Raindrop size distribution (RSD) characteristic variations between two southern Indian stations [Gadanki (13.5° N, 79.2° E) Kadapa (14.47° N, 78.82° E)] using ground based parsivel disdrometer data are studied. Number concentration of mid and large drops is more over Gadanki when compared to Kadapa precipitation. The mean value of mass weighted mean diameter (Dm) is higher in Gadanki than Kadapa precipitation. Both monthly and diurnal variations of Dm show higher values of Dm over Gadanki than Kadapa. After classifying the precipitations systems into stratiform and convective, Gadanki has higher (lower) Dm than Kadapa in stratiform (convective).
The initial and boundary conditions are critical to the numerical weather prediction (NWP) model. It is known that satellite observations can overcome the limitations of the terrain, especially over the oceans where conventional observations are difficult to obtain. Therefore, the use of satellite data will expect to improve those regions where lack of traditional observation. The Advanced Microwave Sounding Unit (AMSU) and Atmospheric InfraRed Sounder (AIRS) onboard NASA’s EOS Aqua satellite, represent microwave and hyperspectral infrared observations, respectively. Both of them may provide atmospheric temperature and moisture soundings with complementary characteristics. For example, AMSU has the advantage to give cloudy retrievals while AIRS may retain the atmospheric gradient due to its finer high spatial resolution. Both data could estimate atmospheric thermodynamic state with substantial accuracy to improve high impact weather forecast In this study, we adopt the Weather Research and Forecasting (WRF) model and the community Gridpoint Statistical Interpolation (GSI) data assimilation system to evaluate the use of AMSU/AIRS retrievals for severe precipitation at Taiwan. The front, UTC 2016/01/05 22Z, is selected to demonstrate the benefit of using sounding data. The preliminary results shows a positive impact on total precipitable water while the time slope may need further investigation.
Many people in Asia regions have been suffering from disastrous rainfalls year by year. The rainfall from typhoons or tropical cyclones (TCs) is one of their key water supply sources, but from another perspective such TCs may also bring forth unexpected heavy rainfall, thereby causing flash floods, mudslides or other disasters. So far we cannot stop or change a TC route or intensity via present techniques. Instead, however we could significantly mitigate the possible heavy casualties and economic losses if we can earlier know a TC’s formation and can estimate its rainfall amount and distribution more accurate before its landfalling. In light of these problems, this short article presents methods to detect a TC’s formation as earlier and to delineate its rainfall potential pattern more accurate in advance. For this first part, the satellite-retrieved air-sea parameters are obtained and used to estimate the thermal and dynamic energy fields and variation over open oceans to delineate the high-possibility typhoon occurring ocean areas and cloud clusters. For the second part, an improved tropical rainfall potential (TRaP) model is proposed with better assumptions then the original TRaP for TC rainfall band rotations, rainfall amount estimation, and topographic effect correction, to obtain more accurate TC rainfall distributions, especially for hilly and mountainous areas, such as Taiwan.
This study used the spectral features of the geostationary satellite infrared window channel and the water vapor channel data to calculate a new parameter, normalized difference convection index (NDCI), to help determine the overshooting areas in typhoon cloud systems and the centers and intensity of typhoons. The results showed that the two-dimensional NDCI analysis helped to identify typhoon convective cloud systems and the positions of overshooting areas. In addition, because the NDCI values near a typhoon eye were rather significant, if a typhoon eye was formed, the NDCI cross-section analysis could help to confirm its position. When the center of a typhoon was covered by the high anvils and cirrus layers, it could still be qualitatively found through two-dimensional analysis. As for determining the intensity of typhoons, this study also tried to perform correlation analyses with NDCI and maximum sustained wind speed. The result showed that in the ranges within circles of 200 to 250 km radii with a typhoon eye as the center, the correlation between the area with the NDCI values <0 and the maximum sustained wind speed is high with a coefficient 0.7. Thus, the NDCI value could be a referential index to determine the intensity of a typhoon.
Hyperspectral infrared (IR) sounder from low earth orbit (LEO) provides temperature and moisture soundings with high
accuracy and high vertical resolution, however, due to its low temporal coverage rate (twice every day for one sounder
instrument), data are usually missing during short range convective storm development. The Advanced Baseline Imager
(ABI) onboard the next generation of geostationary (GEO) satellite, on the other hand, provides very fast coverage rate
but lower vertical resolution and less accurate profiles. Combination of GEO ABI measurements and LEO hyperspectral
IR sounder data may provide atmospheric evolution with high temporal resolution and fairly vertical structure. An
algorithm is developed for monitoring the sounding evolution from combined GEO imager and LEO IR sounder data.
