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Showing papers on "Longitude published in 1991"


Journal ArticleDOI
TL;DR: Two records of the Blake geomagnetic event have been obtained from marine cores in the Mediterranean and the upper bound for duration of the event, calculated from accurate oxygen isotope stratigraphy and/or tephrochronology, is ∼ 4000 years as mentioned in this paper.

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors used the tropical Pacific expendable bathythermograph (XBT) ship-of-opportunity tracks to determine statistical parameters required for optimal interpolation.

85 citations


Journal ArticleDOI
TL;DR: In this paper, the long-term trend and variability of the total column amount of atmospheric nitric acid (HNO3) have been investigated based on time series of infrared solar absorption spectra recorded at two sites.
Abstract: The long-term trend and variability of the total column amount of atmospheric nitric acid (HNO3) have been investigated. The study was based on time series of infrared solar absorption spectra recorded at two sites, the International Scientific Station of the Jungfraujoch (ISSJ) in the Swiss Alps (altitude 3.6 km, latitude 46.5 N, longitude 8.0 E) and the National Solar Observatory McMath solar telescope facility on Kitt Peak (altitude 2.1 km, latitude 31.9 N, longitude 111.6 W), Arizona. Measurements of HNO3 absorption features recorded at Kitt Peak between 1980 and 1990 and measurements of the same features in ISSJ solar spectra obtained in June 1951 and June 1986 to June 1990 provide quantitative estimates of the long-term trend in the HNO3 total vertical column. It is found that the trend deduced for each site is equal to zero within the measurement uncertainty. The modern ISSJ measurements show that the fitted trend is (-0.16 + or - 0.50) percent/yr, 2 sigma, which indicates that there has been no detectable change in HNO3 total column over three decades. The Kitt Peak measurements show marked variability in the HNO3 total column, but no obvious seasonal cycle is observed.

55 citations


Journal ArticleDOI
TL;DR: The global transport and dispersion of the Pinatubo aerosol cloud are simulated by means of a high-resolution stratospheric version of the NCAR Community Climate Model (CCM2) with an annual cycle as discussed by the authors.
Abstract: The global transport and dispersion of the Pinatubo aerosol cloud are simulated by means of a high-resolution stratospheric version of the NCAR Community Climate Model (CCM2) with an annual cycle. A passive tracer was injected into the model stratosphere over the Philippine Islands on June 15, and the transport was simulated for 180 d using an accurate semi-Lagrangian advection scheme. The simulated volcanic aerosol cloud initially drifted westward and expanded in longitude and latitude. The bulk of the aerosol cloud dispersed zonally to form a continuous belt in longitude, and remained confined to the tropics, centered near the 20-mb level for the entire 180-d model run, although a small amount was transported episodically into the upper troposphere in association with convective disturbances. Aerosol transported to the troposphere was dispersed within a few weeks into the Northern Hemisphere extratropics. In the Southern Hemisphere, the aerosol was mixed into the region equatorward of the core of the polar night jet during the first 50 d, but penetration into southern polar latitudes was delayed until the final warming in November.

46 citations


Journal ArticleDOI
TL;DR: In this article, a 10-50-day bandpass filter was applied to daily ECMWF analyses for 1980-88 to examine the effect of wave propagation on the Southern Hemisphere atmospheric circulation.
Abstract: Intraseasonal variations in the Southern Hemisphere atmospheric circulation have been examined through the application of a 10–50–day bandpass filter to daily ECMWF analyses for 1980–88. Variations on this time scale contribute more than 40% of the daily variance in 500 hPa geopotential over much of the middle and high latitudes of the Southern Hemisphere. EOF analysis of the unnormalized variance for all seasons shows that 49% of this variance can be explained by zonal wave trains centered on the South Pacific and southern Atlantic/Indian oceans, a high-latitude mode of global extent, and a wavenumber 3 pattern at midlatitudes. These modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hPa typically lag those at 1000 hPa by around 1o° longitude. There appears to be little interaction with the low-latitude circulation. All of the leading modes propagate eastward but the most consistent movement is shown by the South Pacific wave train represented ...

