Frequencies of wave packets of whistler-mode chorus inside its source region: a case study

Whistler-mode chorus is a structured wave emission observed in the Earth's magnetosphere in a frequency range from a few hundreds of Hz to several kHz. We investigate wave packets of chorus using high-resolution measurements recorded by the WBD instrument on board the four Cluster spacecraft. A night-side chorus event observed during geomagnetically disturbed conditions is analyzed. We identify lower and upper frequencies for a large number of individual chorus wave packets inside the chorus source region. We investigate how these observations are related to the central position of the chorus source which has been previously estimated from the Poynting flux measurements. We observe typical frequency bandwidths of chorus of approximately 10% of the local electron cyclotron frequency. Observed time scales are around 0.1 s for the individual wave packets. Our results indicate a lower occurrence probability for lower frequencies in the vicinity of the central position of the source compared to measurements recorded closer to the outer boundaries of the source. This is in agreement with recent research based on the backward wave oscillator theory

Observations of the relationship between frequency sweep rates of chorus wave packets and plasma density

International audience[1] Chorus emissions are generated by a nonlinear mechanism involving wave‐particle interactions with energetic electrons. Discrete chorus wave packets are narrowband tones usually rising (sometimes falling) in frequency. We investigate frequency sweep rates of chorus wave packets measured by the Wideband data (WBD) instrument onboard the Cluster spacecraft. In particular, we study the relationship between the sweep rates and the plasma density measured by the WHISPER active sounder. We have observed increasing values of the sweep rate for decreasing plasma densities. We have compared our results with results of simulations of triggered emissions as well as with estimates based on the backward wave oscillator model for chorus emissions. We demonstrate a reasonable agreement of our experimental results with theoretical ones. Citation: Macúšová, E., et al. (2010), Observations of the relationship between frequency sweep rates of chorus wave packets and plasma density

Potential Distribution of the Invasive Species Metcalfa pruinosa (Hemiptera, Flatidae) and Perspectives of its Classical Biocontrol in Ukraine

The study used GIS software and climate projections to assess the distribution potential of the citrus planthopper Metcalfa pruinosa (Say, 1830) in Ukraine, taking into account global climate change. The model showed that climatic conditions in Ukraine meet the requirements of the species in the European part of its range, considering various indicators such as the sum of active temperatures, mean annual temperature and precipitation. The whole territory of Ukraine could potentially be a range for M. pruinosa due to suitable climatic conditions and the presence of host plants, with Zakarpattia, Crimea and the forest and woodland and steppe zones of Ukraine being the most favourable. Current phytosanitary measures are not sufficient to prevent its spread and a pest management system is needed to reduce the damage. The parasitoid Neodryinus typhlocybae (Ashmead, 1893) (Hymenoptera, Dryinidae) from North America could serve as a classical biological control agent, and suitable areas in southern Ukraine have been identified using GIS modelling. To manage the risk effectively, it is recommended that M. pruinosa be added to the list of regulated, non-quarantined pests in Ukraine

The relationship between auroral hiss at high altitudes over the polar caps and the substorm dynamics of aurora

Strong variations of intensity and cutoff frequency of the auroral hiss were observed by INTERBALL-2 and POLAR satellites at high altitudes, poleward from the auroral oval. The hiss intensifications are correlated with the auroral activations during substorms and/or pseudo-breakups. The low cutoff frequency of auroral hiss increases with the distance between the aurora and the satellite footprint. Multicomponent wave measurements of the hiss emissions on board the POLAR spacecraft show that the horizontal component of the Poynting flux of auroral hiss changes its direction in good accordance with longitudinal displacements of the bright auroras. The vertical component of the Poynting flux is directed upward from the aurora region, indicating that hiss could be generated by upgoing electron beams. This relationship between hiss and the aurora dynamics means that the upgoing electron beams are closely related to downgoing electron beams which produce the aurora. During the auroral activations the upgoing and downgoing beams move and change their intensities simultaneously.<br><br> <b>Keywords.</b> Magnetospheric physics (Auroral phenomena; Plasma waves and instabilities; Storms and substorms