Showing papers in "Journal of Applied Meteorology and Climatology in 1985"
TL;DR: In this article, the authors present a preprocessor for air pollution modeling based on the state of the planetary boundary layer (PCL) and a more accurate description of diffusion, which is intended for application in generally level but not necessarily homogeneous terrain.
Abstract: This paper gives the outline of a “meteorological preprocessor” for air pollution modeling. It is shown how significantly more information can be extracted from routinely available measurements than the traditional Pasquil stability classes and power law wind speed profiles. Also it is shown how additional special measurements—if available—can be accommodated. The methods are primarily intended for application in generally level, but not necessarily homogeneous terrain. The improved characterization of the state of the planetary boundary layer allows a more modern and probably more accurate description of diffusion. The paper is an extended version of an introductory paper presented during the “Workshop on Updating Applied Diffusion Models” Clearwater, Florida, January 1984.
397 citations
TL;DR: In this article, a technique for extracting cloud cover parameters from multispectral satellite radiometric measurements is described, where three channels from the Advanced Very High Resolution Radiometer (AVHRR) on NOAA polar orbiting satellites are used to retrieve four parameters for each pixel: cloud fraction within the FOV, optical thickness, cloud-top temperature and a microphysical model parameter.
Abstract: A technique is described for extracting cloud cover parameters from multispectral satellite radiometric measurements. Utilizing three channels from the AVHRR (Advanced Very High Resolution Radiometer) on NOAA polar orbiting satellites, it is shown that one can retrieve four parameters for each pixel: cloud fraction within the FOV, optical thickness, cloud-top temperature and a microphysical model parameter. The last parameter is an index representing the properties of the cloud particle and is determined primarily by the radiance at 3.7 microns. The other three parameters are extracted from the visible and 11 micron infrared radiances, utilizing the information contained in the two-dimensional scatter plot of the measured radiances. The solution is essentially one in which the distributions of optical thickness and cloud-top temperature are maximally clustered for each region, with cloud fraction for each pixel adjusted to achieve maximal clustering.
254 citations
TL;DR: In this paper, a downward-looking lidar system over the Atlantic Ocean during a cold air outbreak was used to observe a convective planetary boundary layer (PBL) with high vertical and horizontal resolution.
Abstract: Observations of a convective planetary boundary layer (PBL) were made with an airborne, downward-looking lidar system over the Atlantic Ocean during a cold air outbreak. The lidar data revealed well-organized, regularly spaced cellular convection with dominant spacial scales between two and four times the height of the boundary layer. It is demonstrated that the lidar can accurately measure the structure of the PBL with high vertical and horizontal resolution. Parameters important for PBL modeling such as entrainment zone thickness, entrainment rate, PBL height and relative heat flux can be inferred from the lidar data. It is suggested that wind shear at the PBL top may influence both entrainment and convective cell size.
230 citations
TL;DR: In this paper, a range of eigenvectorial methods are applied to 1949-80 data for a regularly spaced network of 402 stations that extends from the Rocky to the Appalachian Mountains and from the Gulf Coast to the Canadian border.
Abstract: This paper presents the results of climatic pattern analyses of three- and seven-day summer (May–August) rainfall totals for the central United States. A range of eigenvectorial methods is applied to 1949–80 data for a regularly spaced network of 402 stations that extends from the Rocky to the Appalachian Mountains and from the Gulf Coast to the Canadian border. The major objectives are to quantitatively assess the sensitivity of eigenvectorial results to several parameters that have hitherto been the subject of considerable qualitative concern, and to identify the potential applications of those results. The entire domain variance fractions cumulatively explained by a) the first 10 correlation-based unrotated Principal Components (PCs) and b) the 10 orthogonally rotated (VARIMAX criterion) PCs derived from them are identical for the same data. They vary between 35–47 percent depending on the data time scale and form, being higher for seven- than three-day totals and further enhanced when those t...
