from the solution to the mathematical model, which is in turn dictated by the tube wall boundary condition. It should not be surprising that a general formulation of this boundary condition poses a difficult challenge because the physical processes at the tube wall are physiochemical in nature and involve various aspects of the kinetic theory of gases, thin film dynamics, phase changes (condensation and evaporation) on clean homogeneous surfaces and on internal tube surfaces contaminated with atmospheric aerosols, and the dynamics of turbulent tube flow.
A43D-1559
Development of a Portable Cavity Ring-Down Spectroscopic Technique for Measuring Stable Isotopes in Atmospheric Methane
Measurements of the isotopic composition of atmospheric CH4 provide a means to disentangle source contributions because sources impart a characteristic isotopic composition. However, because of the high precision needed to detect small changes in isotopic ratios, measurements are typically time consuming, expensive, and performed on large non-field-deployable instruments. We are developing a portable device that will provide a technique enabling large-scale measurement campaigns with improved granularity in space and time. Our measurement system is based on Cavity Ringdown Spectroscopy (CRDS), a promising methodology that may be packaged into a portable device while still capable of the precision demands necessary to measure variability in atmospheric isotopic composition of CH4. CRDS uses an absorption cell with highly reflective mirrors which enhance the intensity when the laser is at a resonant frequency of the cell. When the laser is shut off, the decay in intensity observed at the output of the cell is related to the absorption (and therefore concentration) by the gas molecules in the cell at that frequency. Our novel approach uses the near-IR spectrum of methane (and its isotopologues) for isotopic ratio measurements (13C/12C, and D/H). This region contains the (ν2+2ν3) vibrational level. For laboratory measurements we are using a near-IR tunable diode laser (1280-1340 nm, with resolution near 0.01 nm). In order to get precision measurements of the isotopic ratios, we must first identify appropriate peaks (strong absorption, spectrally separable but within scanning range) for all three isotopologues. However, accurate simulation of the ro-vibrational spectra in this region is computationally prohibitive (due to high degeneracy resulting from the symmetry of CH4), and to our knowledge there are no measurements for 13CH4 or CH3D in this spectral range. Our current status is the measurement of the spectra for CH4 and its isotopologues in the near IR region. Here we present: (1) description of our laboratory-based CRDS system, (2) measured spectra for methane and its isotopologues in near-IR, (3) system requirements for a portable CRDS system, and (4) preliminary design of a portable system.
A43D-1560
Flight tests, laboratory studies, and intercomparisons of the NSF/NCAR Gulfstream-V VCSEL hygrometer
New observation platforms and state-of-the-art science requirements place challenging demands on the development of new instrumentation. Instruments are desired be faster, smaller, lighter while still maintaining excellent accuracy, precision, and even offering new observational capabilities. New measurements understandably require a large body of evidence documenting their performance before much acceptance in the community. In this context, we will discuss the performance of our recently-developed water vapor sensor designed for the NSF/NCAR Gulfstream-V aircraft by showing results from the first flight tests, laboratory experiments, flow modeling studies of the pylon design, and intercomparison campaigns. Water vapor plays critical roles in atmospheric dynamics, radiative properties, and chemistry throughout the troposphere and lower stratosphere, but there are many measurement challenges due to the large dynamic range in concentration, extreme heterogeneity, presence of cloud particles, and efficient adsorption to instrument surfaces. The Gulfstream-V water vapor instrument uses a fiberized vertical cavity surface emitting laser (VCSEL) operating near a wavelength of 1854 nm to measure water vapor at 25 Hz with <3% precision and 5% accuracy over a range from 1 ppmv (-92 C frost point at 50 hPa) to 40,000 ppmv (+30 C dew point at sea level). The instrument operates unattended, has a mass of 5 kg, and consumes 5 W power. Extensive flight testing of the instrument was performed in spring and summer of 2007 as part of the NSF Pacific Dust Experiment (PACDEX) and HIAPER Experimental Flight Tests. The instrument showed excellent response in clouds ranging from stratocumulus to cirrus. Detailed cloud structure was observed in both cases at 25 Hz that can increase the understanding of cloud entrainment/detrainment processes. In addition, a relatively homogeneous flight segment near the tropopause at 14.8 km (135 hPa) allowed for in-flight checks of the instrument precision (as opposed to laboratory conditions). Under flight conditions of ~ 3 ppmv water vapor, 25 Hz measurements had a standard deviation of 2.1%, thereby placing an upper limit on the precision of the system as some of the variability originated from the real atmosphere. Allan deviation experiments in the laboratory at similar concentrations show about 1% precision, but more importantly, suggest that long-term drift for experiments lasting several days is negligible. Determination of the accuracy of the sensor is being conducted by three methods: calibrations using standard dilution of flows, immersion of the sensor at ice saturated conditions in constant-temperature ice/organic baths, and through studies at the upcoming AIDA International Water Vapor Intercomparison campaign (October 2007). In combination, these results will be used to assess the overall performance of the VCSEL hygrometer and identify where outstanding issues remain.
