Seasonal variations of the gravity wave momentum flux in the Antarctic mesosphere and lower thermosphere


first_imgAirglow imager and dynasonde/imaging Doppler interferometer (IDI) radar wind measurements at Halley Station, Antarctica (75.6degreesS, 26.6degreesW) have been used to estimate the seasonal variation of the vertical fluxes of horizontal momentum carried by high-frequency atmospheric gravity waves. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from sodium (Na) airglow imager data collected during the austral winter seasons of 2000 and 2001. These were combined with wind velocity variances from coincident radar measurements to estimate the daily averaged upper limit of the vertical flux of horizontal momentum due to gravity waves. The resulting momentum flux at the Na airglow altitudes, while displaying a large day-to-day variability, showed a marked rotation from the northwest to the southeast throughout the winter season. Calculations show that this rotation is consistent with seasonal changes in the wind field filtering of gravity waves below the Na airglow region. The calculations also indicate that while the magnitude of the meridional wind is small, this filtering leads to the observed seasonal changes in the meridional momentum flux.last_img read more

Student heckles former Pakistani leader


first_imgA United Nations report earlier this year found that Musharraf’s government failed to provide former Prime Minister Benazir Bhutto with adequate security on her return to Pakistan, and that elements within the military establishment may even have played a role in her death in December 2007.Kanishka Narayan, President of IRSoc, said that Musharraf was the most important guest in the society’s history. “He’s controversial but I don’t see that as a reason for denying his significance. Musharraf is a very significant figure in Pakistani politics.  He will have a massive impact in the upcoming future and it’s important people get to hear him.“I received no complaints about the invitation; we did, however, receive congratulatory notes and more requests for attendance than could be entertained, despite the venue being one of the largest in Oxford.”Narayan stressed that although some questions were submitted in advance, there was no vetting of difficult or controversial issues. He told student Ata Rahman before the talk, “We will be selecting questions we think are the best and most interesting, not the ones we feel President Musharraf wishes us to choose.”However Rahman felt that the manner in which the event was organised amounted to censorship. He said, “I think the IRSoc committee has to accept responsibility for the fact that they allowed Musharraf to completely evade the most controversial aspects of his career thanks to the pre-screening of questions.”Ticket-holders were required to sign up in advance and state their nationality. Questions for the question and answer session also had to be submitted in advance, although Musharraf did take an additional number of impromptu questions from the floor.Guests were requested to bring only their ticket and Bod Card and no bags, phones, cameras or metal objects were allowed inside the Town Hall.Ghazald Mirza, a British citizen of Pakistani descent, said that she believed that the full venue indicated the seriousness with which Musharraf was taken. She said, “The dynamics of Pakistan have changed so much that if he runs for re-election it’s very important to see if he has changed too.”Musharraf’s talk gave a history of Pakistan’s involvement on the world stage from World War Two to the present day, with much focus on extremism in Afghanistan and Pakistan’s troubled relationship with India.He is not the only political speaker to have attracted controversy this year. The visit of the Israeli deputy Foreign Minister Danny Ayalon in Hilary term was marked by protests and interruptions such as “You are a racist” and “You are a war criminal” from members of the audience. The visit of the former President of Pakistan, Perez Musharraf, to Oxford last Friday caused several students to voice concern over freedom of speech and censorship issues.Musharraf gave a speech in the Town Hall on ‘The state of the Pakistani state: national and international implications’, an event organised by the Oxford University International Relations Society.At the start of the question and answer session Musharraf removed his jacket, joking, “jacket off, I’m ready for a fight.”An audience member soon challenged Musharraf over his plans to return to power. He told the former general, “You seem remarkably fresh for a man on the run, involved in the death of the Prime Minister, treason, and subverting the constitution.”This opened a dialogue in which Musharraf lost his temper, dismissing the efforts of Pakistan’s other political parties as “damaging to the state”. Some of the exchange was conducted in Urdu.When the student left the room shortly afterwards, Musharraf called out after him, “Thank you for going!”Aranyani Bhargav, a student at Wolfson college, was displeased with Musharraf’s conduct. She said, “I accept that it was not a particularly comfortable question, but that was unacceptable and unprofessional behaviour.It’s just not something you would expect from a former head of state”.During the event Musharraf repeatedly stressed a desire for peace. He claimed “Pakistan is not a military state”, although he also said that “the military is the only organisation holding Pakistan together”, calling it the country’s “centre of gravity”. He stated that “military rulers have done better for Pakistan, there is no doubt”, a comment which was met with applause from some members of the audience.Musharraf answered all of the audience’s questions, including sensitive subjects such as US and Indian relations.The former general seized power in Pakistan in a military coup in 1999. He was forced to resign in 2008 following an impeachment over his declaration of a state of emergency in 2007, which postponed a general election and placed high court judges and their families under house arrest.last_img read more