Showing papers by "Cooperative Institute for Research in the Atmosphere published in 2010"

Estimating Snow Water Equivalent Using Snow Depth Data and Climate Classes

Abstract: In many practical applications snow depth is known, but snow water equivalent (SWE) is needed as well. Measuring SWE takes ∼20 times as long as measuring depth, which in part is why depth measurements outnumber SWE measurements worldwide. Here a method of estimating snow bulk density is presented and then used to convert snow depth to SWE. The method is grounded in the fact that depth varies over a range that is many times greater than that of bulk density. Consequently, estimates derived from measured depths and modeled densities generally fall close to measured values of SWE. Knowledge of snow climate classes is used to improve the accuracy of the estimation procedure. A statistical model based on a Bayesian analysis of a set of 25 688 depth–density–SWE data collected in the United States, Canada, and Switzerland takes snow depth, day of the year, and the climate class of snow at a selected location from which it produces a local bulk density estimate. When converted to SWE and tested against t...

Biomass burning smoke aerosol properties measured during Fire Laboratory at Missoula Experiments (FLAME)

Abstract: [1] During the Fire Laboratory at Missoula Experiments (FLAME), we studied the physical, chemical, and optical properties of biomass burning smoke from the laboratory combustion of various wildland fuels. A good understanding of these properties is important in determining the radiative effects of biomass burning aerosols, with impacts on both local and regional visibility and global climate. We measured aerosol size distributions with two instruments: a differential mobility particle sizer (DMPS) and an optical particle counter (OPC). Volume size distributions from different burns varied from monomodal to multimodal, with geometric mean diameters ranging from 0.20–0.57 μm and geometric standard deviations ranging from 1.68–2.97. By reconciling the differences between the two sizing instruments, we estimated aerosol effective refractive indices with values ranging from 1.41 to 1.61. We reconstructed aerosol chemical composition for each burn using data from filters collected and analyzed with the Interagency Monitoring of Protected Visual Environments (IMPROVE) samplers and protocols. Aerosols were generally comprised of carbon with organic species accounting for the largest mass fraction in most cases. We used composition data to calculate aerosol density, which ranged from 1.22–1.92 g cm−3, and real and imaginary refractive indices, which had ranges of 1.55–1.80 and 0.01–0.50 respectively. Aerosol physical, chemical, and optical characterizations were combined to calculate dry mass scattering (MSE) and absorption (MAE) efficiencies at 532 nm. These parameters had values between 1.6–5.7 m2 g−1 and 0.04–0.94 m2 g−1.

Performance of an Eddy Diffusivity-Mass Flux Scheme for Shallow Cumulus Boundary Layers

Abstract: Comparisons between single-column (SCM) simulations with the total energy‐mass flux boundary layer scheme (TEMF) and large-eddy simulations (LES) are shown for four cases from the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) 2006 field experiment in the vicinity of Houston, Texas. The SCM simulations were run with initial soundings and surface forcing identical to those in the LES, providing a clean comparison with the boundary layer scheme isolated from any other influences. Good agreement is found in the simulated vertical transport and resulting moisture profiles. Notable differences are seen in the cloud base and in the distribution of moisture between the lower and upper cloud layer. By the end of the simulations, TEMF has dried the subcloud layer and moistened the lower cloud layer more than LES. TEMF gives more realistic profiles for shallow cumulus conditions than traditional boundary layer schemes, which have no transport above the dry convective boundary layer. Changes to the formulation and its parameters from previous publications are discussed.

Carbon source/sink information provided by column CO 2 measurements from the Orbiting Carbon Observatory

