Precipitation Radar Data Research Articles

Rain profiling algorithm for TRMM Precipitation Radar data

This paper describes the TRMM standard algorithm 2A25 which estimates the instantaneous vertical profile of rain from Precipitation Radar (PR) data. Major challenges in rain profilling from the TRMM PR lie in the corrections for the effects of rain attenuation and non-uniform beam filling (NUBF) and in the rejection of surface clutter. A combination of the Hitschfeld-Bordan and surface reference methods is used to correct the attenuation effect in radar returns. The NUBF effects are estimated from the spatial variations of the estimated total path integral of attenuation from the top of the rain to the surface in the vicinity of the radar beam concerned. This paper outlines the critical part of the algorithm, and shows some results of comparisons of data taken nearly simultaneously by the TRMM PR and a ground-based radar.

対流雲と層雲の判別に基づくTRMMマイクロ波放射計降雨強度推定法

Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer brightness temperature data in the 85 GHz channel (T85) reveal distinct local minima (T85min) in a regional map containing a Mesoscale Convective System (MCS). This is because of relatively small footprint size (approximately 5.5 km) and strong extinction properties in this channel of the TMI. A map of surface rain rate for that region, deduced from simultaneous measurements made by the Precipitation Radar (PR) on board the TRMM satellite, reveals that these T85(sub min), produced by scattering, correspond to local PR rain maxima. Utilizing the PR rain rate map as a guide, we infer empirically from TMI data the presence of three different kinds of thunderstorms or Cbs. These Cbs are classified as young, mature, and decaying types, and are assumed to have a scale of about 20 km on the average. Two parameters are used to classify these three kinds of Cbs based on the T85 data: a) the magnitude of scattering depression deduced from local T85(sub min) and b) the mean horizontal gradient of T85 around such minima. Knowing the category of a given Cb, we can estimate the rain rate associated with it. Such estimation is done with the help of relationships linking T85min to rain rate in each Cb type. Similarly, a weak background rain rate in all the areas where T85 is less than 260 K is deduced with another relationship linking T85 to rain rate. In our rain retrieval model, this background rain constitutes stratiform rain where the Cbs are absent. Initially, these relationships are optimized or tuned utilizing the PR and TMI data of a few MCS events. After such tuning, the model is applied to independent MCS cases. The areal distribution of light (1-10 mm/hr), moderate (10-20 mm/hr), and intense (>= 20 mm/hr) rain rates are retrieved satisfactorily. Accuracy in the estimates of the light, moderate, and intense rain areas and the mean rain rates associated with such areas in these independent MCS cases is on the average about 15 %. Taking advantage of this ability of our retrieval method, one could derive the latent heat input into the atmosphere over the 760 km wide swath of the TMI radiometer in the tropics.

Assimilation of radar precipitation data in NWP Models — a review

The COST 717 Action has a working group (No 3) on ‘Using Radar Information for Assimilation into Atmospheric Models’. As an initial part of its plan, the group is reviewing previous attempts to assimilate radar data. The main techniques used to assimilate precipitation data — physical initialization, latent heat nudging and variational assimilation are described. Most previous studies have worked with surface rain rate estimates, but attempts to assimilate reflectivity directly are also covered.

A Study on the Relation between Terminal Velocity and VHF Backscatter from Precipitation Particles Using the Chung-Li VHF Radar

Abstract The relationships between the mean Doppler terminal velocities VT of the hydrometeors with different phases and the range-corrected VHF backscatter P from the corresponding precipitation particles are investigated by using the Chung-Li VHF radar. The radar precipitation data employed for the analysis were taken from four independent experiments conducted on different weather conditions. They show that the observed α and β values in the power-law approximation VT = αPβ above the melting layer are generally smaller than those below the layer, while in the bright band the values of β (α) are enormously smaller (greater) than those above and below the bright band. Theoretical analysis shows that the mathematical relationship between α and β can be approximated very well by a simple exponential function, which is in excellent agreement with the observations. A new method for estimating the coefficient A and exponent B in the fall speed–diameter relationship V(D) = ADB with respect to still air on the ...

