Showing papers on "Longitude published in 1996"

On the nature of decadal anomalies in North Atlantic sea surface temperature

Abstract: North Atlantic sea surface temperature data from the Comprehensive Ocean-Atmosphere Data Set were used to investigate the behavior of temperature anomalies on multiple-year timescales during the period 1948-1992. Monthly anomaly time series for each 2° square from the equator to 70°N were low-pass filtered at 4 years and normalized by the local standard deviation. Attention is focused on the extreme events, the upper and lower deciles, of the anomaly time series. A 45 -year sequence of January maps shows the already familiar phenomena of generally cold conditions prior to 1951, a long warm interval from 1951 through 1967, and again a cold period from 1968 through 1977. The years 1978 through 1982 were largely devoid of persistent strong anomalies, but moderate cold conditions returned during 1983-1986. Warm conditions dominated the North Atlantic from 1987 onward. Within these thermal epochs, however, a total of five cold anomaly features and nine warm anomaly features have been identified. These features have individual lifetimes of 3 to 10 years. A typical size is 20° of latitude or longitude, but they range from barely detectable to spanning the width of the basin, the latter especially in lower latitudes. Most of the anomalies move long distances along certain preferred paths. These paths generally follow the routes of the subarctic and subtropical gyres. Anomalies originating off North America along the boundary between the gyres move northeastward toward the Norwegian Sea along the approximate route of the North Atlantic Current. Midlatitude anomalies originating at the eastern boundary tend to spread both northward and southward along the coast. The speed of these movements (1-3 km d -1 ) is generally less than the expected speed of the near-surface ocean circulation. Simple ideas about the effects of beta dynamics and air-sea heat exchanges are briefly considered but do not provide a satisfactory explanation for the movements of the anomalies. The long timescale of these extreme events and the continuity of their movements suggest a useful degree of predictability of sea surface temperature based on persistence and propagation of features.

GPS phase fluctuations in the equatorial region during the MISETA 1994 campaign

Abstract: In this paper we present the first coordinated use of Global Positioning System (GPS) multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns. Thirty second samples of total electron content (TEC) obtained from GPS phase differences between 1.2- and 1.6-GHz signals are used to study phase fluctuations at several stations. Comparisons were made with various types of ground measurements during the multi-instrument studies of the equatorial thermosphere aeronomy (MISETA) period. Depletions of 6300A airglow emission from Arequipa, Peru, correlated with phase fluctuations recorded at the same site. Phase fluctuations at Arequipa occurred at the times when the Jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes. Levels of phase fluctuations noted at Arequipa varied considerably on nights when only thin layers of irregularities were observed by the Jicamarca radar. Differences of ionospheric conditions between the two sites, separated by only 5.5° geographic longitude, may account for the different behavior patterns of irregularities noted. Similar differences in the general behavior pattern of phase fluctuations were shown when data from Arequipa and Fortaleza, Brazil, were compared. These stations, 33° apart, but at the same dip latitude had different patterns for some days. During a magnetic storm, a very high altitude plume was observed by the radar and by phase fluctuations noted at Santiago at 18° dip latitude. This correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995.

Ocean circulation variations associated with the Antarctic Circumpolar Wave

Abstract: Altimeter data analysis indicates persistent sea surface height (SSH) anomalies propagating eastward about the Antarctic continent. The spatial and temporal characteristics match variations in the atmosphere and sea surface temperature (SST) that are associated with the Antarctic Circumpolar Wave (ACW). During the observation time period, the SSH appears quasiperiodic with a dominant 4 year period and 180° longitude wavelength. Thus, the SSH signature of the ACW appears as two anomalies on opposite sides of the Antarctic continent propagating eastward at 10 cm/s. The SSH response to observed wind forcing agrees in terms of amplitude and phase with simple quasigeostrophic dynamics.