Abstract: . We quantify how well column-integrated CO2 measurements from the Orbiting Carbon Observatory (OCO) should be able to constrain surface CO2 fluxes, given the presence of various error sources. We use variational data assimilation to optimize weekly fluxes at a 2°×5° resolution (lat/lon) using simulated data averaged across each model grid box overflight (typically every ~33 s). Grid-scale simulations of this sort have been carried out before for OCO using simplified assumptions for the measurement error. Here, we more accurately describe the OCO measurements in two ways. First, we use new estimates of the single-sounding retrieval uncertainty and averaging kernel, both computed as a function of surface type, solar zenith angle, aerosol optical depth, and pointing mode (nadir vs. glint). Second, we collapse the information content of all valid retrievals from each grid box crossing into an equivalent multi-sounding measurement uncertainty, factoring in both time/space error correlations and data rejection due to clouds and thick aerosols. Finally, we examine the impact of three types of systematic errors: measurement biases due to aerosols, transport errors, and mistuning errors caused by assuming incorrect statistics. When only random measurement errors are considered, both nadir- and glint-mode data give error reductions over the land of ~45% for the weekly fluxes, and ~65% for seasonal fluxes. Systematic errors reduce both the magnitude and spatial extent of these improvements by about a factor of two, however. Improvements nearly as large are achieved over the ocean using glint-mode data, but are degraded even more by the systematic errors. Our ability to identify and remove systematic errors in both the column retrievals and atmospheric assimilations will thus be critical for maximizing the usefulness of the OCO data.

Three‐dimensional variational data assimilation of ozone and fine particulate matter observations: some results using the Weather Research and Forecasting—Chemistry model and Grid‐point Statistical Interpolation

Abstract: In operational air-quality forecasting, initial concentrations of chemical species are often obtained using previous-day forecasts with limited or no account for the observations. In this article we assess the role that assimilation of surface measurements of ozone and fine aerosols can play in improving the skill of air-quality forecasts. An assimilation experiment is performed using the Weather Research and Forecasting—Chemistry model and Grid-point Statistical Interpolation, a three-dimensional variational assimilation tool. The modelling domain covers the northeastern region of North America. The measurements come from the United States Environmental Protection Agency AIRNow network and are available hourly. Background error covariance statistics are derived from forecasts in July 2004. Comparison of forecasts issued in August and September 2006 and initialized with and without the assimilation follows. Results show that forecasts of ozone and fine aerosol concentrations benefit from the assimilation in terms of standard verification scores for a period of at least 24 hours. However, significant reduction of errors as a consequence of the assimilation is accompanied by fast model error growth in the early forecast hours. Published in 2010 by John Wiley & Sons, Ltd.

Greenland Ice Sheet Surface Mass-Balance Modeling in a 131-Yr Perspective, 1950–2080

Abstract: Fluctuations in the Greenland ice sheet (GrIS) surface mass balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. A state-of-the-art snow-evolution modeling system (SnowModel) was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the Intergovernmental Panel on Climate Change scenario A1B modeled by the HIRHAM4 regional climate model (RCM) using boundary conditions from the ECHAM5 atmosphere–ocean general circulation model (AOGCM) from 1950 through 2080. In situ meteorological station [Greenland Climate Network (GC-Net) and World Meteorological Organization (WMO) Danish Meteorological Institute (DMI)] observations from inside and outside the GrIS were used to validate and correct RCM output data before they were used as input for SnowModel. Satellite observations an...

The Influence of Air Temperature Inversions on Snowmelt and Glacier Mass Balance Simulations, Ammassalik Island, Southeast Greenland

Abstract: In many applications, a realistic description of air temperature inversions is essential for accurate snow and glacier ice melt, and glacier mass-balance simulations. A physically based snow evolution modeling system (SnowModel) was used to simulate 8 yr (1998/99–2005/06) of snow accumulation and snow and glacier ice ablation from numerous small coastal marginal glaciers on the SW part of Ammassalik Island in SE Greenland. These glaciers are regularly influenced by inversions and sea breezes associated with the adjacent relatively low temperature and frequently ice-choked fjords and ocean. To account for the influence of these inversions on the spatiotemporal variation of air temperature and snow and glacier melt rates, temperature inversion routines were added to MircoMet, the meteorological distribution submodel used in SnowModel. The inversions were observed and modeled to occur during 84% of the simulation period. Modeled inversions were defined not to occur during days with strong winds and ...

