Showing papers on "Longitude published in 1987"

Retrograding Wintertime Low-Frequency Disturbances over the North Pacific Ocean

Abstract: Retrograding (westward-moving) features over the middle and high latitudes of the Northern Hemisphere during winter are examined in observations and data from a GCM simulation, using complex principal component analysis. The first eigenvector of the low-frequency middle troposphere geopotential height over the North Pacific has a zonal scale of 120–160 deg longitude and a dipole-like meridional structure, with maximum amplitude over the Gulf of Alaska and the Bering Sea. These disturbances propagate westward and go through a life cycle of growth and decay over a period of about three weeks. The temporal evolution of the energy and its conversions during the life cycle of the simulated Pacific disturbances are composited, using the time-dependent coefficient of the principal component analysis as an index for their occurrence. The composite energy cycle indicates that the kinetic and available potential energy of these disturbances grow and decay together. Both baroclinic and barotropic conversion...

Satellite observations of a western boundary current in the Bay of Bengal

Abstract: Satellite infrared observations of the Bay of Bengal during the latter part of February 1985 reveal the existence of two bands of warm water that resemble western boundary currents along the east coasts of India and Sri Lanka. A recently formed elliptical warm core eddy, with a major axis of nearly 150 km, appears at longitude 90°E and latitude 19°N at the end of the axis of the current. Color infrared images of sea surface temperature are used to illustrate the sea surface temperature patterns and to estimate their displacements with time.

A comparison of magnetic signatures and DMSP auroral images at substorm onset: Three case studies

Abstract: The authors explore the relationship between mid-latitude and synchronous orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms. Mid-latitude data come from the Air Force Geophysics Laboratory Magnetometer Network, synchronous orbit data form the satellites GOES 2 and 3, and auroral data from Defense Meteorological Satellite Program auroral images and auroral magnetograms. They find that the surge forms with its western edge {approximately} 1 hour west of the longitude where the major axis of the mid-latitude Pi 2 polarization ellipse is along magnetic north and where the D component perturbation of the magnetic bay is near zero. These observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east. At synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar.

Intraseasonal Atmospheric Teleconnection Patterns during the Northern Hemisphere Summer

Abstract: At times the 30–60 day filtered outgoing longwave radiation (OLR) perturbations exhibited a systematic eastward propagation across the equatorial Indian Ocean–western Pacific during the five summers (1 May–30 September) of 1979–83. Such occasions are defined as “E” phase, while periods of irregular movement are designated as “NE” phase. Global-scale behavior of the 30–60 day filtered streamfunction and velocity potential fields differs significantly from E to NE phase. During E phase at 200 mb, a series of time-clustered, space-overlapping disturbances develop over the northern as well as the southern subtropics. Although individual disturbances are nearly stationary, a wave packet clearly propagates eastward with an approximate phase speed of 8° longitude per day and a space scale of wavenumber 1. Sandwiched between the Southern and Northern hemisphere wave packets are relatively weak equatorial zonal wind perturbations which also move eastward. At 850 mb, E phase behavior is characterized by st...

Long waves in the equatorial Atlantic Ocean during 1983

Abstract: Long waves appeared at a zonally oriented sea surface temperature (SST) front in the eastern equatorial Atlantic during June and July of 1983. The low frequency, westward moving long waves (1000 km, 24 days) are monitored in the NOAA 7 satellite infrared images as meridional displacements of the front. The long waves observed in the Atlantic are similar to the waves previously seen in the eastern equatorial Pacific with several exceptions. The Atlantic long waves have a shorter duration (nearly three wave cycles at 15°W), and the wave amplitude is limited eastward of longitude 10°W. The Atlantic equatorial front appears to have a minimum north-south displacement between longitudes 5°W and 10°W, while westward of 10°W the displacements exceed 400 km. Several buoys were launched south of the equator at longitude 4°W by the Programme Francais Ocean-Climat en Atlantique Equatorial group on June 21, 1983. For the first 3 weeks, three of the buoys moved westward parallel to the equatorial SST front and measured relatively constant temperatures at 2 m. During mid-July, changes were observed in the buoy temperatures, the buoy trajectories, and the long-wave pattern. A comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of SST show a residual dependence of the satellite data on the zenith angle, even when the angle is limited to 45°. In general, the satellite SST measurements reproduce the trends observed in the buoy measurements, but small bias differences occur between buoys and between day and nighttime SST comparisons. Equatorial cross sections by ship and satellite over a 7-day interval in June 1983 also show that SST trends are comparable in both sets of data.