The collocated geolocation of GEO imager and LEO sounder systems can (1) provide LEO sounder sub-pixel cloud
characterization (mask, amount, phase, layer information, etc.) within the large sounder footprint; (2) be used for LEO
sounder cloud-clearing for partly cloudy footprints; (3) provide background information in variational retrieval of cloud
properties with sounder cloudy radiances; (4) provide real-time background information for GEO imager instantly
without Numerical Weather Prediction (NWP) data. The Moderate-Resolution Imaging Spectroradiometer (MODIS)
and the Atmospheric Infrared Sounder (AIRS) measurements from the Earth Observing System's (EOS) Aqua satellite
provide the opportunity to study the synergistic use of advanced imager and sounder measurements. The combined
MODIS and AIRS data for various scenes are analyzed to study the utility of synergistic use of ABI products and LEO
sounder radiances for better retrieving atmospheric soundings and cloud properties.
Algorithm has been developed for retrieving atmospheric temperature and moisture profiles from hyperspectral infrared
(IR) sounder radiances under both clear and cloudy skies. Focus has been on handling surface emissivity and clouds in
IR only sounding retrieval.
The Atmospheric Infrared Sounder (AIRS) and MODerate-Resolution Imaging Spectroradiometer (MODIS) on board the EOS Aqua spacecraft measure the upwelling infrared radiance used for numerous remote sensing and climate related applications. AIRS provides high spectral resolution infrared radiances while MODIS provides collocated high spatial resolution radiances at sixteen broad infrared bands. An optimal algorithm for cloud-clearing has been developed for AIRS cloudy soundings at the University of Wisconsin-Madison where the spatially and spectrally collocated AIRS and MODIS data has been used to verify this algorithm. A global analysis and characterization of the AIRS cloud-clearing using the bias and the standard deviation between AIRS cloud-cleared brightness temperature and the nearby clear brightness temperature are studied.
The Advanced Baseline Imager (ABI) and the Hyperspectral Environmental Suite (HES) on GOES-R and beyond will enable improved monitoring of the distribution and evolution of atmospheric thermodynamics and clouds. The HES will be able to provide hourly atmospheric soundings with spatial resolution of 4 ~ 10 km with high accuracy using its high spectral resolution measurements. However, presence of clouds affects the sounding retrieval and needs to be dealt with properly. The ABI is able to provide at high spatial resolution (0.5 ~ 2km) a cloud mask, surface and cloud types, cloud phase mask, cloud top pressure (CTP), cloud particle size (CPS), and cloud optical thickness (COT), etc. The combined ABI/HES system offers the opportunity for atmospheric and cloud products improved over those possible from either system alone. The key step for synergistic use of ABI/HES radiance measurements is the collocation in space and time. Collocated ABI can (1) provide HES sub-pixel cloud characterization (mask, amount, phase, layer information, etc.) within the HES footprint; (2) be used for HES cloudclearing for partly cloudy HES footprints; (3) provide background information in variational retrieval of cloud properties with HES cloudy radiances. The Moderate-Resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS) measurements from the Earth Observing System's (EOS) Aqua satellite provide the opportunity to study the synergistic use of advanced imager and sounder measurements. The combined MODIS and AIRS data for various scenes are analyzed to study the utility of synergistic use of ABI products and HES radiances for better retrieving atmospheric soundings and cloud properties. In order to derive sounding from combined ABI and HES radiances under HES partly cloudy footprint where no microwave sounding unit is available, an optimal cloud-removal or cloud-clearing algorithm is developed. MODIS and AIRS are used to verify the algorithm. AIRS clear column radiances are retrieved from the combined MODIS IR clear radiances and the AIRS cloudy radiances on a single footprint basis. The AIRS cloud-removed or cloudcleared radiance spectrum is convoluted to all the MODIS IR spectral bands with spectral response functions (SRFs), and the convoluted brightness temperatures (BTs) are compared with MODIS clear BT observations within all successful cloud-cleared footprints. The bias and the standard deviation between the convoluted BTs and MODIS clear BT observations is less than 0.25 K and 0.5 K, respectively, over both water and land for most MODIS IR spectral bands. The AIRS cloud-cleared BT spectrum is also compared with its nearby clear BT spectrum, the difference, accounting the effects due to scene non- uniformity, is reasonable according the analysis. It is found that more than 30% of the AIRS cloudy (partly and overcast) footprints in this study have been successfully cloud-cleared using the optimal cloud-clearing method, revealing the potential application of this method on the operational processing of hyperspectral IR sounder cloudy radiance measurements when the collocated imager IR data is available.