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.

Longitude structure of ionospheric total electron content at low latitudes measured by the TOPEX/Poseidon satellite

Abstract: The longitude structure of ionospheric total electron content (TEC) at low latitudes has been evaluated using the NASA/Centre Nationale d'Etudes Spatiales TOPEX/Poseidon satellite. The TEC data set is given by the ionospheric range correction, which is computed from TOPEX dual-frequency altimeter measurements. The satellite's orbit allows analysis of vertically measured TEC values at approximately 30° intervals of longitude across the world at local time differences of only 6–12 min. Patterns of longitudinal dependence of the equatorial anomaly were observed during the equinoxes, summers, and winters of 1993, 1994, and 1995. TOPEX observations reveal occurrence of relative maximum anomaly TEC values in the Indian/Asian longitude sector. This dominance in TEC is seen most consistently in the Asian Southern Hemisphere. Also, a relative decrease in anomaly TEC values is evident in the western American region, which is observed primarily during equinox and winter. This configuration of the equatorial anomaly TEC is observed on a day-to-day basis at particular periods of local time. Global theoretical ionospheric model results are presented in an attempt to reproduce the distinctive longitude structure. Variability in E × B vertical drift velocity within specific longitude sectors is shown to be a primary factor in the longitude dependence of equatorial anomaly TEC.

The longitudinal variation of the daily mean thermospheric mass density

Abstract: [1] This study uses the GRACE (Gravity Recovery And Climate Experiment) and CHAMP (CHAllenging Minisatellite Payload) accelerometer measurements from 2003 to 2008. These measurements gave thermospheric mass densities at ~480 km (GRACE) and ~380 km (CHAMP), respectively. We found that there are strong longitude variations in the daily mean thermospheric mass density. These variations are global and have the similar characteristics at the two heights under geomagnetically quiet conditions (Ap < 10). The largest relative longitudinal changes of the daily mean thermospheric mass density occur at high latitudes from October to February in the Northern Hemisphere and from March to September in the Southern Hemisphere. The positive density peaks locate always near the magnetic poles. The high density regions extend toward lower latitudes and even into the opposite hemisphere. This extension appears to be tilted westward, but mostly is confined to the longitudes where the magnetic poles are located. Thus, the relative longitudinal changes of the daily mean thermospheric mass density have strong seasonal variations and show an annual oscillation at high and middle latitudes but a semiannual oscillation around the equator. Our results suggest that heating of the magnetospheric origin in the auroral region is most likely the cause of these observed longitudinal structures. Our results also show that the relative longitude variation of the daily mean thermospheric mass density is hemispherically asymmetric and more pronounced in the Southern Hemisphere.

Observations of optical emissions from precipitation of energetic neutral atoms and ions from the ring current

Abstract: In the present investigation, results obtained at three different locations are compared, taking into account the McDonald Observatory (latitude 30.7 deg N, longitude 101.0 deg W, altitude 2050 m), Mt. Haleakala (latitude 20.7 deg N, longitude 156.6 deg W, altitude 3050 m), and Cachoeira Paulista (latitude 22.7 deg S, longitude 45.0 deg W, altitude 500 m). The intercomparison of results from the three well-separated sites makes it possible to make evaluations of the local time, storm time, and latitude variation of the ring current precipitation.

Layered Structure Associated with Low Potential Vorticity near the Tropopause Seen in High-Resolution Radiosondes over Japan

Abstract: Horizontal wind and temperature data obtained from operational radiosondes over Japan have recently been available with high vertical resolution. Analyzing these data over 4 yr has indicated horizontal velocity layers with vertical scales of about 5 km lasting for a week or more. The layers appear frequently in winter at several stations simultaneously and are dominant in the height range of 8‐16 km. An empirical orthogonal function (EOF) analysis for the time series of layered disturbance amplitude in winter indicates that there are two dominant principal components. The first component (EOF1) describes layered disturbances in the middle of Japan (308‐ 378N) and the second one (EOF2) describes disturbances in the south of Japan (238‐308N). Using global analysis data, the background field of the layered disturbances was examined. An interesting result is that the background potential vorticity (PV) is approximately zero or negative for EOF2 disturbances even though located in a relatively high-latitude region. This fact suggests that the EOF2 disturbances are due to inertial instability. It is also shown that negative PV occurs more than 30% of the time in winter, in a zonally elongated region of 238‐ 298N in the western Pacific, on an isentropic surface of 345 K (;10 km altitude). Such a high frequency of negative PV is not observed at other longitudes in this latitude band. To determine the origin of the anomalous PV, backward trajectories were analyzed. For EOF2 disturbances, air parcels having mostly negative PV are traced back to the equatorial region in the longitude band 208W‐1408E within a few days. This is due to a strong northward branch of the Hadley circulation associated with deep convection over the Maritime Continent and a strong northeastward subtropical jet stream. On the other hand, the background PV is low but scarcely negative for EOF1 disturbances. Air parcels at EOF1 stations are traced back to the far west because they are advected mostly by a strong eastward jet stream. Thus, it is inferred that the EOF1 disturbances may be due to inertia‐gravity waves trapped in a duct of the westerly jet core.