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Analysis of Ice-to-Liquid Ratios during Freezing Rain and the Development of an Ice Accumulation Model

WEATHER AND FORECASTING 2016年第4期31卷 1041-1060页

作者： Sanders, Kristopher J. Barjenbruch, Brian L. NOAA Natl Weather Serv 1116 NE Strait Ave Topeka KS 66616 USA

Substantial freezing rain or drizzle occurs in about 24% of winter weather events in the continental United States. Proper preparation for these freezing rain events requires accurate forecasts of ice accumulation on various surfaces. The Automated Surface Observing System (ASOS) has become the primary surface weather observation system in the United States, and more than 650 ASOS sites have implemented an icing sensor as of March 2015. ASOS observations that included ice accumulation were examined from January 2013 through February 2015. The data chosen for this study consist of 60-min periods of continuous freezing rain with precipitation rates >= 0.5 mm h(-1) (0.02 in. h(-1)) and greater than a trace of ice accumulation, yielding a dataset of 1255 h of observations. Ice:liquid. ratios (ILRs) were calculated for each 60-min period and analyzed with 60-min mean values of temperature, wet-bulb temperature, wind speed, and precipitation rate. The median ILR for elevated horizontal (radial) ice accumulation was 0.72:1 (0.28:1), with a 25th percentile of 0.50:1 (0.20:1) and a 75th percentile of 1.0:1 (0.40:1). Strong relationships were identified between ILR and precipitation rate, wind speed, and wet-bulb temperature. The results were used to develop a multivariable Freezing Rain Accumulation Model (FRAM) for use in predicting ice accumulation incorporating these commonly forecast variables as input. FRAM performed significantly better than other commonly used forecast methods when tested on 20 randomly chosen icing events, with a mean absolute error (MAE) of 1.17 mm (0.046 in.), and a bias of -0.03 mm (-0.001 in.).

关键词： Physical Meteorology and Climatology Freezing precipitation Icing observational techniques and algorithms Automatic weather stations Mathematical and statistical techniques Numerical analysis/modeling Forecasting Forecasting Forecasting techniques

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Algorithm for Determining the Statistical Properties of Cloud Particles through In Situ Ensemble Measurements

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第9期33卷 1985-2000页

作者： Hayman, Matthew Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA

An algorithm is described for inverting individual particle properties from statistics of ensemble observations, thereby dispelling the notion that coincident particles create inherently erroneous data in particle probes. The algorithm assumes that the observed property obeys superposition, that the particles are independently randomly distributed in space, and that the particle distribution is stationary over the accumulation distance. The fundamental principle of the algorithm is based on a derived analytical relationship between ensemble and individual particle statistics with fully defined derivatives. This enables rapid convergence of forward inversions. Furthermore, this relationship has no dependence on the particular instrument realization, so the accuracy of the relationship is not fundamentally constrained by the accuracy to which a measurement system can be characterized or modeled. This algorithm is presented in terms of a single observed property, but the derivation is valid for correlated multiparameter retrievals. Because data are collected in histograms, this technique would require relatively little storage and network bandwidth on an aircraft data system. This statistical analysis is derived here for measuring particle geometric extinction cross sections, but it could also be applied to other particle properties, such as scattering cross-section and phase matrix elements. In this example application, a simulated beam passes through a sampled environment onto a single detector to periodically measure beam extinction. This measured extinction may be the result of one or more particles, but it is shown that the probability distribution function of the ensemble (multiparticle) extinction measurement can be used to obtain the distribution of individual particle extinction cross sections (used here as a proxy for particle size distribution).

关键词： Aircraft observations algorithms Cloud retrieval In situ atmospheric observations Instrumentation/sensors Mathematical and statistical techniques observational techniques and algorithms Statistical techniques

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Integrated Optimal Fingerprinting: Method Description and Illustration

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JOURNAL OF CLIMATE 2016年第6期29卷 1977-1998页

作者： Hannart, Alexis Inst Francoargentin Etudes Climat & Impacts CNRS Buenos Aires DF Argentina