211 citations
TL;DR: In this article, the authors measured the surface albedo of snow-covered land in the middle and high latitudes of the Northern Hemisphere from satellite imagery in A 1×1° latitude-longitude cells.
Abstract: Areally weighted clear sky surface albedo of snow-covered land in the middle and high latitudes of the Northern Hemisphere was measured from satellite imagery in A 1×1° latitude-longitude cells. The study area included 87% of the land polewards of 25°N, where Dickson and Posey found the probability of the seasonal occurrence of snow cover over −2.5 cm deep to be greater than zero. Albedo is 0.60 in Eurasia and 0.56 in North America, approximately 3.5 times greater than snow-free conditions. The highest average value for a 5° latitudinal zone is 0.77 at 70–75°N. The lowest is 0.43 at 60–75°N, which includes 0.36 in Eurasia and 0.58 in North America. The low albedo is due to the masking of snow covered ground by the canopy of coniferous forests. Data were obtained by image processor analyses of Defense Meteorological Satellite Program imagery. Scene brightness was converted to surface albedo by linear interpolation between bright and dark snow-covered surfaces with known albedo. The resulting chart...
182 citations
TL;DR: In this article, a model for computing global solar radiation at the surface was formulated for use with satellite observations, and a compromise in the approach was necessary, whereby the model accuracy and the inherent limitations of satellite observations were made compatible.
Abstract: A model for computing global solar radiation at the surface was formulated for use with satellite observations. A compromise in the approach was necessary, whereby the model accuracy and the inherent limitations of satellite observations were made compatible. A three-layer model atmosphere was used. The part of the solar spectrum from 0.3 to 0.7 μm was split into four equally spaced spectral intervals; the region from 0.7 to 4 μm was divided into eight nonspectral intervals. Use was made of the Delta–Eddington approximation, and parameterization was applied to the optical properties of Rayleigh scattering, water vapor absorption, aerosol absorption and scattering, and cloud absorption and scattering. Ozone absorption was also accounted for. The primary driving input of the model is the cloud optical depth, which can be inferred either from satellite observations (Experiment A) or from surface cloud observations (Experiment B). In Experiment A, the model was run for the months of May–August 1982 t...
141 citations
TL;DR: In this paper, a simple model is presented that, in a cloud-free atmosphere, calculates solar spectral direct and diffuse irradiance and directional radiance at the surface, spectral absorption within the atmosphere and the upward reflected spectral irradiance or directional radiances at the top of the atmosphere.
Abstract: A simple model is presented that, in a cloud-free atmosphere, calculates solar spectral direct and diffuse irradiance and directional radiance at the surface, spectral absorption within the atmosphere and the upward reflected spectral irradiance or directional radiance at the top of the atmosphere. The irradiance model, based on similar approaches by Brine and Iqbal and others, evaluates the spectral irradiances between 0.29 and 4.0 μm, with a resolution that varies from 0.005 to 0.1 μm. Absorption by water vapor, ozone and the uniformly mixed gases is included, as are both scattering and absorption by atmospheric aerosols, which are modeled with simple wavelength-dependent optical depth, single scattering albedo and asymmetry parameter functions. Comparisons are presented of the model results with spectral irradiance and radiance computed by other more sophisticated models and with measurements from both ground-based and satellite instruments. The reasonable accuracy and simplicity of the model ...
140 citations
139 citations
TL;DR: In this article, Lagrangian statistical Monte Carlo simulations of mean and fluctuating concentration fields due to turbulent dispersion are reviewed and an attempt is made to justify some of these by appeal to special and limiting cases.
Abstract: Lagrangian statistical (Monte Carlo) simulations of the mean and fluctuating concentration fields due to turbulent dispersion are critically reviewed. Attention has been restricted to work in which particle trajectories are modeled directly, which in effect means simulations based on the Langevin equation (or in finite difference form, Markov-chains) and its generalization. The material covered has been selected and presented so as to achieve an orderly progression from simple to more complex turbulent flows. At present this field involves many heuristic modeling assumptions and an attempt is made to justify some of these by appeal to special and limiting cases.
