Showing papers on "Longitude published in 1997"

A new global gridded radiosonde temperature data base and recent temperature trends

Abstract: We present a new analysis of global radiosonde temperature data. From 1979 onwards, the data from the Australasian region have been corrected for instrument-related discontinuities with the help of comparisons with collocated retrievals from satellite-based Microwave Sounding Units (MSU) and metadata: in future work, adjustments will be applied worldwide and extended to earlier years. The data are stored as monthly anomalies from a 1971–1990 reference period on a 5° latitude × 10° longitude grid at 8 levels from 50 hPa to 850 hPa. Seasonal and annual temperature anomalies have also been created on a 10° × 20° grid using an eigenvector reconstruction method to filter noise. Latitude-height profiles of zonal-mean temperature changes since the 1960s show significant cooling in the lower stratosphere, especially in middle and high latitudes of the Southern Hemisphere, but the cooling over Australasia is less than shown by unadjusted data. Warming dominates the troposphere but is not a maximum in the tropical upper troposphere. In the annual mean, tropospheric warming is greatest around 45°N and possibly in the data-sparse high latitudes of the Southern Hemisphere.

Homogenization of swedish temperature data. part ii: homogenized gridded air temperature compared with a subset of global gridded air temperature since 1861

Abstract: Homogeneity tests of long seasonal temperature series from Sweden, Denmark, Finland, and Norway indicate that homogeneous series are rare and that an abrupt change of the relative mean level is a much more common type of nonhomogeneity than a gradual change. Furthermore, negative shifts were 20% more common than positive shifts. Homogenized temperature anomaly series that were constructed for six 5 degrees latitude x 5 degrees longitude grid boxes indicate that the temporal pattern of temperture changes has been similar in different parts of Sweden since 1861. The annual mean temperature over Sweden was found to have increased by 0.68 degrees C from the period 1861-1890 to 1965-1994. The corresponding changes for the seasons were: +0.18 degrees C (winter), +1.40 (spring), +0.42 (summer) and +0.60 (autumn). A direct comparson shows that non-homogeneities in the temperature series from individual grid boxes in a global data set can be as large as the total changes observed. We estimate that a 95 per cent confidence interval for the error, due to non-homogeneous long station records, in estimates of hemispheric temperature changes over land regions since the period 1861-1890 is +/-0.1 degrees C for the Northern Hemisphere and the globe and +/-0.25 degrees C for the Southern Hemisphere. For a region consisting of about five grid boxes, this error is +/-0.5 degrees C. The large non-homogeneities in individual grid-box series in the global data set is partly a consequence of the fact that homogeneous climate data are not always easily available for the open research community. We urge that efforts are made to improve this situation.

Effects of instability waves in the mixed layer of the equatorial Pacific

Abstract: Data from more than 1900 Lagrangian drifters in the equatorial Pacific Ocean from 1980 to 1994 together with velocity records from two Tropical Ocean-Global Atmosphere - Tropical Atmosphere Ocean (TOGA-TAO) equatorial moorings at 11° and 140°W, advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) product, and European Centre for Medium-Range Weather Forecasts (ECMWF) winds were used to investigate the effects and energetics of currents associated with the tropical instability waves (TIWs). Adaptive multitaper spectral analysis was used to estimate how spectral energy varied in the 15-to-30-day period TIW band. The drifter data was analyzed separately for high and low values of the TIW energy in regions of 20° longitude by 20° latitude centered at 0°N, 110°W and 0°N, 140°W to construct meridional profiles of energetics of the TIW region. High TIW energy values typically occurred around October when the South Equatorial Current (SEC) and the North Equatorial Countercurrent (NECC) both became stronger and the eddy kinetic and potential energy production at 140°W was noticeably larger. At 110°W the eddy kinetic and potential energy production existed all the time without large differences between the periods of high and low TIW activity. The meridional kinetic energy was enhanced in the region between the equator and 10°N from 150° to 100°W, with the largest values occurring between 110° and 140°W in longitude and around 5°N in latitude. The largest terms in the horizontal kinetic energy production equation were u′υ′¯U¯y and υ′υ′¯V¯y with maxima in the region of anticyclonic shear between SEC and NECC, from 2° to 6°N. The temperature variance, or the potential energy production, peaked closer to the equator at 3°N. The linear growth timescale of the instability was about 10 days. The time-variable wind supplied energy to the current fluctuations during the TIW off period, but for the TIW on period the wind energy input was reduced (at 110W) or even reversed (at 140°W, between 1°S and 7°N), suggesting that air-sea interaction was important in the total energy balance of the waves. The effect of instability was to reduce the shear of the mean current and to warm the equatorial cold tongue. These calculations suggest that there exists a balance between energy production and dissipation in the TIWs.

