Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.

The longitude dependence of the dayside F region trough: A detailed model‐observation comparison

Abstract: The nighttime main F region trough extends into the sunlit afternoon sector. This trough feature exhibits both a strong magnetic activity dependence and a longitude (UT) dependence. Whalen (1987), using International Geophysical Year (IGY) ionosonde data, showed that both of these effects are readily extracted from f{sub 0}F{sub 2} observations. In this study the authors show that the longitude effect is the same as that contained in the Utah State University time-dependent ionospheric model. It arises from the offset of the geomagnetic axis from the geographic axis. The magnetic activity dependency is associated with the westward convection in the afternoon sector. It is also contained in the ionospheric model via the empirical magnetospheric convection model. This one-to-one observational-model agreement is unique; to date no other magnetic activity dependent ionospheric feature has been simulated this systemtically.

Asymmetrical characteristics of the Earth's magnetic disturbance‐field

Abstract: Asymmetries in the Earth's magnetic disturbance-field are considered in relation to the asymmetries in the Earth's main field, using data of 32 stations. The auroral-zone curve of terrestrial magnetism, in north polar regions, is elongated in a direction roughly parallel to the elongation of Hsoclinic curves. It agrees roughly with the curve of maximum auroral frequency, as given by Fritz, except in regions where his auroral data were scanty. The curve appears to undergo regionally a small diurnal oscillation. The amplitude of the disturbance diurnal variation (SD) is approximately symmetrical with respect to the geographical equator in low latitudes, is zonal-symmetrical with respect to the auroral zone, and has a zero vertical component near the north pole given by the eccentric dipole. No change in amplitude with longitude has been detected, and it is concluded that induced earth-currents in the oceans contribute little to SD. The local time-phase of the mainly sinusoidal variation SD shows a range of about four hours with longitude. But if in defining time the geographic north pole be replaced by the north pole given by the eccentric dipole, then at the auroral zone there is no significant variation in time-phase with longitude. This suggests that the auroral zone has a controlling and initiating influence over the world-wide electric currents responsible for SD. Average asymmetries in the geographical distribution of magnetic disturbance and aurora are compared. The average force-vectors for the daily means of disturbance are perpendicular to the average directions of homogeneous auroral arcs, to a high degree of approximation, in polar regions. The SD electric current-system of magnetic storms proposed by Chapman shows good general agreement with the extensive data here considered. Certain changes are suggested whereby the fit with observation may be improved.

Modeling 3-D crustal velocities in the United States and Canada

Abstract: A numerical model for three-dimensional (3-D) crustal velocities has been derived for most of the United States and Canada, primarily from repeated geodetic data. This model provides a foundation for a prototype of the TRANS4D software. TRANS4D is being developed to enable geospatial professionals and others to transform 3-D positional coordinates across time. The derived model reveals several macroscopic features of the 3-D velocity field, including the pervasive presence of the glacial isostatic adjustment associated with the past melting of the ice fields that formed more than 19,000 years ago during the Last Glacial Maximum. In this study, the present-day 3-D velocity field associated with this melting (as estimated via the recently published ICE-6G_C (VM5a) model) was subtracted from this study's total 3-D velocity field to identify features of the residual velocity field. In particular, this study introduces the NA_ICE-6G reference frame in which residual horizontal velocities have magnitudes that are less than 2 mm/yr everywhere east of longitude 104°W and south of latitude 60°N, except in southern Texas. Residual horizontal velocities of greater magnitude are found west and/or north of these two boundaries, and they are due mostly to interactions among tectonic plates with localized pockets due to other geophysical phenomena. Large residual vertical velocities, some with values exceeding 30 mm/yr, are found in southeastern Alaska. The uplift occurring here is due to present-day melting of glaciers and ice fields formed during the Little Ice Age glacial advance that occurred between 1550 A.D. and 1850 A.D.

M 2 ocean tide parameters and the deceleration of the Moon's mean longitude from satellite orbit data

Abstract: An estimation is made of the principal long-period spherical harmonic parameters in the representation of the M2 ocean tide from the orbital histories of the three satellites 1967-92A, Starlette, and GEOS 3. The data used are primarily the evolution of the orbital inclinations of the satellites in conjunction with the longitude of the ascending node from GEOS 3. Analysis procedure and analytic formulation, as well as ocean tidal parameter estimation and deceleration of the lunar mean longitude are outlined. The credibility of the M2 ocean tide solution is further enhanced by the close accord between the computed value for the deceleration of the lunar mean longitude and other recently reported estimates. It is evident from the results presented that studies of close earth satellite orbits are able to provide important information about the tidal forces acting on the earth.

Direct observations of Venus upper mesospheric temperatures from ground based spectroscopy of CO2

Abstract: [1] We report direct observations of temperatures in the Venus upper mesosphere around 110 km altitude (0.15 Pa). Information about temperatures at these altitude regions are sparse especially for the dayside of Venus. Data was acquired during three observing campaigns between March and June 2009 at the McMath-Pierce Solar Telescope of the National Solar Observatory on Kitt Peak, Arizona, using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS). The linewidths of fully resolved non-thermal emission lines in the 10.6 μm band of CO 2 were used to derive temperatures on the Venus dayside. Temperatures were measured with high spatial resolution at 115 positions on the Venus dayside between 67°N and 90°S and various offsets from the apparent discs central meridian longitude (CML) providing the first extensive dataset for the dayside mesosphere. The retrieved temperatures show a strong local time and latitude dependence. Values of 160 K are observed close to the terminator and at the South pole while temperaturs reach 250 K at the sub solar point. These high values are in disagreement with the predictions of the Venus International Reference Atmosphere model but are consistent with earlier measurements from 2007.