135 citations
TL;DR: In this paper, the authors used ground-based observations from land stations and from ships in the ocean to investigate the frequency of observation and the co-occurrence of different cloud types, and the geographical and seasonal variations of these cooccurrences.
Abstract: Cloud observations from land stations and from ships in the ocean are used to investigate the frequency of observation and the co-occurrence of different cloud types, and the geographical and seasonal variations of these co-occurrences. Ground-based observations are used because they provide a more definitive identification of clouds by type than do satellite observations. The clouds are grouped into six types (cirrus + cirrostratus + cirrocumulus, altostratus + altocumulus, stratus + stratocumulus, nimbostratus, cumulus, and cumulonimbus). The results are expressed as frequency of occurrence of different cloud types and as contingency probabilities; that is, given that one cloud type is present, the probability that another particular type is also present is computed. Several sources of bias are identified, and their effects on the results are estimated. It is found that, on the average at all latitudes and in all seasons, clear skies occur more frequently, by a factor of about 4, over land than...
132 citations
TL;DR: In this paper, the effect of volcanic eruptions on surface temperature was examined using temperature records extending back to 1781, with a cooling most evident following the Asama and Laki eruptions in Japan and Iceland.
Abstract: Examined is the effect on surface temperature of the volcanic eruptions of Asama and Laki in 1783, Tambora in 1815, Coseguina in 1835, Krakatoa in 1883, Santa Maria, Soufriere and Pelee in 1902, and Agung in 1963, using temperature records extending back to 1781. These records include New Haven, Connecticut, in North America; Edinburgh, De Bilt, Copenhagen, Berlin and Vilnius in Northern Europe; Geneva, Basel, Hohen-peissenberg, Vienna and Budapest in Central Europe; the “Central England” data of Manley; and the merged Northern Hemisphere data of Groveman and Landsberg and Jones et al. At New Haven and in Europe there is more evidence of a cooling following eruptions in subtropical and temperate latitudes than in equatorial latitudes (despite the similarity in mean dust-veil index), with a cooling most evident following the Asama and Laki eruptions in Japan and Iceland, and next most evident following the Coseguina eruption in Nicaragua. Following the tremendous Tambora eruption, the eruption wit...
TL;DR: In this article, the atmospheric circulation changes associated with the warming of the 1920s are examined using the historical surface weather maps, surface zonal and meridional wind components and station air temperature data.
Abstract: A sharp increase in the Arctic mean winter temperature occurred around 1920. The occurrence of consistently positive temperature anomalies at Spitsbergen (starting in 1919), Iceland (1921) and Greenland (1926) subjoined the more gradual warming trend over northern Europe which had been in progress since the mid-1890s. The atmospheric circulation changes associated with the warming of the 1920s are examined using the historical surface weather maps, surface zonal and meridional wind components and station air temperature data. From 1900 to 1925, when European winters were gradually becoming milder, winters in Greenland were generally colder than the 1851–1960 normal. The mean Icelandic Low reached maximum intensity and a northernmost position at about 65°N latitude throughout the period. After 1925, the Low shifted closer to the southern tip of Greenland; this was accompanied by a slight weakening of the westerlies and an increase in meridional flow (southerly) over Greenland and Baffin Bay. In no...
TL;DR: In this article, the influence of changes in the land-surface fluxes over the Indian subcontinent, on the monsoon circulation and rainfall is presented, and a comparison of ensemble means of the data is provided; a decrease in rainfall is observed when the surface albedo is increased and the surface roughness reduced.