A43D-1561
Evaluation of the Time-Response of a Chemiluminescence Ozone Sensor for the NSF/NCAR Gulfstream-V Airborne Platform
Results are presented on time response tests of a chemiluminescence ozone instrument under development for the HIAPER platform. Laboratory tests were conducted in preparation for field testing during the Pacific Atmospheric Sulfur Experiment, which took place in August and September, 2007. Preliminary analysis of field data confirms the instrument has at least a 4-Hz frequency response. Laboratory results indicate the present design is likely capable of detecting even faster transients in the atmospheric ozone field. The impact of instrument design choices on time response will be discussed in detail. Beginning in calendar year 2008, this completed instrument will become available for requestable deployment on NSF LAOF platforms.
A43D-1562
Miniaturized instrumentation for routine measurement of aerosol and gas phase pollution by lightweight autonomous unmanned aircraft.
The upcoming California AUAV Pollution Profiling project (CAPPS) will routinely monitor the vertical distribution of aerosol and gas pollutants over California during 2008 using autonomous lightweight unmanned aircraft. The measurements will be used to evaluate the impact of pollutants on California's climate, detect long range transport, and to validate satellite measurements. Proven miniaturized instrumentation for collecting aerosol parameters (concentration, size distribution, absorption), atmospheric solar radiation (flux, heating rates, albedo) and meteorological parameters (thermodynamic structure, water vapor) that were flown during previous studies will be deployed. Validation of these instruments is reviewed. New miniaturized instruments to collect the concentration of gas species are being developed to compliment these established measurements. An ozone monitor with a resolution of 2 ppb has been successfully integrated into the flight package. Results from the laboratory validation of this instrument are presented. In addition, progress on a miniaturized carbon monoxide sensor and NOx sensor are also presented.
A43D-1563
An Evaluation of Infrared Sky Imagers for the Atmospheric Radiation Measurement Program
To obtain retrievals of fractional sky cover over its research sites, the Atmospheric Radiation Measurement Program Climate Research Facility uses Total Sky Imagers (TSIs), which provide real-time processing and visible images of daytime sky conditions. However, for a continuous picture of cloud life-cycles, a nighttime visual technology is needed. Therefore, a field campaign was conducted in September 2007 at the Southern Great Plains site to compare measurements of cloud fraction from five different types of infrared sky imagers and to compare the daytime values with an operational TSI. Each instrument captures hemisphere infrared images of the sky during both the day and night. The inter-comparison study provided an operational testing and evaluation period to verify reliability and performance of the systems, as well as to understand the characteristics of the data, especially the nighttime cloud fraction product.
