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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.


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Journal ArticleDOI
TL;DR: In this article, a sampling strategy to determine the annual mean air-sea CO 2 fluxes in the high-latitude North Pacific and North Atlantic was developed using a combination of signal-to-noise ratios and 2D Fourier transforms in conjunction with a coupled climate carbon model.
Abstract: A sampling strategy to determine the annual mean air–sea CO 2 fluxes in the high-latitude North Pacific and North Atlantic was developed using a combination of signal-to-noise ratios and 2D Fourier transforms in conjunction with a coupled climate carbon model. To account for unresolved mesoscale variability in our simulations, we used summer and winter cruises to determine the magnitude of this variability and estimate its impact on the air–sea fluxes. From our analysis, we propose a regular sampling strategy of every 6° in latitude and 10° in longitude every 3 months for the North Pacific and North Atlantic. Applying this sampling strategy to the simulation returned an annual mean air–sea flux value within ±15% of the total simulated value, when applied now and into the future. Our study highlights several key points for measuring annual mean basin-scale CO 2 fluxes: (1) the combination of temporal and spatial sampling dramatically reduces the noise in the observations and provides a good representation of the fluxes with far fewer measurements than required for resolving the spatial or temporal signals independently; (2) that sampling at higher than recommended frequencies in time and space provides little improvement in the estimated annual mean flux; (3) the uncertainty in the decadal annual mean uptake is limited by interannual variability and not by sampling error or unresolved mesoscale variability; and (4) our high-latitude sampling strategies remain valid until at least the end of this century.

15 citations

Journal ArticleDOI
TL;DR: In this paper, two methods of analysis, involving rotation rate and total number of rotations, are applied to the Bangkok observations to determine the electron content when the angle between the ray path and the geomagnetic field is 90° (transverse position).
Abstract: At the Electronics Laboratory of the Military Research and Development Center, Bangkok, Thailand (13.7°N latitude, 100.1°E longitude), Faraday rotation observations of the 54-MHz signal from the Transit 4-A (1961 Omicron 1) satellite were made during 10 months of a sunspot minimum period (1964). The satellite has an essentially circular orbit with an inclination of 67° and a spin-stabilized linear-polarized antenna. In this paper, two methods of analysis, involving rotation rate and total number of rotations, are applied to the Bangkok observations. The rotation-rate method is used to determine the electron content when the angle between the ray path and the geomagnetic field is 90° (transverse position). The total-rotations method is used to determine the latitudinal variations of the electron content for five selected satellite passes from a joint analysis of observations at three stations, Singapore, Bangkok, and Hong Kong. A comparison of the calculated critical frequency with observed ionosonde critical frequencies at Singapore, Bangkok, and Macao shows some evidence that the equivalent slab thickness may be considered independent of latitude near the magnetic equator.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysis datasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations.
Abstract: . This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysis datasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO-dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD reaches a minimum near the Equator and is largest in the polar regions. Along the Equator, the zonal wind SD is smallest around the longitude of Singapore, where consistently high-quality near-equatorial radiosonde observations are available. Interestingly, the near-Singapore minimum in SD is evident to at least ∼3 hPa , i.e., considerably higher than the usual ∼10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa , such as its detailed time variation and the displacement off the Equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa . One of the reanalyses in our study also has a version produced without assimilating satellite observations, and a comparison of the SAO in these two versions demonstrates the very great importance of satellite-derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.

15 citations

Journal ArticleDOI
TL;DR: In this article, a large database of more than 18,000 subauroral ion drift (SAID) events from DMSP observations from 1987 to 2012 is used to systematically investigate the features of SAID.
Abstract: A large database of more than 18,000 subauroral ion drift (SAID) events from DMSP observations from 1987 to 2012 is used to systematically investigate the features of SAID. SAID occurs mostly at ~62°/−60° magnetic latitude (MLAT) and ~22:15/22:45 magnetic local time (MLT) for geomagnetically quiet conditions and at ~58°/−56° MLAT and ~22:15/22:45 MLT for geomagnetically disturbed conditions in the North Hemisphere (NH)/South Hemisphere (SH), respectively. Significant north-south asymmetries in SAID occurrence, shape, and geomagnetic activity variations are found in this statistical study. The latitudinal width of a SAID is larger in the NH than in the SH. An interesting finding of this work is that the SAID occurrence probability peaks have an ~180° difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions. The SAID width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of ~80°–120° in both hemispheres. Significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of SAIDs. The SAID is highly correlated to geomagnetic activity, indicating that the location and evolution of the SAID might be influenced by global geomagnetic activity, auroral dynamics, and the dynamics of ring currents.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the predicted electron density at 600 km altitude obtained from the Japanese Hinotori Satellite during February 1981-June 1982 is used to assess the predictability of the International Reference Ionosphere (IRI) within ± 25° geomagnetic latitude along 75°E meridian.

15 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023240
2022432
202142
202042
201960
201851