Abstract: Integrations made with general circulation models to investigate the influence of changes in the land-surface fluxes, over the Indian subcontinent, on the monsoon circulation and rainfall are presented. The experiments conducted include: (1) a control, (2) increased land-surface albedo, (3) increased land-surface albedo and reduced land-surface roughness, and (4) increased land-surface albedo, reduced surface roughness, and no evapotranspiration. A comparison of ensemble means of the data is provided; a decrease in rainfall is observed when the surface albedo is increased and the surface roughness reduced. Low surface roughness makes the horizontal transport of planetary boundary layer (PBL) westerly, reducing cross-isobaric moisture and thereby rainfall. Evapotranspiration had no influence on rainfall because of the PBL motion and moisture convergence. The correlation between surface albedo, surface roughness and vegetation is examined.
TL;DR: A brief review of data bases which have been used for developing diffusion parameterizations for the convective boundary layer (CBL) is made in this article. But this review is limited to a limited amount of buoyant plume data, and a radically different approach is needed when the dimensionless buoyancy flux exceeds 0.1.
Abstract: A brief review is made of data bases which have been used for developing diffusion parameterizations for the convective boundary layer (CBL). A variety of parameterizations for lateral and vertical dispersion, σy and σz, are surveyed; some of these include mechanical turbulence, source height, or buoyancy effects. Recommendations are made for choosing among these alternatives, depending on the type of source. Because observations of passive plumes indicate that the Gaussian model does a poor job of describing vertical diffusion in the CBL, alternative models for predicting dimensionless crosswind integrated ground concentration, Cy, are reviewed and compared. These include an analytical equation which closely approximates laboratory results; this equation can be applied to any source height > 0.04zi, where zi is the mixing depth. An analysis of a limited amount of buoyant plume data indicates that a radically different approach is needed when the dimensionless buoyancy flux, F*, exceeds 0.1. Such...
TL;DR: Starting times of thunderstorms for 450 stations in the conterminuos United States for a 25-year period were analyzed using harmonic analysis techniques as mentioned in this paper, which indicated that the country can be divided into nine thunderstorm regions.
Abstract: Starting times of thunderstorms for 450 stations in the conterminuos United States for a 25-year period were analyzed using harmonic analysis techniques. Diurnal variations were expressed as both the time of maximum storm occurrence and the concentration of activity around this time. Distinct seasonal and spatial variations in diurnal activity occur. Analysis of these variations indicates that the country can be divided into nine thunderstorm regions. In the central states the majority of storms occur at night, but storms are frequent at any time. In both the east and the west there is a marked concentration of storms in the afternoon. In the west and northeast winter storms are rare, while along the Pacific Coast summer thunder is uncommon.
TL;DR: In this paper, the authors documented the variation of the lifting condensation level (LCL) of surface layer air based on data from the BLX83 field experiment in Oklahoma.
Abstract: Variations of the lifting condensation level (LCL) of surface layer air are documented based on data from the BLX83 field experiment in Oklahoma. For example, within a 25 km long region near Chickasha, the local LCL height was found to vary by 15–30% of its average height. This zone of variation, centered on the mean LCL height, is identified as the “LCL zone”. It is analogous to the entrainment zone for the local mixed layer depth. Cumulus clouds first form when the top of the entrainment zone reaches the bottom of the LCL zone. As more of the entrainment zone overlaps and reaches above the LCL zone, the cloud cover increases. Two case studies are presented to demonstrate the diagnosis of cumulus onset time and cloud cover amount using this overlap technique. Combined radar, aircraft, rawinsonde, and surface observations indicate that some of the air observed at cloud base has the same low LCL as that of the mean surface layer air. This leads us to speculate that some surface layer air is rising...
TL;DR: The analysis of air temperature data for a period of 22 years in the meteorological network stations in the greater Athens area shows clearly the effect of the urban heat island due to the city as mentioned in this paper.