Water-property distributions along an eastern Pacific hydrographic section at 135W

Abstract: As part of the World Ocean Circulation Experiment, full-depth CTD/hydrographic measurements with high horizontal and vertical resolutions were made in June-August 1991 along a line extending from 34N to 33S at a nominal longitude of 135W with an additional short leg that connects it to the California coast roughly along 34N. The line spans the major part of the subtropical and intertropical circulation regime of the eastern North and South Pacific. The primary purpose of this paper is to present vertical sections of various properties from CTD and discrete water-sample measurements along this line and to give an overview of some important features as a basis for more comprehensive basin-scale studies. These features include: the frontal structures found in the surface-layer salinity field in the North Pacific; relatively high-salinity water that dominates the subpycnocline layer between the equator and 17N; troughs of the subpycnocline isopycnals for 26.8-27.5 σ θ found at 12N and 12.5S; a permanent thermostad at 9-10°C observed between 4.5N and 15N; the pycnostad of the Subantarctic Mode Water centered at 27.0-27.05 σ θ and developed south of 22S; two types of the Antarctic Intermediate Water representing the subtropical and equatorial circulation regimes; a thick tongue of high silica centered at 3000 m (45.8 σ 4 ) and extending southward across the entire section; deep (2000-3000 m) westward flows at 5-8N and 10-15S separated by an eastward flow at 1-2S; and dense, cold, oxygen-rich, nutrient-poor bottom waters, which are associated with fracture zones and believed to represent the pathways of eastward flows into the Northeast Pacific Basin of the bottom waters separated from the northward-flowing western boundary undercurrent. This work once again demonstrates the usefulness of long lines of high-quality, high-resolution hydrographic stations such as the one described herein in advancing the understanding of the large-scale ocean circulation.

Multi-instrument ground-based observations of a travelling convection vortices event

Abstract: A coordinated ground-based observational campaign using the IMAGE magnetometer network, EISCAT radars and optical instruments on Svalbard has made possible detailed studies of a travelling convection vortices (TCV) event on 6 January 1992. Combining the data from these facilities allows us to draw a very detailed picture of the features and dynamics of this TCV event. On the way from the noon to the drawn meridian, the vortices went through a remarkable development. The propagation velocity in the ionosphere increased from 2.5 to 7.4 km s−1, and the orientation of the major axes of the vortices rotated from being almost parallel to the magnetic meridian near noon to essentially perpendicular at dawn. By combining electric fields obtained by EISCAT and ionospheric currents deduced from magnetic field recordings, conductivities associated with the vortices could be estimated. Contrary to expectations we found higher conductivities below the downward field aligned current (FAC) filament than below the upward directed. Unexpected results also emerged from the optical observations. For most of the time there were no discrete aurora at 557.7 nm associated with the TCVs. Only once did a discrete form appear at the foot of the upward FAC. This aurora subsequently expanded eastward and westward leaving its centre at the same longitude while the TCV continued to travel westward. Also we try to identify the source regions of TCVs in the magnetosphere and discuss possible generation mechanisms.

Path of the Mean Rotational Pole From 1899 to 1994

Abstract: SUMMARY Historical sources of polar motion are analysed together with modern data in order to compile a set of coordinates of the mean pole in a reference system consistent with that of the International Earth Rotation Service. the trend and quasi-periodic motion of the pole are investigated, and we find that the rotational pole appears to be moving at the rate of 0.333 arcsec century−1 in the direction of 75.0° west longitude. Modern data also appear to be consistent with the possible existence of very low-frequency periodic motion (Markowitz wobble).

Scales of Variability in the Equatorial Pacific Inferred form Tropical Atmosphere-Ocean Buoy Array

Abstract: The highly temporally resolved time series from the Tropical Atmosphere-Ocean moored buoy array are used to evaluate the scales of thermal variability in the upper equatorial Pacific. The TAO array consists of nearly 70 deep-ocean moorings arranged nominally 15° longitude and 2°–3° latitude apart across the equatorial Pacific. The bulk of the data from the array consists of daily averages telemetered in real time, with some records up to 15 years long. However, at several sites more finely resolved data exist, in some cases with resolution of 1 minute. These data form the basis for spectral decomposition spanning virtually all scales of variability from the Brunt-Vaiala frequency to the El Nino-Southern Oscillation timescale. The spectra are used to define the signal to noise ratio as a function of sample rate and frequency, and to investigate the effects of aliasing that results from sparser sampling, such as ship-based observational techniques. The results show that the signal to noise ratio is...

