Showing papers on "Longitude published in 1988"

Principal oscillation pattern analysis of the 30- to 60-day oscillation in general circulation model equatorial troposphere

Abstract: A new technique is described for identifying time-dependent patterns (i.e., “principal oscillation patterns,” or POPs) in a set of geophysical time series. POPs are defined as the normal modes of a linear dynamical representation of the data in terms of a first-order autoregressive vector process with residual noise forcing. POPs associated with real eigenvalues represent nonpropagating, nonoscillatory patterns which decay exponentially. POPs associated with complex eigenvalues occur in complex conjugate pairs and can represent standing wave structures (if one pattern is much stronger than the other), propagating waves (if both patterns are periodic and have the same structure except for a quarter-wavelength shift) or, in general, an arbitrary amphidromal oscillation. After the POPs have been defined for a selected set of primary variables, associated correlation or composite patterns may be derived for additional secondary fields to gain further insight into the structure of the interaction mechanisms. The method is illustrated by analyzing the tropical variability structure of a 10-year numerical simulation with the T21 general circulation model (GCM) of the European Centre for Medium Range Weather Forecasts, Reading, England. The POP analysis is applied to the 200-hPa horizontal divergence field along the equator for time scales shorter than 10 weeks. The associated patterns are determined for a number of additional fields in the tropical belt between 30°S and 30°N. One dominant POP pair is found. Its spatial scale corresponds to zonal wave number 1. The patterns travel eastward, with an average period of 24 days and an e-folding decay time of 10 days. The maximum variance occurs in the area with maximum tropical precipitation, between 100°E and the dateline. These features correspond rather closely to the characteristics of the observed tropical “30- to 60-day wave,” except for the smaller period. A frequency–wave number analysis confirms that this 30- to 60-day wave is the most dominant regular oscillation in the tropical GCM troposphere. The associated patterns of sea level pressure, precipitation, and other quantities exhibit a number of intriguing aspects, namely, (1) the phase velocity of the 30- to 60-day wave varies with longitude from 6 m s−1 in the Indonesian area to more than 30 m s−1 over the eastern Pacific, small phase speeds being associated with large amplitudes and high phase speeds with small amplitudes; (2) in the high-amplitude regions, rainfall and upper air velocity potential are in phase, while in the low-amplitude regions, rainfall and velocity potential appear uncorrelated; (3) at the surface a pattern strongly resembling Gill's theoretical response to an equatorial heating source is found, with a trough to the east and two off-equatorial cyclones to the west of the heating. The lack of meridional winds is probably related to the disregard of the seasonal asymmetries.

Average Vertical Motions in the Tropical Atmosphere Observed by a Radar Wind Profiler on Pohnpei (7°N Latitude, 157°E Longitude)

Abstract: Average vertical profiles of the vertical wind obtained under clear sky conditions as weal as under conditions of both light-to-moderate and heavy rainfall am presented from data obtained using a radar wind profiler located on the island of Pohnpei (latitude 7°N, longitude 157°E). The average profiles for the precipitation conditions were obtained, insofar as possible, under conditions similar to those present within the stratiform and convective regions of tropical mesoscale convective complexes. Comparison between the vertical wind profiles obtained from the wind profiler and vertical wind profiles obtained earlier by wore conventional methods (i.e., deduced from the convergence-divergence of mesoscale horizontal winds) shows that, while the general features of the profiles obtained by both techniques are similar, the profiler results exhibit somewhat more detail. The profiler is able to resolve long-term average vertical motions down to the, ∼cm s−1 subsidence that occurs under clear air condi...

Deep Currents in the Central Subarctic Pacific Ocean

Abstract: Sections of closely spaced CTD stations along Longs. 165°W, 175°W and 175°E, in combination with 14-month current records from the central longitude, define two deep, nearly zonal currants, with speed increasing upward, in the subarctic Pacific. One flows eastward above the Aleutian Rise and Aleutian Trench, and appears to be a concentration of geostrophic flow forced by the bottom topography. The other flows westward along the Aleutian Island Arc, and is the northern-boundary current predicted by deep-circulation theory. Both currents reach to the sea surface, the boundary current being simply the deep part of the Alaskan Stream. The current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal-wind calculations they suggest, at 175°W, (1) a transport of 28 × 106 m3 s−1 for the Alaskan Stream, of whch 5 × 106 m3 s−1 was found below 1500 m, and (2) a transport of around 20 × 1O6 m3 s−1 for the eastward jet, of wh...

