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[en] The equilibration of a two-level primitive equation model forced by relaxation towards a fixed axisymmetric temperature profile is studied as a function of the forcing equator-to-pole temperature difference. It was found that the mean equilibrated temperature gradient rises quickly with the forcing. It is found also that the mean eddy momentum flux convergence induces a strong barotropic jet at mid-to-high latitudes. It was suggested that, as found in previous work, the barotropic governor effect induced by the jet is responsible for the sensitivity of the equilibrated temperature gradient to the forcing
[en] Complete text of publication follows. We have studied the spectral contents and latitudinal structure of magnetic Pc3-4 pulsations on the dayside using data acquired by the Mid-continent Magnetoseismic Chain (McMAC) at L =1.46 -3.40. We display the magnetometer data in a keogram format and find that the pulsations in the H component consist of oscillations with time-dependent amplitude and period and that these oscillations generally exhibit poleward phase propagation. By spectral analysis of Pc3 and Pc4 pulsation events identified in the keograms we find that the latitude of the amplitude peak depends on the pulsation frequency and that the phase changes by ∼180 degrees across the amplitude peak, a signature of field line resonance. Occurrence of field line resonance is further confirmed from the fact that the amplitude peak occurs at the latitude where the pulsation frequency matches the fundamental toroidal wave frequency that is determined using the cross phase technique.
[en] Trend analysis of hourly wind direction angle recorded at nine meteorological stations across Southern Canada (in the 43oN-53oN belt) identified wind direction rotation periods in the range of 7-9 days. Rotation persists during the 'summertime' season from May to mid-October during 1953-2001. Rotation with a 7.5 day period was also established in the 850 hPa geostrophic summertime wind over the Canadian province of Saskatchewan in 2000. Hodographs built from wind vectors corresponding to consecutive days of the . day period (summertime average vectors of winds binned into separate days of the period) formed nearly elliptical loops centered around the terminate point of the net westerly transport vector which ranged from 0.5 to 1.3 m/s, and was either smaller or of comparable magnitude to the zonal and meridional oscillations of wind. The observed rotations appear quasi-periodic rather than purely periodic, because nearly elliptical loops of relatively large amplitude were present at different hodographs constructed at each location for sampling periods of 6.5, 7.0, 7.5, 8.0 days. For sampling periods outside the ∼6.5-8.0 days range the rotational magnitude in hodograph appears diminished due to partial cancellation of wind vectors in corresponding hodograph bins. Quasi-periodical rotation occurs in the clockwise direction. (author)
[en] Complete text of publication follows. All-sky nightglow imaging observations made over low latitude site Panhala (17degN, 74.2degE Geographic; 8.43degN Geomagnetic latitude) during February 1, 2008 revealed anomalous filamentary structure formation (referred to as 'streaks') in OI 557.7nm emission. These structures were observed on pre-midnight sector only in OI 557.7nm emission and are not seen on other wavelengths including OI 630.0nm. They were transient and extended from south to north with a tilt of ∼13deg to the geomagnetic meridian. In addition they possessed westward drift with speeds of 30-50 m/s. They are narrow with widths up to 10 km and lengths ranging from few tens of km to ∼200km. These estimations were based on an assumed height of 100 km for the OI 557.7 nm emission. A recurrent geomagnetic storm of moderate strength (minimum quick look Dst = -44) was on progress during the observation of streaks. Equatorial ionospheric soundings made over Tirunelveli (8.7degN, 77.8degE Geographic; 0.17degN Geomagnetic latitude) showed intense blanketing after midnight confirming excessive night time ionization on that day. Wide plasma depletion was observed on OI 630.0 nm emission while streaks were observed in OI 557.7nm emission. In this work we discuss the observations in detail and speculate about their possible cause. This is an extremely puzzling observation made from very low geomagnetic latitude during the main phase of a moderate recurrent geomagnetic storm in the declining phase of solar cycle. Hence understanding of such unusual and rare events is expected to substantiate our knowledge on the coupling processes at equatorial region.