Abstract: The analysis of air temperature data for a period of 22 years in the meteorological network stations in the greater Athens area shows clearly the effect of the urban heat island due to the city. This effect appears with different intensity according to the season and to minimum and maximum temperatures. In particular, the analysis of the data pointed out the variations caused by natural processes and anthropogenic activities. The influence of the growth of the city on the mean minimum temperature is evident.
TL;DR: In this article, an infrared radiative transfer model was used to derive cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths.
Abstract: Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes. The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.
TL;DR: In this article, an algorithm was developed for using the reflection of solar radiation in the oxygen A-band to determine cloud-top altitude, which was applied to an aircraft field experiment in conjunction with CCOPE.
Abstract: An algorithm has been developed for using the reflection of solar radiation in the oxygen A-band to determine cloud-top altitude. Because of multiple scattering and molecular absorption inside the cloud, the reflection of clouds is substantially modified in comparison with a mirror cloud, which is assumed to have a 100 percent reflection. To infer true cloud-top altitude, therefore, it is necessary to accurately estimate the amount of 'photon penetration'. Theoretical calculations indicate that the amount of photon penetration depends on the altitude, the scaled volume scattering coefficient, and the scaled optical thickness of the cloud. Algorithms using the reflection in the oxygen A-band to determine the cloud-top pressure have been applied to an aircraft field experiment in conjunction with CCOPE, 1981. Results of this study are very encouraging, especially for extended clouds.
TL;DR: In this article, the authors defined a systematic modes of spatial and temporal variation in a 48-year record of streamflow using principal components, calculated from a matrix of annual streamflow departures for 106 grid cells covering the United States in the years 1931-78.
Abstract: Systematic modes of spatial and temporal variation in a 48-year record of streamflow are defined using principal components. The components were calculated from a matrix of annual streamflow departures for 106 grid cells covering the United States in the years 1931–78. Five statistically significant components are found to account for more than 56% of the total variance. A varimax orthogonal rotation of the original components describes regional anomaly cores located in the middle Mississippi Valley, Pacific Northwest, Far West, Northeast, and northern Great Plains. Each of these patterns is an enhancement of a less well defined spatial form apparent in the unrotated solution. Temporal variations in the scores of all five components closely agree with contemporaneous national and regional departure patterns in several climatic variables.
TL;DR: In this paper, the teleconnection patterns known from the instrumental record to be associated with the Southern Oscillation also appear to be present in both dependent and independent tree-ring reconstructions of climate during the 19th and 20th centuries.
Abstract: Variations of the Southern Oscillation (SO) significantly influence surface climate over a large part of the globe. In the first part of this study we show that teleconnection patterns known from the instrumental record to be associated with the SO also appear to be present in both dependent and independent tree-ring reconstructions of climate during the 19th and 20th centuries. Reconstructions of surface temperature and precipitation appear to be more closely related to the SO than those of pressure. Since these dendroclimatic reconstructions appear to be responsive to climate anomalies related to the SO, it should be possible to reconstruct past values of the SO directly from tree-ring width variations. Thus, we attempted to reconstruct an index of the SO back to 1600 A.D. using tree-ring chronologies from both western North America and the Southern Hemisphere. The best estimates were derived from the western North American chronologies alone. These estimates calibrate about 50 percent of the S...
TL;DR: In this article, a scanning multichannel microwave radiometer measured brightness temperatures of the earth-atmosphere system at 6.6, 10.7, 18, 21, and 37 GHz, and from these data water vapor content was derived.
Abstract: Atmospheric water vapor content over the global oceans is measured to study the air-sea interactions associated with El Nino/Southern Oscillation. A scanning multichannel microwave radiometer measured brightness temperatures of the earth-atmosphere system at 6.6, 10.7, 18, 21, and 37 GHz, and from these data water vapor content is derived. The seasonal mean distribution of water vapor for the regular season cycle from 1979-1981 are examined; the minima associated with the subtropical anticyclones in the Pacific and Atlantic Oceans in the Northern and Southern hemispheres, and the Walker circulation in the tropical Pacific Ocean are analyzed. The positive and negative anomalies in water vapor during the 1982-1983 El Nino event, which correspond to convergence and enhanced convective activity, are investigated. It is concluded that during El Nino events a system of convection and subsidence exists; the subsidence slows the supply of water vapor and cloud growth in the convectively active center and the Walker circulation is reversed.