Effect of Aerosol on the Susceptibility and Efficiency of Precipitation in Warm Trade Cumulus Clouds

Abstract: Large-eddy simulations of warm, trade wind cumulus clouds are conducted for a range of aerosol conditions with a focus on precipitating clouds. Individual clouds are tracked over the course of their lifetimes. Precipitation rate decreases progressively as aerosol increases. For larger, precipitating clouds, the polluted clouds have longer lifetimes because of precipitation suppression. For clean aerosol conditions, there is good agreement between the average model precipitation rate and that calculated based on observed radar reflectivity Z and precipitation rate R relationships. Precipitation rate can be expressed as a power-law function of liquid water path (LWP) and Nd, to reasonable accuracy. The respective powers for LWP and Nd are of similar magnitude compared to those based on observational studies of stratocumulus clouds. The time-integrated precipitation rate represented by a power-law function of LWP, Nd, and cloud lifetime is much more reliably predicted than is R expressed in terms of...

CloudSat Precipitation Profiling Algorithm—Model Description

Abstract: Identifying and quantifying the intensity of light precipitation at global scales is still a difficult problem for most of the remote sensing algorithms in use today. The variety of techniques and algorithms employed for such a task yields a rather wide spectrum of possible values for a given precipitation event, further hampering the understanding of cloud processes within the climate. The ability of CloudSat’s millimeter-wavelength Cloud Profiling Radar (CPR) to profile not only cloud particles but also light precipitation brings some hope to the above problems. Introduced as version zero, the present work uses basic concepts of detection and retrieval of light precipitation using spaceborne radars. Based on physical principles of remote sensing, the radar model relies on the description of clouds and rain particles in terms of a drop size distribution function. Use of a numerical model temperature and humidity profile ensures the coexistence of mixed phases otherwise undetected by the CPR. It ...

On water vapor Jacobian in fast radiative transfer model

Abstract: [1] The Community Radiative Transfer Model (CRTM) is a powerful numerical software used for satellite data assimilation and remote sensing applications. Its accuracies in simulating satellite radiances and their gradients relative to water vapor (or Jacobians) are improved through this study when the CRTM includes additional gaseous absorbers. Three water vapor transmittance regression methods (labeled with A–C, respectively) are discussed that differ primarily in vertical coordinates and the application of constraints to smooth vertical structures of the regression coefficients. Method A computes optical depth profiles at fixed pressure levels, whereas method B computes the profiles at fixed levels of the integrated absorber amount. Method C is a derived version of method B with an addition that a polynomial function is applied to the regression coefficients to improve the water vapor Jacobians. The intercomparison focuses on the modeling of 22 sounding channels routinely used at numerical weather prediction (NWP) centers: 9 Atmospheric Infrared Radiance Sounder channels, 4 High-Resolution Infrared Sounder channels, 4 Advanced Microwave Sounding Unit-A channels, and 5 Microwave Humidity Sounder channels. An ensemble of 48 diverse atmosphere profiles at the University of Maryland at Baltimore County was used to test the results. The results were compiled for methods A and C for water vapor line absorption only while keeping the other components the same under the CRTM framework. The comparison quantities include the water vapor Jacobians, temperature Jacobians, and the forward top-of-the-atmosphere brightness temperature (BT). In the infrared, the forward models mean errors are very small (less than 0.03 K) compared to the line-by-line model. Temperature and water vapor Jacobian goodness-of-fit measure values are very small and sufficient for NWP application, except for some dry atmospheric profiles. For the cold and dry atmospheric profiles, method C can significantly improve the water vapor Jacobian profile and remove the unphysical kinks (oscillations) that appear in method A. The improved water vapor Jacobian profile results in the improved temperature Jacobian. For the microwave channels, the forward BTs show very small biases less than 0.1 K for all the channels, and the overall water vapor Jacobian using method A is better than those using method C, especially for warm and wet atmospheric profiles.

Two-Dimensional Continuous Wavelet Analysis and Its Application to Meteorological Data

Abstract: The two-dimensional continuous wavelet transform (2D CWT) has become an important tool to examine and diagnose nonstationary datasets on the plane. Compared with traditional spectral analysis methods, the 2D CWT provides localized spectral information of the analyzed dataset. It also has the advantage over the 2D discrete wavelet transform (DWT) in that it covers the domain of the analyzed data with a continuous analysis from which detailed, shift-invariant spectral information of different positions and orientations can be obtained. In this paper, a brief introduction of the 2D CWT and some of the most common wavelet mother functions are given, and some practical issues arising from the implementation and applications of the 2D CWT are discussed. The 2D CWT is applied to several test functions to illustrate the effects of the transforms. To demonstrate its practical application, the 2D CWT is used to analyze a set of meteorological data obtained from a numerical model stimulation.

