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.

Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index

Abstract: [1] We proposed to identify the sources of desert dust aerosols with local maxima of the TOMS aerosol index distribution averaged for the long period Being simpler than the approach based on a dusty days occurrence, our method gives the same results It was first shown that in spring-summer, the flux of dust from the sources located at latitude � 16� N and longitude � 16� E and around latitude � 19� N and longitude � 6� W exceed the sinks due to settling and transport As a result the atmosphere over North Africa is almost permanently loaded with a significant amount of mineral desert dust in spring and in summer It is also shown that the Chad basin source located around latitude 16� N and longitude 16� E is relatively more stable with a maximum activity around April The region around latitude 19� N and longitude 6� Wappears as a more variable source with maximum in July Low pressure systems, called Sharav cyclones, mobilize the already suspended mineral dust and transport it eastward and northward along the Mediterranean basin A new method for description of dust plumes propagation was applied to the study of dust events in the Mediterranean Sea and enabled us to follow their dynamics Identifiable dust plumes appear first in the western sector of the sea and then move eastward with a speed of about 7 to 8 degrees per day In spring, this motion continues at least up to the eastern coast of the Mediterranean In summer the dustplume is prevented from penetrating further east of about 15� E INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 4801 Oceanography: Biological and Chemical: Aerosols (0305); KEYWORDS: Aerosols, desert dust, dust storms, dust sources, Mediterranean Citation: Israelevich, P L, Z Levin, J H Joseph, and E Ganor, Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index, J Geophys Res, 107(D21), 4572, doi:101029/2001JD002011, 2002

Mapping Global Shipping Density from AIS Data

Abstract: Mapping global shipping density, including vessel density and traffic density, is important to reveal the distribution of ships and traffic. The Automatic Identification System (AIS) is an automatic reporting system widely installed on ships initially for collision avoidance by reporting their kinematic and identity information continuously. An algorithm was created to account for errors in the data when ship tracks seem to ‘jump’ large distances, an artefact resulting from the use of duplicate identities. The shipping density maps, including the vessel and traffic density maps, as well as AIS receiving frequency maps, were derived based on around 20 billion distinct records during the period from August 2012 to April 2015. Map outputs were created in three different spatial resolutions: 1° latitude by 1° longitude, 10 minutes latitude by 10 minutes longitude, and 1 minute latitude by 1 minute longitude. The results show that it takes only 56 hours to process these records to derive the density maps, 1·7 hours per month on average, including data retrieval, computation and updating of the database.

Sun Navigation in Homing Pigeons

Abstract: 1. The accumulated data of a long series of homing experiments carried out with young pigeons is examined in statistical detail. 2. Bico-ordinate navigation can only be demonstrated in sunny conditions, and with overcast skies the birds scatter at random. This holds for a number of different experimental situations. 3. The hypothesis that pigeons use a form of sun-navigation, deriving latitude and longitude from the sun position alone is re-examined in detail. None of the requirements are outside the theoretical range of the organ concerned, or beyond the bounds of possibility. 4. Examination of the errors made under sunny conditions shows that their nature and variation are as expected on the basis of the hypothesis. So also is the variation in error with the length of time of observation. 5. By excluding sun and sky for a number of days before release a re-orientation away from home was obtained. This could only be explained if the birds were failing to correct for the seasonal variation in the sun's altitude, and deriving their latitude from altitude measurements. 6. Radical changes in accustomed release times produced some increase in longitude errors. 7. After treatment aimed at desynchronizing any internal chronometer a disorientation was obtained in the field. It is therefore very probable that longitude determination is on a time basis, as proposed in the hypothesis. 8. Future lines of research in this problem are indicated.

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

Abstract: [1] We investigate the response of the equatorial ionosphere at dusk to the intense magnetic storms of 30 October 2003 and 20 November 2003, different aspects of which have been widely studied by the community. We present here a very complete set of space and ground-based diagnostics that provide the vertical and latitudinal structures of the ionosphere within the South Atlantic magnetic anomaly (SAMA) region and the contiguous parts of South America and Africa. We show that for both storms, the dusk sector corresponding to the universal time (UT) interval between the fast decrease of the SYM-H index and minimum SYM-H value determines uniquely the longitude interval populated by equatorial plasma bubbles and depletions. Further, we find that the UT of these storms is such that the ionospheric density perturbations occur in the SAMA region, which are most extended in latitude and altitude compared with other regions of the globe. In the dusk sector, the eastward penetration electric field, associated with rapid SYM-H decrease, adds to the postsunset eastward E-field because of the F region dynamo, which may be specially enhanced in this longitude interval because of the increased zonal conductivity gradient caused by energetic particle precipitation. This enhanced E-field at dusk causes a rapid uplift of the ionosphere and sets off plasma instabilities to form bubbles or bite-outs. The decreased ion density seen in the Defense Meteorological Satellite Program (DMSP) in situ data at 840 km indicates that the ionospheric plasma has been lifted above the DMSP altitude and transported away from the region by diffusion along magnetic field lines. Plasma bubbles and bite-outs impact satellite communication and navigation systems by introducing scintillations and steep density gradients. This paper corroborates that intense magnetic storms follow the framework, developed by Su. Basu et al. (2001) for moderate storms, that specifies the longitude interval in which such disturbances are most likely to occur.