Multiyear variability in the near-surface temperature structure of the midlatitude western North Atlantic Ocean

Abstract: Between 1966 and 1995, subsurface temperature data have been collected in the western North Atlantic Ocean using expendable bathythermographs. Data coverage is sparse in both time and space, but evidence for decadal variability in the upper 400 m of the water column is found. The data were averaged by month onto a 2° of latitude by 4° of longitude grid. Thirty-one quadrangles in the region bounded by 17°N and 43°N and 78°W and 66°W have sufficient data to provide consistent results. Anomaly time series at 0, 100, 200, 300, and 400 m were estimated by subtracting a mean monthly climatology. The individual records were detrended and filtered to highlight the longer-period signals. The analysis resulted in 25-year records (1969–1993) for study. Within the thermocline of the subtropical gyre and the Gulf Stream at 100 and 200 m, periods of predominately positive temperature anomaly end in 1971, 1982, and 1990, while periods of negative anomaly end in 1976 and 1985. Only the events ending in 1971, 1976, and 1990 are in the majority of the records at 300 and 400 m. Most of the events also appear in the sea surface temperature (SST) records but are somewhat masked by significant noise at the surface. Meridional-vertical temperature sections through the subtropical gyre show that transitions from negative to positive anomaly events are characterized by a deepening of the isotherms throughout the section and transitions from positive to negative events by a rising of the isotherms. Significant lateral migration of the axis of the Gulf Stream, although possibly masked by the 2° averaging, is not necessary to explain either type of event. The transitions in the SST and 100-m temperature time series occur at essentially the same time as the transitions in an index of the North Atlantic Oscillation (NAO) that has also been detrended (i.e., 1971, 1976, 1980, 1984, 1988). The 1971, 1976, and 1988 NAO events are also observed at 300 and 400 m as described earlier. Periods of positive subsurface temperature anomaly are coincidental with periods of positive NAO index, and periods of negative subsurface temperature anomaly are coincidental with periods of negative NAO index. Thus earlier results showing connections between the NAO and western Atlantic SST at decadal timescales are now extended to at least 400 m in the water column. Trends were computed from the individual 25-year records. The trends at all depths are predominately negative north of 38°N and positive south of 38°N. Inferences from the horizontal distribution of the trends and results from earlier studies suggest that the 1969–1993 period may be a phase of a 30- to 50-year signal observed in the northern Atlantic since the beginning of the century.

Rates of scattering occurrence in routine HF radar observations during solar cycle maximum