Freshwater flux to Sermilik Fjord, SE Greenland

Abstract: . Terrestrial inputs of freshwater flux to Sermilik Fjord, SE Greenland, were estimated, indicating ice discharge to be the dominant source of freshwater. A freshwater flux of 40.4 ± 4.9×109 m3 y−1 was found (1999–2008), with an 85% contribution originated from ice discharge (65% alone from Helheim Glacier), 11% from terrestrial surface runoff (from melt water and rain), 3% from precipitation at the fjord surface area, and 1% from subglacial geothermal and frictional melting due to basal ice motion. The results demonstrate the dominance of ice discharge as a primary mechanism for delivering freshwater to Sermilik Fjord. Time series of ice discharge for Helheim Glacier, Midgard Glacier, and Fenris Glacier were calculated from satellite-derived average surface velocity, glacier width, and estimated ice thickness, and fluctuations in terrestrial surface freshwater runoff were simulated based on observed meteorological data. These simulations were compared and bias corrected against independent glacier catchment runoff observations. Modeled runoff to Sermilik Fjord was variable, ranging from 2.9 ± 0.4×109 m3 y−1 in 1999 to 5.9 ± 0.9×109 m3 y−1 in 2005. The sub-catchment runoff of the Helheim Glacier region accounted for 25% of the total runoff to Sermilik Fjord. The runoff distribution from the different sub-catchments suggested a strong influence from the spatial variation in glacier coverage, indicating high runoff volumes, where glacier cover was present at low elevations.

High resolution modelling of snow transport in complex terrain using downscaled MM5 wind fields

Abstract: Snow transport is one of the most dominant pro- cesses influencing the snow cover accumulation and ablation in high mountain environments. Hence, the spatial and tem- poral variability of the snow cover is significantly modified with respective consequences on the total amount of water in the snow pack, on the temporal dynamics of the runoff and on the energy balance of the surface. For the present study we used the snow transport model SnowModel in combina- tion with MM5 (Penn State University - National Center for Atmospheric Research MM5 model) generated wind fields. In a first step the MM5 wind fields were downscaled by us- ing a semi-empirical approach which accounts for the eleva- tion difference of model and real topography, and vegetation. The target resolution of 30 m corresponds to the resolution of the best available DEM and land cover map of the test site Berchtesgaden National Park. For the numerical mod- elling, data of six automatic meteorological stations were used, comprising the winter season (September-August) of 2003/04 and 2004/05. In addition we had automatic snow depth measurements and periodic manual measurements of snow courses available for the validation of the results. It could be shown that the model performance of SnowModel could be improved by using downscaled MM5 wind fields for the test site. Furthermore, it was shown that an estimation of snow transport from surrounding areas to glaciers becomes possible by using downscaled MM5 wind fields.

Measured and modeled humidification factors of fresh smoke particles from biomass burning: role of inorganic constituents

Abstract: . During the 2006 FLAME study (Fire Laboratory at Missoula Experiment), laboratory burns of biomass fuels were performed to investigate the physico-chemical, optical, and hygroscopic properties of fresh biomass smoke. As part of the experiment, two nephelometers simultaneously measured dry and humidified light scattering coefficients (bsp(dry) and bsp(RH), respectively) in order to explore the role of relative humidity (RH) on the optical properties of biomass smoke aerosols. Results from burns of several biomass fuels from the west and southeast United States showed large variability in the humidification factor (f(RH)=bsp(RH)/bsp(dry)). Values of f(RH) at RH=80–85% ranged from 0.99 to 1.81 depending on fuel type. We incorporated measured chemical composition and size distribution data to model the smoke hygroscopic growth to investigate the role of inorganic compounds on water uptake for these aerosols. By assuming only inorganic constituents were hygroscopic, we were able to model the water uptake within experimental uncertainty, suggesting that inorganic species were responsible for most of the hygroscopic growth. In addition, humidification factors at 80–85% RH increased for smoke with increasing inorganic salt to carbon ratios. Particle morphology as observed from scanning electron microscopy revealed that samples of hygroscopic particles contained soot chains either internally or externally mixed with inorganic potassium salts, while samples of weak to non-hygroscopic particles were dominated by soot and organic constituents. This study provides further understanding of the compounds responsible for water uptake by young biomass smoke, and is important for accurately assessing the role of smoke in climate change studies and visibility regulatory efforts.

