Echoing mixed-path whistlers near the dawn plasmapause, observed by direction-finding receivers at two Antarctic stations

first_imgDuct coupling, in which part of the energy of a downcoming whistler-mode wave becomes trapped in a different duct after upward reflection in the ionosphere, manifests itself in the phenomenon of the mixed-path whistler. Using VLF data from direction-finding receivers at Halley and Palmer stations, Antarctica, we analyse a case near dawn in which the path structure was particularly simple. One-hop and three-hop whistlers observed at both stations implied the existence of two ducts inside the plasmasphere (at L ~ 3) and of wave coupling between them. The most intense of the three-hop echoes was a mixed-path rather than a single-path component; this is explained in terms of bi-directional coupling between the ducts in both northern and southern conjugate ionospheres. The locations of the ionospheric exit points for signals leaving the ducts were found from whistler arrival bearings measured at the two stations (the first results of crossed bearings from the IMS Antarctic VLF observing programme); these points were about 300 km apart. An echo trace seen only on the Halley record implied coupling to a third path outside the plasmapause (at Lpp ≅ 3.3). We discuss the significance of such path coupling in relation to the spreading of ducted and unducted wave energy in the magnetosphere, and to the triggering of chorus.last_img read more

Kagawa: No regrets over United move

first_img As he also suffered a significant knee injury that kept him out for nearly two months, the 24-year-old could be forgiven if he felt a rather big mistake had been made with his career. Yet he insists watching Dortmund lose that all-German final against Bayern Munich at Wembley in May just made him more determined. “I was proud to see my former team play in the Champions League final, and I was very excited for them – but it didn’t make me feel I had made the wrong choice,” he said. “In fact it made me feel stronger because I want to be on the same field in future.” There were high points, in particular a hat-trick against Norwich in April. But Kagawa summed up his feelings in a Japanese TV interview shortly after linking up with his team-mates for the latest leg of their five-match pre-season tour. “It was a tough time for me with a lot going on in my head. I am not happy with my performance for the team at all,” he said. “I didn’t score that much and I also had my injury. Kagawa was a central figure in Dortmund’s back-to-back Bundesliga triumphs, but left Germany last summer when he opted to join Manchester United in a £17million deal. Dortmund boss Jurgen Klopp claimed it broke his heart to see Kagawa leave, and then end up playing on the left wing rather than his preferred central position. Shinji Kagawa has a renewed sense of purpose after watching Borussia Dortmund reach last season’s Champions League final. “It was great we won the league. I just don’t feel that I achieved everything that I wanted. “For me personally, it wasn’t a good season.” Kagawa clearly has a lot of affection for Dortmund. Indeed, he claims he would like to return one day if the conditions were right. However, he has important work ahead of him, proving to new manager David Moyes he is a top-class talent and just the man to step in for Wayne Rooney should the England forward get his wish to join Chelsea. According to Moyes, predecessor Sir Alex Ferguson spoke “in glowing terms” of Kagawa. But those words will mean little unless he matches them with deeds on the pitch. “I have met the manager for the first time and we had a talk in the car on the way here,” Kagawa said as he addressed the media ahead of Tuesday’s encounter with Yokohama F Marinos. “We still need to spend more time together to get to know each other. “I am looking forward to building a relationship with him.” Press Associationlast_img read more

Flare lines up Ascot run

first_img The Cheltenham Festival-winning four-year-old, who finished second in the Galway Hurdle on his last outing, was rarely out of second gear in the Hurdle and jumped to the front from the pacesetting Choisilady at the third-last flight. Davy Condon soon had the race in safe keeping and though Massini’s Trap was driven to within a length near the finish, there was never any threat from that quarter and the 1-9 favourite eased over the line. Flaxen Flare will be pointed towards the Ladbroke Hurdle at Ascot following a facile success in a three-runner race at Cork. Winning trainer Gordon Elliott, who won the Ladbroke last year with Cause Of Causes, said: “It was an ideal race for him and he jumped around nice and safe. He’ll have a little break and come back for the Ladbroke Hurdle at Ascot. We might find a little Flat race for him as well.” It was plain sailing again for Condon when he completed his double with an easy success on Noel Meade’s 1-3 favourite Curley Bill in the Family Day Out Maiden Hurdle. The five-year-old, who brought smart Flat form into the race, quickened into the lead between the final two flights and won with plenty in hand even though Fantasy King ran on strongly to get to within two and a quarter lengths. Meade said: “It was simple enough, he didn’t have that much to beat. He won easily. He should be a force in those good novice races. He’ll jump better when they are going quicker. We will put his Flat career on hold until next year. “He might go to Listowel for a novice hurdle. He’ll have a rest over the winter during the worst of the ground.” Paul Flynn’s 5-1 joint-favourite Limpopo Tom was strongly challenged all the way down the straight in the Martinstown Opportunity Handicap Hurdle, but Brian Cawley kept him going to hold Goal by a length and three-quarters. The trainer said: “Keith Donoghue rode him the last day and he said to drop him back in trip, and it was the right thing to do. If he keeps improving he’ll pick up another one. We might bring him to England for better ground if we have to. He doesn’t seem to like Dundalk so we might bring him somewhere on the Flat like Wolverhampton.” center_img Press Associationlast_img read more