Determination of rock type on Mercury and the Moon through remote sensing in the thermal infrared

Abstract: Thermal infrared emission spectra of the moon and Mercury have been obtained using the Si:As photoconductor and circular variable filter at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Lunar spectra from 7.2 to 12.2 microns for two different locations in the south polar highlands have Christiansen frequency peaks at 8.1 microns and 7.9 microns, respectively. This indicates different compositions at the two locations; mafic in the first case, more felsic in the second. Emission spectra from Mercury are not as spatially localized,; however, the longitude of maximum contribution to the spectrum can be calculated from thermal models of the earth-facing disk. Results for areas centered at two longitudes have been obtained. Two locations in the intercrater plains were observed. At 40-deg longitude (very near the crater Homer), a peak at 7.9 microns indicates mafic igneous rock type. Spectra emanating from 46-deg longitude have peaks at 7.8 microns, indicating a region borderline between mafic and intermediate composition.

Spatial and Temporal Variability Within the Southern Ocean

Abstract: The Southern Ocean is not radially symmetric; many circulation and water mass features vary markedly with longitude. This recommends care in making generalizations of the ocean dynamics and ventilation for the Southern Ocean. The Antarctic Circumpolar Current (ACC) varies in latitude from a position slightly north of 50°S in the Atlantic sector to near 60°S southeast of New Zealand. The ACC displays significant temporal variation, ranging from mesoscale structures of meanders and eddies, to broad regional low frequency variations. South of the ACC are vast areas of more sluggish flow, many of which are organized into cyclonic circulation gyres. The largest is the Weddell Gyre; smaller gyres are located north and east of the Ross Sea, east of the Kerguelan Plateau. Variation in the strength of the western boundary current of the Weddell Gyre may be a primary factor in driving variations in the biology of the region. Wind-induced variations, perhaps coupled to changes in the freshwater balance, would also influence the vertical stability of the water column, the vertical heat flux and the sea ice cover extent. The oceanography along the continental margins is also very dependent on longitude. These variations are related to changes in the geometry of the shelf, the characteristics of the adjacent glacial ice, and on the wind field.

Geographic distribution of lightning-induced electron precipitation observed as VLF/LF perturbation events

Abstract: Expected occurrence characteristics of lightning-induced electron precipitation (LEP) events at longitudes of the western (110° W) versus eastern (71° W) United States are considered from the point of view of available trapped particle flux at the edge of the loss cone. Considering published data on nighttime fluxes of >68 keV electrons observed at L ≃ 2.5, and for “direct” precipitation into the northern hemisphere induced by northern hemisphere lightning, the occurrence rate and flux levels are expected to be a factor of 20–200 higher in the west than in the east, assuming no significant variation in lightning source activity with longitude. Again assuming lightning sources in the north, it is predicted that at 71° W, “mirrored” precipitation into the southern hemisphere would involve precipitation fluxes 30–300 times higher than “direct” precipitation into the northern hemisphere. However, at 110° W and again assuming lightning in the north, southern hemisphere precipitation would tend to be limited to that small fraction of particles that were initially scattered into the northern loss cone and that were then backscattered from the northern atmosphere so as to reach the south. Preliminary experimental investigation of these predictions is based on observations of lightning-associated perturbations of two geographically separate subionospheric VLF/LF signal paths, one (48.5 kHz) originating at Silver Creek, Nebraska, and observed at Stanford, California, and the other (28.5 kHz) originating at Aguadilla, Peurto Rico, and observed at Lake Mistissini, Quebec. The association of the characteristic VLF signal perturbations with lightning is generally evidenced by simultaneous (within ∼1 s) observation of single or multiple radio atmospherics. In most cases, high-resolution measurements of event signatures reveal a ∼0.5–1 s delay between the atmospheric and event onset, as well as an ∼1-s onset duration, consistent with theoretical predictions of a test particle model of the gyroresonant whistler-particle interaction. The data, considered in the light of previous observations in the southern hemisphere, provide qualitative support for several of the predictions based on considerations of the trapped flux level near the loss cone, in particular the prediction of comparable rates in the north at 110° W and the south at 71° W, and the prediction of substantially larger rates in the south than in the north near 71° W.

Winter observations of iceberg frequencies and sizes in the south Atlantic Ocean

Abstract: The numbers and apparent sizes of icebergs in the South Atlantic Ocean in midwinter were measured by radar and visually from F. S. Polarstern during the 1986 Winter Weddell Sea Project cruise. Results show that in a heavy sea (sea state 7–8), icebergs have to be at least 115 m in diameter to be detected at all and that detectability falls off severely for all bergs at ranges exceeding 8 n. mi. (15 km); that most bergs had diameters of less than 1 km with a preferred size of 400–500 m; and that a high density of icebergs in the latitude band 53°–56°S at longitude 19°–30°W contrasted with a virtual absence of bergs in the same latitude band at longitude 1°–9°E. The latter effect is ascribed to melt and wave–induced deterioration causing the disappearance of this iceberg population between the two sets of longitudes.

