Tomoo Ushio

Global Precipitation Map using Satelliteborne Microwave Radiometers by the GSMaP Project : Production and Validation

This paper documents the production and validation of retrieved rainfall data obtained from satellite-borne microwave radiometers by the Global Satellite Mapping of Precipitation (GSMaP) Project. Using various attributes of precipitation derived from Tropical Rainfall Measuring Mission (TRMM) satellite data, the GSMaP has implemented hydrometeor profiles derived from Precipitation Radar (PR), statistical rain/no-rain classification, and scattering algorithms using polarization-corrected temperatures (PCTs) at 85.5 and 37 GHz. Combined scattering-based surface rainfalls are computed depending on rainfall intensities. PCT85 is not used for stronger rainfalls, because strong depressions of PCT85 are related to tall precipitation-top heights. Therefore, for stronger rainfalls, PCT37 is used, with PCT85 used for weaker rainfalls. With the suspiciously strong rainfalls retrieved from PCT85 deleted, the combined rainfalls correspond well to the PR rain rates over land. The GSMaP algorithm for the TRMM Microwave Imager (TMI) is validated using the TRMM PR, ground radar [Kwajalein (KWAJ) radar and COBRA], and Radar Automated Meteorological Data Acquisition System (AMeDAS) precipitation analysis (RA). Monthly surface rainfalls retrieved from six microwave radiometers (GSMaP_MWR) are compared with the gauge-based dataset. Rain rates retrieved from the TMI (GSMaP_TMI) are in better agreement with the PR estimates over land everywhere except over tropical Africa in the boreal summer. Validation results of the KWAJ radar and COBRA show a good linear relationship for instantaneous rainfall rates, while validation around Japan using the RA shows a good relationship in the warm season. Poor results, connected to weak-precipitation cases, are found in the cold season around Japan.

A survey of thunderstorm flash rates compared to cloud top height using TRMM satellite data

The relationship between cloud height and lightning activity is examined using data from the Tropical Rainfall Measuring Mission (TRMM) satellite. Coincident data from the precipitation radar (PR) and Lightning Imaging Sensor aboard the TRMM satellite are used to examine whether lightning flash rate is proportional to the fifth power of cloud top height. This study is unique in that (1) the relationship between instantaneous rather than maximum storm height and flash rate is obtained and (2) relatively unbiased full data sets for different locations and seasons over the globe are used. The relationship between thunderstorm height and flash rate is nonlinear with large variance. The overall trend shows that flash rate increases exponentially with storm height. Some tall thunderstorms do not have large flash rates, but the reverse situation never occurs. The fifth power dependency that is derived from scaling laws is not inconsistent with, but not necessarily required by, the observed data.

The global satellite mapping of precipitation (GSMaP) project

Precipitation is one of the most important parameters on the earth system, and the global distribution of precipitation and its change are essential data for modeling the water cycle, maintaining the ecosystem environment, agricultural production, improvements of the weather forecast precision, flood warning and so on. In the GPM (Global Precipitation Measurement) project, the microwave radiometers observing microwave emission from rain will be placed on many low-orbit satellites, to reduce the interval to about 3 hours in observation time for each location on the earth. Although the GPM can provide the global precipitation fields with 3 hour resolution, the precipitation map with higher resolution (< 1 hour) is required for some operational users such as flash flood warning systems and also the monthly based precipitation map is required from the climatology studies. In this presentation, the GSMaP_MVK which is a product of surface rainfall rate with 0.1 degree and 1 hour resolution on a global basis and GSMaP_Gauge which is a gauge adjusted product to the GSMaP_MVK for climatological studies are introduced, focusing particularly on structure and performance of the algorithm and some initial evaluation tests.

Evaluation of GSMaP Precipitation Estimates over the Contiguous United States

Abstract Precipitation estimates from the Global Satellite Mapping of Precipitation (GSMaP) project are evaluated over the contiguous United States (CONUS) for the period of 2005–06. GSMaP combines precipitation retrievals from the Tropical Rainfall Measuring Mission satellite and other polar-orbiting satellites, and interpolates them with cloud motion vectors derived from infrared images from geostationary satellites, to produce a high-resolution dataset. Four other satellite-based datasets are also evaluated concurrently with GSMaP, to provide a better perspective. The new Climate Prediction Center (CPC) unified gauge analysis is used as the reference data. The evaluation shows that GSMaP does well in capturing the spatial patterns of precipitation, especially for summer, and that it has better estimation of precipitation amount over the eastern than over the western CONUS. Meanwhile, GSMaP shares many of the challenges common to other satellite-based products, including that it underestimates in winter...