[en] Transfers from geosynchronous transfer orbits (GTO) to geosynchronous orbits (GSO) using electric propulsion have been optimized in the current study. Both time-optimal and fuel-optimal trajectories are generated. Three-dimensional equations of motion are considered for the system dynamics. The indirect approach based on optimal control theory is followed and the resulting two-point boundary value problem is solved using differential evolution, a search-based global optimization technique. Optimal trajectories for various mission scenarios are obtained using differential evolution and compared to transfers presented in literature. (author)
[en] Some global atmospheric electrical parameters like atmospheric conductivity, air-earth current density, electric field, atmospheric potential, etc. have been estimated over different places of India, China and Korea of Asian continent. These calculations have been made by assuming fair weather conditions and taking into account the small scale (0.5° grid in latitude and longitude) orographic and latitudinal effects. Mean values of conductivity and air-earth current density over various places of India, China and Korea have been found to be 5.97 × 10-13, 5.46 × 10-13, 2.82 × 10-13 S m-1 and 6.58 × 10-12, 6.04 × 10-12, 3.16 × 10-12 A m-2, respectively whereas average electric field and atmospheric potential over these places are 110.9, 110.81, 112.08 V m−1 and 269.52, 272.90, 286.64 kV, respectively. It has been found from the results that latitudinal variation is very much smaller than orographic variation over these three countries of Asian region. (author)
[en] Complete text of publication follows. The foF2 data obtained at Alma-Ata [43.25degN, 76.92degE] are analyzed to investigate the upper ionosphere variability in relation with stratospheric warming and springtime transition events. The geomagnetic activity and the middle stratosphere dynamics, involving planetary wave (PW) activity, analyzed for understanding the physical conditions and processes that can explain the observed ionosphere variability.
[en] The modified-inertia MOND is an approach that proposes a change in Newton's second law at small accelerations as an alternative to dark matter. Recently it was suggested that this approach can be tested in terrestrial laboratory experiments. One way of doing the test is based on the static high-latitude equinox modified-inertia effect: around each equinox date, 2 spots emerge on the Earth where static bodies experience spontaneous displacement due to the violation of Newton's second law required by the modified-inertia MOND. Here, a detailed theory of this effect is developed and estimates of the magnitude of the signal due to the effect are obtained. The expected displacement of a mirror in a gravitational-wave interferometer is found to be about 10-14 m. Some experimental aspects of the proposal are discussed
[en] Complete text of publication follows. The dawn-to-dusk convection electric field propagates instantaneously from the polar ionosphere to the equator, and causes the DP2 current system consisting of two-cell current vortices at high latitude and eastward current amplified by the Cowling effect at the dayside geomagnetic equator. Reversed currents have often been observed at subauroral-equatorial latitudes, when the convection electric field reduces its intensity because of northward turning of the IMF. The reversed current has been explained by means of an overshielding electric field due to the Region-2 field-aligned current. In this paper, we show overshielding that initiated at a substorm expansion onset, accompanying an increase in the DP2 currents at auroral latitudes as observed with the IMAGE and Greenland magnetometer arrays. With the SuperDARN observations, we confirmed that sunward plasma flow was enhanced at the afternoon auroral latitude as overshielding occurred and that the reversed current corresponded to an anti-sunward convection flow equatorward of the sunward auroral flow. In addition to the conventional features, the overshielding has new features that the convection electric field increased concurrently and its onset was a few minutes earlier than the onset of the positive bay in the midnight. All these data infer that both the Region-1 and the Region-2 field-aligned currents were intensified at the onset of the substorm, and that the electric field associated with the Region-2 field-aligned currents overcame that of the Region-1 field-aligned currents at mid-equatorial latitudes. The substorm current system (DP1 current) should be modified so as to include the ionospheric currents at the dayside mid - equatorial latitudes.
[en] One of the most widely accepted epidemiological features of multiple sclerosis (MS) is its tendency to increase as latitude increases, in both directions from the equator. The worldwide distribution of MS may be an indirect reflection of some cause which varies by latitude, the most obvious environmental factor being climate. The possible role of ultraviolet radiation (UVR ) in MS etiology was first proposed in 1960 and has recently received increasing attention. This issue of the Canadian Journal of Neurological Sciences includes a paper by Sloka et al which correlates MS prevalence and UVR globally, along with latitude and other factors that might contribute to the geographic distribution of MS. While this study furthers our understanding of the relative bearing which UVR may have on MS distribution, it also highlights some of the difficulties inherent in examining UVR's impact. (author)