Diurnal variation of outgoing longwave radiation

Abstract: The global and monthly distribution of the diurnal variation of outgoing longwave radiation (OLR) has been calculated by compositing estimates of the planetary OLR obtained from polar orbiting satellites at different equator crossing times. These data include NOAA and NASA polar orbiting satellites for the year 1974 through 1983, giving a total of ten different local observations per day throughout the whole data period. A Fourier analysis was then applied to calculate the phase and amplitude of the diurnal cycle on a 2.5° latitude/longitude grid for each month of the year. Assumption was implicitly made that the first harmonic alone explains most of the diurnal variation. The results are represented on maps extending from 55° south to 55° north for four different seasons from which a large seasonal variability of the diurnal harmonic primarily experienced by the mid-latitude continents was clearly depicted. Over land areas the amplitude of the diurnal variation was large. In desert and semi-arid areas it seem to be clearly related to surface solar heating i.e. phases of maximum OLR generally occurring near noon during summer and afternoon during winter months. Over the oceans, the amplitude is generally small even in the convectively active regions, such as the ITCZ, and the diurnal cycle appears to be modulated primarily by clouds. Finally, a ‘harmonic dial’ was constructed to examine the most dramatic features of the diurnal variation representative of such areas as the ITCZ, deserts, tropical convective clouds regions and highly variable mid-latitude areas. Results of this study are consistent with other studies of the diurnal variability of clouds and radiation budget parameters.

Longitudinal differences in electron precipitation near L = 4

Abstract: The origin of the significant differences revealed in data on electron precipitation characteristics obtained above Siple Station, Antarctica, and Kerguelen Islands was investigated. The two stations are both in the Southern Hemisphere at nearly the same magnetic latitude (L=4) and at longitudes that place them roughly at equal distances east and west of the center of the South Atlantic magnetic anomaly. The primary data used in the study were counting rates from rocket-borne parachute-deployed scintillation counters and VLF data from ground-based and rocket-borne receivers. The two locations were found to differ in two major respects: (1) the precipitation background at Kerguelen Islands is very low, with high levels of wave activity being required to produce any detectable precipitation, and (2) X-ray microbursts, very common at Siple, were found to be essentially absent at Kerguelen. This observation supports models of the microburst generation process which predict maximum pitch angle scatterings of only a few tenths of a degree.

Global annual snow accumulation by months

Abstract: : The compilation of observed mean monthly snow accumulations for the globe was taken from a variety of climatological sources and formats. They were reformatted to fit the global 4 latitude by 5 longitude grid of the RAND coupled two-level oceanic and two-level atmospheric general circulation model (GCM). The results are presented in the form of machine-analyzed isopleths on global maps, global grid-point tabulations, and global means. These products were used at RAND to initialize GCM calculations, to facilitate comparisons with global integrations from the GCM, and as the global climatological summary. The snow- accumulation data given here were derived from observed data from various sources, presented in a variety of formats. Most of the monthly measurements were from scheduled snow-depth observations made in the Northern Hemisphere that were published before 1976. These data were gathered and developed into monthly climatologies, expressing conditions representative of the last day of each month, by the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL). To supplement the CRREL summaries, a pseudoclimatology of monthly snow accumulations was developed at RAND for the 4 latitude by 5 longitude grid points through the data-sparse areas of China, Greenland, the Arctic basin, and the Antarctic. (sdw)

Paleomagnetism of Late Cretaceous and Eocene limestones and chalks from Haiti: Tectonic interpretations

Abstract: We have conducted a paleomagnetic study of limestones and chalks from Haiti which suggests that the island of Hispaniola is a composite of at least two tectonically independent blocks. Sampling sites are distributed among three widely separated localities, namely: Les Cayes (nine sites; 18.3°N. Latitude; 73.6°W. Longitude) and Beloc (five sites; 18.4°N. Latitude; 72.6°W. Longitude) which are located on the southern peninsula of Haiti, and a northern locality, Ennery (six sites; 19.5°N. Latitude; 72.5°W. Longitude). Stable magnetization components of dual polarity and moderately high blocking temperature were revealed through progressive thermal demagnetization of samples from all of the Beloc and Ennery sites, while seven of the nine Les Cayes sites possessed unstable magnetizations. Mean paleolatitudes calculated from Beloc and Ennery data show 8° of latitudinal separation that is of at least Eocene age. Pole positions (Beloc: 43.2°N. Latitude; 185.8°E. Longitude, α95=25.1° and Ennery: 66.1°N. Latitude; 31.3°E. Longitude, α95=19.7°) show both colatitudinal and angular discordance with the North American apparent polar wander path. Based on these disparities, we demonstrate that the implied tectonic displacements tend to support some aspects of previously published Caribbean plate tectonic models.