A43D-1564
Proof-of-Concept for an Advanced Sunphotometer
Aerosols have a profound effect on the radiation balance of the atmosphere. Current estimates of the direct and indirect effects are -0.9 to -0.1 and -1.8 to -0.3 W m-2, respectively, but remain highly uncertain (IPCC, 2007). These uncertainties are tied to our inability to accurately estimate spatial and temporal distributions of aerosol concentrations, size, and composition. Measurements of aerosol optical depth (AOD) are needed from widely distributed locations, both over land and ocean. AOD measurements from the surface are routinely made by sunphotometers. Most notably, NASA's AERONET system makes routine measurements of AOD at many sites throughout the globe. The problem is that very few measurements are made over the ocean because of operational considerations, i.e. ships do not present a stable platform and the salt water spray is damaging to the mechanisms used by the sunphotometers to track the sun. This paper reports on the development of a sunphotometer that can obtain AOD without moving parts. Such an instrument has the potential to be small, lightweight, and rugged. Potential applications are use in extreme environments, on ships and ocean buoys, and perhaps in unmanned aerial systems (UAS). Due to its small size and light weight, the Advanced Sun Photometer can be adapted for use on extraterrestrial bodies with sensible atmospheres, such as Mars or Titan. Concept: Eliminating the need for a tracking mechanism can significantly reduce instrument weight and size while increasing system robustness. The Advanced Sunphotometer uses a compact optical system to provide a hemispherical field of view, removing the need for a sun tracking mechanism. A CCD array is placed at the base of the optical system captures and records the light. Measurements at specific wavelengths are achieved by interposing various interference filters into the light path by means of a filter wheel. The instrument measures the diffuse radiation as well as the direct sun beam. Computer algorithms are used to separate the direct from the diffuse radiation. Current work: Although the CCD array records both the diffuse light entering the cone as well as the direct solar beam, current efforts are have been focused on validating the direct beam measurements of AOD. Efforts have been primarily focused on characterizing the instrument angular response, as well as validating measurements of aerosol optical depth, and water-vapor columnar abundance. Comparisons of the Advanced Sunphotometer AOD measurements will be made with the AOD readings taken with a commercial Microtops II handheld sunphotometer.
A43D-1565
Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR): Airborne Concepts and Ground Prototype Measurements
A collaboration between NASA Ames Research Center and Battelle Pacific Northwest Division is exploring new instrument concepts that combine sky scanning and spectroscopy with the direct sun transmission measurement capabilities of previous instruments like the NASA Ames Airborne Tracking Sunphotometers (AATS). Additional technical goals are to reduce instrument size, weight, and power requirements while increasing autonomy, so as to permit operation on a wider range of aircraft, including unmanned aerial vehicles (UAVs). The overall science goal for the new instruments is to improve knowledge of atmospheric constituents and their links to climate using a variety of airborne measurement approaches including satellite validation. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sunphotometry alone. The spectroscopic capability will improve measurements of gas constituents (e.g., H2O, O3, NO2, SO2) . Concepts explored to date for an airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR-Air) include using fiber optics to link a spectrometer inside the aircraft to optical entrance ports in a relatively small tracking/scanning head outside the aircraft. 4STAR feasibility depends on overcoming three technological hurdles: 1. Maintaining calibration to 1% stability over a period of months. 2. Demonstrating stray light rejection to permit measuring skylight within a few degrees of the sun. 3. Devising a fiber optic coupling that maintains 1% calibration stability with as many as possible of the following desirable characteristics: detachable during assembly before calibration; detachable between calibration and scientific measurements; rotatable during measurements. To investigate ways to overcome these hurdles we have developed a ground-based prototype, 4STAR-Ground. To date 4STAR-Ground has been calibrated with an integrating sphere, and its performance has been characterized in many tests, including comparisons of its sun-tracking and sky-scanning measurements to AATS-14 and an AERONET Cimel sun-sky photometer, respectively. This poster includes concepts for 4STAR-Air and results of the above 4STAR-Ground measurements.
A43D-1566
Ceilometer instrument in NIR for continuous observations of aerosols.
The need for a 24 - 7 vertical aerosol observation is critical to aerosol transport and prediction. To this end, an eye-safe ceilometer usually used only for cloud base measurements was deployed to observe aerosols. We found in direct comparisons with 1064nm lidar measurements that the ceilometer backscatter provides reasonably accurate aerosol backscatter to approximately 1km using spatial bins of 100meters and time averages of 30 minutes baqsed on temporal regression analysis where the 1064nm lidar in the range bin from 900m to 1000m was compared to the ceilometer. Further comparisons at lower altitudes however show that the regression performance is in general good between 500-1000m but an optimum height for best intercomparison is not clear. On the other hand, we note that by 2km, the correlation for "aerosol" signatures has degraded. To assess the utility of the ceilometer instrument, the noise statistics of the ceilometer were explored by examining the range dependence of the mean and std of the signal where we use a threshold of 5e-3 to filter out clouds. The results of the magnitude of the noise signal are presented which determine the minimum optical depth needed to measure a PBL height of a homogeneous layer at a given SNR.
