Geographically weighted regression based methods for merging satellite and gauge precipitation

Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004–06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometercalculated reflectivity of 40 dBZ, the number concentration was 700 100 drops m 3 , while the liquid water content and rain rate were 0.90 0.05 g m 3 and 18.5 0.5 mm h 1 , respectively. The mean mass diameter, on the other hand, was 1.67 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized intercept parameter had an increasing trend with reflectivity. The shape parameter, on the other hand, decreased in a reflectivity range from 10 to 20 dBZ and remained steady at higher reflectivities. Considering the repeatability of the characteristics of the raindrop size distribution, a second impact disdrometer that was located 5.3 km away from the primary site in Wallops Island, Virginia, had similar size spectra in selected tropical cyclones.

Raindrop Size Distribution Measurements in Tropical Cyclones

1 Seela, B. K., Janapati, J., Lin, P.-L.,Wang, P. K., & Lee, M.-T. (2018). Raindrop size distribution characteristics of summer and winter season rainfall over north Taiwan. Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1029/2018JD028307. Balaji Kumar Seela Taiwan International Graduate Program (TIGP) Earth System Science (ESS) Program Research Center for Environmental Changes (RCEC), Academia Sinica, Taiwan Institute of Atmospheric Science, National Central University, Jhongli City, Taiwan

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JD028307

Raindrop Size Distribution Characteristics of Summer and Winter Season Rainfall Over North Taiwan

Understanding the spatial and temporal controls of precipitation δ 18 O in the southern Tibetan Plateau of central Asia is necessary for paleoclimate reconstructions from the wealth of regional archives (ice cores, lake sediments, tree ring cellulose, and speleothems). While classical interpretations of such records were conducted in terms of local precipitation, simulations conducted with atmospheric general circulation models enabled with water stable isotopes have suggested that past changes in south Asia precipitation δ 18 O may be driven by remote processes linked to moisture transport. Studies conducted at the event scale can provide constraints to assess the drivers of precipitation δ 18 O and the validity of simulated mechanisms. Here, we take advantage of new event precipitation δ 18 O monitored from January 2005 to December 2007 at two southern Tibetan Plateau stations (Lhasa and Nyalam). The drivers of daily to seasonal variations are investigated using statistical relationships with local and regional temperature, precipitation amount and convective activity based on in situ data and satellite products. The strongest control on precipitation δ 18 O at Lhasa during the monsoon season at event and seasonal scales is provided by the integrated regional convective activity upstream air mass trajectories, cumulated over several days. In contrast, the integrated convection appears to be the main driver of precipitation δ 18 O at Nyalam only in July and August, and the situation is more complex in other months. Local climate variables can only account for a small fraction of the observed δ 18 O variance, with significant differences between both stations. This study offers a better constraint on climate archives interpretation in the southern Tibetan Plateau. The daily data presented here also provides a benchmark to evaluate the capacity of isotopically enabled atmospheric general circulation models (iGCMs) to simulate the response of precipitation δ 18 O to convection. This is illustrated using a nudged and zoomed simulation with the LMDZiso model. While it successfully simulates some seasonal and daily characteristics of precipitation δ 18 O in the southern Tibetan Plateau, it fails to simulate the correlation between δ 18 O and upstream precipitation. This calls for caution when using atmospheric models to interpret precipitation δ 18 O archives in terms of past monsoon variability. Keywords: stable isotopes, precipitation, regional convection, southern Tibetan Plateau (Published: 31 October 2013) Citation: Tellus B 2013, 65 , 21043, http://dx.doi.org/10.3402/tellusb.v65i0.21043

https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v65i0.21043

What controls precipitation δ 18 O in the southern Tibetan Plateau at seasonal and intra-seasonal scales? A case study at Lhasa and Nyalam

The availability of accurate precipitation data with high spatial resolution is deemed necessary for many types of hydrological, meteorological, and environmental applications. The Tropical Rainfall Measuring Mission (TRMM) data sets can provide effective precipitation information, but at coarse resolution (0.25°), so it is very important to improve their resolution. There is a strong relationship between precipitation and other environment variables (e.g. vegetation and topography). The existing precipitation-downscaling methods attempt to describe this relationship by using a uniform empirical model. However, in the real world, the relationship is disturbed due to the influence of certain factors such as soil type, hydrological conditions, and human activities. In this study, a new downscaling method considering this spatial heterogeneity was proposed to downscale version 7 of the TRMM 3B43 precipitation product, which assumes that the relationship varies spatially but is the same in a local region. At ...