Overview of the Uranian radio emissions: Polarization and constraints on source locations

Abstract: Radio emission from Uranus was discovered a few days before the closest approach of Voyager 2 with Uranus on January 24, 1986. The planetary radio astronomy experiment recorded several types of emissions in the frequency range 1–900 kHz; they differ by their spectral, temporal, and polarization characteristics. The analysis of the observations led us to distinguish two smooth radio components, one occurring in the lowest frequency range (SLF) from 20 kHz to 347 kHz, and the other one reaching the highest observed frequencies, i.e., 865 kHz (SHF). The SLF component is left-hand polarized when observed in the northern magnetic hemisphere and right-handed in the southern magnetic hemisphere, without polarization reversal from dayside to nightside. The SHF component is only observed in the nightside of Uranus, and it is left-hand polarized. Several bursty emissions were observed: some of them are broadband bursts and occur in the 78- to 750-kHz range (b-bursty), others are narrow-band bursts and occur in the 40- to 270-kHz range (n-bursty). The broadband bursts were observed at low magnetic latitudes of the spacecraft and mainly when it was in the southern magnetic hemisphere; their polarization is left-handed. The narrow-band bursts were observed in the northern magnetic hemisphere and are not correlated with the magnetic latitude of the spacecraft; their polarization is right-handed. Sporadic bursts of short duration were observed mainly in the northern magnetic hemisphere with right-hand polarization. Two periodic events were observed, ahead of the inbound bow shock and inside the magnetosphere of Uranus. Very low frequency emissions at 1.2 and 20.4 kHz are also discussed; some of them are correlated with in situ phenomena. From the polarization study we deduce the possible source locations of the main components in the frame of our hypothesis. The source regions are characterized by the latitude and longitude of the footprints of the magnetic field lines through the source expressed in the Uranographic longitude system (ULS). The SLF source would be fixed in magnetic longitude at the northern magnetic pole in the range 13°< latitudeULS<38°, 26°

Interannual Westward-Propagating Baroclinic Long-Wave Activity on Line P in the Eastern Midlatitude North Pacific

Abstract: For the period 1959–81, quasi-zonal hydrographic sections have been made between the southern coast of Vancouver Island (49°N, 126°W) and Ocean Station P (50°N, 145°W) approximately every two months. Along this section (called Line P) hydrographic-STD stations were repeated at nearly the same locations, approximately 2° of longitude apart and at closer intervals near the coast. As such, 13 stations in all were made nearly every two months over the 23-year period. Thus, the Line P dataset has particular value in verifying the existence of interannual baroclinic long waves near 50°N. In previous studies, White, Kang and Magaard, and White and Saur, had found evidence of annual and interannual baroclinic long-wave activity in the eastern midlatitude North Pacific over the range 20°–40°N, but earlier attempts could not discover these westward-traveling waves along Line P. In this study, both spectral analysis and complex empirical orthogonal function analysis are used to do just that. Concentrating u...

Observed Dynamic Structure of an Intense Oceanic Cyclone

Abstract: A major extratropical cyclone developed over the East China Sea during the initial phase of the AMTEX'75. Using cross-section analyses the dynamic structure of the cyclone is investigated with an emphasis on obtaining a better understanding of the physical mechanisms controlling the development and maintenance of this intense oceanic system. The dynamic and kinematic variables examined include ageostrophic acceleration, potential and absolute vorticity, and vertical and horizontal motions. During the 24-h period following 1200 UTC 14 February, the surface cyclone moved eastward more than 22° longitude, while the upper-level trough propagated only about 15°. In the same period, the central pressure at the surface dropped more than 20 mb while the areas extent of the closed circulation showed little change. Vertical decoupling of the wave-cyclone system is suggested by this discrepancy in phase speed, and by the temporal evolution of the trough axis and the height fields during the lust 12 h. Laten...

A modified time-longitude diagram applied to 500 mb heights along 50" north and south

Abstract: The common time-longitude section (or Hovmoller diagram) shows longitude and intensity of troughs and ridges as a function of time. It is modified to a time-longitude lag-correlation diagram to yield statistically relevant estimates of zonal wavelengths, phase and group velocities. Different scales can be distinguished after the data sets have been treated by band- and low-pass filters. The lag-correlation analysis is applied to the 500 mb geopotential height along 50°N and 50°S for individual basepoints and averaged over the latitude circle. This technique is also useful if the local or zonally averaged dynamics of numerical models is to be statistically verified.