A43D-1567
Improvements to the Passive Ozone Measurement System Used by GLOBE Schools
A study was conducted to improve the accuracy of the passive ozone sensor Eco-Badge test card/Zikua system (Vistanomics, Inc). Specifically we have determined the relationship between ozone concentration and absorbance (color change) of the tin(II)-diphenylcarbazide complex used on the test cards, and the dependence of the color change upon temperature and humidity. Over 700 ambient measurements of hourly test card absorbances with concurrent temperature and humidity, as well as an independent measurement of ambient ozone (2B Technologies, Model 202) collected during the summer 2006 were used to derive a calibration equation for ozone concentration that compensates for temperature and humidity interactions and provides an uncertainty estimate of the measured ozone using rigorous statistical methods. The equation was then applied to previously reported GLOBE surface ozone data to correct for temperature and humidity. Several GLOBE sites were chosen that had consistently reported concomitant measurements of ozone, temperature and humidity and were also in close proximity geographically to an EPA ozone monitoring station. Preliminary results suggest improved agreement between the revised data and EPA values.
A43D-1568
Odin/SMR Satellite Observations of Ozone and its Isotopes in the Middle Atmosphere
The global distribution of isotopic composition of atmospheric ozone has been studied by SubMillimeter Radiometer (SMR) onboard the Odin satellite with retrievals being performed by the Optimal Estimation Method. Odin/SMR launched in February 2001, employs 4 tunable single-sideband Schottky-diode heterodyne receivers in the 485-580GHz spectral range. Vertical profiles for the main isotopomer (16O16O16O) as well as the profiles of the minor isotopomers (16O16O18O, 16O18O16O) were then retrieved for day and night. Results are compared to previous ground-based FTIR, balloon-born FIR, and satellite measurements of isotopic enrichments in atmospheric ozone and found to have smaller uncertainties in the mid-latitude region. The results should therefore provide useful data for validating proposed mechanisms for the isotopic enrichments in atmospheric ozone in the middle atmosphere.
A43D-1569
Validation of Ozone Measurements From the SBUV/2 and OMI Data Sets
Ozone is an important atmospheric constituent that shields the Earth's surface from harmful ultraviolet radiation and also plays a critical role in radiation forcing, thus affecting climate change. NOAA's second generation Solar Backscatter Ultraviolet Instruments (SBUV/2) employ the nadir-viewing backscattered ultraviolet technique to measure ozone concentration profiles in the atmosphere on a global scale. The Ozone Monitoring Instrument (OMI) is an imaging spectrometer with daily global coverage that measures columns of gases like ozone, NO2, BrO, and SO2. A comparison of the ozone data sets from SBUV/2 and OMI is discussed for the period when data are available from those experiments. The study of consistency among the data sets of various instruments is important in developing confidence in those data records and in determining their value in trend analyses. In order to establish the validity of the ozone data records, one needs to show that different measurement techniques based on various physical principles give similar ozone estimates. We employ advanced statistical techniques to validate the NOAA-16, NOAA-17, and NOAA-18 SBUV/2 Version-8 data sets and to compare with OMI retrievals. The SBUV/2 data are from operational and preliminary reprocessing. We consider the ozone data from these experiments co-located in time and space and analyze the time series of differences. We examine the time dependence of the bias between measurements. We also present additional validation in the form of comparisons with Dobson Station overpass match up values.
