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.

Climatology of the inter-hemispheric field-aligned current system in the equatorial ionosphere as observed by CHAMP

Abstract: . From geomagnetic field observations of CHAMP during 2001–2009 we extracted characteristic signatures of inter-hemispheric field-aligned currents (IHFACs) in the equatorial ionosphere. The results are in general agreement with previous observations. Nighttime IHFACs are negligibly small. Solstitial IHFACs flow from the summer to winter (from winter to summer) hemisphere at dawn (around noon). Duskside IHFACs flow southbound irrespective of season. We have also found some new IHFAC properties, which may have been predicted by theories, but are not yet given observational support. IHFACs clearly exhibit a longitude dependence, which is modulated by the South Atlantic Anomaly, the offset between geographic and magnetic equators, and tidal waves. IHFACs show little dependence on the solar cycle. We provide a comprehensive assessment of the IHFAC modulation by non-migrating tides.

Pi1 magnetic pulsations in space and at high latitudes on the ground

Abstract: Nightside, high-latitude (68°–80° magnetic) Pi1 waves, measured with a ground array of induction magnetometers, are studied and compared with magnetic field measurements made at synchronous orbit near the meridian of the ground measurements. The objectives of the study are to relate the ground signatures of Pi1B and PiC to the auroral substorm and its manifestation at synchronous orbit in an attempt to understand the origin of the Pi1 waves. Pi1 waves are measured in the equatorial plane by the GOES spacecraft and appear to be initiated by the dipolarization process of the nightside tail magnetic field at the onset of substorms. Across two meridional arrays of ground stations the earliest onset of Pi1B generally occurred at the lowest-latitude station and, in many instances, this burst was superimposed on a ground signature of a sudden onset of the westward electrojet. In one instance, where good coverage of ground optical data was available, this sudden onset Pi1B was time related to the overhead passage of a westward traveling auroral surge. The timing of maximum Pi1B across the array in both longitude and latitude agrees with the westward motion of the local auroral surge and the poleward motion of the aurora after the surge has arrived at a given site, suggesting a local ionospheric source for some of the Pi1 waves. However, across the entire array, extending about 12° in latitude and 20° in longitude, there often was nearly simultaneous Pi1B wave power at all sites which occurred before the maximum signal at a given site (and presumably local aurora), suggesting horizontal ducting of wave power from the onset of PiIB seen earlier at the auroral zone latitude. Prompt turn-on of PiC waves across the array also indicates ducting of these waves. The narrow bandwidth of the PiC waves themselves suggests a resonant cavity source for them which would indicate that some wave power enters the ionosphere from space (consistent with the GOES in situ data) as the trigger wave for this resonant source mechanism. In conclusion, this study finds evidence for local ionospheric currents, magnetospheric waves, and resonant cavity modes as sources for Pi1 ground waves.

Simulation of the Pinatubo aerosol cloud in general circulation model

Abstract: The global transport and dispersion of the Pinatubo aerosol cloud are simulated by means of a high-resolution stratospheric version of the NCAR Community Climate Model (CCM2) with an annual cycle. A passive tracer was injected into the model stratosphere over the Philippine Islands on June 15, and the transport was simulated for 180 d using an accurate semi-Lagrangian advection scheme. The simulated volcanic aerosol cloud initially drifted westward and expanded in longitude and latitude. The bulk of the aerosol cloud dispersed zonally to form a continuous belt in longitude, and remained confined to the tropics, centered near the 20-mb level for the entire 180-d model run, although a small amount was transported episodically into the upper troposphere in association with convective disturbances. Aerosol transported to the troposphere was dispersed within a few weeks into the Northern Hemisphere extratropics. In the Southern Hemisphere, the aerosol was mixed into the region equatorward of the core of the polar night jet during the first 50 d, but penetration into southern polar latitudes was delayed until the final warming in November.

A calculation of ionospheric currents due to semidiurnal antisymmetric tides

Abstract: The fully developed equivalent circuit method is used to calculate the ionospheric electric current flow due to the (2,3) and (2,5) tidal modes. The (2,5) mode currents are of negligibly small amplitude. the (2,3) current pattern has meridional currents in the same direction at a given local time in both north and south hemispheres. There is also sometimes a minimum in the zonal current around 10{degree} dip latitude and the equatorial electrojet pattern may be different in different longitude zones. These features may be possible explanations of (1) the meridional current pattern observed at Saint-Santin, (2) current flows on abnormal quiet days (AQDs), (3) the reverse equatorial electrojet, (4) the seasonal phase anomaly in the lunar geomagnetic tide, and (5) the invasion of one hemisphere's current pattern by that from the opposite hemisphere. The recent detection of antisymmetric semidiurnal winds just below the dynamo region further demonstrates the importance of these modes.