Broad band interferometric measurement of rocket triggered lightning in Japan

A broad band interferometer to investigate the location of radio sources due to lightning flashes in two dimension has been manufactured and evaluated during the Rocket Triggered Lightning Experiment in Japan. Having high digitization rate, a broad band interferometer is not able to record the entire radiation process emitted by a lightning discharge. Therefore, we introduced a method of sequential triggering for each electromagnetic pulse that allows to record as long periods of radiation as we need. We obtained several data sets of upward stepped leaders for both negative polarity and positive one during the experiment. The apparent speed of an upward negative leader is estimated at 6 × 105 m/sec. The time intervals between successive electromagnetic pulses are from 11 to 93 microseconds with a mean of 22 microseconds. A triggered lightning to an experimental power transmission tower, normally it is called an altitude triggered lightning, is also conducted. One of the altitude triggered lightning lowered negative charges to the tower. In this case both the negative downward leader and the positive upward one can be generated. Some isolated pulses emitted by the downward negative stepped leader which attaches to the transmission tower are observed and located. Pulses emitted by the positive upward leader penetrated into a negatively charged region of a thundercloud are also observed. The location of radiation sources are distributed within a few degrees of azimuth. The time intervals between successive pulses are from 14 to 188 microseconds with a mean of 78 microseconds.

MMSE Beam Forming on Fast-Scanning Phased Array Weather Radar

A fast-scanning phased array weather radar (PAWR) with a digital beam forming receiver is under development. It is important in beam forming for weather radar observation with temporally high resolution to form a stable and robust main lobe and adaptively suppress sidelobes with a small number of pulses in order to accurately estimate precipitation profiles (reflectivity, mean Doppler velocity, and spectral width). A minimum mean square error (MMSE) formulation with a power constraint, proposed in this paper, gives us adaptively formed beams that satisfy these demands. The MMSE beam-forming method is compared in various precipitation radar signal simulations with traditional beam-forming methods, Fourier and Capon methods, which have been applied in atmospheric research to observe distributed targets such as precipitation, and it is shown that the MMSE method is appropriate to this fast-scanning PAWR concept.

Broadband radio interferometer utilizing a sequential triggering technique for locating fast-moving electromagnetic sources emitted from lightning

A broadband radio interferometer to investigate the location of fast-moving electromagnetic sources emitted from lightning discharges has been designed and tested. A sequential triggering technique was applied to the system for recording the data of electromagnetic pulses, once the electromagnetic pulse is detected and its amplitude exceeds a threshold level, the triggering circuit is turned on to record the waveform for 1 microsecond and ready to acquire another pulse afterwards. This technique can record 2000 electromagnetic pulses maximum. We have implemented our system to locate and retrace fast-moving electromagnetic sources emitted from lightning discharges during a field experiment in Australia in December 1997. We succeeded in reconstructing a cloud to ground lightning discharge and displayed it in two dimensions and in time sequences.

Electric fields of initial breakdown in positive ground flash

Pulse trains superimposed on the initial part of the electric field change of positive ground flashes are investigated. The characteristics of these pulse trains are found to be different from those of negative ground flashes and cloud flashes. Each pulse included in a pulse train appears as a bipolar waveform with pulse width from 5 to 52 μs and a mean of 18 μs. The time intervals between successive pulses are 10 to 180 μs with a mean of 54 μs. For each bipolar pulse, the ratio of the peak amplitude of the initial polarity to the maximum overshoot amplitude ranges from 0.4 to 4.7 with a mean value of 1.3. The ratio of maximum peak amplitude of successive pulses to the amplitude of the following return-stroke peak ranges from 0.02 to 1.9 with a mean of 0.27.

Lightning‐initiator type of narrow bipolar events and their subsequent pulse trains

Previous observations show that some narrow bipolar events (NBEs) can initiate intracloud discharges, but the role of NBE as lightning initiation is still unclear. During the summer of 2013, 827 NBEs were detected with a 3-D LF lightning location system in Osaka, Japan. Out of 638 positive NBEs, 103 occurred as the initial events of lightning flashes. These initiator-type NBEs, called “INBEs” in this paper, are always followed by positive pulse trains whose locations show upward propagations probably from the main negative charge region to the upper positive charge region. Most of INBEs develop into intracloud flashes. Only two INBEs develop into positive ground flashes and five INBEs develop into negative ground flashes. Pulse widths and peak amplitudes of electric field change waveforms of INBEs are almost the same as those of normal NBEs. A major difference is that INBEs have much lower discharge heights. Most of INBEs are lower than 10 km while normal NBEs are mainly higher than 10 km. Characteristics of positive pulse trains following INBEs are closely related with discharge heights of INBEs. Higher INBEs are usually followed by weaker, fewer, and less frequent positive pulses with slower upward propagations. As the height increases to above 10 km, NBEs are usually no longer followed by such positive pulses.

Broadband and narrowband RF interferometers for lightning observations

Two-dimensional locations of VHF/UHF radiation sources emitted by lightning discharges are measured by both conventional narrowband and recently developed broadband interferometers during a field campaign in Darwin, Australia. Lightning channel images are recorded by an all sky video camera simultaneously. Observation results are compared with each other to confirm the function of the broadband interferometer. The conclusion of comparisons is that these observations show excellent agreement from the aspects of accuracy in azimuth and elevation. The potential capability of the broadband interferometer is evaluated. Advantages and disadvantages of both interferometers are discussed by introducing 2D mapping for additional flashes. It is shown that the broadband interferometer can locate multiple radiation sources, which propagate simultaneously through branching, in time and space.