437 research outputs found

    WRF Simulations of the 20-22 January 2007 Snow Events over Eastern Canada: Comparison with In-Situ and Satellite Observations

    Get PDF
    One of the grand challenges of the Global Precipitation Measurement (GPM) mission is to improve cold season precipitation measurements in middle and high latitudes through the use of high-frequency passive microwave radiometry. For this, the Weather Research and Forecasting (WRF) model with the Goddard microphysics scheme is coupled with a satellite data simulation unit (WRF-SDSU) that has been developed to facilitate over-land snowfall retrieval algorithms by providing a virtual cloud library and microwave brightness temperature (Tb) measurements consistent with the GPM Microwave Imager (GMI). This study tested the Goddard cloud microphysics scheme in WRF for two snowstorm events, a lake effect and a synoptic event, that occurred between 20 and 22 January 2007 over the Canadian CloudSAT/CALIPSO Validation Project (C3VP) site in Ontario, Canada. The 24h-accumulated snowfall predicted by the WRF model with the Goddard microphysics was comparable to the observed accumulated snowfall by the ground-based radar for both events. The model correctly predicted the onset and ending of both snow events at the CARE site. WRF simulations capture the basic cloud properties as seen by the ground-based radar and satellite (i.e., CloudSAT, AMSU-B) observations as well as the observed cloud streak organization in the lake event. This latter result reveals that WRF was able to capture the cloud macro-structure reasonably well

    What can we learn from the cloudsat radiometric mode observations of snowfall over the ice-free ocean?

    Get PDF
    The quantification of global snowfall by the current observing system remains challenging, with the CloudSat 94 GHz Cloud Profiling Radar (CPR) providing the current state-of-the-art snow climatology, especially at high latitudes. This work explores the potential of the novel Level-2 CloudSat 94 GHz Brightness Temperature Product (2B-TB94), developed in recent years by processing the noise floor data contained in the 1B-CPR product; the focus of the study is on the characterization of snow systems over the ice-free ocean, which has well constrained emissivity and backscattering properties. When used in combination with the path integrated attenuation (PIA), the radiometric mode can provide crucial information on the presence/amount of supercooled layers and on the contribution of the ice to the total attenuation. Radiative transfer simulations show that the location of the supercooled layers and the snow density are important factors affecting the warming caused by supercooled emission and the cooling induced by ice scattering. Over the ice-free ocean, the inclusion of the 2B-TB94 observations to the standard CPR observables (reflectivity profile and PIA) is recommended, should more sophisticated attenuation corrections be implemented in the snow CloudSat product to mitigate its well-known underestimation at large snowfall rates. Similar approaches will also be applicable to the upcoming EarthCARE mission. The findings of this paper are relevant for the design of future missions targeting precipitation in the polar regions

    Falling Snow Estimates from the Global Precipitation Measurement (GPM) Mission

    Get PDF
    Retrievals of falling snow from space represent an important data set for understanding the Earth's atmospheric, hydrological, and energy cycles, especially during climate change. Estimates of falling snow must be captured to obtain the true global precipitation water cycle, snowfall accumulations are required for hydrological studies, and without knowledge of the frozen particles in clouds one cannot adequately understand the energy and radiation budgets. While satellite-based remote sensing provides global coverage of falling snow events, the science is relatively new and retrievals are still undergoing development with challenges remaining. This work reports on the development and testing of retrieval algorithms for the Global Precipitation Measurement (GPM) mission Core Satellite, launched February 2014, with a specific focus on meeting GPM Mission requirements for falling snow

    CloudSat-based assessment of GPM Microwave Imager snowfall observation capabilities

    Get PDF
    The sensitivity of Global Precipitation Measurement (GPM) Microwave Imager (GMI) high-frequency channels to snowfall at higher latitudes (around 60◦N/S) is investigated using coincident CloudSat observations. The 166 GHz channel is highlighted throughout the study due to its ice scattering sensitivity and polarization information. The analysis of three case studies evidences the important combined role of total precipitable water (TPW), supercooled cloud water,and background surface composition on the brightness temperature (TB) behavior for different snow-producing clouds. A regression tree statistical analysis applied to the entire GMI-CloudSat snowfall dataset indicates which variables influence the 166 GHz polarization difference (166∆TB)and its relation to snowfall. Critical thresholds of various parameters (sea ice concentration (SIC), TPW, ice water path (IWP)) are established for optimal snowfall detection capabilities. The 166∆TB can identify snowfall events over land and sea when critical thresholds are exceeded (TPW \u3e 3.6 kg·m−2, IWP \u3e 0.24 kg·m−2 over land, and SIC \u3e 57%, TPW \u3e 5.1 kg·m−2 over sea). The complex combined 166∆TB-TB relationship at higher latitudes and the impact of supercooled water vertical distribution are also investigated. The findings presented in this study can be exploited to improve passive microwave snowfall detection algorithms

    Global Precipitation Measurement

    Get PDF
    This chapter begins with a brief history and background of microwave precipitation sensors, with a discussion of the sensitivity of both passive and active instruments, to trace the evolution of satellite-based rainfall techniques from an era of inference to an era of physical measurement. Next, the highly successful Tropical Rainfall Measuring Mission will be described, followed by the goals and plans for the Global Precipitation Measurement (GPM) Mission and the status of precipitation retrieval algorithm development. The chapter concludes with a summary of the need for space-based precipitation measurement, current technological capabilities, near-term algorithm advancements and anticipated new sciences and societal benefits in the GPM era

    Application of the Electrically Scanning Microwave Radiometer (ESMR) to classification of the moisture condition of the ground