A43D-1570
Aerosol Optical Properties Characterization By Means Of The CNR-IMAA Multi-Wavelength Raman Lidar
A Raman/elastic lidar for tropospheric aerosol study is operational at CNR-IMAA (40°36'N, 15°44'E, 760 m above sea level) since May 2000 in the framework of EARLINET. Since August 2005, this system provides aerosol backscatter coefficient profiles at 1064 nm, and independent measurements of aerosol extinction and backscatter coefficient profiles at 355 and 532 nm. In this way, lidar ratio (i.e. extinction to backscatter ratio) profiles at 355 and 532 nm are also obtained. In addition, depolarization ratio measurements at 532 nm are obtained by means of detection of components of backscattered light polarized perpendicular and parallel to the direction of the linearly polarized transmitted laser beam. Depolarization ratio measurements provide information about shape and orientation of aerosolic particles, while lidar ratio measurements and wavelength dependences of both backscatter and extinction are important for aerosol characterization in terms of aerosol type and size. In addition, high quality multi-wavelength measurements (3 backscatter + 2 extinction) can allow the determination of microphysical aerosol properties (refractive index, single-scattering albedo and effective particles radii). Systematic measurements are performed three times per week according to the EARLINET schedule since May 2000, and further measurements are performed in order to investigate particular events, like dust intrusions, volcanic eruptions and forest fires. This extended dataset allows the optical characterization of aerosol located close to the surface, namely in the Planetary Boundary Layer, as well as in the free troposphere. In the free troposphere, an high occurrence of Saharan dust intrusions at CNR-IMAA (about 1 day of Saharan dust intrusion every 10 days) has been identified by means of back-trajectory analysis and in accordance with satellite images, because of the short distance from the Sahara region. In addition, CNR-IMAA is pretty close to Etna, the largest European volcano, providing the opportunity to characterize volcanic aerosol properties too. Moreover, forest fires contribution to the aerosol load is not negligible during summer, when large forest fires typically occur in Southern Europe. Therefore the CNR-IMAA multi-wavelength Raman lidar system allows the characterization of aerosol optical properties for a large variety of events and atmospheric situations and to study the aerosol properties modification processes occurred during their transportation over continental scale. ACKNOWLEDGMENTS The financial support for EARLINET by the European Commission under grant RICA-025991 is gratefully acknowledged.
A43D-1571
A triple-etalon imaging interferometer for Earth and planetary remote sensing
A prototype for a space-borne, high spectral resolution interferometer is being developed under the NASA Earth Science Technology Office Instrument Incubator Program. The instrument includes three vacuum or air spaced Fabry-Perot etalons, each of them tunable by piezoelectric adjustment of the etalon gaps. Together with imaging optics and a two dimensional array detector, the instrument acquires a 2-D, very narrow band image of a scene. By stepping all three etalons together, each pixel scans a spectrum with resolution on the order of 0.0025~nm. Combination of three etalons with appropriately selected free spectral ranges improves rejection of out-of-band light, so that the interferometer can achieve good performance in the presence of a strong continuum background. This instrument concept could be applied to any remote sensing application requiring very high resolution spectra acquired over a two dimensional scene. The curent instrument is a prototype for global observation of cloud parameters from geosynchronous orbit. The Geostationary Imaging Fabry-Perot Spectrometer (GIFS) would derive cloud top pressure, optical depth, and cloud fraction from the pressure-broadened line shape of O2 absorption lines near 690~nm. Other potential applications include mapping of trace gas concentrations or chlorophyll fluorescence. Though current work centers on applications in the visible and near infrared using CCD detectors, the concept could be extended to the infrared with, for example, 2-D HgCdTe array detectors. We will report on the status of the testing and calibration of the instrument. We will also describe plans for upcoming aircraft flight tests in early 2008. GIFS will be flown on a NASA P3 acquiring cloud parameter measurements, while a Langley King Air flying in formation observes the same clouds with lidar (HRLS) and an O2 atmospheric band spectrometer (LAABS) for validation.
A43D-1572
Calibration of a Three Wavelength Lidar for Size Discriminated Ambient Particulate Measurement
A three wavelength Lidar has been developed at Utah State University's Space Dynamics Laboratory for the measurement of size segregated ambient particulate matter concentrations as part of the AgLite program. The AgLite program, primarily funded by the U.S. Department of Agriculture's Agricultural Research Service, was developed to quantify particulate emissions from diffuse area sources, such as those typically found around confined animal feeding operations (CAFOs) and tillage operations. The Lidar system is capable of scanning horizontally and vertically across a suspected source area and can identify both spatial and temporal concentration fields which, when combined with locally measured wind field data, can be used to derive source emission estimates. The Lidar measures the relative magnitude of optical scattering by the atmosphere, which is a function of aerosol concentration. A Lidar scan around a source area gives a map of relative aerosol concentration. During an operational experiment, a scan is calibrated by point-sensors collocated with one or more points of the Lidar scan. In order to minimize potential systematic errors, a detailed calibration experiment was designed to compare Lidar return signals with Met One Instruments 8-channel Optical Particle Counters (Model 9722) and Airmetrics MiniVol filter-based samplers configured for collection of TSP, PM10, PM2.5, and PM1. The Lidar calibration experiment was performed in July 2007 at a farm owned and operated by Utah State University near Cache Junction, Utah. Multiple datasets were collected during which the Lidar moved between three stares, each a minute in duration, that were collocated with a cluster of MiniVols sampling the four size fractionations and an OPC. Sampler duration was between three and eight hours, depending upon background particulate concentrations. Prior to comparison of these instruments with the Lidar, the MiniVols and OPCs were compared against collocated PM2.5 and PM10 Federal Reference Method (FRM) samplers operated by the State of Utah Division of Air Quality at the designated air quality sampling site in Logan, Utah to ensure the accuracy of the point sensors. Preliminary analysis demonstrates the average concentrations measured by the MiniVols were within eight percent of the concentrations measured by the FRM samplers at ambient levels greater than 10 μg m-3 for PM2.5 and 14 percent for PM10 at 35 μg m-3. The volume-based concentration determined from the OPCs demonstrated a consistent relationship with the MiniVols filter-based mass concentrations across the observed size ranges. Results of the Lidar comparison with the OPCs and MiniVols will also be presented.