37 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared VLF data from four L {approx equal} 4 Antarctic stations from a 2-day period in June 1982, and found that wave generation occurs simultaneously over relatively wide longitude (or local time) sectors (approximately gt} 30{degrees) or 2 hours).
Abstract: Whistler activity at L {approx equal} 4 is known to be a function of longitude, peaking in the Weddell Sea sector of Antarctica; a combination of source and propagation factors, the latter possibly partly associated with the South Atlantic geomagnetic anomaly, is believed to be responsible. There is evidence, for example from satellite surveys, that chorus and hiss activity may also be longitude dependent. To investigate this further, the authors have compared VLF data from four L {approx equal} 4 Antarctic stations from a 2-day period in June 1982. Siple, Halley, and Sanae form a closely spaced ({approximately}20 {degree}- 0{degree} geomagnetic longitude) triplet, while Kerguelen is {approximately}120{degrees} (geomagnetic) to the east, on the opposite side of the anomaly. To a large extent there was a repeatable diurnal variation in activity at all stations on the two days. Events observed at Siple tended to be similar to those observed {approximately} 9 hours earlier (the same MLT) at Kerguelen on the same day. There was a very marked drop-off in both whistler and VLF emission activity between Siple and Halley on the one hand and Sanae on the other. The reason for this is not clear; it may be either a sourcemore » effect such as the lower occurence of lightning over eastern North America compared to the adjacent Atlantic Ocean, or else a wave-particle interaction effect whereby the conditions for wave growth or amplification are more favorable, or substorm particle injections penetrate the magnetosphere more deeply, at the longitude of Siple than further east. Comparison of the spectral forms of whistler mode activity at neighboring stations suggests that wave generation occurs simultaneously over relatively wide longitude (or local time) sectors ({approx gt} 30{degrees} or 2 hours). Individual interaction regions are smaller than this, {approx lt} 5{degrees} in longitude, comparable with the previously inferred sizes of whistler ducts.« less

26 citations


Journal ArticleDOI
TL;DR: In this paper, a model with two active layers, a mixed layer and a pycnocline layer, over a semipassive deep ocean is described, which is used to simulate a climatological seasonal cycle in the upper North Pacific.
Abstract: A model with two active layers, a mixed layer and a pycnocline layer, over a semipassive deep ocean is described. The model is used to simulate a climatological seasonal cycle in the upper North Pacific. The formulation is similar to that in Cherniawsky et al. (1990). The model resolution is 1° latitude by 1.5° longitude, extending from 62°N to the equator. It is driven with monthly wind stress (Hellerman and Rosenstein, 1983) and with Newtonian heat and freshwater fluxes, which were inferred from climatological (Levitus, 1982) sea‐surface monthly temperatures and annual mean salinities. The monthly temperature anomalies (without the annual mean) are multiplied by a prescribed gain factor and advanced in time, compensating for time delay in the response of the mixed layer. No‐slip and no‐flux constraints are applied on north, east, west and land boundaries, while the following open boundary conditions are used at the equator: (a) free‐slip on zonal velocities in the two layers; (b) a prescribed m...

26 citations


Journal ArticleDOI
TL;DR: In this article, the authors compare mean seasonal cycles of zonal and meridional velocity in the Pacific South Equatorial Current based on current meter mooring data, drifting buoy data, and ship drift data.
Abstract: In this note we compare mean seasonal cycles of zonal and meridional velocity in the Pacific South Equatorial Current based on current meter mooring data, drifting buoy data, and ship drift data Monthly averages of ship drift and drifting buoy data were computed over 2° latitude by 10° longitude rectangles centered at the positions of multiyear current meter moorings near 0°, 110°W, and 0°, 140°W All three representations of the flow field show the basic character of the annual mean and its variations, provided that the sampling characteristics associated with each measurement technique are taken into account In particular we find that more than 15 days of drifter data (regardless of year) are required on a 2° latitude by 10° longitude basis to produce monthly mean estimates that agree with moored estimates to within about 5–10 cm s−1 rms We also infer that windage affects climatological monthly mean ship drift velocities, although uncertainties in the data limit a precise determination of the windage magnitude An upper bound appears to be about 3% of the surface wind speed, though the actual effect of windage may be considerably smaller