Meltwater flux and runoff modeling in the ablation area of Jakobshavn Isbræ, West Greenland

Abstract: The temporal variability in surface snow and glacier melt flux and runoff were investigated for the ablation area of lakobshavn Isbrae, West Greenland. High-resolution meteorological observations both on and outside the Greenland Ice Sheet (GrIS) were used as model input. Realistic descriptions of snow accumulation, snow and glacier-ice melt, and runoff are essential to understand trends in ice sheet surface properties and processes. SnowModel, a physically based, spatially distributed meteorological and snow-evolution modeling system was used to simulate the temporal variability of lakobshavn Isbrre accumulation and ablation processes for 2000/01-2006/07. Winter snow-depth observations and MODIS satellite-derived summer melt observations were used for model validation of accumulation and ablation. Simulations agreed well with observed values. Simulated annual surface melt varied from as low as 3.83 x 10{sup 9} m{sup 3} (2001/02) to as high as 8.64 x 10{sup 9} m{sup 3} (2004/05). Modeled surface melt occurred at elevations reaching 1,870 m a.s.l. for 2004/05, while the equilibrium line altitude (ELA) fluctuated from 990 to 1,210 m a.s.l. during the simulation period. The SnowModel meltwater retention and refreezing routines considerably reduce the amount of meltwater available as ice sheet runoff; without these routines the lakobshavn surface runoff would be overestimated by anmore » average of 80%. From September/October through May/June no runoff events were simulated. The modeled interannual runoff variability varied from 1.81 x 10{sup 9} m{sup 3} (2001/02) to 5.21 x 10{sup 9} m{sup 3} (2004/05), yielding a cumulative runoff at the Jakobshavn glacier terminus of {approx}2.25 m w.eq. to {approx}4.5 m w.eq., respectively. The average modeled lakobshavn runoff of {approx}3.4 km{sup 3} y{sup -1} was merged with previous estimates of Jakobshavn ice discharge to quantify the freshwater flux to Illulissat Icefiord. For both runoff and ice discharge the average trends are similar, indicating increasing (insignificant) influx of freshwater to the Illulissat Icefiord for the period 2000/01-2006/07. This study suggests that surface runoff forms a minor part of the overall Jakobshavn freshwater flux to the fiord: around 7% ({approx}3.4 km{sup 3} y{sup -1}) of the average annual freshwater flux of {approx}51.0 km{sup 3} y{sup -1} originates from the surface runoff.« less

Source attribution of climatically important aerosol properties measured at Paposo (Chile) during VOCALS

Abstract: . Measurements of submicron aerosol composition, light scattering, and size distribution were made from 17 October to 15 November 2008 at the elevated Paposo site (25° 0.4' S, 70° 27.01' W, 690 m a.s.l.) on the Chilean coast as part of the VOCALS* Regional Experiment (REx). Based on the chemical composition measurements, a receptor modeling analysis using Positive Matrix Factorization (PMF) was carried out, yielding four broad source categories of the aerosol mass, light scattering coefficient, and a proxy for cloud condensation nucleus (CCN) concentration at 0.4% supersaturation derived from the size distribution measurements assuming an observed soluble mass fraction of 0.53. The sources resolved were biomass burning, marine, an urban-biofuels mix and a somewhat ambiguous mix of smelter emissions and mineral dust. The urban-biofuels mix is the most dominant aerosol mass component (52%) followed by biomass burning (25%), smelter/soil dust (12%) and marine (9%) sources. The average (mean±std) submicron aerosol mass concentration, aerosol light scattering coefficient and proxy CCN concentration were, 8.77±5.40 μg m−3, 21.9±11.0 Mm−1 and 548±210 cm−3, respectively. Sulfate is the dominant identified submicron species constituting roughly 40% of the dry mass (3.64±2.30 μg m−3), although the indentified soluble species constitute only 53% of the mass. Much of the unidentified mass is likely organic in nature. The relative importance of each aerosol source category is different depending upon whether mass, light scattering, or CCN concentration is being considered, indicating that the mean size of aerosols associated with each source are different. Marine aerosols do not appear to contribute to more than 10% to either mass, light scattering, or CCN concentration at this site. Back trajectory cluster analysis proved consistent with the PMF source attribution. *VOCALS: VAMOS** Ocean-Cloud-Atmosphere-Land Study (VOCALS) **VAMOS: Variability of American Monsoon System