Longitude variations in ion composition in the morning and evening topside equatorial ionosphere near solar minimum

Abstract: Ion composition data from the Defense Meteorological Satellite Program (DMSP) F10 have been averaged by geographic longitude and dip latitude for the months of June, September, and December 1993. The data were taken under near solar minimum conditions. Near 800 km at two fixed local times near 0920 hours and 2120 hours, and at all longitudes, significant variation in local time and season are found. Longitude variations are consistent with modulation of the F peak height by meridional and zonal neutral winds. The components of these winds parallel to the magnetic field lines act to raise and lower the height of the F peak and, additionally, at night, to modulate the plasma decay rate. Zonal winds were found to have significant effects in the longitude regions 150°E to 270°E and 300°E to 360°E, where the magnetic declination is significant. Under solstice conditions, the summer to winter meridional winds play a dominant role in regulating the F peak height, with the zonal winds enhancing or opposing the effects of the meridional winds at longitudes with significant magnetic declination. Zonal winds dominate the regulation of the F peak height near equinox, when the meridional winds are fairly symmetric about the dip equator. The longitude variations are most clearly seen in the O+ and H+ concentrations when O+ is the dominant ion and is in equilibrium with H+. These conditions were found during the daytime during all seasons. H+ is frequently the dominant ion near 800 km, and at night, the longitudinal variations clearly seen in the O+ concentrations were not as easily seen in the H+ concentrations due to the larger scale height of H+.

Planetary-Scale Climatology of Explosive Cyclogenesis and Blocking

Abstract: A climatology of the relationship between explosive cyclogenesis and atmospheric blocking has been constructed from an investigation of sea level pressure and 500-mb height analyses over the Northern Hemisphere during seven winter seasons. Planetary-scale 500-mb geostrophic u and v wind components and component anomalies (u′ and v′) were calculated over each explosive cyclone center and compared to the times and locations of block onsets. Blocking episodes were defined by the persistence, for at least 5 days, of negative zonal index (500-mb height at 40°N less than that at 60°N) spanning at least 18.75° of longitude. Thirty-three percent (43%) of the explosive cyclones that were not analyzed during blocking episodes over the Atlantic (Pacific) sector of the Northern Hemisphere and over which there were anomalously strong planetary-scale southerly winds (v′ > 0), anomalously weak westerly winds (u′ u/2 were followed, in not more than 5 days and within 60° of longitude, by the onset o...

Large-Scale Storms in Saturn's Atmosphere During 1994

Abstract: Large-scale storms are rarely observed in Saturn's atmosphere, but their appearance traces the wind velocity field, providing information on the vertical structure of the clouds and on the dynamics of the atmosphere. Two large-scale atmospheric disturbances formed by clouds highly reflective in the visible part of the spectrum were observed on Saturn during 1994. An equatorial disturbance with a longitudinal size of ∼27,000 kilometers drifted in longitude with a velocity of 273.6 meters per second. A second disturbance, a rapidly evolving convective storm with an initial size ∼7000 kilometers, was observed at 56 degrees south, moving with a zonal velocity of 15.5 meters per second.

A magnetic cloud as a distended flux rope occlusion in the heliospheric current sheet

Abstract: A magnetic cloud was detected both near Earth by IMP 6–8 and 30° of longitude away from Earth by Pioneer 11 at 4.8 AU. The nearly identical magnetic signatures at the two spacecraft imply that its radial dimension increased little between them. The magnetic field within the cloud rotated from toward to away polarity, marking sector boundary passage at both locations. Interpreted in terms of a flux rope, its axis was highly inclined to the ecliptic plane, implying that its cylindrical cross section in the ecliptic plane was distended by at least 30° of longitude, forming an extensive occlusion in the heliospheric current sheet. A similar magnetic signature was observed at the same sector boundary by Pioneer 10 at 6.1 AU, at a longitude between Earth and Pioneer 11. Its radial dimension, however, was diminished by a factor of 3. We suggest that it was the same cloud, compressed by a second, oncoming transient that was observed behind the cloud at 1 AU.

Impact of orographically induced gravity-wave drag in the GLA GCM

Abstract: The influence of gravity-wave drag (GWD) parametrization has been investigated in the Goddard Laboratory for Atmospheres general-circulation model with the resolution of 4° latitude × 5° longitude in the horizontal and 17 sigma layers in the vertical. The simulations showed several overall beneficial effects in the extended-range forecast as well as the seasonal simulation for both winter and summer conditions. The key results include the following: (1)The mid-latitude westerlies, which were shifted poleward (equatorward) in northern (southern) winter, have been corrected. Consequently, the systematic bias of low (high) sea level pressure over the north (south) polar region has been largely eliminated. (2)There is a significant improvement in the simulation of the winter hemisphere stationary waves; this can be attributed to the GWD induced Rossby-wave propagation. Over the northern Pacific region, as the storm track is simulated better, precipitation distribution improves remarkably. (3)In cooperation with the improved regional zonal-mean flow, an adjustment of the mean meridional circulation is found over the Asian summer-monsoon region, leading to an improvement in the precipitation distribution. (4)Spurious absorption of gravity waves at the model top (10 mb) has been removed by applying an open upper-boundary condition. The vertical propagation of the tropospherical gravity wave into the upper stratosphere and mesosphere over mid-latitudes of the northern hemisphere in winter is consistent with observational studies as well as the middle-atmospheric dynamics.

