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[1] The connectivity of runoff sources is considered one of the main factors controlling the hydrology of sparsely vegetated landscapes. However, the empirical demonstration of this role is very limited, partly because of the scarcity of suitable connectivity metrics. In this work, we derived and tested a spatial metric, Flowlength, for quantifying the connectivity of runoff source areas considering both vegetation pattern and topography. Flowlength is calculated as the average of the runoff pathway lengths from all the cells in a raster-based map of the target site. We evaluated the relationships between the connectivity of runoff sources, measured with Flowlength, and the runoff and sediment yields from six plots and three catchments in semiarid southeast Spain. Flowlength distinguished varying degrees of connectivity between differing vegetation patterns with similar vegetation cover. The connectivity increased with the grain size of the bare areas and was positively related to plot runoff and sediment yields. Flowlength also correctly ranked the three catchments according to total runoff yielded during the study period. The inclusion of microtopographic information in the quantification of Flowlength improved the relationships between the pattern of runoff sources and the measured fluxes, highlighting the importance of topographic features in the connectivity of surface flows. In general, the microtopography had a net decreasing effect on the connectivity, which was mainly attributed to an increase in the amount of runoff sink areas caused by the sediment terracettes developed upslope of plants. Our results confirm that the connectivity of runoff sources is a key factor controlling runoff and erosion in semiarid lands and support the potential of Flowlength as a surrogate for the hydrological functioning of ecosystems with patchy vegetation.Citation: Mayor, Á . G., S. Bautista, E. E. Small, M. Dixon, and J. Bellot (2008), Measurement of the connectivity of runoff source areas as determined by vegetation pattern and topography: A tool for assessing potential water and soil losses in drylands, Water Resour. Res., 44, W10423,

High-resolution X-band polarimetric radar data were collected in 19 snowstorms over northern Colorado in early 2013 as part of the Front Range Orographic Storms (FROST) project. In each case, small, vertically erect convective turrets were observed near the echo top. These ''generating cells'' are similar to those reported in the literature and are characterized by ;1-km horizontal and vertical dimensions, vertical velocities of 1-2 m s 21 , and lifetimes of at least 10 min. In some cases, these generating cells are enshrouded by enhanced differential reflectivity Z DR , indicating a ''shroud'' of pristine crystals enveloping the larger, more isotropic particles. The anticorrelation of radar reflectivity factor at horizontal polarization Z H and Z DR suggests ongoing aggregation or riming of particles in the core of generating cells. For cases in which radiosonde data were collected, potential instability was found within the layer in which generating cells were observed. The persistence of these layers suggests that radiative effects are important, perhaps by some combination of cloud-top cooling and release of latent enthalpy through depositional and riming growth of particles within the cloud. The implications for the ubiquity of generating cells and their role as a mechanism for ice crystal initiation and growth are discussed.

This paper describes a winter weather nowcasting system called Weather Support to Deicing Decision Making (WSDDM), designed to provide airline, airport, and air traffic users with winter weather information relevant to their operations. The information is provided on an easy to use graphical display and characterizes airport icing conditions for nonmeteorologists. The system has been developed and refined over a series of winter-long airport demonstrations at Denver's Stapleton International Airport, Chicago's O'Hare International Airport, and New York's LaGuardia Airport. The WSDDM system utilizes commercially available weather information in the form of Next Generation Weather Radar WSR-88D radar reflectivity data depicted as color coded images on a window of the display and Aviation Routine Weather Report (METAR) surface weather reports from Automated Surface Observating System stations and observers. METAR information includes wind speed and direction, air temperature, and precipitation type/rate, which are routinely updated on an hourly basis or more frequently if conditions are changing. Recent studies have shown that the liquid equivalent snowfall rate is the most important factor in determining the holdover time of a deicing fluid. However, the current operational snowfall intensity reported in METARs is based on visibility, which has been shown to give misleading information on liquid equivalent rates in many cases due to the wide variation in density and shape of snow. The particular hazard has been identified as high visibility-high snowfall conditions. The WSDDM system addresses this potentially hazardous condition through the deployment of snow gauges at an airport. These snow gauges report real-time estimates of the liquid equivalent snowfall rate once every minute to WSDDM users. The WSDDM system also provides 30-min nowcasts of liquid equivalent snowfall rate through the use of a real-time calibration of radar reflectivity and snow gauge snowfall rate. This paper discusses the development of the system, including the development of new wind shields for snow gauges to improve catch efficiency, as well as the development of the above mentioned real-time method to convert radar reflectivity to snowfall rate on the ground using snow gauges. In addition, we discuss results from a user evaluation of the system, as well as results from an efficiency and safety benefits study of the system.

Real-time ground-clutter identification and subsequent filtering of clutter-contaminated data is addressed in this two-part paper. Part I focuses on the identification, modeling, and simulation of S-band ground-clutter echo. A new clutter identification parameter, clutter phase alignment (CPA), is presented. CPA is a measure primarily of the phase variability of the in-phase and quadrature-phase time series samples for a given radar resolution volume. CPA is also a function of amplitude variability of the time series. It is shown that CPA is an excellent discriminator of ground clutter versus precipitation echoes. A typically used weather model, time series simulator is shown to inadequately describe experimentally observed CPA. Thus, a new technique for the simulation of ground-clutter echo is developed that better predicts the experimentally observed CPA. Experimental data from the Denver Next Generation Weather Radar (NEXRAD) at the Denver, Colorado, Front Range Airport (KFTG), and NCAR’s S-band dual-polarization Doppler radar (S-Pol) are used to illustrate CPA. In Part II, CPA is used in a fuzzy logic algorithm for improved clutter identification.

R e c e n t a d va n ce s in c o m m u n ity -b a s e d s o ftw a r e d e v e lo p m e n t have d e m o n s tr a te d t h a t o p e n -s o u rc e s o ftw a r e can b e a re a l b e n e fit t o t h e ra d a r c o m m u n ity .ince the emergence of weather radar technology in the 1940s, research has sought to tap the full potential of weather radar observations. During the digital age, improvements in radar technology have been closely linked to advancements in com puter science and software engineering. Making use of modern radars is not possible without software.

The National Center for Atmospheric Research (NCAR) operates a state-of-the-art S-band dual-polarization Doppler radar (S-Pol) for the National Science Foundation (NSF). This radar has some similar and some distinguishing characteristics to the National Weather Service (NWS) operational Weather Surveillance Radar-1988 Doppler Polarimetric (WSR-88DP). One key difference is that the WSR-88DP is used for operational purposes where rapid 360° volumetric scanning is required to monitor rapid changes in storm characteristics for nowcasting and issuing severe storm warnings. Since S-Pol is used to support the NSF research community, it usually scans at much slower rates than operational radars. This results in higher resolution and higher data quality suitable for many research studies. An important difference between S-Pol and the WSR-88DP is S-Pol’s ability to use customized scan strategies including scanning on vertical surfaces ([range–height indicators (RHIs)], which are presently not done by WSR-88DPs. RHIs provide high-resolution microphysical structures of convective storms, which are central to many research studies. Another important difference is that the WSR-88DP simultaneously transmits horizontal (H) and vertical (V) polarized pulses. In contrast, S-Pol typically transmits alternating H and V pulses, which results in not only higher data quality for research but also allows for the cross-polar signal to be measured. The cross-polar signal provides estimates of the linear depolarization ratio (LDR) and the co- to cross-correlation coefficient that give additional microphysical information. This paper presents plots and interpretations of high-quality, high-resolution polarimetric data that demonstrate the value of S-Pol’s polarimetric measurements for atmospheric research.

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