Abstract: The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide continuous monitoring of the high-latitude ionosphere over large areas in both the northern and southern hemispheres. The HF technique generates estimates of the E×B convective drift of ionospheric plasma when suitable small-scale (∼10 m) irregularities are present and viewed under favorable magnetic aspect conditions (radar k vector ⊥ to B). In this paper we report on the statistics of HF scattering occurrence. The study period encompasses 5.5 years (1988 to mid-1993) of routine observations with the HF radar located at Goose Bay, Labrador, Canada, and corresponds to the most recent period of solar cycle maximum. The data were carefully filtered for those instances when high-confidence F region velocity measurements were obtained within 1°×3° magnetic latitude/longitude regions and 12-min UT intervals. For average conditions the rates at which scatter occurred at particular values of invariant latitude ranged from 40% with MLT. The probability of making velocity measurements somewhere in the radar field of view varied from ∼80% on the nightside to ∼45% on the noon meridian. When scatter was detected, the average latitudinal coverage varied from a minimum of 4° Λ on the dayside to over 6° Λ on the nightside. There were significant dependencies on Kp and season. The highest occurrence rates (>60%) were obtained on the nightside for quiet conditions and in the afternoon for disturbed conditions. Winter was the most active season. HF scattering was limited by the equatorward boundary of the Feldstein oval but extended poleward of the oval into the polar cap. Scattering in the noon sector was associated with the aggregate cusp/mantle/low-latitude boundary layer region. The scattering activity was notably suppressed in the morning sector under disturbed conditions and in the noon and afternoon sectors in summer. We discuss the geophysical factors that influence the likelihood of generating HF scatter. These results have value for the design of experiments involving the SuperDARN HF radars.

Solar activity variations in the composition of the low-latitude topside ionosphere

Abstract: Ion composition data from the retarding potential analyzer onboard the Defense Meteorological Satellite Program (DMSP) F10 have been analyzed for the months of June and September for the years 1991–1994 when the solar F10.7 flux changed from near 200 to less than 100. Low-latitude composition data have been averaged by dip latitude and geographic longitude for morning and evening passes to investigate variations attributable to solar variability. In 1991 the dominant ion is O+ in both the morning and the evening, but by 1994, O+ is the dominant ion only at certain locations in the morning. The O+ −H+ transition height is well above the DMSP altitude (800 km) in 1991, but the transition height is near or below 800 km in 1994. Neutral wind induced longitude variations in the topside are present under all levels of solar activity, but the differing role of interhemispheric plasma transport at different solar activity levels dramatically changes the latitude distributions resulting from the winds. At high solar activity the O+ −H+ transition height is well above 800 km, and interhemispheric transport of O+ in the flux tubes connecting the northern and southern hemispheric topside reduces the latitude asymmetry in O+ while producing the minimum observable H+ asymmetries at night. At lower solar activity levels, H+ dominates the topside ionosphere above 800 km, and larger latitudinal asymmetries in the O+ concentration are observed, while the H+ latitude distribution remains quite symmetric at all local times.

CUTLASS/IMAGE observations of high-latitude convection features during substorms

Abstract: . The CUTLASS Finland HF radar has been operational since February 1995. The radar frequently observes backscatter during the midnight sector from a latitude range 70–75° geographic, latitudes often associated with the polar cap. These intervals of backscatter occur during intervals of substorm activity, predominantly in periods of relatively quiet magnetospheric activity, with Kp during the interval under study being 2- and ΣKp for the day being only 8-. During August 1995 the radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14 s, and measurement of a full spatial scan of line-of-sight convection velocities every four minutes. Data from such scans reveal the radar to be measuring return flow convection during the interval of substorm activity. For three intervals during the period under study, a reduction in the spatial extent of radar backscatter occurred. This is a consequence of D region HF absorption and its limited extent in the present study is probably a consequence of the high latitude of the substorm activity, with the electrojet centre lying between 67° and 71° geomagnetic latitude. The high time resolution beam of the radar additionally demonstrates that the convection is highly time dependent. Pulses of equatorward flow exceeding ~600 m s–1 are observed with a duration of ~5 min and a repetition period of ~8 min. Their spatial extent in the CUTLASS field of view was 400–500 km in longitude, and 300–400 km in latitude. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. The transient features are interpreted as being due to ionospheric current vortices associated with field aligned current pairs. The relationship between these observations and substorm phenomena in the magnetotail is discussed.

Greenwich Time and the Longitude

Abstract: The history of the Royal Observatory, Greenwich has been revised to coincide with the Millenium. Color illustrations and updated text tell the story of Greenwich from its foundations in 1676 to its present status as Longitude 0, the world's Prime Meridian for measuring longitude and time. The book covers the importance of longitude for navigation and traces the history of Greenwich Time, the basis of universal time-keeping. The book is co-published with the National Maritime Museum, where Derek Howse was the former Head of Navigation and Astronomy.