    Get PDF
    The ability of the Nimbus 5 ESMR to characterize the moisture condition of the uppermost portion of the soil was evaluated. In the absence of snow cover, ESMR-5 brightness temperatures were compared with computed upper soil zone moisture values from a soil moisture budgeting scheme. The study was conducted over the U.S. Great Plains for the late summer and early fall in 1974 and 1975. Favorable results were limited by the relatively high vegetative cover and infrequent substantial rainfalls at that time of year. Satisfactory characterization of the general moisture condition was deemed feasible in agricultural regions at times of the year when fields were nearly bare. An additional evaluation demonstrated that ESMR-6 data could delineate the active boundary of a snow pack

    Surface and Atmospheric Contributions to Passive Microwave Brightness Temperatures

    Get PDF
    Physically-based passive microwave precipitation retrieval algorithms require a set of relationships between satellite observed brightness temperatures (TB) and the physical state of the underlying atmosphere and surface. These relationships are typically non-linear, such that inversions are ill-posed especially over variable land surfaces. In order to better understand these relationships, this work presents a theoretical analysis using brightness temperature weighting functions to quantify the percentage of the TB resulting from absorption/emission/reflection from the surface, absorption/emission/scattering by liquid and frozen hydrometeors in the cloud, the emission from atmospheric water vapor, and other contributors. The results are presented for frequencies from 10 to 874 GHz and for several individual precipitation profiles as well as for three cloud resolving model simulations of falling snow. As expected, low frequency channels (<89 GHz) respond to liquid hydrometeors and the surface, while the higher frequency channels become increasingly sensitive to ice hydrometeors and the water vapor sounding channels react to water vapor in the atmosphere. Low emissivity surfaces (water and snow-covered land) permit energy downwelling from clouds to be reflected at the surface thereby increasing the percentage of the TB resulting from the hydrometeors. The slant path at a 53deg viewing angle increases the hydrometeor contributions relative to nadir viewing channels and show sensitivity to surface polarization effects. The TB percentage information presented in this paper answers questions about the relative contributions to the brightness temperatures and provides a key piece of information required to develop and improve precipitation retrievals over land surfaces

    Polarized signals from oriented frozen hydrometeors using passive microwave radiometry

    Get PDF
    Ice clouds play a significant role in energy budget of the earth-atmosphere system, and they also participate in global hydrological cycle. Thick ice clouds which are associated with precipitation transfer energy and water between the atmosphere and the earth. The net effects of ice clouds on the earth-atmosphere system highly depend on their microphysical properties. However, the complex and variable structure of ice clouds makes it difficult to capture them well in models. The oversimplified microphysical properties of ice clouds in retrievals introduce significant uncertainties in weather and climate studies. The knowledge on the orientation of ice particles is very limited. The orientation of frozen hydrometeors which induces polarization signatures determines the magnitude of polarized signals. In order to investigate the potential polarized signatures induced by the oriented frozen hydrometeors, ground-based polarization observations have been performed at “Umweltforschungsstation Schneefernerhaus” (UFS) on Mount Zugspitze (German Alps) at 2650 m above sea level. In this study, the polarization observations carried out by a ground-based dual polarized microwave radiometer (DPR) at 150 GHz are investigated together with auxiliary instruments deployed at UFS, i.e., a second microwave radiometer (HATPRO) and a K-band micro rain radar (MRR). HATPRO measures liquid water path (LWP) and integrated water vapor (IWV) during snowfall, and MRR operating at 24.1 GHz provides indirect snow water path (SWP) information. Based on the observations, the analysis of a single snow case and one-year snowfall data show that the brightness temperature (TB) differences between the vertical and horizontal polarizations reach up to −10 K at an elevation angle of 34.8^o during snowfall. The polarized signals during snowfall can be explained well by the occurrence of oriented snow particles. The analysis of the synergic observations shows the effects of snowfall parameters on polarization differences (PDs) observed with DPR at 150 GHz. The dependencies of the measured PD and TB on MRR integrated radar reflectivity and independently derived LWP are discussed. It shows that the high SWP indicated by high values of MRR integrated reflectivity enhances both TB and PD due to the scattering effects of snow particles. Meanwhile, TBs are found to be enhanced during snowfall when supercooled liquid water is present, while PD resulting from oriented snow particles is damped by the increase of LWP. The polarization observations support the potential role of polarization measurements in improving retrievals of snowfall microphysical parameters. To evaluate the effects of SWP and LWP on PD and TB, radiative transfer (RT) simulations assuming horizontally aligned snow oblates using a polarized RT model have been performed. PD and TB observations can be captured well by the RT model with given reasonable assumptions on the microphysical parameters of oriented snow oblates. Additionally, the uncertainties of PD and TB caused by snow microphysical properties are fully examined in the RT simulations. The “damping (enhancing)” effects of supercooled liquid water on PD (TB) are further interpreted by a simple physical model where the height of cloud liquid varies with respect to the dichroic snow layer. From the ground-based observations, it is found that PD resulting from oriented snow particles is absorbed by supercooled liquid below snow layers. When supercooled liquid water is located above snow layers, PD is damped since it is compensated by the emission of supercooled liquid water penetrating the snow layer. TB is generally enhanced by the presence of LWP: the warmer the supercooled liquid water, the larger the TB. The polarization observations promote the design of new instruments further. Under an assumption that ice particles are oriented, RT simulations are performed for the space-borne satellite FengYun-4 (FY-4) channels to examine polarization information content for ice cloud characterization. The results show that polarization can be beneficial for ice cloud retrievals and additional information can be provided by polarized signals to quantify ice cloud parameters, especially at high frequency channels. Therefore, the present work strongly suggests the deployment of microwave polarization channels for ice cloud observations
    corecore