Mixed Gaussian‐lognormal four‐dimensional data assimilation

Abstract: In this paper, the current methods that are used for deriving the Gaussian cost function in four-dimensional variational (4D VAR) data assimilation, are extended to lognormal and mixed, lognormal and Gaussian, random variables (rv). It is also shown that transforming a lognormal rv into a Gaussian rv to use in a Gaussian based 4D VAR results in the analysis state being similar to a median in lognormal space. An alternative version of the functional approach is derived so that the minimum of this alternative cost function is the mode in lognormal space. However, the current approaches do not allow for a generalized probability density function (pdf) approach, to overcome this a general probability model is derived so that the mode is found for any pdf from Bayesian networks and conditional independence properties. It is shown that the current Gaussian cost function and the lognormal can be found by the probability model method. The paper is finished by comparing the median approach with the modal approach in the Lorenz 1963 model for both weak and strong constraint 4D VAR and show that the mode is a more reliable analysis statistic than the median under certain circumstances.

Multidisciplinary Analysis of an Unusual Tornado: Meteorology, Climatology, and the Communication and Interpretation of Warnings*

Abstract: On 22 May 2008, a strong tornado—rated EF3 on the enhanced Fujita scale, with winds estimated between 136 and 165 mi h−1 (61 and 74 m s−1)—caused extensive damage along a 55-km track through northern Colorado. The worst devastation occurred in and around the town of Windsor, and in total there was one fatality, numerous injuries, and hundreds of homes significantly damaged or destroyed. Several characteristics of this tornado were unusual for the region from a climatological perspective, including its intensity, its long track, its direction of motion, and the time of day when it formed. These unusual aspects and the high impact of this tornado also raised a number of questions about the communication and interpretation of information from National Weather Service watches and warnings by decision makers and the public. First, the study examines the meteorological circumstances responsible for producing such an outlier to the regional severe weather climatology. An analysis of the synoptic and mes...

Runoff and mass-balance simulations from the Greenland Ice Sheet at Kangerlussuaq (Søndre Strømfjord) in a 30-year perspective, 1979-2008

Abstract: This study provides insights into surface mass- balance (SMB) and runoff exiting the Watson River drainage basin, Kangerlussuaq, West Greenland during a 30 year pe- riod (1978/1979-2007/2008) when the climate experienced increasing temperatures and precipitation. The 30-year sim- ulations quantify the terrestrial freshwater output from part of the Greenland Ice Sheet (GrIS) and the land between the GrIS and the ocean, in the context of global warming and in- creasing GrIS surface melt. We used a snow-evolution mod- eling system (SnowModel) to simulate the winter accumu- lation and summer ablation processes, including runoff and SMB, of the ice sheet: indicating that the simulated equi- librium line altitude (ELA) was in accordance with indepen- dent observations. To a large extent, the SMB fluctuations could be explained by changes in net precipitation (precipi- tation minus evaporation and sublimation), with 8 out of 30 years having negative SMB, mainly because of relatively low annual net precipitation. The overall trend in net precipita- tion and runoff increased significantly, while SMB increased insignificantly throughout the simulation period, leading to enhanced precipitation of 0.59 km 3 w.eq. (or 60%), runoff of 0.43 km 3 w.eq. (or 55%), and SMB of 0.16 km 3 w.eq.

Characteristics of an African Easterly Wave Observed during NAMMA

Abstract: The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006. Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and...

