1,721,044 research outputs found
Evaluation of differential absorption radars in the 183&thinspGHz band for profiling water vapour in ice clouds
Full text linkRelative humidity (RH) measurements in ice
clouds are essential for determining ice crystal growth processes and rates. A differential absorption radar (DAR) system with several frequency channels within the 183.3 GHz
water vapour absorption band is proposed for measuring RH
within ice clouds. Here, the performance of a DAR system
is evaluated by applying a DAR simulator to A-Train observations in combination with co-located European Centre
for Medium-Range Weather Forecasts (ECMWF) reanalysis. Observations from the CloudSat W-band radar and from
the CALIPSO lidar are converted first into ice microphysical properties and then coupled with ECMWF temperature
and relative humidity profiles in order to compute scattering
properties at any frequency within the 183.3 GHz band. A
self-similar Rayleigh–Gans approximation is used to model
the ice crystal scattering properties. The radar reflectivities
are computed both for a space-borne and airborne and a
ground-based DAR system by using appropriate radar receiver characteristics. Sets of multi-frequency synthetic observation of attenuated reflectivities are then exploited to retrieve profiles of water vapour density by fitting the line
shape at different levels. A total of 10 d of A-Train observations are used to test the measurement technique performance for different combinations of tones when sampling
ice clouds globally. Results show that water vapour densities
can be derived at the level that can enable ice process studies (i.e. better than 3 %), both from a ground-based system
(at the minute temporal scale and with circa 100 m vertical
resolution) and from a space-borne system (at 500 m vertical resolution and with circa 5 km integration lengths) with
four tones in the upper wing of the absorption line. Deploying ground-based DAR system at high latitudes and high altitudes is highly recommended to test the findings of this work
in the field
Recommended from our members
The diurnal cycle of precipitation according to multiple decades of global satellite observations, three CMIP6 models, and the ECMWF reanalysis
Full text linkNASA Precipitation Measurement Mission observations are used to evaluate the diurnal cycle of precipitation from three CMIP6 models (NCAR-CESM2, CNRM-CM6-1, CNRM-ESM2-1) and the ERA5 reanalysis. NASA’s global-gridded IMERG product, which combines spaceborne microwave radiometer, infrared sensor and ground-based gauge measurements, provides high spatio-temporal resolution (0.1°, half-hourly) estimates that are suitable for evaluating the diurnal cycle in models, as determined against the CONUS ground-based radar network. IMERG estimates are coarsened to the spatial and hourly resolution of the state-of-the-art CMIP6 and ERA5 products, and their diurnal cycles are compared across multiple decades of June-July-August in the 60°N–S domain (IMERG and ERA5: 2000–2019; NCAR and CNRM: 1979–2008). Low precipitation regions (and weak amplitude regions when analyzing the diurnal phase) are excluded from analyses in order to assess only robust diurnal signals. Observations identify greater diurnal amplitudes over land (26–134% of the precipitation mean; 5th–95th percentile) than over ocean (14–66%). ERA5, NCAR and CNRM underestimate amplitudes over ocean, whilst ERA5 overestimates over land. IMERG observes a distinct diurnal cycle only in certain regions, with precipitation peaking broadly between 14–21 LST over land (21–6 LST over mountainous and varying-terrain regions) and 0–12 LST over ocean. The simulated diurnal cycle is unrealistically early compared with observations, particularly over land (NCAR-CESM2-AMIP: –1 hour; ERA5: –2 hours; CNRM-CM6-1-AMIP: –4 hours on average) with nocturnal maxima not well represented over mountainous regions. Furthermore, ERA5’s representation of the diurnal cycle is too simplified, with less interannual variability in the time of maximum compared to observations over many regions
Characterization of surface clutter signal in the presence of orography for a spaceborne conically scanning W-band Doppler radar
Full text linkThe Earth's surface radar reflection is one of the most important signals received by spaceborne radar systems. It is used in several scientific applications, including geolocation, terrain classification, and path-integrated attenuation estimation. A simulator based on the ray-tracing approach has been developed to reproduce the clutter reflectivity and the Doppler velocity signal for a conically scanning spaceborne Doppler radar system. The simulator exploits topographic information through a raster digital elevation model, land types from a regional classification database, and a normalized radar surface cross-section look-up table. The simulator is applied to the WInd VElocity Radar Nephoscop (WIVERN) mission, which proposes a conically scanning W-band Doppler radar to study in-cloud winds. Using an orbital model, detailed simulations for conical scans over