The South Carolina Coastline on Historical Maps: A Cartometric Analysis

Abstract: Historical maps of the South Carolina coastline were examined to determine their accuracy. Length and direction of error vectors were analyzed for statistically significant differences between individual maps and among regions within maps. Accuracy generally improved over time, but one map was found to be less accurate than expected, given its date. The direction of the error vectors tended to be aligned more with longitude than latitude. Segments of the coast with larger populations were generally more accurate than less populated areas. The northern portion of the coastline had significantly more error associated with it than other parts of the coast.

Mars: High Resolution VLA Observations at Wavelengths of 2 and 6 cm and Derived Properties

Abstract: Observations of Mars at wavelengths of 2 and 6cm were made using the VLA in its A configuration. Two seasons were observed; late spring in the northern hemisphere (LS ~ 60°) and early summer in the southern summer (LS ~ 300°). The sub-earth latitudes were 25°N and 25°S, for each of these seasons respectively. So the geometry for viewing the polar region was optimal in each case. Whole-disk brightness temperatures were estimated to be 193.2 K ± 1.0 at 2 cm and 191.2 K ± 0.6 at 6 cm for the northern data set and 202.2 K ± l.0 at 2 cm and 195.4 K ± 0.6 at 6 cm for the southern data set (formal errors only). Since measurements of the polarized flux were taken at the same time, whole-disk effective dielectric constants could be estimated and from these, estimates of sub-surface densities could be made. The results of these calculations at 2cm yielded whole-disk effective dielectric constants of 2.34 ± 0.05 and 2.02 ± 0.03 which imply sub-surface densities of 1.24 g cm-3 ± 0.06 and 1.02 g cm-3 ± 0.05 for the north and south, respectively. The same calculations at 6 cm yielded effective densities of 1.45 g cm-3 ± 0.10 and 1.31 g cm-3 ± 0.07 from effective dielectric constants of 2.70 ± 0.09 and 2.48 ± 0.06 for the north and south data sets, respectively. From the mapped data these parameters were also estimated as a function of latitude between latitudes of 15°S and 60°N for the north data set; and between latitudes of 30°N and 60°S for the south data set. A region in which the brightness temperature behaves in an anomalous manner was discovered in both data sets. This region lies between about 10°S and 40°S. Here the brightness temperatures at both wavelengths in both data sets appears lower, by 4 K to 8 K, than a nominal model would predict. In addition to the effective dielectric constant and sub-surface density the radio absorption length of the sub-surface was estimated. The radio absorption length for most of these latitudes was about 15 wavelengths with formal errors on the order of 5 or 10 wavelengths. This is true for both data sets. The estimation of the effective dielectric constant at most latitudes was between 2 and 3.5 with only slight differences between the two different wavelengths. The two data sets show the same relative trends, but are off by a scaling factor. These estimates of the dielectric constant lead to estimation of the sub-surface densities as a function of latitude. Most calculations of the sub-surface density yielded results between 1 and 2 g cm-3 with errors on the order of 0.5 g cm-3. These results seem to imply that the sub-surface is not much different than the surface as observed by the Viking and Mariner missions. In line with this, an examination of the correlation of the dielectric constant at each wavelength with the thermal inertia, determined by the Viking infrared measurements, shows a relatively strong correlation, at both wavelengths, for the North data set. The South data set, however, shows little to nocorrelation between the radio parameters and the thermal inertia. Since the South data set is primarily composed of latitudes which contain the anomalous region, it is not suprising that the South data set shows no correlation. In addition, the thermal-radiative model used to estimate the above parameters was used to estimate the variability of the whole-disk brightness temperature of Mars. This was done in an effort to establish a background for those astronomers wishing to use Mars as a calibration source. The parameters investigated for their effect on the whole-disk brightness temperature of Mars were: the sub-earth longitude, the sub-earth latitude, the sub-earth time of day, the dielectric constant, and the radio absorption length. A nominal model was first created which established the variation of the brightness temperature as a function of season and radio absorption length. A nominal value of 2.2 was used for the dielectric constant, and the sub-earth latitude was set at 0°N and the sub-earth longitude was set at 75°W. The sub-earth time of day was held at noon for this nominal model. This is equivalent to a 0° phase angle. The most important geometric factor was the sub-earth latitude. The error in estimating the whole-disk brightness temperature of Mars by using the wrong sub-earth latitude can be as large as 5 to 10%. The charts presented will be useful to estimate the whole-disk brightness temperature which the thermal model would predict. It is believed that the error in this estimate is less than or equal to 5 K.