Spatial downscaling of TRMM 3B43 precipitation considering spatial heterogeneity

Rain attenuation is an important aspect of signal propagation above 10GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modifled by incorporating an efiective slant path model. The efiective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007{2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.

/pdf/improving-rain-attenuation-estimation-modelling-of-effective-4cqle4qq9w.pdf

Improving Rain Attenuation Estimation: Modelling of Effective Path Length Using Ku-Band Measurements at a Tropical Location

Microphysical characteristics of clouds and precipitation during pre-monsoon and monsoon period over a tropical Indian station

The phenomenon of scintillations in relation to rain attenuation of Ku-band satellite signals has been studied at a tropical location. The standard deviation (σ) of scintillations increases with attenuation up to a value in the range of 6-7 dB, beyond which σ decreases with attenuation. A technique is proposed to obtain some effective values of structure constant (Cn2) of refractive-index variation from the experimental observations of σ and rain rate (R). The value of Cn2 also increases with attenuation up to values in the 6-7-dB range and decreases beyond that value. The eddies in turbulent raining medium grow with rain rate, and consequently with attenuation, causing an increase in the outer scale (LO) of turbulence and thus increasing σ until LO reaches the size of the first Fresnel zone. In a further development, the contribution of LO toward Cn2 decreases, resulting in the decrease of fast fluctuations with rain attenuation.

Rain-Induced Scintillations and Attenuation of Ku-Band Satellite Signals at a Tropical Location

A severe cyclone, named Aila, passed over Kolkata on 25 May 2009. The strong convective activities manifested through rainfall during the cyclone were studied with multi-technique observations involving micro rain radar, disdrometer, rain gauges, and a Ku-band satellite signal receiving system. A number of features of precipitation, namely the presence of large rain drops, the large vertical extent of the precipitating layer, an unusual enhancement of cross-polar component, and strong scintillations of the co-polar component of the satellite signal due to strong turbulences associated with the cyclone, were observed. This study leads to a more comprehensive understanding of the precipitation associated with a cyclonic storm.

Multi-technique observations on precipitation and other related phenomena during cyclone Aila at a tropical location

Two significant propagation characteristics of Ku-band satellite signal, namely rain attenuation and depolarization have been studied over Kolkata (22°34'N, 88°29'E), a tropical location. The existing Simple Attenuation Model (SAM) for rain attenuation estimation has been improved by incorporating the effective rain rate at different rain rates. The impact of rain drop size distribution (DSD) on determining the extent of depolarization at the tropical location is investigated. The lognormal distribution has been found to be more accurate than the gamma distribution to model rain drop sizes in the present case. Rain DSD varies for different types of rain, even during different phases of rain event and is found to influence the cross-polar enhancement of Ku-band signal. The annual variation of cross-polar enhancement indicates the dominance of different types of rain during different seasons of the year.

http://nopr.niscair.res.in/bitstream/123456789/14755/1/IJRSP%2041%284%29%20481-487.pdf

Aniruddha Bhattacharya

Papers

Improving Rain Attenuation Estimation: Modelling of Effective Path Length Using Ku-Band Measurements at a Tropical Location

Microphysical characteristics of clouds and precipitation during pre-monsoon and monsoon period over a tropical Indian station

Rain-Induced Scintillations and Attenuation of Ku-Band Satellite Signals at a Tropical Location

Multi-technique observations on precipitation and other related phenomena during cyclone Aila at a tropical location

Some characteristics of earth-space path propagation phenomena at a tropical location