A redefinition of Jupiter's rotation period

Abstract: We measured the rotation period of Jupiter's inner magnetosphere with precision previously unattainable, using 35 years of observations of the Jovian decametric radiation at the University of Florida Radio Observatory at frequencies between 18 and 22.2 MHz. The new rotation period is the weighted mean of 13 independent 24-year average determinations. Each of these was found by measuring the drift of the histogram of occurrence probability versus System III (1965) central meridian longitude over an interval of approximately 24 years. The measured drift was used to correct the System III (1965) period to obtain the new value. Our weighted mean is 9 hours 55 min 29.6854 s, with a standard deviation of the weighted mean (σ) of 0.0035 s. This new rotation period is 7.4σ shorter than that of the System III (1965), indicating that the latter is in need of revision. Our measurements indicate an upper limit of about 4 ms/year on any possible Jovian rotation period drift.

Method of navigating using position-information-codes which include information regarding the latitude and longitude of a desired location

Abstract: A method of navigating including decoding a position-information code represented by a string of codes including the latitude and the longitude of a position entered via an input means into original information on the position including the latitude and the longitude of the position. Information created from the recovered original information resulting from the decoding of the position-information code and map data read out from a map-information storage unit are presented to the user by using a display means and a sound outputting means.

An exact conversion from an Earth-centered coordinate system to latitude, longitude and altitude

Abstract: Present combat systems are being upgraded to properly meet the new capabilities being developed against tactical ballistic missiles. The local coordinate systems are being upgraded to a global (WGS-84) coordinate system so that the correct exchange of threat information with other defending units can be done correctly and in a timely manner. This coordinate system upgrade is also used to properly track these threats, The computation of an Earth-centered coordinate (X/sub ECC/, Y/sub ECC/, Z/sub ECC/) system for a track referenced by altitude, latitude, and longitude is straightforward in biaxial (WGS-84) ellipsoid Earth. The problem arises using the Earth-centered coordinate system for the inverse operation to recompute the altitude, latitude and longitude of the track. This computation can only be done approximately. This article introduces a unique analytic derivation to calculate exactly the latitude, longitude, and altitude of a track from an Earth centered coordinate system. The problem is transformed into solving for a root of an eighth-order polynomial, which can then be reduced and solved by rewriting as a quartic equation. A robust, iterative numerical algorithm for computer implementation is also presented for platforms having computational and memory constraint. An example is given and comparisons made to show the application of these techniques.

On the significance of regional trace gas distributions as derived from aircraft campaigns in PEM‐West A and B

Abstract: With the help of a chemical transport model we calculate the global distributions of three synthetic tracers with uniform emission rates over the continents, zero emissions over the ocean, and constant lifetimes of 5, 20, and 100 days. These distributions serve as a first approximation to those of the lower alkanes and are analyzed in detail for the region between 115°E and 155°E longitude, 0°N and 56°N latitude, within which the Pacific Exploratory Mission-West (PEM-West) A and B campaigns took place. We show that the longitudinally averaged latitude by altitude distributions of the tracers over that domain obtained from sampling the model data along the flight tracks closely represent those obtained from complete averages over the full data sets for the months March and September when the campaigns took place. We further show that for each campaign the modeled distributions closely resemble those measured for ethane and propane, although these distributions change significantly between the two seasons. Taken together, this demonstrates that the average distributions of ethane and propane measured during PEM-West A and B describe reasonably well the true pattern of these gases between 0°N and 50°N latitude and 115°E and 155°E longitude in both seasons, despite incomplete and irregular sampling of that domain. In turn, the measured distributions can be used to test the model, mainly for correct parameterization of transport.