TL;DR: In this article, a band model of atmospheric transmission is used to investigate some of the multichannel sea surface temperature (MCSST) algorithms that are currently in use, and the model results also show that in most cases it is necessary to take account of the satellite view angle.
Abstract: A band model of atmospheric transmission is used to investigate some of the multichannel sea surface temperature (MCSST) algorithms that are currently in use. The model is used with a set of atmospheric data to derive algorithms for the AVHRR and VAS radiometers that are on the operational NOAA and GOES satellites respectively. For the AVHRR instrument good agreement is found between the model algorithms and those derived in a recent study by McClain. The model results also show that in most cases it is necessary to take account of the satellite view angle. Poorer agreement is found between the theoretical (model) algorithms for the VAS split-window channels and those obtained by regression analyses of satellite data against a multitude of buoy measurements. Intensive ground-truth data are used to evaluate the algorithms. A comparison between measured deficits (sea surface temperatures minus satellite brightness temperatures) and model deficits suggests that the water vapor absorption coefficient...
TL;DR: In this paper, a histogram of the pixel radiance counts from the METEOSAT IR window channel, for regions of dimensions 250 to 1000 km, was constructed and the evolution with time was studied.
Abstract: For any given area, diurnal variation of the emitted longwave radiation reveals the response of the surface and atmosphere to the astronomical diurnal forcing. However, the diurnal rhythm can be masked locally by changes in cloud cover linked to passage of weather systems. To eliminate this weather “noise” we construct histograms of the pixel radiance counts from the METEOSAT IR window channel, for regions of dimensions 250 to 1000 km, and we study their evolution with time. We find that considerable information on the diurnal variation, both of surface temperature and of cloud cover at all levels, can be obtained from short sequences (3 days) of hourly METEOSAT data. In West Africa, diurnal variation of clear-sky emergent radiances, corresponding to amplitudes of 30–50 K in surface skin temperature, is found not only in the Saharan desert regions but also during the dry season in the Sahel–Sudan–Guinea zone. In the August wet season, in this last area, the amplitude is lower, while diurnally var...
TL;DR: Using satellite and weather radar data, a simple clustering analysis has been used in order to differentiate between rain and non-raining clouds as mentioned in this paper, resulting in an average probability of detection of about 66% and an average false alarm ratio of about 37%.
Abstract: Using satellite and weather radar data, a simple clustering analysis has been used in order to differentiate between raining and nonraining clouds. Based on these results, a scheme is proposed for instantaneous rain area delineation in the midlatitudes. Delineation of the rain areas will not require coextensive radar data which are only used to develop and evaluate the method. Warm season data during daylight hours were used to test the scheme. Results indicate that the proposed scheme has very good skills in delineating rain areas in the midlatitudes, resulting in an average probability of detection of about 66% and an average false alarm ratio of about 37%.
TL;DR: In this paper, exploratory data analysis is used to examine several characteristics of more than 31 years of primitive precipitation events based on hourly precipitation data at Salem, Oregon, and it is demonstrated that the marginal (i.e., unconditional) distributions of the characteristics are positively skewed.
Abstract: The use of a concept called a precipitation “event” to obtain information regarding certain statistical properties of precipitation time series at a particular location and for a specific application (e.g., for modeling erosion) is described. Exploratory data analysis is used to examine several characteristics of more than 31 years of primitive precipitation events based on hourly precipitation data at Salem, Oregon. A primitive precipitation event is defined as one or more consecutive hours with at least 0.01 inches (0.25 mm) of precipitation. The characteristics of the events that are considered include the duration, magnitude, average intensity and maximum intensity of the event and the number of hours separating consecutive events. By means of exploratory analysis of the characteristics of the precipitation events, it is demonstrated that the marginal (i.e., unconditional) distributions of the characteristics are positively skewed. Examination of the conditional distributions of some pairs of...