Polarimetric Radar Observations of Convection in Northwestern Mexico during the North American Monsoon Experiment

Abstract: The spatial and temporal variability of convection during the North American Monsoon Experiment (NAME)wasexaminedviaanalysisofthree-dimensionalpolarimetricradardata.Terrainbandsweredefined as the Gulf of California (over water) and elevations of 0‐500 m above mean sea level (MSL; coastal plain), 500‐1500 m MSL, and .1500 m MSL.Convectiverainfallover the Gulf typicallyfeaturedthe smallestvalues of median volume diameter (D0) regardless of rain rate. Gulf convection also contained reduced precipitationsized ice water mass but proportionally more liquid water mass compared to convection over land. These maritime characteristics were magnified during disturbed meteorological regimes, which typically featured increased precipitation over the Gulf and adjacent coastal plain. Overall, the results suggest increased reliance on warm-rain collision and coalescence at the expense of ice-based precipitation growth processes for convective rainfall over the Gulf, relative to the land. Over land D0, ice, and liquid water mass all increased with decreasing terrain elevation, suggesting intensification of convection as it moved off the Sierra Madre Occidental. The results are consistent with the hypothesis that both warm-rain and ice-based rainfall processes play important roles in precipitation formation over land. Coastal-plain convection underwent microphysical modifications during disturbed meteorological regimes that were similar to Gulf convection, but the changes were less dramatic. High-terrain convection experienced little microphysical variability regardless of meteorological regime.

Mesoscale satellite data assimilation: impact of cloud-affected infrared observations on a cloud-free initial model state

Abstract: This work presents the results of assimilating cloud-affected radiances from geostationary, infrared window and water vapour channels into a mesoscale, cloud-resolving model using a four-dimensional variational assimilation system for the case of an altocumulus cloud over the Great Plains of the United States. In this case, the initial model state, based on reanalysis data, was virtually cloud-free. The impacts of cloudy-scene radiances on a cloud-free model state (and, more generally, accurate satellite observations on inaccurate model initial conditions) in a four-dimensional variational assimilation framework are discussed. Results indicate that, in a cloud-free model state, the assimilation of cloudy radiances modifies the initial conditions as if no cloud exists. This results in a cooling of the surface and lower troposphere upon assimilation of infrared window channels, and an increase in mid- to upper tropospheric humidity upon assimilation of water vapour channels in an attempt to minimize the differences between the modelled and observed radiances. Neither modification of the initial conditions leads to the formation of the observed cloud. The size of the domain and the background error covariance are found to have a significant impact on the results.

Diagnostic study of generalized moist potential vorticity in a non-uniformly saturated atmosphere with heavy precipitation

Abstract: A Meiyu front accompanied by a band of heavy precipitation in East Asia is typically characterized by a much larger moisture gradient than temperature gradient. Many previous studies have suggested use of equivalent potential temperature as a thermodynamic variable under this circumstance. However, dynamic variables coupled with such a thermodynamic variable, e.g. a derived moist potential vorticity (MPV) based on equivalent potential temperature, does not provide useful dynamic insight into these systems. In this study, generalized moist potential vorticity (GMPV) is derived based on a generalized form of potential temperature. Diagnoses of numerical simulations for three typical Meiyu rainfall events show that GMPV provides remarkably accurate tracking of rainfall location, suggesting its potential use as a dynamic tracer for heavy rainfall events such as Meiyu rain bands. Copyright © 2010 Royal Meteorological Society

Comparison between observed and synthetic 6.5 and 10.7 μm GOES-12 imagery of thunderstorms that occurred on 8 May 2003

Abstract: Over the past few years, a numerical system to produce synthetic satellite images has been developed at the Cooperative Institute for Research in the Atmosphere. This is being done to better understand imagery from current and future sensors. This system consists of a mesoscale model and an observational operator. Synthetic imagery of a boundary layer capped stratus cloud and an idealized thunderstorm have been produced by past investigators. In this publication, this system was applied to a thunderstorm event that occurred over the central plains of the USA on 8 May 2003. The main purpose of this study is to extend previous research by comparing observed and synthetic GOES-12 imagery of thunderstorms from an observed event. Synthetic 6.5 and 10.7 μm GOES-12 satellite imagery was produced and compared to actual 6.5 and 10.7 μm GOES-12 imagery from 8 May 2003. Multiple two-way interactive nested grids and two-moment microphysics were employed in this study. Various statistics were used to compare synthetic satellite imagery with observed satellite imagery. Results show that the synthetic imagery was reasonably similar to observed imagery. An approximate 2% cold bias, though, was evident in the synthetic imagery associated with the tops of the simulated thunderstorms. When the calculation of brightness temperatures was done a second time, the number of vertical levels was increased an order of magnitude: the 2% cold bias remained. This led to the conclusion that the bias was related to simulated thunderstorms that were more intense than observed thunderstorms and possibly cooler simulated tropopause temperatures.

