Radar observations of tropical cyclones over the Indian Seas

ABSTRACT. A review is presented of the radar observation of tropical cyclones in the Indian seas. The use of radar in operational cyclone tracking and forecasting as well as the knowledge gained from radar observations of the structure, wind and rainfall distribution and motion of cyclones are discussed. In the context of the expected introduction of operational Doppler ra1ars in India, the future prospects in the use of radar for operations and research are outlined. Some important areas where our understanding of cyclones can be improved by studies with radar in conjunction with other observations are listed.

Hydrometeor Classification of Winter Precipitation in Northern China Based on Multi-Platform Radar Observation System

Hydrometeor classification remains a challenge in winter precipitation cloud systems. To address this issue, 42 snowfall events were investigated based on a multi-platform radar observation system (i.e., X-band dual-polarization radar, Ka-band millimeter wave cloud radar, microwave radiometer, airborne equipment, etc.) in the mountainous region of northern China from 2016 to 2020. A fuzzy logic classification method is proposed to identify the particle phases, and the retrieval result was further verified with ground-based radar observation. Moreover, the hydrometeor characteristics were compared with the numerical simulations to clarify the reliability of the proposed hydrometeor classification approach. The results demonstrate that the X-/Ka- band radars are capable of identifying hydrometeor phases in winter precipitation in accordance with both ground observations and numerical simulations. Three particle categories, including snow, graupel and the mixture of snow and graupel are also detected in the winter precipitation cloud system, and there are three vertical layers identified from top to bottom, including the ice crystal layer, snow-graupel mixed layer and snowflake layer. Overall, this study has the potential for improving the understanding of microphysical processes such as freezing, deposition and aggregation of ice crystal particles in the winter precipitation cloud system.

Observing meteors by creating artificial luminous clouds in the Earth’s atmosphere

В статье дается предварительная теоретическая оценка возможности применения нового способа наблюдения метеоров в атмосфере Земли с помощью искусственных светящихся облаков. При попадании метеоров в такие облака, образованные веществом с потенциалом ионизации в несколько раз меньшем потенциала ионизации атмосферных газов, происходит быстрая ионизация реагента облака за счет термического и ударного воздействия метеорного тела, приводящая к увеличению светимости метеорных следов. Предполагается, что такой эффект будет способствовать увеличению яркости слабых метеоров, находящихся на пороге обнаружения современных телевизионных камер. Это позволит проводить исследования метеоров и метеорных потоков, доступных ранее только радиолокационными методами наблюдения. The article provides a preliminary theoretical assessment of the possibility of using a new method of observing meteors in the Earth’s atmosphere using artificial luminous clouds. When meteors hit such clouds formed by a substance with an ionization potential several times lower than the ionization potential of atmospheric gases, the cloud reagent is rapidly ionized due to the thermal and impact effects of the meteor body, which leads to an increase in the luminosity of meteor tracks. It is assumed that this effect will increase the brightness of weak meteors, which are on the threshold of detection by modern TV cameras. This will make it possible to conduct studies of meteors and meteor showers that were previously available only by radar observation methods.

Interpreting estimated observation error statistics of weather radar measurements using the ICON-LAM-KENDA system

Assimilation of weather radar measurements including radar reflectivity and radial wind data has been operational at the Deutscher Wetterdienst, with a diagonal observation error (OE) covariance matrix. For an implementation of a full OE covariance matrix, the statistics of the OE have to be a priori estimated, for which the Desroziers method has been often used. However, the resulted statistics consists of contributions from different error sources and are difficult to interpret. In this work, we use an approach that is based on samples for truncation error in radar observation space to approximate the representation error due to unresolved scales and processes (RE) and compare its statistics with the OE statistics estimated by the Desroziers method. It is found that the statistics of the RE help the understanding of several important features in the variances and correlation length scales of the OE for both reflectivity and radial wind data and the other error sources from the microphysical scheme, radar observation operator and the superobbing technique may also contribute, for instance, to differences among different elevations and observation types. The statistics presented here can serve as a guideline for selecting which observations are assimilated and for assignment of the OE covariance matrix that can be diagonal or full and correlated.

The Apparent Behavior of Electron Density during an Alternating O/X-Mode Heating Experiment

We present the observations of the artificial ionospheric modification experiment of EISCAT on 18 October 2012 in Tromsø, Norway. When the pump of alternating O mode and X mode is switched on, the UHF radar observation shows some strong enhancements in electron density, ion lines and plasma lines. Based on some existing theories, we find the following: First, during the experiment, the frequency of plasma line (), ion line () and pump () matches = − 3 and = − 5 occasionally demonstrated that the cascade process occurred. Second, through quantitative calculation, we found that the O-mode component mixed in X-mode wave satisfies the thresholds of the parametric decay instability and the oscillation two-stream instability, from which we infer that the HF-induced plasma lines (HFPLs) and HF-enhanced ion lines (HFILs) observed in X-mode pulse could have been caused by the O-mode component mixed in X-mode wave. Third, the UHF radar observation shows some apparent enhancements over a wide altitude range (from approximately the reflection altitude to ~670 km) in electron density during X-mode pulse, which also does not, in fact, correspond to a true increase in electron density, but due to the enhancement in ion line or the enhancement in radar backscatter induced by some unknown mechanism.