The present paper introduces and illustrates methodological developments intended for so-called optimal fingerprinting methods, which are of frequent use in detection and attribution studies. These methods used to involve three independent steps: preliminary reduction of the dimension of the data, estimation of the covariance associated to internal climate variability, and, finally, linear regression inference with associated uncertainty assessment. It is argued that such a compartmentalized treatment presents several issues;an integrated method is thus introduced to address them. The suggested approach is based on a single-piece statistical model that represents both linear regression and control runs. The unknown covariance is treated as a nuisance parameter that is eliminated by integration. This allows for the introduction of regularization assumptions. Point estimates and confidence intervals follow from the integrated likelihood. Further, it is shown that preliminary dimension reduction is not required for implementability and that computational issues associated to using the raw, high-dimensional, spatiotemporal data can be resolved quite easily. Results on simulated data show improved performance compared to existing methods w.r.t. both estimation error and accuracy of confidence intervals and also highlight the need for further improvements regarding the latter. The method is illustrated on twentieth-century precipitation and surface temperature, suggesting a potentially high informational benefit of using the raw, nondimension-reduced data in detection and attribution (D&A), provided model error is appropriately built into the inference.

关键词： observational techniques and algorithms Climate records Mathematical and statistical techniques Pattern detection Regression analysis Models and modeling Climate models

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Assessing Surface Solar Radiation Fluxes in the CMIP Ensembles

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JOURNAL OF CLIMATE 2016年第20期29卷 7231-7246页

作者： Loew, Alexander Andersson, Axel Trentmann, Joerg Schroeder, Marc Univ Munich Luisenstr 37 D-80333 Munich Germany Max Planck Inst Meteorol Hamburg Germany Deutsch Wetterdienst Offenbach Germany Deutsch Wetterdienst Satellite Based Climate Monitoring Offenbach Germany

Earth system models are indispensable tools in climate studies. The Coupled Model Intercomparison Project (CMIP) is a coordinated effort of the Earth system modeling community to intercompare existing models. An accurate simulation of surface solar radiation fluxes is of major importance for the accuracy of simulations of the near-surface climate in Earth system models. The present study provides a quantitative assessment of the accuracy and multidecadal changes of surface solar radiation fluxes for model results from two phases of CMIP. The entire archives of phase 5 of CMIP (CMIP5) and its predecessor phase 3 (CMIP3) are analyzed for present-day climate conditions. A relative model ranking is provided, and its uncertainty is quantified using different global observational records. It is shown that the choice of an observational dataset can have a major influence on relative model ranking between CMIP models. However the multidecadal variability of surface solar radiation fluxes, also known as global "dimming" or "brightening," is largely underestimated by the CMIP models.

关键词： Physical Meteorology and Climatology Radiation budgets Shortwave radiation observational techniques and algorithms Climate records Remote sensing Satellite observations Models and modeling Climate models

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Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第4期46卷 1285-1307页

作者： Thompson, Andrew F. Lazar, Ayah Buckingham, Christian Garabato, Alberto C. Naveira Damerell, Gillian M. Heywood, Karen J. CALTECH Environm Sci & Engn MC 131-24 Pasadena CA 91125 USA Univ Southampton Natl Oceanog Ctr Southampton Hants England Univ E Anglia Sch Environm Sci Norwich NR4 7TJ Norfolk England

The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km(2) region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (~20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September-November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December-March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the open-ocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

关键词： Boundary layer Geographic location/entity Profilers, oceanic Atm/Ocean Structure/ Phenomena Seasonal variability Instability Variability Turbulence North Atlantic Ocean Circulation/ Dynamics observational techniques and algorithms

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Improvements in Land-Use Classification for Estimating Daytime Surface Temperatures and Sea-Breeze Flows in Southern California

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EARTH INTERACTIONS 2016年第16期20卷 1-32页

作者： Sequera, Pedro Gonzalez, Jorge E. McDonald, Kyle LaDochy, Steve Comarazamy, Daniel CUNY City Coll Dept Mech Engn 140th St & Convent AveSteinman HallRoom T-238 New York NY 10031 USA CUNY City Coll Dept Earth & Atmospher Sci New York NY 10031 USA Calif State Univ Los Angeles Dept Geosci & Environm Los Angeles CA 90032 USA CUNY City Coll NOAA CREST Ctr New York NY 10031 USA