A 1961-90 climatology for Africa south of the Equator and a comparison of potential evapotranspiration estimates

Abstract: A 1961-90 mean monthly climatology for Africa south of the Equator was constructed at a resolution of 0.5° latitude/longitude for a suite of eight surface climate variables: minimum, maximum and mean air temperature; rainfall; sunshine hours; vapour pressure; wind speed; and rain day (>0.1 mm)frequencies. This climatology was constructed from observed station data distributed across the region with station frequencies ranging from 288 (wind speed) to 916 (rainfall). Over 92% of these data is based on observations between 1961-90 and over 85% has been supplied by national meteorological agencies from the region. Additionally, for mean temperature and rainfall, monthly anomalies with respect to the 1961-90 average have been calculated at the same spatial resolution for each month from January 1961 to December 1994. This paper describes the dataset which has been compiled for this work, the interpolation methods which have been used, together with some assessment of the accuracy of the resulting climate surfaces. The interpolation of the 1961-90 normals uses elevation, as well as longitude and latitude, as predictor variables and this enables three climate surfaces to be constructed for each variable, reflecting the 'minimum', mean and 'maximum' elevation within each 0.5° cell. The interpolation of the anomaly fields uses a simpler method in which elevation is not considered. These anomaly time series enable fields of interannual variability to be established for mean temperature and rainfall. The second part of the paper uses this climatology to construct fields of mean monthly potential evapotranspiration (PET) for the region using a number of different calculation methods. A comparison of the resulting PET estimates highlights significant spatial and seasonal biases due to differences in climate input variables and in the theoretical representation of PET. The climatology, described and analysed here is available from the authors for use in climate modelling and the study of climate change in Africa south of the Equator.

Simultaneous mesospheric wind measurements near South Pole by optical and meteor radar methods

Abstract: Simultaneous and co-located measurements of mesospheric winds near South Pole, by high-resolution optical and meteor radar methods, show that these two methods determine very similar motions at slightly different heights of observation. The measured atmospheric motions by the two techniques show that a) The mean wind during 12 days in June, 1995 was found to have a 7 m/s amplitude flowing towards the 5°E longitude direction. The latter direction is different from the 30E° direction found earlier during August 1991 and 1992. b) The observed dominant oscillations in the wind at both heights of observation are those of zonal wavenumber one character. Westward phase propagation was determined for the observed short-period (∼0 hours) oscillations and eastward phase propagation for the longer-period (∼3 days) oscillations, respectively. Because of the neighboring heights of observation by the optical and meteor radar methods, the in situ vertical wavelengths of propagation of the observed waves have been determined to be greater than 100 km for the 10-hr oscillations and near 65 km for the longer period oscillations. With this new information we are able to independently establish the earlier assignment of the nearly 10-hr oscillations as the different meridional modes of a zonal wavenumber one Lamb wave. The determined vertical wavelength and eastward phase progression of the longer periodicity waves indicate these oscillations are likely to be the gravest inertio-gravity wave, which has the appropriate equivalent depths at these periods of oscillation. The simultaneous absence of statistically significant kinetic temperature and optical-tracer emission rate oscillations at the frequencies corresponding to the wind motions, provides independent support to the earlier deductions on the ability of the atmosphere near the rotational poles to support only certain zonal character oscillations.

Airborne nitrous oxide observations over the western Pacific Ocean: September–October 1991

Abstract: The Langley tunable diode laser instrument package incorporated an additional channel to measure nitrous oxide (N2O) during the Pacific Exploratory Mission (PEM) West A. These measurements represent the first airborne, fast response (5-s) N2O data set obtained within the troposphere. Most data were recorded over the western Pacific between 0°N and 45°N latitude, 110°E and 180°E longitude, and 0.3 to 12 km altitude. Important observations include a decreasing N2O latitude gradient of approximately 0.4 parts per billion volume (ppbv) from northern midlatitudes to the equator, a decreasing N2O longitude gradient of 0.4 ppbv from the western Pacific to the central Pacific at northern midlatitudes, and an enhancement of 0.2 ppbv in the boundary layer (altitudes below 0.5 km) relative to the rest of the tropospheric vertical profile. Other observations include increased N2O mixing ratios within both urban and biogenic affected air masses and reduced N2O mixing ratios in stratospheric intrusions. These relationships with air mass source characteristics are exhibited in the large-scale correlations between N2O and CO, CH4, and CO2 in the free troposphere. Atmospheric inputs of N2O are examined and the relative strengths of continental biogenic and anthropogenic/industrial sources are estimated. The data set is also examined for evidence of an oceanic source of N2O.