Global variations of the POGO electrojet parameters during the solstices

Abstract: A method of analysis has been used to obtain electrojet parameters from the POGO Satellites' data during the solstitial seasons. This yields enormous values about 432 each, of electrojet's halfwidth w, peak eastward intensity J0, and total eastward current I+, -covering the entire 360° longitudes round the earth, and within 6 hours of local day time in the December and June solstitial months of the years 1968 and 1969 respectively. The daytime all-longitude averages of these parameters for the combined solstices are: (226±11)km for w, (207±28) Akm-1 for J0 and (51±7)×103 A for I+. This second coverage of the earth, with a new set of data, shows that J0 and I+ vary considerably with longitude, unlike w, which remains fairly constant throughout the globe. Interestingly, we find that, apart from the expected maximum in J0 and I+ around longitude 280°E, subsidiary maxima also occur at about 100°E, and 190°E, in confirmation of the equinoctial results of ONWUMECHILI and AGU (1981). It is suggested that the longitudinal variations in J0 and I+, may arise from the longitudinal differences in conductivities, wind systems and possibly changes in electric field at electrojet altitudes.

Effect of Diffuse Solar Radiation on the Efficiency of an Array of Silicon Solar Cells

Abstract: The variation of the optimum efficiency of an array of silicon solar cells with diffuse ratio has been investigated experimentally. Data collected from two geographical locations in Nigeria (Port Harcourt, which is on latitude 4.43°N and longitude 7.10°E; and Enugu, which is on latitude 6.20°N, and longitude 7.30°E), show that the optimum efficiency of an array of silicon solar cells increases with diffuse ratio. Under clear and partly overcast weather conditions, a change of 0.1 in the diffuse ratio results in 5 to 10% change in efficiency, while the same change under overcast weather conditions, results in 20 to 35% increase in optimum efficiency. Temperature fluctuations contribute less than 4,26% of the total change in efficiency.

On the Correlation of the Midlatitude Lower Ionosphere with Solar and Meteorological Parameters during the MAP/WINE Winter of 1983/1984

Abstract: The behaviour of the midlatitude lower ionosphere (Central Europe, USSR, Spain) is studied for the winter of 1983/84. The lower ionosphere is found to be governed by neutral atmosphere variability. The ionospheric data are divided into two groups according to altitude (not latitude or longitude). The principal component analysis method shows that the opposite response to the meteor zone (~ 95 km) meridional and partly also zonal wind variability appears to be responsible for this division. There is a negative correlation of ionospheric data and zonal wind (~ 95 km) with the 10 hPa temperature, stronger for the North Pole than for the quasi-local Berlin temperature. This seems to be caused mainly by longer-term trends, i.e., by the fact that the polar 10 hPa temperature reflects well the global behaviour of polar vortex.

Electron precipitation bursts in the nighttime slot region measured simultaneously from two satellites

Abstract: Based on data acquired in 1982 with the Stimulated Emission of Energetic Particles payload on the low-altitude (170-280 km) S81-1 spacecraft and the Space Environment Monitor instrumentation on the NOAA 6 satellite (800–830 km), a study has been made of short-duration nighttime electron precipitation bursts at L = 2.0–3.5. From 54 passes of each satellite across the slot region simultaneously in time, 21 bursts were observed on the NOAA 6 spacecraft, and 76 on the S81-1 satellite. Five events, probably associated with lightning, were observed simultaneously from the two spacecraft within 1.2 s, providing a measure of the spatial extent of the bursts. This limited sample indicates that the intensity of precipitation events falls off with width in longitude and L shell but individual events extend as much as 5° in invariant latitude and 43° in longitude. The number of events above a given flux observed in each satellite was found to be approximately inversely proportional to the flux. The time average energy input to the atmosphere over the longitude range 180°E to 360°E at a local time of 2230 directly from short-duration bursts spanning a wide range of intensity enhancements was estimated to be about 6 × 10−6 ergs/cm² s in the northern hemisphere and about 1.5 × 10−5 ergs/cm² s in the southern hemisphere. In the south, this energy precipitation rate is lower than that from electrons in the drift loss cone by about 2 orders of magnitude. However, on the basis of these data alone we cannot discount weak bursts from being a major contributor to populating the drift loss cone with electrons which ultimately precipitate into the atmosphere.

A Compilation of Moored Current Meter Data from the North Pacific, (The 'Zonal' Experiment, 1983-1985). Volume 41.