A43D-1573
Characterizing Tropospheric Winds by Combining MISR Cloud-Track and QuikSCAT Surface Wind Vectors
Numerous studies have found that the inclusion of wind observations results in a significantly greater improvement in operational weather forecasts compared to the addition of temperature or pressure observations alone. However, global tropospheric wind measurements are only available from 12-hourly rawinsonde launches from selected locations, primarily over land. For years the world's oceans were "data voids" in terms of wind measurements. Only recently have satellites begun to fill this gap. The SeaWinds scatterometer on the QuikSCAT satellite obtains winds referenced to 10 meters above the surface over the global oceans under nearly all weather conditions. The wind speed and direction data from QuikSCAT have been extensively tested against surface observations and are of such quality that these data are routinely assimilated into numerical weather prediction models run by both the National Center for Environmental Prediction (NCEP) and the European Centre for Medium Range Weather Forecasting (ECMWF). However, scatterometer data only provide wind information near the ocean surface. This information can be complemented with satellite cloud-track winds that provide information about winds in the free troposphere over the ocean, as well as over land, where scatterometer data are not available. In particular, the height resolved cloud motion vectors from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on the NASA EOS Terra satellite yield wind speeds for clouds at altitudes less than approximately 2.5 km that are shown to compare favorably with the QuikSCAT winds globally. In addition, the direction of the MISR winds is similar to the QuikSCAT wind vectors when compared on the same basis. The synergistic use of these two sets of wind observations has the potential to make possible a variety of new studies: from improved forecast and climate model validation; to increased understanding of tropospheric water vapor transport; to observations of the coupling between the ocean surface and lower atmosphere in a variety of conditions, such as during strong El Nino or La Nina events.
A43D-1574
AIRS measurements of stratospheric temperature
The Atmospheric Infrared Sound (AIRS) is one of the six Earth-observing instruments aboard NASA's Aqua satellite launched in May 2002. It continuously measures infrared spectra (3.7-15.4 micron, 2378 channels) in the nadir and sub-limb scanning mode. AIRS samples the atmosphere with high horizontal resolution: The nadir footprint is about 1.1° times 0.6°. A typical 'granule' of AIRS data is acquired in 6 minutes' time and consists of 135 swaths along the satellite track, each containing 90 individual sub-limb measurements across- track. The operational retrieval for AIRS does not provide temperature data at the full AIRS horizontal resolution, but instead uses nine pixels to derive a cloud-cleared radiance spectrum and a single temperature profile. By restricting ourself to cloud-free, stratospheric measurement channels, we are able to retrieve temperature data from the 4.2 and 15 micron carbon dioxide emissions at full horizontal resolution. In this presentation we briefly describe our new fast forward model for AIRS and the retrieval method applied. We show first comparisons of retrieved temperature data against independent measurements. The new temperature data set is of particular interest for studies of small-scale temperature features caused by gravity waves. We finally show several case studies of spectacular gravity wave events as observed by AIRS during its five year measurement period.
