A survey of natural electromagnetic noise in the frequency range f = 1–10 kHz at Halley station, Antarctica: 1. Radio atmospherics from lightning

first_imgThis paper presents results from the first systematic survey of VLF wave activity at Halley, Antarctica (76 °S, 27 °W, L = 4.3). Beginning in 1971, the peak, average and minimum (P, A, M) signal levels observed in four frequency bands centred on 0.75 kHz, 1.25 kHz, 3.2 kHz and 9.6 kHz have been recorded every 5 min. At these frequencies the observed radio noise is largely natural, the waves being generated either in the magnetosphere (e.g. chorus, hiss, etc.) or near the ground, the latter principally from lightning discharges (radio atmospherics, or “spherics”) which reach the receiver after propagating some distance in the Earth-ionosphere waveguide (lightning does not occur in the immediate vicinity of Halley). Here we analyse the observations for 1984, the first complete year for which we have data in digital form, in terms of thunderstorm regions, as a benchmark for more extended studies of possible long-term change in global lightning activity. The data are presented in compressed colour graphic format which facilitates the identification of periodic (diurnal and annual) and aperiodic variations. At 3.2 kHz, attenuation in the Earth-ionosphere waveguide is severe, and only relatively few spherics, from close lighting source regions, are observed. Thus, whilst the 3.2 M channel is insensitive to lightning, and responds mostly to magnetospheric emissions, the 3.2 P channel is dominated by spherics. The 3.2 P data show a marked diurnal and seasonal variation symmetrical about Halley local noon and about the solstices, consistent with nearby sources and attenuation rates for subionospheric propagation which are much greater during the day than at night. At 9.6 kHz, waveguide attenuation is much lower (and there is less difference between day and night), and the minimum channel is dominated by a continuum of spheric noise originating from globally distributed distant source regions, notably those in the tropics. Consequently, there is no control by the local dawn-dusk terminator; the diurnal and seasonal variation is not symmetrical about Halley local noon and the solstices but consists of a quasi-sinusoidal diurnal variation, in which the phases of the minimum and maximum vary during the year: ~07 LT (LT∼-UT−2h at Halley) and ~17 LT in December (summer) and ~10 LT and ~21 LT in June (winter). Agreement between the observations and the CCIR (1983) empirical model is poor. A somewhat better fit is given by a simple model in which thunderstorm regions consist of point sources having radiated powers which vary with local time and season, the total effect at Halley being modelled as the sum of contributions from these sources.last_img read more

Woodroof lecture April 2

first_imgRhona Applebaum, a food-industry leader with The Coca-Cola Company, will deliver the 2009 Woodroof Lecture April 2 at the University of Georgia in Athens, Ga. Her lecture on “Through the Looking Glass – Perspectives from a Career in Food Science: Past, Present and Future” will be at 2 p.m. in Masters Hall at the Georgia Center for Continuing Education. The lecture is free and open to the public.As chief regulatory officer, Applebaum leads the company’s scientific and regulatory affairs. The SRA department sponsors scientific research, communicates regulatory policy and provides system guidance on regulatory, safety, nutrition and health issues. Prior to working with The Coca-Cola Company, she was executive vice-president and chief science officer for the National Food Processors Association, where she oversaw the direction of three laboratory centers and regulatory and international affairs. Each year, a leader in food research, education, industry or policy is invited to lecture in honor of the late J.G. Woodroof, a pioneer in food science research. Woodroof began his food science research work in 1929. He organized the food science department at the Georgia Experiment Station in Griffin around 1940. Today, the UGA College of Agricultural and Environmental Sciences’ food science department and the UGA Center for Food Safety are among the preeminent food science research centers in the country. After the lecture, a reception will be in the Georgia Center Atrium. For more information, call (706) 542-2286.last_img read more

Tennis: Federer steps into Wimbledon land of the giants

first_img“Being the favourite or not the favourite doesn’t matter. These other guys are all big hitters. I feel like they will have their say in the outcome of the matches.“They’ve got big serves, big forehands, they are big hitters.”Federer has made the semi-finals without dropping a set and has been broken just three times.He even managed to match Milos Raonic — who boasts the second fastest serve of the tournament at a blistering 142mph (228.5km/h) — with 11 aces in his quarter-final victory.Federer is the second oldest semi-finalist after Ken Rosewall who finished runner-up in 1974 at the age of 39.He is also the overwhelming favourite after ‘Big Four’ rivals Andy Murray and Novak Djokovic suffered injury-hit exits on Wednesday and Rafael Nadal lost in the last 16.Federer is reaping the rewards of pruning his schedule with Wimbledon just his seventh event of 2017.He skipped the 2016 and 2017 French Opens which were won by Djokovic and Nadal.Share on: WhatsApp Pages: 1 2 London, United Kingdom | AFP | Roger Federer stands just two wins away from a record eighth Wimbledon title but faces a perilous trip through the land of the giants if he is to become the tournament’s oldest champion.The 35-year-old Swiss has defied time and logic to reach a 12th semi-final at the All England Club where he will face Tomas Berdych, the 2010 runner-up, on Friday.If he gets past the Czech for the 19th time in 25 meetings, Federer will face either Sam Querrey or Marin Cilic in Sunday’s final.The contrast between the 18-time Grand Slam title winner and the other three contenders could not be more stark.Federer stands 6ft 1in (1.85m) and weighs in at 187lbs (85kg); Berdych is 6ft 5ins (1.95m) and 200 lbs (91kg).Querrey and Cilic tower over him at 6ft 6ins (1.97m) and 210lbs (95kg) and 196lbs (89kg) respectively.Federer, bidding to reach an 11th final at Wimbledon, is therefore aware of the physical threats posed by his rivals.“All three guys are taller and stronger than I am,” said Federer.“I’ve got to figure out a different way, carve my way through somehow with my slice and my spins, my consistency.last_img read more