Observations and parameterization of the stratospheric electrical conductivity

Abstract: Simultaneous in situ measurements of the stratospheric electrical conductivity, made from multiple balloon platforms during the 1992–1993 Extended Life Balloon-Borne Observatories (ELBBO) experiment, have yielded the most comprehensive data set on the stratospheric electrical conductivity. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, beginning November 10, 1992, and lasting through March 18, 1993. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the South Pole to 28°S, and circled around the southern hemisphere several times. On average, the positive polar conductivity (conductivity of positive ions alone) was about 15% higher than that of the negative conductivity, suggesting that differences may exist between the mobilities of positive and negative ions. Data from each polarity of polar conductivity also indicate persistent, apparently organized, short-term and localized variations, with amplitude within 30% of the mean value. In corrected geomagnetic (CGM) coordinates the conductivity variations were found to be a function of latitude but not of longitude. The total conductivity can increase 150% from low latitude to high latitude, and does remain nearly constant at latitudes above 55° (namely, the cosmic ray knee latitude). Calculations based on ionization theory demonstrate that the latitudinal variations in the conductivity measurements were mainly due to the latitudinal variations in incident galactic cosmic ray intensity, with only little effect from the air temperature variations. The calculations shown here also suggest that small ions (as opposed to large ions) provide the main contribution to the stratospheric conductivity. The comparisons between conductivity measurements and models show that commonly used models can underestimate the latitudinal variation by a factor of 2. In this paper the stratospheric conductivity is parameterized based on the measurements, and a simple empirical model is presented in geographic coordinates.

Columbus's Method of Determining Longitude: An Analytical View

Abstract: On 14 September 1494, Christopher Columbus observed a lunar eclipse while at the island of Saona near the eastern tip of Hispaniola. He later recorded in his Libro de las Profecias that, from his timing of the eclipse, he determined his longitude to be ‘five hours and more than one half’west of Cape San Vicente. His actual longitude was three hours and 59 minutes west of Cape San Vicente, so Columbus was off by over an hour and a half, some 23 degrees of longitude.

Equatorial F1 characteristics and the international reference ionosphere model

Abstract: Average values of the F1 critical frequency (f0F1) and the height of the F1 ledge (hmF1) for Ibadan (Latitude 7.4°N, Longitude 3.9°E) were used for this study. Well-defined F1 characteristics are observed during winter at low solar activity. International reference ionosphere (IRI) does not predict F1 parameters during this season. Deviation of predicted F1 electron density (NF1) by the IRI model from observed values are less than 10% for all seasons of low solar activity, when IRI predicts NF1. Higher percentage deviations are observed during summers of high solar activity. IRI overestimates hmF1. Deviations from experimental values vary from 4 to 35%.

Method and system for alarming projection of crane out of working area thereof

Abstract: PURPOSE: To surely alarm when a part of a crane such as a boom is projected out of the working area even in the case where the maximum height of the boundary surface of the working area is complex. CONSTITUTION: Receivers 2, 5 know the longitude x0 , the latitude y0 , and height z0 of the well known reference point and the longitude x1 , the latitude y1 and the height z1 of the tip 3 of a crane boom on the basis of the electric wave transmitted from plural artificial satellites 8 through an in-site reference point antenna 1 and a GPS antenna 4. The receiver 5 corrects the longitude x1 , the latitude y1 and the height z1 on the basis of the data of the longitude x0 , the latitude y0 and the height z0 so as to obtain the data of the longitude (x), the latitude (y) and the height (z) of the accurate position of the tip 3 of the crane boom on the ground surface, and furthermore, converts the data of the height z' to the data of the height (z) on the surface at 0 of height, and outputs it to a computer 6. The computer 6 compares the height (z) with the previously stored maximum height of the boundary surface of the working area, and in the case where the former is larger than the later, an alarm device 7 is operated so as to generate the alarm.