Abstract: : Summaries of long-term current, temperature and pressure measurements from moored instruments in the western Pacific Ocean (ranging from 152 W to 165 E longitude and 31 N to 41 N latitude) are presented. There were two consecutive settings of instruments, referred to as Zonal I and Zonal II, each spanning a one-year interval. There were, for the first time, 2 two-year mooring deployment, which were successful. Tables, plots and statistics include filtered and unfiltered data, as well as merged and single setting data. The objective of the experiment was to define the basic properties of the low frequency variability in the mid-latitude North Pacific.

The spatial component of ionospheric electron flow derived from two-dimensional drift measurements

Abstract: The electron drift velocities in the ionosphere can be measured as a function of both latitude and longitude using coherent radar systems like STARE and SABRE. The temporal resolution of the observations is high compared to the time it takes for the field of view to corotate with the earth over a longitude interval equal to its longitudinal width. An analysis technique is developed that allows us to determine whether an observed time variation is caused by spatial effects or by real time changes. Three events, during which the flow was dominated by spatial variations, have been analyzed and are found to show good agreement with model predictions.

Observed cloud level circulation on Venus - Temporal variations and solar longitude dependence

Abstract: This paper presents data on the atmospheric circulation of Venus, obtained by the Mariner 10 (1974) and Pioneer (1979-1986) observations. The results yielded evidence of relatively stable zonal circulation at the cloud level. On the other hand, changes on a yearly time scale appear in both the zonal and the meridional components of motion. Solar thermal tides and large-scale planetary waves are also seen in averaged zonal and meridional cloud motions. The relationship between the large-scale circulation and global cloud structure is discussed.

The detection of global convection on the sun by an analysis of line shift data of the John M. Wilcox Solar Observatory at Stanford University

Abstract: The first significant signatures of the real existence of the global convection in the Sun were found in the absorption line shift data of the John M. Wilcox Solar Observatory at Stanford University. The signatures consist of persistent periodic time variations in the east-west component of the velocity fields defined by fitting a slope to the line shift data in a certain longitude window at a specified latitude and longitude by a least square method. The variations show that the amplitude of the velocity fields is on the order of 100 m/s. The spacial structure of the east-west flows on the visible hemisphere of the Sun propagates along with the rotation of the Sun at a slightly slower speed than that of the Sun at the equator. The structure extends across the equator as predicted by theory. The periodicity of the time variation indicates that the wave numbers of the structure are 7 and 5 in Septembers of 1979 and 1981 with faster propagation velocity for the larger wave number during these two time intervals, when clear signals of the global convection were found. This implies that several modes of the global convection are coexisting in the solar convection zone. A personal account of the analysis and its interpretation are given.

Extraction of Cloud Parameters from Bispectral Measurements

Abstract: NOAA-9 AVHRR data on May 24, 1985 were used in the paper. Two regions, each about 4°×4° longitude by latitude, centered on 39.4°N, 113.0°E and 44.6°N, 112.0°E are selected for analysis. Two-dimensional histogram and dynamic clustering are made for these two regions. The cloud top temperature, emissivity and optical depth of those clusters are retrieved. Synoptic map at the same time are shown for comparison.

Tidal evolution of the earth-sun system

Abstract: The tidal decrease in the Earth's heliocentric longitude generated by the Sun has been computed. It represents the increase in the length of year∼10−7 s per century. The resonant angular velocity of the Earth's rotation is approximately equal to the present Earth's mean motion, however, for the model used, i.e., considering the Sun as the point-mass.

Comparison of magnetic signatures and DMSP (Defense Meteorological Satellite Program) auroral images at substorm onset. Three case studies

Abstract: The relationship is explored between mid-latitude and synchronous-orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms Mid-latitude data come from the Magnetometer Network, synchronous orbit data from the satellites GOES 2 and 3, and auroral data from Defense Meteorological Satellite Program auroral images and auroral magnetograms It was found that the surge forms with its western edge about 1 hour west of the longitude where the major axis of the mid-latitude Pi 2 polarization ellipse is along magnetic north and where the D component perturbation of the magnetic bay is near zero These observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east At synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar

Magnetospheric currents and estimation of theSq focal latitude

Abstract: The average latitude of theSq(X) focus along the longitude 75°E has been estimated using the Tsyganenko model (Tsyganenko, 1981) of the external magnetic field for storm time conditions of the magnetosphere. It is observed that the shift of the focal latitudes, due to magnetospheric currents, is only about 1 to 2° even during strong storms. It is also shown that the shift is asymmetric about the equator and longitude dependent. The day to day changes in observed focal position are much larger and the magnetospheric currents cannot, therefore, be regarded as a dominant mechanism of focal movement.