A one degree beamwidth, multi-frequency (20 to 30 and 89GHz), dual-polarization radiometer with full azimuth and elevation scanning capabilities was built with the purpose of improving the detection of in-flight icing hazards to aircraft in the near airport environment. This goal was achieved by collocating the radiometer with Colorado State University's CHILL polarized Doppler radar and leveraging the similar beamwidth and volume scan regiments of the two instruments. The collocated instruments allowed for the liquid water path and water vapor measurements derived from the radiometer to be merged with the radar moment fields to determine microphysical and water phase characteristics aloft. The radiometer was field tested at Colorado State University's CHILL radar site near Greeley, Colorado during the summer of 2009. Instrument design, calibration, and initial field testing results are discussed in this paper.

This study documents a very rapid increase in convective instability, vertical wind shear, and mesoscale forcing for ascent leading to the formation of a highly unusual tornado as detected by a ground-based microwave radiometer and wind profiler, and in 1-km resolution mesoanalyses. Mesoscale forcing for the rapid development of severe convection began with the arrival of a strong upper-level jet streak with pronounced divergence in its left exit region and associated intensification of the low-level flow to the south of a pronounced warm front. The resultant increase in stretching deformation along the front occurred in association with warming immediately to its south as low-level clouds dissipated. This created a narrow ribbon of intense frontogenesis and a rapid increase in convective available potential energy (CAPE) within 75 min of tornadogenesis. The Windsor, Colorado, storm formed at the juncture of this warm frontogenesis zone and a developing dryline. Storm-relative helicity suddenly increased to large values during this pretornadic period as a midtropospheric layer of strong southeasterly winds descended to low levels. The following events also occurred simultaneously within this short period of time: a pronounced decrease in midtropospheric equivalent potential temperature theta(e) accompanying the descending jet, an increase in low-level theta(e) associated with the surface sensible heating, and elimination of the capping inversion and convective inhibition. The simultaneous nature of these rapid changes over such a short period of time, not fully captured in Storm Prediction Center mesoanalyses, was likely critical in generating this unusual tornadic event.

An improved version of the vibrating wire sensor, used to measure supercooled cloud liquid water content, was developed by Anasphere Inc. and tested during early 2012. The sensor works on the principle that supercooled liquid will freeze to the vibrating wire and reduce the frequency at a known rate proportional to the liquid water content as the sensor rises through the cloud attached to a weather balloon and radiosonde. The disposable Anasphere sensor interfaces with an InterMet Systems iMet radiosonde. This updated sensor reduces the weight of the instrument while updating the technology when compared to the preceding balloon-borne sensor that was developed in the 1980's by Hill and Woffinden.Balloon-borne test flights were performed from Boulder, Colorado during February and March of 2012. These flights provided comparisons to integrated liquid water and profiles of liquid water content derived from a collocated multichannel microwave radiometer, built and operated by Radiometrics Corporation. Inter-comparison data such as these are invaluable for calibration, verification and validation of remote-sensing instruments. The data gathered from this sensor are potentially important to detection of icing hazards to aircraft, validation of microphysical output from numerical models, and calibrating remote sensors measuring supercooled liquid water. (C) 2014 The Authors. Published by Elsevier B.V.

Microwave radiometers (MWRs) can be useful for the detection of mesoscale phenomena because they provide thermodynamic profiles in a minute time scale. These profiles are mainly used in non-precipitation conditions due to degraded accuracy of the MWR measurements in precipitation. Recently, Radiometrics Corporation used proprietary neural network methods to retrieve temperature, humidity and liquid profiles from off-zenith (15° elevation) radiometer observations to provide higher accuracy during precipitation. In this paper, using the MWR-retrieved temperature and humidity profiles with collocated radiosondes from June 2010 to September 2013 in Wuhan, the impact of precipitation on the MWR measurement accuracy as well as the effect of off-zenith neural network methods on it is investigated. In precipitation, the correlation coefficients of the MWR temperature and vapor density profiles against radiosondes are smaller than those in non-precipitation, and the bias and RMS against radiosondes also increase, especially around 2 km heights. For the MWR relative humidity profile, the correlation coefficient in precipitation is obvious smaller than that in non-precipitation below 4.5 km, and the bias and RMS against radiosondes are clearly larger above 5.5 km. Moreover, the differences between the precipitation and non-precipitation cases mostly are statistically significant. Compared with the results of the zenith observation, the off-zenith observation makes a positive effect on reducing the impact of precipitation on the accuracy of MWR temperature and vapor density retrievals. On the whole, the MWR temperature bias and RMS against radiosondes in precipitation are reduced from 3.6 and 4.2 K to 1.3 and 3.1 K, respectively, and the MWR vapor density bias is also reduced from 1.10 g/m3 to 0.18 g/m3 with the RMS decreasing from 2.90 g/m3 to 1.91 g/m3. The temperature correlation coefficient between the MWR and radiosonde in precipitation is clearly improved above 3 km heights, and the temperature bias and RMS are significantly reduced at most heights. For the MWR vapor density retrievals in precipitation, the correlation coefficient, bias and RMS against radiosondes are clearly improved above 2 km heights. Additionally, the off-zenith observations during non-precipitation cases are also better compared to zenith observations. Therefore, off-zenith observations generally are better than zenith observations. This could be due to the fact that the off-zenith observations are more representative of the conditions in which radiosonde observations are also taken.