Total electron content over the Pan‐American longitudes: March‐April 1994

Abstract: An experimental campaign to measure diurnal changes in total electron content (TEC) over the wide latitude range from approximately 50°N to 40°S was carried out from March 28 through April 11, 1994, by monitoring the differential carrier phase from the U.S. Navy Navigation Satellite System using a chain of ground stations aligned along the approximate 70°W longitude meridian. This Pan-American campaign was conducted primarily to study the day-to-day variability of the equatorial anomaly region. The experimental plan included using the received values of TEC from the chain of stations to construct profiles of electron density versus latitude using tomographic reconstruction techniques and, then, to compare these reconstructions against a theoretical model of the low-latitude ionosphere. The diurnal changes in TEC along this latitude chain of stations showed a high degree of variability from day to day, especially during a magnetic storm which occurred near the beginning of the campaign. The equatorial anomaly in TEC showed large changes in character in the two hemispheres, as well as differences in magnitude from day to day. The latitudinal gradients of TEC, especially in the lower midlatitudes, also showed large differences between magnetic storm and quiet conditions. Comparisons of the TEC data with the theoretical model illustrate the sensitivity of the model calculations to changes in magnetic E×B drift and serves to validate the strong influence that these drifts have on the formation and the strength of the equatorial anomaly regions.

Longitude structure of the ionosphere F region from TOPEX/Poseidon and ground-based data during January 20-30, 1993, including the quasi 2-day oscillation

Abstract: The global structure of the F region ionosphere during January 20-30, 1993, is examined with emphasis on longitudinal variations. The database consists of total electron content (TEC) measurements from the TOPEX/Poseidon dual-frequency altimeter experiment from -66° to +66° geographic latitude for prenoon and premidnight conditions, and hourly f o F 2 and hmF 2 values from eight ionosonde stations between -42° and +26° geographic latitude in the Pacific sector. The 10-day averaged daytime TEC data reveal latitude versus longitude structures whose salient features are captured (within ∼10 TEC units) by the 1990 International Reference Ionosphere (IRI-90), and which can be explained by dynamically induced neutral composition changes due to a combination of solar and magnetically driven circulation systems. The premidnight TEC data at low latitudes reveal the double-banded structure of the equatorial ionization anomaly with, however, pronounced variations in amplitude and position as a function of geomagnetic longitude. None of these features, which probably reflect some combination of electric field and neutral wind effects, are captured by IRI-90. Time series analyses of the f 0 F 2 and hmF 2 data, and space-time Fourier spectra of the TEC data, reveal the presence of a quasi 2-day (QTD) oscillation in the ionosphere which is associated with QTD wind and temperature oscillations in the mesosphere and lower thermosphere previously documented for this time period. The satellite-based QTD results are subject to significant caveats described herein. Nevertheless, the TOPEX/Poseidon TEC data set clearly represents an important resource for global studies of ionospheric structure and plasmaneutral interactions.

Device and method fop encoding/decoding position information and device and method for processing map information

Abstract: PROBLEM TO BE SOLVED: To easily and surely send position information on an internet, for example, and easily displaying a position on a map from this position information SOLUTION: A map information server 1 is provided on an internet 4 When any position is inputted on the map, the map information server 1 performs services for retrieving the information of latitude and longitude corresponding to that position, encoding this latitude/longitude information to character strings based on prescribed rules and displaying them When the latitude/longitude information encoded to the character string is inputted, services are performed for retrieving that position and displaying it on the map Besides, when the latitude/longitude information is inputted, the map information server 1 performs services for encoding this latitude/longitude information to character string codes based on prescribed rules and when the latitude/ longitude information encoded to character string is inputted, services are performed for decoding the character strings to the latitude/longitude information Since the latitude/longitude information encoded to the character string is used as the position information, the number of codes is reduced and the position information can be easily sent

Observation of an ultraslow large‐scale wave near the tropical tropopause

Abstract: An analysis is made of very high resolution radiosonde data taken at seven western Pacific island stations during TOGA-COARE (Tropical Ocean-Global Atmosphere and Coupled Ocean-Atmosphere Response Experiment) Evidence is found for a wave near the tropopause with periods ∼30-40 days and with very slow (∼3 m s -1 ) eastward propagation This oscillation appears quite coherent across the region considered (a 37° longitude spread) The oscillation has a short vertical wavelength (∼3 km) and is strongly attenuated above the tropopause and thus would be very hard to observe in either satellite data or conventional meteorological analyses

