A comparison of wave mode identification techniques

Abstract

Abstract. The four point measurements available from the Cluster mission enable spatiotemporal effects in data sets to be resolved. One application of these multipoint measurements is the determination of the wave vectors and hence the identification of wave modes that exist within the plasma. Prior to multi-satellite missions, wave identification techniques were based upon the interpretation of observational data using theoretically defined relations. However, such techniques are limited by the quality of the data and the type of plasma model employed. With multipoint measurements, wave modes can be identified and their wave directions determined purely from the available observations. This paper takes two such methods, a phase differencing technique and k-filtering and compares their results. It is shown that both methods can resolve the k vector for the dominant mirror mode present in the data. The phase differencing method shows that the nature of the wave environment is constantly changing and as such both methods result in an average picture of the wave environment in the period analysed. The k-filtering method is able to identify other modes that are present.

Wave properties in the magnetic reconnection diffusion region with high β: Application of the k‐filtering method to Cluster multispacecraft data

“…Our time interval is shorter and is free of such reversals, which yields a more accurate estimation of the average flow speed. Second, there are intrinsic differences between the two methods (the k-filtering and the phase difference) used to estimate the characteristic of the waves [Walker et al, 2004]. For instance, Chaston et al [2005] claim to resolve scales smaller than the spacecraft separations and also analyzed frequencies up to 10 Hz in the spacecraft frame (these limits were not discussed by Chaston et al [2009]), which most likely involve spatial aliases as shown by Sahraoui et al [2010].…”

“…Borg et al [2005] and Chaston et al [2009] have studied this event and confirmed that the Cluster spacecraft encountered a diffusion region around 2330 UT. Chaston et al [2009] have, furthermore, estimated the wave vectors of the fluctuations using an interferometry method that makes use of measured phase differences between the satellites [Walker et al, 2004]. They showed that waves observed in the diffusion region were consistent with KAWs.…”

Low frequency wave sources in the outer magnetosphere, magnetosheath, and near Earth solar wind

“…The highly changeable nature of the waves for this particular interval was already noticed by Walker et al (2004). The nature of the waves differs from interval to interval and from frequency to frequency for a given interval.…”

“…Tjulin et al (2005) confirm the presence of mirror modes for the same interval by analyzing the electric field fluctuations after using both magnetic and electric field as input for the k-filtering. Walker et al (2004) compare the results obtained via k-filtering with those obtained via phase differencing method (Balikhin et al, 1997) applied to the same 164 s data interval. They find a mixture of slow, Alfvén and mirror waves with their wave vectors close to the orthogonal direction to the average magnetic field.…”

The wave surveyor technique for fast plasma wave detection in multi-spacecraft data

“…Matsui et al (2007) applied a phase differencing technique to Cluster observations to study broadband ULF waves near the dayside polar cap boundary. For a detailed comparison of the phase differencing approach with the k-filtering technique using Cluster STAFF and EFW measurements, the reader is referred to Walker et al (2004). For a review of the wave distribution determination problem, see Storey (1999).…”