Understanding the interactions between large-scale atmospheric and oceanic circulation patterns and changes in land cover and land use (LCLU) due to urbanization is a relevant subject in many coastal climates. Recent studies by Lebassi et al. found that the average maximum air temperatures during the summer in two populated California coastal areas decreased at low-elevation areas open to marine air penetration during the period of 1970-2005. This coastal cooling was attributed to an increase in sea-breeze activity. The aims of this work are to better understand the coastal flow patterns and sea-land thermal gradient by improving the land-cover classification scheme in the region using updated airborne remote sensing data and to assess the suitability of the updated regional atmospheric modeling system for representing maritime flows in this region. This study uses high-resolution airborne data from the NASA Hyperspectral Infrared Imager (HyspIRI) mission preparatory flight campaign over Southern California and surface ground stations to compare observations against model estimations. Five new urban land classes were created using broadband albedo derived from the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) sensor and then assimilated into the Weather Research and Forecasting (WRF) Model. The updated model captures the diurnal spatial and temporal sea-breeze patterns in the region. Results show notable improvements of simulated daytime surface temperature and coastal winds using the HyspIRI-derived products in the model against the default land classification, reaffirming the importance of accounting for heterogeneity of urban surface properties.

关键词： Circulation/dynamics Atmosphere-land interaction Atmosphere/ocean structure/phenomena Sea breezes observational techniques and algorithms Remote sensing Mathematical and statistical techniques Classification Models and modeling Mesoscale models Applications Land use

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Uncertainty Characteristics of Total Water Path Retrievals in Shallow Cumulus Derived from Spaceborne Radar/Radiometer Integral Constraints

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第8期33卷 1597-1609页

作者： Lebsock, Matthew D. Suzuki, Kentaroh CALTECH Jet Prop Lab Pasadena CA USA Univ Tokyo Dept Earth & Planetary Sci Tokyo Japan

A precipitating marine cumulus cloud simulation is coupled to radiation propagation models to simulate active and passive microwave observations at 94 GHz. The simulations are used to examine the error characteristics of the total water path retrieved from the integral constraints of the passive microwave brightness temperature or the path-integrated attenuation (PIA) using a spatial interpolation technique. Three sources of bias are considered: 1) the misdetection of cloudy pixels as clear, 2) the systematic differences in the column water vapor between cloudy and clear skies, and 3) the nonuniform beamfilling effects on the observables. The first two sources result in biases on the order of 5-10 g m(-2) of opposite signs that tend to cancel. The third source results in a bias that increases monotonically with the water path that approaches 50%. Nonuniform beamfilling is sensitive to footprint size. Random error results from both instrument measurement precision and the natural variability in the relationship between the water path and the observables. Random errors for the retrievals using the CloudSat PIA are estimated to be the larger of either 20 g m(-2) or 30%. A radar/radiometer system with a measurement precision of 0.3 K or 0.05 dB could reduce this error to the larger of either 10 g m(-2) or 30%. All error mechanisms reported here result from variability in either the spatial structure of the atmosphere or the hydrometeor drop size distribution. The results presented here are specific to the cloud simulation and in general the magnitude will vary globally.

关键词： Cloud retrieval Microwave observations observational techniques and algorithms Radars/Radar observations Remote sensing Satellite observations

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Radiative Impacts of the 2011 Abrupt Drops in Water Vapor and Ozone in the Tropical Tropopause Layer

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JOURNAL OF CLIMATE 2016年第2期29卷 595-612页

作者： Gilford, Daniel M. Solomon, Susan Portmann, Robert W. MIT Dept Earth Atmospher & Planetary Sci 77 Massachusetts Ave Cambridge MA 02139 USA NOAA Earth Syst Res Lab Div Chem Sci Boulder CO USA

An abrupt drop in tropical tropopause layer (TTL) water vapor, similar to that observed in 2000, recently occurred in 2011, and was concurrent with reductions in TTL temperature and ozone. Previous studies have indicated that such large water vapor variability can have significant radiative impacts. This study uses Aura Microwave Limb Sounder observations, the Stratospheric Water Vapor and Ozone Satellite Homogenized dataset, and two radiative transfer models to examine the radiative effects of the observed changes in TTL water vapor and ozone on TTL temperatures and global radiative forcing (RF). The analyses herein suggest that quasi-isentropic poleward propagation of TTL water vapor reductions results in a zonal-mean structure with wings of extratropical water vapor reductions, which account for about half of the 2011 abrupt drop global radiative impact. RF values associated with the mean water vapor concentrations differences between 2012/13 and 2010/11 are between -0.01 and -0.09 W m(-2), depending upon the altitude above which perturbations are considered. TTL water vapor and ozone variability during this period jointly lead to a transient radiative cooling of similar to 0.25-0.5 K in layers below the tropopause. The 2011 abrupt drop also prolonged the reduction in stratospheric water vapor that followed the 2000 abrupt drop, providing a longer-term radiative forcing of climate. Water vapor concentrations from 2005 to 2013 are lower than those from 1990 to 1999, resulting in a RF between these periods of about -0.045 W m(-2), approximately 12% as large as, but of opposite sign to, the concurrent estimated CO2 forcing.