TL;DR: In this paper, a dry two-dimensional version of the Colorado State Cloud/Mesoscale Model was used to study the morning, inversion destruction cycle in a variety of deep mountain valley configurations.
Abstract: A dry two-dimensional version of the Colorado State Cloud/Mesoscale Model was used to study the morning, inversion destruction cycle in a variety of deep mountain valley configurations. Eleven simulations were run to examine the effects of valley width, surface heating rate, wind shear above the valley, valley orientation, sidewall slope, initial stability and variable surface albedo on the evolution of the daytime boundary layer in the valley. Each was initiated with a stable layer filling the valley to ridgetop with a neutral layer above the ridge. The model was driven at the lower surface by a sinusoidally varying potential temperature flux which approximates the diurnal heating cycle. All simulations show that the initial inversion layer is destroyed by a combination of three processes; a growing surface based neutral layer over the valley floor, the destabilization of the stable air mass by the recirculation of air warmed over the slopes and the descent of the inversion top by the transport ...
TL;DR: In this paper, an alternative measure of time-aggregated precipitation for use in short-term climate studies is developed, which is defined as the number of days per month or season with total amounts ≥ 2.54 mm (0.10 inch).
Abstract: An alternative measure of time-aggregated precipitation for use in short-term climate studies is developed. This measure, precipitation frequency, is defined as the number of days per month or season with total amounts ≥ 2.54 mm (0.10 inch). Newly created data sets for the period 1951–80 are used as a basis for describing large-scale spatial and temporal features of precipitation frequency for the mainland United States. Comparisons between precipitation frequency and the conventional statistic, total precipitation, indicate that frequency is more normally distributed and more spatially coherent than total precipitation. Factor analysis and an orthogonal rotation to the varimax criterion are used to identify synoptic-scale, spatially coherent regions of precipitation frequency. The regions are generally consistent with previously documented cyclone trajectories.
TL;DR: In this article, a unique method that provides for relating radar-measured reflectivity factors to snowfall rates at the ground is presented, and a best-fit power-law relationship between hourly-averaged snowfall rate (depth) and radar reflectivity factor is determined.
Abstract: A unique method that provides for relating radar-measured reflectivity factors to snowfall rates at the ground is presented. Data were provided by a CPS-9, 3.2 cm radar from six 1978 Massachusetts snowstorms A best-fit power-law relationship between hourly-averaged snowfall rate (depth) and radar reflectivity factor is determined. This derived relationship is found to be Z = 5.07S1.65 with a correlation coefficient of 0.91. With this relationship hourly snowfall rates are found to be accurate to within +41 to −29% and total storm snowfall accumulation to within +44 to −31%.
TL;DR: The standard eigenvalue estimator is nonnormally distributed and biased: the largest one becomes overestimated, the smallest one underestimated as discussed by the authors, and the variance of the eigen value estimate is large.
Abstract: Statistical properties of estimated nonisotropic principal vectors [empirical orthogonal functions (EOFs)] are reviewed and discussed. The standard eigenvalue estimator is nonnormally distributed and biased: the largest one becomes overestimated, the smallest ones underestimated. Generally, the variance of the eigenvalue estimate is large. The standard eigenvalue estimator may be used to define an unbiased estimator, which, however, exhibits an increased variance. If a fixed set of EOFs is used, the FOF coefficients are not stochastically independent. The variances of the low-indexed coefficients become considerably overestimated by the respective estimated eigenvalues, those of the high-indexed coefficients underestimated. If the ratio of degrees of freedom to sample size is one-half or even less, these disadvantages are still current as is demonstrated by an example.