Observed tidal variation in the lower thermosphere through the 20th century and the possible implication of ozone depletion

first_imgClimatological change in the tides in the lower thermosphere has been estimated at five different latitudes using wavelet analysis of geomagnetic data series extending back to the beginning of the 20th century. The tidal signature present in the geomagnetic data is a consequence of atmospheric tides in the dynamo region between approximately 120 and 140 km altitude. The diurnal and semidiurnal spectral power have been accumulated through each year. The effect of solar and geomagnetic drivers has been minimized through use of proxy indices (aa index, sunspot number, F10.7 solar flux) to leave a residual which shows ∼20% reduction in both diurnal and semidiurnal amplitudes at midlatitudes since the middle of the century. This midlatitude reduction is qualitatively similar to the decrease observed using wind data from 1964 onward at approximately 90 km altitude over a range of latitudes by Bremer et al. (1997), but quantitatively it is about half the magnitude. At high latitude a similar decrease would be a statistically insignificant measurement because the estimation becomes sensitive to errors in the aa index. At low latitude there is no significant change throughout the century. The observed decrease at midlatitudes appears consistent with that predicted by Ross and Walterscheid (1991) for the dynamo region current as a consequence of global ozone depletion. Reduced tidal heating of the stratosphere during the latter half of the 20th century and the consequent reduction in tidal power propagating up to the lower thermosphere is implicated.last_img read more

USA: SM-6 Attains Initial Operation Capability

first_img Share this article The SM-6 tactical missile has reached initial operation capability, the US Navy announced on Wednesday, with SM-6s successfully loaded onboard USS Kidd (DDG 100) in San Diego, Calif.The SM-6 is designed to provide naval vessels with extended range protection against cruise missiles, unmanned aerial vehicles and fixed and rotary wing aircraft. “We’re very pleased to achieve [initial operational capability] on schedule,” said Capt. Mike Ladner, the major program manager of Surface Ship Weapons, whose portfolio includes SM-6. “The SM-6, with its ability to extend the battle space, truly improves shipboard air defense capability. I’m very proud of the entire Standard Missile team on this historic achievement.”SM-6 has entered full rate production and the program has already delivered 50 missiles ahead of schedule and under budget. Follow-on test and evaluation will continue in 2013 and 2014 to validate the integrated fire control capability in an operationally realistic environment.[mappress]Press Release, November 29, 2013 Equipment & technology November 29, 2013center_img Back to overview,Home naval-today USA: SM-6 Attains Initial Operation Capability USA: SM-6 Attains Initial Operation Capabilitylast_img read more