Disdrometer

About: Disdrometer is a research topic. Over the lifetime, 930 publications have been published within this topic receiving 23092 citations.

On the distinctiveness of observed oceanic raindrop distributions

Abstract: . Representation of the drop size distribution (DSD) of rainfall is a key element of characterizing precipitation in models and observations, with a functional form necessary to calculate the precipitation flux and the drops' interaction with radiation. With newly available oceanic disdrometer measurements, this study investigates the validity of commonly used DSDs, potentially useful a priori constraints for retrievals, and the impacts of DSD variability on radiative transfer. These data are also compared with leading satellite-based estimates over ocean, with the disdrometers observing a larger number of small drops and significantly more variability in number concentrations. This indicates that previous appraisals of raindrop variability over ocean may have been underestimates. Forward model errors due to DSD variability are shown to be significant for both active and passive sensors. The modified gamma distribution is found to be generally adequate to describe rain DSDs but may cause systematic errors for high-latitude or stratocumulus rain retrievals. Depending on the application, an exponential or generalized gamma function may be preferable for representing oceanic DSDs. An unsupervised classification algorithm finds a variety of DSD shapes that differ from commonly used DSDs but does not find a singular set that best describes the global variability.

Specific attenuation and depolarisation in rain from 2-dimensional video disdrometer data

Abstract: Data from 2-dimensional video disdrometers (2DVD) taken in different locations are used to derive the specific attenuation for horizontal and vertical polarisations at 20 GHz. The data include both drop-size distribution and their axis ratio distributions. T-matrix calculations using data over 1 min integration time show a power-law dependence on rain rate. The best-fit coefficients are compared with those given in the ITU-R Recommendation P. 838, both versions 2 and 3. Closest agreement is seen for vertical polarisation for version 2 and the largest discrepancies are seen for horizontal polarisation for version 3. The discrepancies are attributed to the different assumptions in the drop-size distributions, as well as the upper limit of integration for deriving the specific attenuation. The variation of the crosspolar discrimination (XPD) against copolar attenuation (CPA) is also examined. The 2DVD data are used to simulate a beacon experimental scenario at 20 GHz, the actual locations of the two instruments being different but climatically similar. Good agreement is seen with one year of beacon measurements, but the latter shows more spread in the variation, partly attributed to drop oscillations. Calculations also show that XPD-CPA variation is sensitive to the assumed drop shapes.

Raindrop size distribution properties associated with vertical air motion in the stratiform region of a springtime rain event from 1290 MHz wind profiler, micro rain radar and Parsivel disdrometer measurements

Abstract: On 12 March 2012, a frontal rain system elongated east–west occurred over the southern coast of Korea, a frequently observation during springtime. Characteristics of raindrop size distributions (RSDs) in the stratiform region of the rain system observed by a 1290 MHz wind profiler collocated with a Parsivel disdrometer and K-band micro rain radar (MRR) are investigated. Temporal RSD variations are in close agreement between the instruments in spite of different sampling volume and height. It is found that number concentrations at small drop range around 1 mm measured from the profiler at 800 m AGL are noticeably fewer particularly at times of high rainfall rates, compared to those at the same drop range from the MRR and disdrometer. This is likely attributed to downdrafts that were enhanced below a strong bright band. Profiler Doppler spectra and RSD retrievals are susceptible to vertical air motion effects (especially at small drop range) at higher levels, compared to surface disdrometer retrievals. Thus, vertical air motion retrievals from profiler Doppler spectra were performed and showed good agreement in comparison with vertical air motions derived from a conventional method (i.e. radar reflectivity–fallspeed relation). Following this, vertical air motion effects on rain rate and mass-weighted mean diameter parameters were examined quantitatively using a profiler spectral model for conditions of updrafts and downdrafts.