the Piedmont region of Italy, which offers a variety of landscape conditions, are presented. The results highlight the strong departure of the reflectivity and Doppler velocity profiles in the presence of marked orography and the significant gradient in the surface radar backscattering properties. The simulations demonstrate the limitations and advantages of using the surface Doppler velocity over land as an antenna-pointing characterization technique. They represent the full strength range of the surface radar clutter over land surfaces for the WIVERN radar. The surface clutter tool applies to other spaceborne radar missions, such as the nadir-pointing EarthCARE and CloudSat Cloud Profiling Radar (CPR), or the cross-track scanning Global Precipitation Measurement (GPM) precipitation radars
Guglielmo II e la ricontestualizzazione dei miti ed eroi germanici: i Nibelunghi all'Esposizione Universale di Parigi dell'anno 1900
No full textIl saggio illustra la utilizzazione del materiale nibelungico all'interno del padiglione tedesco alla Esposizione Universale parigina del 1900. Riferimenti sono presenti sia sulla facciata dell'edificio che all'interno, fra cui merita particolare attenzione una stampa del Nibelungenlied a cura di J. Sattler. Il saggio prende in considerazione - in maniera più ampia - anche la ricezione del mondo germanico antico da parte dell'imperatore Guglielmo II, illustrando come tutto il passato germanico fosse inteso come azione politica auto-celebrativa e di esaltazione del nuovo costituito Reich tedesco
Disentangling Mie and attenuation effects in rain using a Ka-W dual-wavelength Doppler spectral ratio technique
Full text linkA novel technique that enables to disentangle Mie and attenuation effects in coincident, beam-matched Ka- and W-band radar observations is presented here. The ratio of the measured radar Doppler spectra at the two frequencies is estimated, and the Doppler velocity regime that corresponds to Rayleigh scatterers is determined. The range variation of the Rayleigh regime "plateau" is directly linked to the differential attenuation between the two wavelengths and does represent the attenuation component of the dual-wavelength ratio. The retrieval technique is applied to a light stratiform rain event and provides plausible results. The proposed Doppler spectral ratio methodology has potential for applications in precipitating snow, liquid and ice clouds and can be extended to other wavelength pairs. Key Points Attenuation and Mie effects ambiguity in dual-wavelength radar techniques Dual-wavelength radar Doppler spectral ratio (DSR) has a quasi-universal shape DSR can help to disentangle the two components of the dual-wavelength ratio ©2013 The Authors. Geophysical Research Letters published by Wiley on behalf of the American Geophysical Union
Reconstruction of the Horizontal Wind Field Inside Weather Systems from the Sparse Sampling Envisaged for the Wind Velocity Radar Nephoscope (WIVERN) Mission
No full textWIVERN, short for WInd VElocity Radar Nephoscope ( www.wivern.polito.it , [1] , [2] ), has been recently proposed in the ESA Earth Explorer 11 call with the specific goal of filling the observational gap of global wind observations inside storms and precipitating systems [3]. WIVERN, currently in Phase A, is one of the two remaining candidate missions with the final selection scheduled for July 2025
Riming-dependent snowfall rate and ice water content retrievals for W-band cloud radar
Full text linkAccurate measurements of snowfall in mid-latitudes and high latitudes are particularly important because snow provides a vital freshwater source and impacts glacier mass balances as well as surface albedo. However, ice water content (IWC) and snowfall rates (SRs) are hard to measure due to their high spatial variability and the remoteness of polar regions. In this study, we present novel ice water content-equivalent radar reflectivity (IWC-Z(e)) and snowfall rate-equivalent radar reflectivity (SR-Z(e)) relations for 40 degrees slanted and vertically pointing W-band radar. The relations are derived from joint in situ snowfall and remote sensing (W-band radar and radiometer) data from the SAIL site (Colorado, USA) and validated for sites in Hyyti & auml;l & auml; (Finland), Ny-& Aring;lesund (Svalbard), and Eriswil (Switzerland). In addition, gauge measurements from SAIL and Hyyti & auml;l & auml; are used as an independent reference for validation. We show the dependence of IWC-Z(e) and SR-Z(e) on riming, which we utilize to reduce the spread in the IWC-Z(e) and SR-Z(e) spaces. Normalized root mean square errors (NRMSEs) are below 25 % for IWC>0.1 g m(-3). For SR, the NRMSE is below 70 % over the whole SR range. We also present relations using liquid water path as a proxy for the occurrence of riming, which can be applied to both ground-based and space-borne radar-radiometer instruments. The latter is demonstrated using the example of the proposed ESA Earth Explorer 11 candidate mission WIVERN. With this approach, NRMSEs are below 75 % for IWC>0.1 g m(-3) and below 80 % for SR>0.2 mm h(-1)
- …