Longitudinal variability of the mesopause SAO

Abstract: A longitudinal variation in the mesopause semi-annual oscillation (SAO) is documented from wind observations made by the High Resolution Doppler Imager satellite instrument. The asymmetry is dominated by a wavenumber 1 pattern with a variable phase. During the easterly phase of the mesopause SAO (equinoxes), maximum tropical easterlies occur over eastern South America and the Atlantic Ocean in the longitude band 300°-360°. During the westerly phase (solstices), the westerly winds descend more rapidly and are larger below ∼80 km in this same (Atlantic) longitude band. To the best that can be determined with sparse data, the longitudinal asymmetries near the stratopause are weak and are in phase with those in the mesosphere.

Comparison of Los Alamos National Laboratory (LANL) Parallel Ocean Program (POP) model velocity fields with Pacific surface drifter measurements

Abstract: : Model fields from the Los Alamos National Laboratory (LANL) Parallel Ocean Program (POP) 1/6 degree global circulation model are compared to measurements from over 1300 satellite-tracked surface drifters that were deployed in the tropical Pacific (20N to 20S), between 1979 and 1994, during the TOGA Pan Pacific Current Study. Geographic averages of 5 days averaged drifter velocity estimates for 2 deg. latitude x 8 deg. longitude bins are compared to similarly binned 3 days model snapshots from September 1992 to October 1994. Eulerian comparisons of the model mean velocities and their observed counterparts show that the model U mean is slightly higher in the equatorial region, while the model V mean is 50% greater in this region. Model SST mean values are 20% less than observed values in the eastern equatorial Pacific. Model variability is about 20% less than the observed quantity in equatorial regions, and 50% less poleward of 10S and 10N. Both model and observed velocity and SST covariance fields imply a net heat convergence toward the equator with the largest values in the region of instability waves north of the equator. Model velocity fields are used to produce simulated Lagrangian trajectories for uniform and non-uniform deployment strategies. Autocorrelation, time and length scales, diffusivity, and polarization are calculated and ensemble averaged by 5 deg. latitude bands for comparison with drifter based Lagrangian statistics. Time and length scales are too long and diffusivities too low compared to observations, but data sampling in the simulated fields was biased by trajectories that overlap current regimes. These differences, in both Eulerian and Lagrangian comparisons, may be related to the lack of a surface mixed layer, inadequate representing of wind forcing, still too coarse grid resolution, and deficiencies in simulating the mean structure of the d

Recording medium for navigation apparatus

Abstract: PROBLEM TO BE SOLVED: To provide a recording medium using a GPS by which the position of a destination can be input simply, whose costs are not increased. SOLUTION: Bar codes 10 on which latitude information and longitude information are recorded are printed on a map or the like. A bar-code reader 2 is installed, and the bar codes 10 on which pieces of information including the latitude information and the longitude information are recorded are read out by the bar-code reader 2. The pieces of information which are read out by the bar-code reader 2 are input as information on a destination. Thereby, the latitude information and the longitude information on the target can be input simply.

Intercomparison of ozone measurements in the lower stratosphere from the UARS Halogen Occultation Experiment and the ER‐2 UV absorption photometer

Abstract: Ozone data obtained by the Halogen Occultation Experiment (HALOE) on the NASA Upper Atmosphere Research Satellite (UARS) have been compared with ozone data obtained by the NOAA dual-beam, UV absorption photometer on the NASA ER-2 aircraft during the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign. This paper describes the measurement characteristics of the two instruments and the precision and accuracy of the two data sets. A total of 26 cases are discussed in which the two different measurements occur within 24 hours, 2.5° latitude, and 10° longitude of each other. Generally, agreement between the two data sets improved the closer in time and space the two measurements occurred. The agreement was better than 10% at ER-2 cruise altitudes (∼50–70 mbar) where the error estimated for HALOE is slightly larger than 18%.