This work presents observations of water phase dynamics that demonstrate the theoretical Wegener-Bergeron-Findeisen concepts in mixed-phase winter storms. The work analyzes vertical profiles of air vapor pressure, and equilibrium vapor pressure over liquid water and ice. Based only on the magnitude ranking of these vapor pressures, we identified conditions where liquid droplets and ice particles grow or deplete simultaneously, as well as the conditions where droplets evaporate and ice particles grow by vapor diffusion. The method is applied to ground-based remote-sensing observations during two snowstorms, using two distinct microwave profiling radiometers operating in different climatic regions (North American Central High Plains and Great Lakes).The results are compared with independent microwave radiometer retrievals of vertically integrated liquid water, cloud-base estimates from a co-located ceilometer, reflectivity factor and Doppler velocity observations by nearby vertically pointing radars, and radiometer estimates of liquid water layers aloft. This work thus makes a positive contribution toward monitoring and nowcasting the evolution of supercooled droplets in winter clouds. (C) 2014 Elsevier B.V. All rights reserved.

Tropospheric observations by a microwave profiling radiometer and six-hour radiosondes were obtained during the Alpine Venue of the 2010 Winter Olympic Games at Whistler, British Columbia, by Environment Canada. The radiometer provided continuous temperature, humidity and liquid (water) profiles during all weather conditions including rain, sleet and snow. Gridded analysis was provided by the U.S. National Oceanic and Atmospheric Administration. We compare more than two weeks of radiometer neural network and radiosonde temperature and humidity soundings including clear and precipitating conditions. Corresponding radiometer liquid and radiosonde wind soundings are shown. Close correlation is evident between radiometer and radiosonde temperature and humidity profiles up to 10 km height and among southwest winds, liquid water and upper level thermodynamics, consistent with up-valley advection and condensation of moist maritime air. We compare brightness temperatures observed by the radiometer and forward-modeled from radiosonde and gridded analysis. Radiosonde-equivalent observation accuracy is demonstrated for radiometer neural network temperature and humidity retrievals up to 800 m height and for variational retrievals that combine radiometer and gridded analysis up to 10 km height.

A case study relative to the observation of unexpected liquid water in an apparently cloudless atmosphere is presented. Microwave radiometer profiler observations on 14 April 2008 at Boulder, Colorado, USA, showed an increase in the liquid water path with values higher than 0.05 mm and corresponding relative humidity saturation from 4.75 to 6.75 km above the ground level in profiles retrieved using a neural network algorithm. The formation of small supercooled droplets identified in the microwave retrieval of the temperature and relative humidity vertical profiles may result from nucleation stimulated by a mountain lee wave. The presented analysis reveals the existence of supercooled liquid water in the mid troposphere related to a wave activity that occurred in a sky condition classifiable as “clear” and describes an atmospheric scenario consistent with the observation of the so‐called twilight zone.

Dynamic exchange among water solid, liquid and vapor phases determines the evolution of cloud and precipitation particles in the atmosphere. This work presents observations of water phase dynamics that demonstrates the theoretical Wegener-Bergeron-Findeisen concepts in mixed- phase winter-cloud systems. For this, the work analyzes vertical profiles of temperature, relative humidity, vapor density, and cloud liquid-water content. All profiles were simultaneously retrieved during two snow storms, using two distinct microwave profiling radiometers operating in different climatic regions (North American Central High Plains and Great Lakes). To corroborate our analyses, we use reflectivity factor and Doppler velocity observations by vertically-pointing radars located near the radiometers. Based only on the magnitude ranking of in-cloud vapor pressures and equilibrium vapor pressures over liquid water and over ice, we identified conditions where liquid droplets and ice particles grow or deplete simultaneously, as well as the conditions where droplets evaporate and ice particles grow by vapor diffusion.

: The goal is to develop GPS remote sensing techniques to determine atmospheric signal delay and bending, and refractivity profiles to aid in the detection of oceanic boundary layers from a ship.

The Global Positioning System (GPS) is being widely used to monitor lithospheric processes with millimeter precision, which it achieves by correcting for signal delays induced by the ionosphere [Ho et al., 1996] and atmosphere [Businger et al., 1996]. Alternatively, uncorrected GPS data can be used to estimate properties of the ionosphere and atmosphere important to meteorology, climate, and space weather.