Kavitoni – nov pojav v območju pred Zemljinim udarnim valom / Cavitons - new fenomenon in the Earth's foreshock

Povzetek: Območje pred Zemljinim udarnim valom (angl. “foreshock region”) je zelo turbulentno. Poseljeno je s fluktuacijami gostote plazme ter magnetnega polja. Poleg fluktuacij, ki jim pravimo valovi, se pojavljajo tudi prehodne strukture, znane kot gostotne luknje (angl. “density holes”), anomalije vročega toka (angl. “hot flow anomalies”) ter votline v območju pred udranim valom (angl. “foreshock cavities”). Nedavno so rezultati globalnih hibidnh simulacij (kinetični ioni, elektroni brezmasna tekočina z nabojem) nakazali obstoj še enega tipa prehodnih struktur, t.i. kavitonov v območju pred udranim valom (angl. “foreshock cavitons”). Kavitoni in votline so si na prvi pogled v marsičem podobni, vendar je njihov nastanek posledica dveh različnih formacijskih mehanizmov. V tem članku na kratko predstavimo območje pred Zemljinim udarnim valom ter opišemo lastnosti najbolj tipičnih populacij delcev, valov ter prehodnih struktur, ki se v njem nahajajo. Posebej natančno, na dveh primerih, primerjamo opazovalne lastnosti votlin ter kavitonov ter razpravljamo o njihovh podobnostnih in razlikah.
Ključne besede: magnetosferna fizika; planetarni uarni valovi; kavitoni v območju pred udarnim valom

Abstract: The region upstream of the earth's bow shock is highly turbulent. It is populated by fluctuations of plasma density and magnetic field. Besides the fluctuations known as waves, there are also transient structures, such as density holes, hot flow anomalies and foreshock cavities. The recent global hybrid (kinetic ions + fluid electrons) simulations results suggested the existence of a new type of transient structures called the foreschock cavitons. At first glimpse, the cavities and the cavitons share many similarities, but they form due to different physical processes. In this work we present the region upstream of the earth's shock, i.e. the earth's foreshock, and describe the properties of the most typical populations of particles, waves and transient structures that populate it. We compare in detail the observational properties of foreshock cavities and cavitons by presenting two case studies and we discuss their similarities and differences.