Effects of Nonuniform Beam Filling on Rainfall Retrieval for the TRMM Precipitation Radar

The Tropical Rainfall Measuring Mission (TRMM) will carry the first spaceborne radar for rainfall observation. Because the TRMM Precipitation Radar (PR) footprint size of 4.3 km is greater than the scale of some convective rainfall events, there is concern that nonuniform filling of the PR antenna beam may bias the retrieved rain-rate profile. The authors investigate this effect theoretically and then observationally using data from the NASA Jet Propulsion Laboratory Airborne Rain Mapping Radar (ARMAR), acquired during Tropical Oceans Global Atmosphere Coupled Ocean Atmosphere Response Experiment in early 1993. The authors' observational approach is to simulate TRMM PR data using the ARMAR data and compare the radar observables and retrieved rain rate from the simulated PR data with those corresponding to the high-resolution radar measurements. The authors find that the path-integrated attenuation and the resulting path-averaged rain rate are underestimated. The reflectivity and rain rate near the top of the rainfall column are overestimated. The near-surface reflectivity can be overestimated or underestimated, with a mean error very close to zero. The near-surface rain rate, however, is usually underestimated, sometimes severely.

Precipitation estimation with satellites and radar

Radar and satellite measurements were simultaneously used for the detailed description of the properties of precipitating clouds. Existing raindrops were detected by digitised data of an MRL-5 radar measuring at 3 and 10 cms. This information was merged with the physical characteristics of precipitating clouds retrieved from the radiance data of the operational meteorological satellites. First, we used infrared and visible METEOSAT data for cloud classification and for a qualitative estimation of precipitation. Second, from the multispectral measurements of the Advanced Very High Resolution Radiometer (AVHRR) on board the polar orbiting NOAA satellites we explicitly derived cloud-top temperature, optical thickness and effective cloud droplet size. We also determined a cloud flag using a thresholding technique. The radar and satellite images were transformed into the same geographic projection format and displayed simultaneously for qualitative evaluation. Empirical relationships were established between coincident ground precipitation measurements, radar data and satellite cloud parameters. The effect of the additional information provided by AVHRR on the quality of the precipitation estimates was evaluated.

Preliminary analysis of atmospheric scavenging processes in the industrial region of Cubatao, Southeastern Brazil

During a German-Brazilian research project on vegetation damage, atmospheric scavenging processes were investigated, considering transport and local emissions. For this goal, radar precipitation data was evaluated together with analyses of fractionated rain samples of one stratiform and one convective rain event. The temporal variation of pollutant concentration in rain water and the meteorological conditions were compared for both rain events at two stations: one at the top of the Serra do Mar mountain ridge (∼ 900 m) with minor influence of local emissions and one at sea level, close to the high indutrialized area of Cubatao. At the station close to the industrial plants, major influence of the local sources on wet deposition was determined. During the stratiform rain event, an additional influence of transport could be observed. On the top of the Serra do Mar, major influence of the local sources could only be observed during the convective rain event, while transport is mainly responsible for wet deposition during the stratiform event.

Resolution considerations in using radar rainfall data for flood forecasting

The objectives of this paper are (1) to show the hydrological effects of changing the spatial resolution of radar-derived rainfall and (2) to show the effect of discretization of radar data on hydrological modeling for flood forecasting. Simulated hydrographs are compared for 2, 5, and 10 km basin grid sizes for the Grand River watershed in Ontario. An eight-level discretization of rainfall is compared with a 256-level scale of rainfall intensities. Spatial averaging tends to reduce the effect of erroneous radar readings and give comparable results with those obtained using finer resolutions. The appropriate level of discretization depends on the area being modeled and appropriate levels are recommended. The level of discretization of radar precipitation data does not significantly affect the generation of hydrographs. Hydrographs based on the radar-derived rainfall generally reproduced measured hydrographs better than those derived from the rain gauge data. Key words: hydrologic models, flood forecasting, weather radar.

Airborne Radar Observations of Eye Configuration Changes, Bright Band Distribution, and Precipitation Tilt During the 1969 Multiple Seeding Experiments in Hurricane Debbie1

Abstract Project Stormfury radar precipitation data gathered before, during, and after the multiple seedings of the eyewall region of hurricane Debbie on Aug. 18 and 20, 1969, are used to study changes in the eye configuration, the characteristics of the radar bright band, and the precipitation tilt. Increases in the echo-free area within the eye followed each of the five seedings on the 18th, but followed only one seeding on the 20th. Changes in major axis orientation followed only one seeding on the 18th, but followed each seeding on the 20th. Similar studies conducted recently on unmodified storms suggest that such changes do not occur naturally. However, the studies do not exclude this possibility. Changes in the radius of maximum winds follow closely the changes in eyewall radius. It is suggested that the different results on the 2 days might be attributable to seeding beyond the radius of maximum winds on the 18th and inside the outer radius of maximum winds on the 20th. The bright band is found in ...