A43D-1575
Enhanced MISR stereoscopic observation of polar stratospheric clouds and smoke plumes
We present a technique for stereoscopically retrieving altitudes of thin cirrus, smoke plumes, and stratospheric clouds viewed by the Multi-angle Imaging SpectroRadiometer (MISR) aboard the EOS-TERRA satellite. This technique differs from the operational MISR stereoscopic retrieval by using oblique perspective and revised algorithms to enhance coverage for features that may exhibit minimal texture at nadir due to homogeneous structure or limited optical depth. Stereoscopic retrievals from this technique are evaluated relative to collocated Geosynchronous Laser Altimeter System observations and operational MISR stereo product retrievals over the Antarctic during the time frame from September 29th to October 12th, 2003. Furthermore, results are applied to case studies of polar stratospheric cloud development, and lofting of smoke plumes into the stratosphere.
A43D-1576
Identification of stratospheric waves in ozone in the tropics from OMI high spectral resolution measurements
Previous studies using Total Ozone Mapping Spectrometer (TOMS) measurements have identified several types of tropical waves in the stratosphere. These waves include Kelvin waves, mixed Rossby-gravity waves, equatorial Rossby waves, and global normal modes. All of these detected waves occur when their zonal phase speeds are opposite the zonal winds in the low-mid stratosphere associated with the Quasi-biennial Oscillation (QBO). Peak-to-peak amplitudes in all cases are typically ~5 DU. While total ozone data from TOMS is sensitive in detecting these tropical waves, they provide each day only a single horizontal cross-sectional map. The high spatial and spectral resolution of the Aura Ozone Monitoring Instrument (OMI) provides a unique means to evaluate 3D structure in these waves including their propagation characteristics. Ozone profiles retrieved from OMI radiances for wavelengths 270-310 nm are utilized to examine the nature of these wave disturbances extending from the lower to upper stratosphere.
A43D-1577
Comparative Hydrology Over Monsoonal Regions Using Seasonal Distributions of Stable Water Isotopes.
The hydrologic regimes of monsoonal regions contain complex balances of large-scale advective supply of water, surface exchange and atmospheric condensation, which are important for the regional energy balance and climate. Stable water isotopes are powerful tools for studying such processes, as isotopic fractionations occurring during evaporation and condensation give rise to measurable variations in the isotopic composition that reflects the history of moist processes for each observed air parcel. The HDO/H2O data set from the Tropospheric Emission Spectrometer (TES) on NASA's Aura spacecraft offers a unique global view of the isotopic composition of water vapor. The TES data set, and the analysis here, is complimentary to previous work using isotopic ratios in precipitation; however it need not be that the simple relationships found in the precipitation data hold for the atmospheric vapor case because of the variability induced by atmospheric mixing and convection. Over tropical continents, the intensity of water vapor recycling, precipitation rates and circulation patterns are thought to dominate the seasonal isotopic composition of water vapor and rainfall. By examining and contrasting the isotopic budgets of the Amazon, north Australia, and Asian monsoon regions, we gain insight into these hydrological processes, show which processes are regionally robust, and expose those processes that are regionally unique. To establish the importance of local processes on the regional isotopic composition, we first examine the relationship between the measured isotopic composition and meteorological parameters that capture the strength of the local processes. Secondly, we use the history of condensation, evaporation and air mass mixing during transport from five-day origin locations to the local TES observations, and the isotopic ratios of vapor at both locations, to examine isotopic changes that occur upstream. Using this information, as well as a simple isotopic exchange model that uses the isotopic ratios as constraints, we provide a unique view of the seasonal contributions of moisture via an evaporative source versus the losses due to condensation. Our results show that during the monsoonal seasons of the regions studied, additional isotopic exchange during intense condensation or through rainfall evaporation can explain the substantial isotopic depletion that deviates from the Rayleigh distillation model. Secondly, we show that local convection introduces intra-seasonal variability in the regional isotopic ratios, which shows local sources of moisture are significant for each region. Thirdly, the isotopic composition reveals substantial subsidence for the dry seasons of the Asian monsoon and N. Australian regions, indicating a seasonal source of dry air. Our results reveal that the regional ratios of moisture gain from an evaporative source versus the moisture loss from condensation vary from close to zero for the wettest months to unity for the dry seasons. These results show that the isotopic ratios of water vapor can further the understanding of the physics of regional hydrology near monsoonal areas.