Comment on “Highly relativistic magnetospheric electrons: A role in coupling to the middle atmosphere?”

Abstract: It is argued that Baker et al. (1987) may have underestimated the electron precipitation rate in the southern hemisphere in the region extending west to about 90 deg in longitude from the southern extension of the center of the South Atlantic geomagnetic anomaly (SAGA). In a reply, it is noted that Baker et al. restricted their study to the case of uniform precipitation in latitude and longitude throughout the outer-zone area, thus entailing a great simplification of the real-world situation. Comments are made on the effects of the SAGA on electron precipitation.

A Statistical Comparison of Methods for Determining Ocean Surface Winds

Abstract: The performance of various techniques which determine ocean surface winds using information from large-scale analyses and forecast models is discussed. The techniques evaluated are the geostrophic relation, a simple empirical law, National Meteorological Center (NMC) 1000-mb winds, a two-region analytically matched boundary layer, a two-region boundary layer based on Rossby number similarity theory, and the Fleet Numerical Oceanography Center (FNOC) marine winds. Statistical comparisons of the model winds were made with observed buoy and ship winds for wind speed, wind direction, and the vector wind. This study is based on analyses and 24-h forecasts made once a day at 0000 UTC from 3 December 1985 through 6 January 1986 on a 2.5 × 2.5 degree latitude, longitude, grid. The statistical results indicate that no one Model was clearly the best. The absolute wind speed difference between all the models and observations is, on the average, about 3 m s−1, and the RMS difference is about 4.O m s−1. Howev...

Indices for mid-latitude North Pacific winter wind systems; an exploratory investigation

Abstract: Biological distributions and fish migrations during the spring and summer in the mid-latitude N Pacific are believed to be affected by the large-scale wind systems during the preceding winter. These wind systems are related to the field of atmospheric pressure which, on a monthly or quarterly time scale, show pronounced interannual variations. This exploratory investigation is concerned with measures of the large-scale wind systems that are indicative of their intensity, location, and size, and that can be derived from monthly or quarterly sea-level pressure distributions. Of interest are the NW, W, and SW wind systems which are related to the pressure gradients between the Siberian High and Aleutian Low, the Aleutian Low and the N Pacific Subtropical High, and the Aleutian Low and the N American High, respectively. Interannual changes in the winter sea-level pressure distribution pattern are primarily the result of changes in the pressure and zonal displacements of the Aleutian Low near 50°N. This property permitted simple derivation of wind indices from grid values of N hemisphere mean winter pressures distributions for the years 1947 to 1985. Indices, presented as normalized anomalies, are for the meridional component of the wind system at 50°N over the ocean W and E of the Aleutian Low, for the westerlies S of the Aleutian Low and for the longitude of this Low. The paper concludes with a discussion of the limitations of the indices in terms of reflecting characteristic atmospheric pressure distribution patterns, an examination of the relationship between wind anomalies and El Nino events, and a discussion of the results in terms of oceanographic, climate, and biological implications.

Solving the problem of longitude

Abstract: the presence of antisperm antibodies by the gelatin agglutination test2 and the tray agglutination test.3 Fourteen women have completed one treatment cycle, with two women having repeat treatment cycles after six months. One singleton pregnancy has been achieved, which resulted in the delivery of a live male infant weighing 623 g at 28 weeks' gestation. In all 16 treatment cycles the women had no serum agglutinating activity detected by the gelatin agglutination test before or after direct intraperitoneal insemination. Two women, however, had weak agglutinating activity in serum before direct intraperitoneal insemination when tested by the tray agglutination test (both 1:4, head-head agglutination). One of these women showed no change in the measured titre after direct intraperitoneal insemination, and the other had a slight increase in titre on days 14 and 28 after direct intraperitoneal insemination (1:8, head-head agglutination). The two women with repeat cycles had not developed any agglutinating activity detectable by either test during the six months between the first and second treatment cycles. It thus appears from these preliminary data that, with the numbers of sperm described here, direct intraperitoneal insemination does not induce the production ofantisperm antibodies to any appreciable degree over the period studied. A larger study, however, with a longer follow up time is required to confirm this finding. Z I Z IBRAHIM B LOWE P L MATSON B A LIEBERMAN Regional IVF Unit, St Mary's Hospital, Manchester M13 OJH