关键词： Circulation Dynamics Stratospheric circulation Atm Ocean Structure Phenomena Tropopause Physical Meteorology and Climatology Ozone Radiative forcing Water vapor observational techniques and algorithms Satellite observations

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Spatial and Temporal Patterns of Cloud Cover and Fog Inundation in Coastal California: Ecological Implications

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EARTH INTERACTIONS 2016年第15期20卷 1-19页

作者： Rastogi, Bharat Williams, A. Park Fischer, Douglas T. Iacobellis, Sam F. McEachern, Kathryn Carvalho, Leila Jones, Charles Baguskas, Sara A. Still, Christopher J. Oregon State Univ Dept Forest Ecosyst & Soc 321 Richardson Hall Corvallis OR 97331 USA Univ Calif Santa Barbara Dept Geog Santa Barbara CA 93106 USA Lamont Doherty Earth Observ Palisades NY USA Columbia Univ Palisades NY USA ARCADIS Strateg Environm Consulting Santa Barbara CA USA Ronin Inst Santa Barbara CA USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA US Geol Survey Western Ecol Res Ctr Channel Islands Field Stn Ventura CA USA Univ Calif Santa Cruz Dept Environm Studies Santa Cruz CA 95064 USA

The presence of low-lying stratocumulus clouds and fog has been known to modify biophysical and ecological properties in coastal California where forests are frequently shaded by low-lying clouds or immersed in fog during otherwise warm and dry summer months. Summer fog and stratus can ameliorate summer drought stress and enhance soil water budgets and often have different spatial and temporal patterns. Here, this study uses remote sensing datasets to characterize the spatial and temporal patterns of cloud cover over California's northern Channel Islands. The authors found marine stratus to be persistent from May to September across the years 2001-12. Stratus clouds were both most frequent and had the greatest spatial extent in July. Clouds typically formed in the evening and dissipated by the following early afternoon. This study presents a novel method to downscale satellite imagery using atmospheric observations and discriminate patterns of fog from those of stratus and help explain patterns of fog deposition previously studied on the islands. The outcomes of this study contribute significantly to the ability to quantify the occurrence of coastal fog at biologically meaningful spatial and temporal scales that can improve the understanding of cloud-ecosystem interactions, species distributions, and coastal ecohydrology.

关键词： Circulation/dynamics Atmosphere-ocean interaction Cloud cover Atmosphere/ocean structure/phenomena Fog Vegetation observational techniques and algorithms Radiosonde observations Remote sensing

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Quantifying the Roles of Changing Albedo, Emissivity, and Energy Partitioning in the Impact of Irrigation on Atmospheric Heat Content

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第8期55卷 1699-1706页

作者： Pryor, S. C. Sullivan, R. C. Wright, T. Cornell Univ Dept Earth & Atmospher Sci Bradfield Hall Ithaca NY 14853 USA Antorcha LLC Logan UT USA

Introduction of irrigated agriculture changes the partitioning of the surface energy flux between sensible and latent heat (H vs LE) and alters the albedo alpha and emissivity epsilon. In the absence of changes in the radiation components of the surface energy balance, the change in the Bowen ratio due to irrigation typically suppresses the local air temperature T but increases the total near-surface atmospheric heat content (as measured using equivalent potential temperature theta(e)). While the effect of irrigation on surface energy partitioning due to enhanced surface and subsurface water availability has long been acknowledged, the roles of associated changes in epsilon and alpha have received less attention, and the scales and magnitudes of these effects remain uncertain. A new methodology designed for application to in situ and remote sensing data is presented and used to demonstrate that the net impact of irrigation on T and theta(e) is strongly dependent on the regional climate, land cover in surrounding areas, and the amount of irrigation in the upwind fetch. The results suggest that the impact of the radiative forcing terms on net available energy is not negligible and may amplify or offset the impact from changed energy partitioning on T and theta(e) depending on the specific regional climate and land cover.

关键词： Geographic location/entity North America Physical Meteorology and Climatology Atmosphere-land interaction Energy budget/balance Fluxes Surface temperature observational techniques and algorithms Remote sensing

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