A dynamic global cloud layer for virtual globes

Abstract: We describe a technique to merge multiple environmental satellite data sets for an hourly updated, near real-time global depiction of cloud cover for virtual globe applications. A global thermal infrared composite obtained from merged geostationary-(GEO) and low-Earth-orbiting (LEO) satellite data is processed to depict clear and cloudy areas in a visually intuitive fashion. This GEO-plus-LEO imagery merging is complicated by the fact that each individual satellite observes a single 'snapshot' of the cloud patterns, each taken at different times, whereas the underlying clouds themselves are constantly moving and evolving. For the cloudy areas, the brightness and transparency are approximated based upon the cloud top temperature relative to the local radiometric surface temperatures (corrected for surface emissivity variations) at the time of the satellite observation. The technique clearly defines and represents mid-to high-level clouds over both land and ocean. Due to their proximity to the Earth's surface, low-level clouds such as stratocumulus and stratus clouds will be poorly represented with the current technique, since warmer temperatures in this case do not correspond to higher cloud transparency. Overcoming this problem requires the introduction of multispectral channel combinations.

Feasibility of Cloud Screening Using Proxy Photon Pathlength Distributions Derived from High-Resolution Spectra in the Near Infrared

Abstract: High-resolution spectra of reflected sunlight in the 2-μm absorption band of CO2 are simulated at the top of the atmosphere using cloud profiles and particle sizes from CloudSat analyzed meteorology from ECMWF, surface bidirectional distribution functions over land derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), and a facet model of ocean reflectance. It is argued that in clear sky the photons will follow the direct path from sun to surface to satellite, because Rayleigh scattering is negligible at 2 μm, so the distribution of photon pathlengths will be a δ function. A proxy for the photon pathlength distribution under any sky condition is recovered from the high-resolution spectrum by representing the distribution as a weighted sum of δ functions. Scenes are classified as clear or cloudy according to how closely the distribution approximates the ideal single δ function for the direct path. The algorithm has an efficiency of approximately 75%, meaning that 25% of the clear...

Design of a temporal variational data assimilation method suitable for deep soil moisture retrievals using passive Microwave radiometer data

Abstract: Our goal is to identify paths to the soil moisture performance objective (soil moisture at depths between 0–80 cm) for US Army and civilian use, and to identify and mitigate algorithm impediments to its potential performance. This work will also enable the Army to more accurately determine the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Soil Moisture Environmental Data Record (EDR) impacts upon DoD-related trafficability, off-road mobility, counter-mine operations, and hydrological stream flow estimation. Interactions and community involvement with a variety of agencies that will use the NPOESS surface and deep soil moisture products are also underway. A temporal variational data assimilation methodology is used to derive deep soil moisture profile sensitivities and tendencies for use with future NPOESS Microwave Imager Sounder (MIS) data. We have successfully completed our individual system component tests. Our current focus is full system integration within targeted DoD operational architectures. The components are being integrated into the development version of the Air Force Weather Agency (AFWA) – Land Information System (LIS). Design details of the various system components will be discussed. The land surface model and its respective adjoint sensitivities are used in a 4D variational (4DVAR) solver. We have adopted the Fletcher non-Gaussian 4DVAR framework, as soil moisture variables have skewed data distributions, and are therefore non-Gaussian. The 4DVAR solver component tests are based on lognormal probability distributions.

Observing Weather from Space

Abstract: On 1 April 1960, the world's first weather satellite, the Television Infrared Observation Satellite 1 (TIROS 1), was launched from Cape Canaveral, Florida, into a 99-min orbit at an altitude of about 725 km. The cylindrical (1.1-m diameter, 0.48-m tall), 120-kg spacecraft was spin-stabilized, rotating between 8 and 12 times per min. It carried two television cameras that pointed parallel to the spin axis and could take 32 pictures per orbit ( 1 ). Although the results were modest by today's standards (see the figure), TIROS 1 revolutionized the field of meteorology.