Cloud microphysical structure analysis based on high-resolution insitu measurements

This study investigates the microphysical parameters and shapes of droplet size distributions (DSDs) along three aircraft traverses of developing convective clouds during Cloud Aerosol Interactions and Precipitation Enhancement EXperiment (CAIPEEX) 2015 at a sampling frequency of 25 Hz. The droplet number concentration (Nc, cm−3), and liquid water content (LWC, gm−3) present steep gradients within a few tens of meters’ zones near the cloud edges and relatively gentle gradients in the strong updraft zones. Sometimes, the horizontal LWC distribution resembles a trapezoid-like shape with steep LWC and Nc gradients near the cloud edges. The LWC maximums (LWCmax) are lower than the adiabatic LWC, but the high adiabatic fractions in the cloud core indicate low dilution. High LWC/LWCmax, largest droplets, and narrow and similarly-shaped DSDs are found in the regions of high updrafts. Zones of low LWC/LWCmax are found close to the cloud edges, where DSDs are highly diverse, containing both large and small droplets. Finally, we analyze the mixing diagrams.Significant in-phase turbulent fluctuations in LWC and Nc were found. The effective radii change slightly across cloud updraft zones but decrease at the low LWC/LWCmax ratio zone close to cloud edges. The spectra of LWC and Nc obey Kolmogorov -5/3 turbulence law. The radii of the correlation of LWC and Nc in updraft zones are of several tens of meters. Filaments up to 120-175 m in size are also noticed.

Modeling of Lightning Events using WRF-derived Microphysical Parameters

Numerical simulation of lightning events in Bangladesh has been carried out by using Weather Research and Forecasting Model with Advanced Research Dynamic solver (WRF-ARW). Three major lightning events have been considered for the case study; Case_1, lightning occurrence in Netrokona district in March 24 2017, Case_2, lightning event in Barishal district in April 23 2017, and case_3, lightning event in Sherpur district in April 29, 2018. The model simulation was run in 9 km and 3 km of horizontal resolution using six hourly NCEP-FNL datasets. Yonsei University (YSU) PBL scheme, Rapid Radiative Transfer Model (RRTM) long-wave scheme for radiation, and Kain-Fritsch cumulus parameterization scheme is used for this study. The obtained results from the simulation could reasonably capture the lightning condition of the atmosphere for all the three cases. The WRF simulation give reasonable agreement with the available observational data with some spatial and temporal variations, for example the Convective Available Potential Energy (CAPE) values observed are 1299 J/Kg, 3150 J/kg, 1221 J/kg and CAPE values simulated are 1618 J/kg, 3275 J/kg and 1023 J/kg for case_1, case_2 and case_3 respectively. The regression analysis of the flash count with the microphysical parameters is also studied. It is found that there is strong correlation between the lightning flash counts with the microphysical parameters. This study will help to understand the lightning better and will help to design a better lightning forecasting system. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(2), 2019, P 41-50

Numerical simulation and analysis of pressure distribution and airflow speed around an airborne cloud microphysics measurements instrument

Clouds have an important impact on Earth’s energetic balance, so measuring accurately the microphysical parameters and using them in research has become one important step in atmospheric studies. Regarding the fact that light scattering probes convert the flow rate to concentration, any wrong assumption or measurement of the flow rate can lead to incorrect results. Applying numerical simulation to an airborne cloud microphysics measurements instrument can provide information that can be measured in any point of the sampling volume, and further used in determination of microphysics parameters, providing more accurate data. Taking this into consideration, in this paper are presented the results of numerical simulation applied to Cloud Aerosol and Precipitation Spectrometer and the comparison with results reported in literature.

A new approach to modelling gamma-ray burst afterglows: using Gaussian processes to account for the systematics

ABSTRACT The afterglow emission from gamma-ray bursts (GRBs) is a valuable source of information to understand the physics of these energetic explosions. The fireball model has become the standard to describe the evolution of the afterglow emission over time and frequency. Because of recent developments in the theory of afterglows and numerical simulations of relativistic outflows, we are able to model the afterglow emission with realistic dynamics and radiative processes. Although the models agree with observations remarkably well, the afterglow emission still contains additional physics, instrumental systematics, and propagation effects that make the modelling of these events challenging. In this work, we present a new approach to modelling GRB afterglows, using Gaussian processes (GPs) to take into account systematics in the afterglow data. We show that, using this new approach, it is possible to obtain more reliable estimates of the explosion and microphysical parameters of GRBs. We present fit results for five long GRBs and find a preliminary correlation between the isotropic energetics and opening angles of GRBs, which confirms the idea of a common energy reservoir for the kinetic energy of long GRBs.

Estimating Rain Microphysical Characteristics Using S-Band Dual-Polarization Radar in South Korea

Raindrop size distribution (DSD) observed using a disdrometer can be represented by a constrained-gamma (C-G) DSD model based on the empirical relationship between shape (µ) and slope (Λ). The C-G DSD model can be used to retrieve DSDs and rain microphysical parameters from dual-polarization radar measurements of reflectivity (ZH) and differential reflectivity (ZDR). This study presents a new µ–Λ relationship to characterize rain microphysics in South Korea using a two-dimensional video disdrometer (2DVD) and Yong-in S-band dual-polarization radar. To minimize sampling errors from the 2DVD and radar measurements, measured size distributions are truncated by particle size and velocity-based filtering and compared with rain gauge measurement. The calibration biases of radar ZH and ZDR were calculated using the self-consistency constraint and vertical pointing measurements. The derived µ–Λ relationship was verified using the mass-weighted mean diameter (Dm) and standard deviation of the size distribution (σm), calculated from the 2DVD, for comparison with existing µ–Λ relationships for Florida and Oklahoma. The Dm–σm relationship derived from the 2DVD corresponded well with the µ–Λ relationship. The µ–Λ relationship derived for the Korean Peninsula was similar to Florida, and both generally had larger µ values than Oklahoma for the same Λ. The derived µ–Λ relationship was applied to retrieve DSD parameters from polarimetric radar data, and the retrieved DSDs and derived physical parameters were evaluated and compared with the 2DVD measurements. The polarization radar-based C-G DSD model characterized rain microphysics more accurately than the exponential DSD model. The C-G DSD model based on the newly derived µ–Λ relationship performed the best at retrieving rain microphysical parameters.

Physics and Phenomenology of Weakly Magnetized, Relativistic Astrophysical Shock Waves

Weakly magnetized, relativistic collisionless shock waves are not only the natural offsprings of relativistic jets in high-energy astrophysical sources, they are also associated with some of the most outstanding displays of energy dissipation through particle acceleration and radiation. Perhaps their most peculiar and exciting feature is that the magnetized turbulence that sustains the acceleration process, and (possibly) the secondary radiation itself, is self-excited by the accelerated particles themselves, so that the phenomenology of these shock waves hinges strongly on the microphysics of the shock. In this review, we draw a status report of this microphysics, benchmarking analytical arguments with particle-in-cell simulations, and extract consequences of direct interest to the phenomenology, regarding, in particular, the so-called microphysical parameters used in phenomenological studies.