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Latitudinal and seasonal variations of quasiperiodic and periodic VLF emissions in the outer magnetosphere

first_imgWe have analyzed ELF-VLF receiver and search coil magnetometer data from five Antarctic stations from 1998 and 1999 to study quasiperiodic emissions (QPs) and periodic emissions (PEs), which occur as ULF-range modulations of ELF-VLF signals between 0.5 kHz and similar to4 kHz. QPs are modulated at frequencies of similar to20-50 mHz, and PEs are modulated at frequencies of similar to200-500 mHz. The stations used covered a range of magnetic latitudes from -62degrees (Halley) to -74degrees (South Pole Station); three automated geophysical observatories (AGOs) were located at intermediate latitudes. Consistent with earlier studies, most QPs were observed with magnetic pulsations of identical period in the Pc3 range ( type I QPs). Of those QPs not observed with simultaneous magnetic pulsations ( type II QPs), nearly all were accompanied by PEs. Type I QPs, PEs, and events during which both appeared together (QPPEs) were found to have different latitudinal, seasonal, and diurnal occurrence patterns: QPs of both types were more likely to occur between -65degrees and -70degrees magnetic latitude, while PEs occurred more often around -60degrees magnetic latitude. QPs were more common during the months of October though March, while PEs were more common during the months of May through September. QPs, whether with or without simultaneous PEs or magnetic pulsations, were predominantly a dayside phenomenon, with a broad maximum near local noon. The occurrence of QPs unaccompanied by PEs was restricted to the dayside, however, while a small number of QPPEs appeared even during nighttime hours. PEs, on the other hand, could be seen at all local times, but with latitudinally dependent diurnal patterns. Most higher-latitude QPs were type I events (observed with magnetic pulsations), while type II QP events (without simultaneous magnetic pulsations) occurred relatively more often at lower latitudes. A case study from 1 August 1999 using wideband data from South Pole and Halley provides evidence of a transition from echoing whistler activity to PE activity and then to QP activity and suggests a causal relationship.last_img read more


Reds duo influenced Borini decision

first_img “They gave me some advice. Obviously Jordan is from Sunderland and Simon was really happy I was coming here. “He told me it was the right place for me to come and I am really looking forward to it.” Italy international Borini arrived, along with full-back Andrea Dossena, during the final hours of the transfer window as manager Paolo Di Canio recruited his 13th and 14th players of a busy summer. The frontman made 20 senior appearances for the Reds last season, although he was hampered by injury, and is looking forward to playing regular football at the Stadium of Light. He said: “It feels good to make the move. I was waiting to get my time to play and I needed to play. “This is the right place to come. It is a great opportunity for me. Playing [regularly] is important for me to achieve my goals for the season.” Sunderland new boy Fabio Borini has revealed Simon Mignolet and Jordan Henderson helped to sell him on a move to Wearside. Press Associationcenter_img The Liverpool striker joined the club on a season-long loan deal on Monday evening, but only after seeking the advice of Anfield team-mates and former Black Cats Mignolet and Henderson. Borini told the club’s official website, www.safc.com: “I asked them a little bit about one or two things about the club. last_img read more