Bird migration flight altitudes studied by a network of operational weather radars

A fully automated method for the detection and quantification of bird migration was developed for operational C-band weather radar, measuring bird density, speed and direction as a function of altitude. These weather radar bird observations have been validated with data from a high-accuracy dedicated bird radar, which was stationed in the measurement volume of weather radar sites in The Netherlands, Belgium and France for a full migration season during autumn 2007 and spring 2008. We show that weather radar can extract near real-time bird density altitude profiles that closely correspond to the density profiles measured by dedicated bird radar. Doppler weather radar can thus be used as a reliable sensor for quantifying bird densities aloft in an operational setting, which—when extended to multiple radars—enables the mapping and continuous monitoring of bird migration flyways. By applying the automated method to a network of weather radars, we observed how mesoscale variability in weather conditions structured the timing and altitude profile of bird migration within single nights. Bird density altitude profiles were observed that consisted of multiple layers, which could be explained from the distinct wind conditions at different take-off sites. Consistently lower bird densities are recorded in The Netherlands compared with sites in France and eastern Belgium, which reveals some of the spatial extent of the dominant Scandinavian flyway over continental Europe

Rotational order in co-intercalated c-60 crystals

Contains fulltext : 98984.pdf (publisher's version ) (Open Access

Twilight ascents by common swifts, Apus apus, at dawn and dusk: acquisition of orientation cues?

Common swifts are specialist flyers spending most of their life aloft, including night-time periods when this species roosts on the wing. Nocturnal roosting is preceded by a vertical ascent in twilight conditions towards altitudes of up to 2.5 km, behaviour previously explained as flight altitude selection for sleeping. We examined the nocturnal flight behaviour of swifts, as uniquely identified by a Doppler weather radar in central Netherlands using continuous measurements during two consecutive breeding seasons. Common swifts performed twilight ascents not only at dusk but also at dawn, which casts new light on the purpose of these ascents. Dusk and dawn ascents were mirror images of each other when time-referenced to the moment of sunset and sunrise, suggesting that the acquisition of twilight-specific light-based cues plays an important role in the progression of the ascents. Ascent height was well explained by the altitude of the 280 K isotherm, and was not significantly related to wind, cloud base height, humidity or the presence of nocturnal insects. We hypothesize that swifts profile the state of the atmospheric boundary layer during twilight ascents and/or attempt to maximize their perceptual range for visual access to distant horizontal landmarks, including surrounding weather. We compare twilight profiling by swifts with vertical twilight movements observed in other taxa, proposed to be related to orientation and navigation. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved

Seasonality.

<p>Top: Seasonal occurrence of migration layers (black dots and solid line) and high-altitude wind optima (bars) in spring (top) and autumn (bottom), 2008 and 2009. Both migration layers and high-altitude wind optima occur most frequently in spring in the months April and May.</p

Operational Solar Monitoring for Improving theHomogeneity of the European Radar Network

The characterization of the melting layer (ML) is an important task for operational radar meteorology. Melting layer identification may be used to establish distances at which radar rainfall estimates become affected by melting hydrometeors, with benefits for operational hydrometeor classification, as snowfall, freezing rain and liquid precipitation. Consequently, this yields a significant performance improvement in radar-based quantitative precipitation estimation (QPE) on ground. Furthermore, knowledge of the ML location is also important for microphysical cloud characterization and the evaluation of icing potential. Several studies and algorithms exist in literature for characterizing ML through radar measurement signature, the most popular being the increase in the radar reflectivity factor known as bright. For dual polarization radar, ML detection can be pursued using specific signatures of dual polarization measurements, such as differential reflectivity ZDR, co-polar correlation coefficient \rhoHV , specific differential phase KDP, and linear depolarization ratio LDR that exhibit well-pronounced ML signatures both in stratiform and even in convective situations. Moreover, ML and rainfall have a strong influence on satellite links signals, as they are attenuated due to the presence of hydrometeors along the propagation path. In stratiform precipitation systems, the ML is the upper limit of the rainfall column height that is responsible of the attenuation of radio signals. Therefore, ML climatology is proficiently used for designing satellites links relative to a specific area. Very recently, a new X-band Doppler, dual-polarization weather radar system has been installed in Florence funded by the Tuscany Region Government within the NEFOCAST project. The latter investigates a new concept system that aims at providing real time precipitation maps trough the attenuation measurements collected by a dense population of new-generation interactive satellite terminals (called SmartLNB, Smart Low-Noise Block converter). A number of SmartLNB has been deployed in the Tuscany region and a test bed has been established in cooperation with the schools of the Florence Metropolitan city. In the present study, the potential of the new weather radar system is investigated for characterizing the ML in terms of height and thickness under different meteorological conditions and cloud systems. Measurements collected in the RangeHeight Indicator (RHI) scan mode along the direction to the Eutelsat 10A satellite (used for the experimental campaign of the NEFOCAST project) have been analysed with the simultaneous attenuation estimation obtained by the SmartLNBs with radar coverage during selected precipitative events. Statistical analyses have been performed based on both weather radar and SmartLNB measurements, supplemented by ancillary observations from some rain gauges (both impact and tipping-bucket types) co-located with SmartLNBs. In addition, a C-band radar system (Polar 55C) located in Rome has also been used for this work. Polar 55C dual polarization measurements have been analysed with respect to co-located SmartLNBs and laser disdrometer. The results of this analysis highlight the effects of ML on radio signal attenuation, as the total attenuation of signal increases also with the increase of ML vertical thickness. Therefore, the characterization of the vertical profile of precipitation is mandatory for implementing accurate QPE on ground, both from radars and satellite links

U and V components of the environmental wind near ground level (100 m AGL, open circles) and at the migration layer's altitude

<p><b> (filled arrow heads) for all layering events in spring 2008 and 2009.</b> The grey connecting lines represent the wind difference vector between the ground and layering strata. For comparison, the black solid arrow represents a bird's airspeed vector into the mean spring migratory direction (41°).</p

Triangle of velocities.

<p>Air, wind and ground speed vectors (, , ) for a fully compensating bird at ground level ( = 0, black arrows) and at a given altitude ( = 1, white arrows). The surface and high altitude geostrophic winds , are related via the thermal wind vector: . Angle equals the wind direction with respect to the preferred migratory direction - , i.e. denotes a full head wind. Angle equals direction of the thermal wind with respect to the preferred direction, i.e. the angle between isotherm and preferred direction. Angles and are defined positive clockwise.</p