The characteristics of raindrop size distributions (DSDs) during a midlatitude continental squall line on 30 July 2014 in east China are studied, and the different life stages are observed by OTT second-generation Particle Size Velocity (Parsivel2) disdrometers at Chuzhou during the mature stage and Nanjing during the declining stage. The observed rainfall is classified into convective line, transition, and stratiform regions based on the structure of the radar reflectivity Z and rainfall intensity R. The results show that the DSD characteristics of the different precipitation types and different squall-line stages are very different. The convective center has the largest number concentration and quantity of large drops corresponding to the highest rain rate; the rain rates in the trailing edge and stratiform regions are similar, although a lower concentration of small drops is present in the latter. Between the two stages, the drop size and number concentration for the convective center decrease, although the leading edge during the declining stage has more numerous larger drops; the number concentration is similar in the stratiform rainfall, but the drops become much smaller. For the normalized distribution, the scaled spectra for the convective center are closer to an exponential distribution, and the μ value during the declining stage is larger than that during the mature stage for the stratiform region and similar during both stages for the convective center. The declining stage has a larger exponent b and smaller coefficient A in the Z–R relationship based on fits for the entire dataset. Moreover, the R(ZH, ZDR) estimator is more accurate than that when using the Z–R relation algorithm.
The nonlinear propagation of femtosecond Airy laser filaments in water is numerically investigated in this paper. We mainly consider the influences of confinement parameter, pulse duration and beam waist on the deposited energy of filaments. The values of confinement parameter are found to have a significant impact on the temporal and spatial dynamics of the pulse. The characteristics of energy deposition also differ widely for Airy beams with different confinement parameters. The less the confinement parameter, the more energy deposited by filamentation. However, the relative deposited energy evolves relatively small changes under different confinement parameters. We also found the longer pulse duration and longer beam waist are beneficial to the total deposited energy increase.
In this study, the heat deposition characteristics of laser filaments formed by femtosecond laser pulses with different initial energy under influences of external focusing are numerically investigated by means of (3D + 1)-dimensional numerical simulations. The results indicate that the numbers and intensity of filaments increase with growth of the input energy. The formation of multiple filaments limits the increase of filament length. When fixing the input energy, radius of the filament becomes narrow while its numbers and intensity are both enhanced under strong focusing. Under stronger focusing, the filaments can also deposit higher laser energy and result in larger energy deposition rate for laser beams with a given input energy, which further leads to dramatic increase in local temperature and pressure. These are likely to affect the filament induced airflow velocity and eventually the mass of formed snow in the cold supersaturated cloud chamber.
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