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.

An Inverse Model of the North Atlantic General Circulation Using Lagrangian Float Data

Abstract: A nonlinear finite-difference inverse model is used for estimating the North Atlantic general circulation between 20° and 50°N. The inverse model with grid spacing 2° latitude and 2.5° longitude is based on hydrography and is in geostrophic and hydrostatic balances. The constraints of the inverse model are surface and subsurface float mean velocities; Ekman pumping derived from wind data; conservations of mass, heat, and salt; and the planetary vorticity equation at the reference level. The mass, heat, and salt conservations are applied in a vertically integrated form. The model does not have explicit mixing or air–sea flux terms. Vertical velocities result from the nondivergence of the 3D velocity field. After inversion, float velocities, hydrographic data, and dynamical constraints are generally compatible within error bounds. A few float velocities are, however, rejected by the model mainly due to inadequate time or space sampling of the 2° latitude by 5° longitude boxes for which mean float v...

Space/time statistics of short‐term climatic variability in the western North Pacific

Abstract: Temperature observations routinely taken over a period of years are analyzed for information on the space/time statistical structure of the short-term, climate-related variability in the western North Pacific. Observations were taken by the RV Ryofu Maru, making winter hydrographic transects along/ 137°E from Japan to the equator each year from 1967–1974, and by the Japanese Far Seas Fisheries Agency, making 120 quasi-meridional bathythermograph sections between 125°E and 180° from Japan to the equator during 1968–1972. Meridional wave number spectra of subsurface temperature over the depth range 100–300 m are calculated from the sections. Spectra vary significantly between the tropical region south of 17.5°N and the subtropical region north of 17.5°N. In both regions, wave number spectra increase in spectral energy density as the inverse square of the wave number from wavelengths of 200–1200 km; this indicates that the spectra derive from a first-order, autoregressive process. Decorrelation scales associated with the first-order process are very different for the two regions. Evaluation of these parameters is obtained by fitting the observed wave number spectra with a model spectrum that is composed of a first-order autoregressive process and a white noise process. The best-fit decorrelation scale of the first-order process is 600 km in the tropics (south of 17.5°N) and 300 km in the subtropics (north of 17.5°N). The model permits the partition of temperature variance into climate-related signal variance, and noise variance that cannot be resolved by routine monitoring. The ratio of noise to signal variance is 0.3 in the tropics and 1.0 in the subtropics. Estimates of the time and zonal space decorrelation scales are determined from autocorrelation analysis of the Japanese Far Seas Fisheries Agency temperature data. Both north and south of 17.5°N, the decorrelation time scale in the subsurface temperature is approximately 6 months. The zonal decorrelation length scale in the subsurface temperature is approximately 10° longitude for the tropical region south of 17.5°N, but only about 2.5° longitude for the subtropical region north of 17.5°N. For equal time scales, it is shown that the spectral shapes and the latitudinal differences in zonal space scale are consistent with the representation of upper ocean thermal variability in terms of nondispersive baroclinic long waves (i.e., Rossby waves). Discussed are implications of this space/time statistical information on the design of monitoring networks used to detect shor-term climate-related variability in thermal structure.

Intraseasonal Atmospheric Teleconnection Patterns during the Northern Hemisphere Summer

Abstract: At times the 30–60 day filtered outgoing longwave radiation (OLR) perturbations exhibited a systematic eastward propagation across the equatorial Indian Ocean–western Pacific during the five summers (1 May–30 September) of 1979–83. Such occasions are defined as “E” phase, while periods of irregular movement are designated as “NE” phase. Global-scale behavior of the 30–60 day filtered streamfunction and velocity potential fields differs significantly from E to NE phase. During E phase at 200 mb, a series of time-clustered, space-overlapping disturbances develop over the northern as well as the southern subtropics. Although individual disturbances are nearly stationary, a wave packet clearly propagates eastward with an approximate phase speed of 8° longitude per day and a space scale of wavenumber 1. Sandwiched between the Southern and Northern hemisphere wave packets are relatively weak equatorial zonal wind perturbations which also move eastward. At 850 mb, E phase behavior is characterized by st...

Diurnal and seasonal variation of GPS-TEC during a low solar activity period as observed at a low latitude station Agra

Abstract: between the two. Further, GIMs of TEC have been analysed for five different latitudes along the common meridian of 80 0 E longitude. The present study has been carried out for three months of the year 2009 in each season. The role of equatorial ionization anomaly (EIA) crest is clearly visible on TEC data. These results are significant for Agra station which is a new location in the low latitude sector of Indian region.

Errors in position‐fixing by GPS in an environment of strong equatorial scintillations in the Indian zone

Abstract: [1] The signal-to-noise ratio (SNR) of the L1 (1.6 GHz) transmission from the GPS and GLONASS satellites has been recorded at Calcutta (22.58°N, 88.38°E geographic; 32°N magnetic dip, 17.35°N dip latitude) since 1999 by a stand-alone coarse acquisition (C/A) code Ashtec receiver. The receiver usually tracks 10–15 satellites, sampling different sections of the ionosphere at different look angles from the station. Simultaneously, L-band (1.5 GHz) signals from geostationary INMARSAT (65°E) (350 km subionospheric point: 21.08°N, 86.59°E geographic; 28.74°N magnetic dip, 15.33°N dip latitude) and VHF (244 MHz) from FLEETSATCOM (73°E) (350 km subionospheric point: 21.10°N, 87.25°E geographic; 28.65°N magnetic dip, 15.28°N dip latitude) are also recorded. Calcutta is situated under the northern crest of the equatorial anomaly in the Indian longitude sector. The SNR of many GPS and GLONASS links, particularly in the southern sky and near overhead, has been found to scintillate frequently in between the local sunset and midnight hours. Scintillations of satellite signals near overhead are caused by irregularities in electron density distribution in an environment of high ambient ionization occurring near the crest of the equatorial anomaly. For the links at lower elevation angles in the southern sky, scintillations occur when satellites are viewed “end-on” through the field-aligned plasma bubbles. During periods of intense scintillations, in the high sunspot number years 1999–2002, it has frequently been observed that seven or eight GPS/GLONASS satellite links out of 15 may simultaneously show scintillations in excess of 10 dB. This paper presents an example of the above when the position determined with GPS shows fluctuations to the extent of 11 m in latitude and 8 m in longitude under such an environment.