26 citations


Journal ArticleDOI
24 Jan 1991-Nature
TL;DR: In this paper, an analysis of Voyager images of Jupiter is used to evaluate the horizontal spatial distribution of visible lightning over most of one hemisphere, and all the detectable activity is confined to very narrow latitude bands at 13.5 N and 49 N. Activity at this latitude is longlived and is most likely associated with moist convective regions deep in Jupiter's atmosphere.
Abstract: An analysis of Voyager images of Jupiter is used to evaluate the horizontal spatial distribution of visible lightning over most of one hemisphere. Essentially all the detectable activity is confined to very narrow latitude bands at 13.5 N and 49 N. The active regions at 49 N are the brightest, most numerous, and periodic in longitude. Activity at this latitude is long-lived and is most likely associated with moist convective regions deep in Jupiter's atmosphere. The longitudinal periodicity of the lightning storms may represent the effects of a planetary scale atmospheric wave trapped at the depth of the moist convection.

25 citations


Journal ArticleDOI
TL;DR: In this article, wave-organized convective features in the southwest Indian Ocean are described using Hovmoller composites of satellite imagery, OLR anomalies and ECMWF precipitable water departures during the southern summer.
Abstract: Wave-organized convective features in the southwest Indian Ocean are described using Hovmoller composites of satellite imagery, OLR anomalies and ECMWF precipitable water departures during the southern summer. Westward movement of large convective elements is noted in the 10–20°S latitude band in about half of the years between 1970 and 1984. A study of 47 convective systems from satellite imagery establishes the climatological features, including zonal propagation speeds for maritime systems in the range −2 to −4 m s−1, wavelengths of 25–35° longitude (3,000 km), lifespans of 10–20 days and convective areas of 7–10° longitude (800 km). Transient convective waves over the tropical SW Indian Ocean are slower and more diverse than their northern hemisphere counterparts. Interannual tendencies in the frequency and mode are studied. Wet summers over SE Africa correspond with an increased frequency of westward moving convective systems, whereas in dry summers convective systems tend to be quasi-stationary. INSAT data composites provide additional insight into the convective structure and show that tropical waves penetrated into southern Africa in February 1988. A more quantitative assessment of transient convective waves is provided by Hovmoller composites of OLR anomalies and precipitable water departures. Both display westward moving systems in 1976 and 1984 and highlight the wide variety and mixed mode character of convective waves. A case study is analyzed which illustrates the deepening of a moist, unstable layer coincident with the westward passage of a convective wave.

24 citations


Journal ArticleDOI
TL;DR: In this article, an objective analysis technique is used to design an optimal oceanographic network for the eastern Pacific Ocean from 160°W-80°W, 20°S-20°N.
Abstract: An objective analysis technique is used to design an optimal oceanographic network for the eastern Pacific Ocean from 160°W–80°W, 20°S–20°N. Expendable bathythermograph observations from a sequence of transequatorial transects (1979–1984) were used to estimate temporal and meridional mean and correlation statistics, while bathy messages in the global telecommunications system (1979–1982) were used to calculate zonal statistics. The variables sea-surface temperature and depth of 20°C isotherm are presented here as representing the thermal structure of both the surface and subsurface layers. In the eastern Pacific, the thermal temporal and spatial signals fluctuate according to the presence and strength of El Nino. During ENSO it is not uncommon for these scales to double in value. To resolve characteristically shorter signals during the typical years, data associated with the larger scales of ENSO events must be excluded. Scales of variability in the thermal field were also determined to be very different in five latitudinally delineated regions corresponding to the major equatorial current system of the eastern Pacific region. In general, space and time scales representative of the subsurface structure are smaller than scales of sea-surface temperature and are consequently the limiting factor in network design. In the design of an XBT network for the entire tropical eastern Pacific, decorrelation scales of 3° latitude, 15° longitude and 2 months are determined as being most representative and capable of resolving the subsurface thermal signal. Sub-regional inhomogeneity of signal-to-noise ratio for the eastern Pacific (ranging from 0.5–1.5) implies that a uniform scale is not appropriate especially for quantitative studies of mapping error. Structure of interpolation errors suggest that optimal sampling is achieved with two to three samples per decorrelation scale i.e. one XBT station every 1°–1.5° latitude and 5°–7.5° longitude.

Journal ArticleDOI
TL;DR: In this paper, all-sky imagery from Sodankyla and Kilpisjarvi and STARE radar data are reported to infer that omega band related phenomena occur on the same day in both hemispheres after local magnetic midnight.

ReportDOI
01 Oct 1991
TL;DR: In this paper, the authors presented land-based monthly surface air temperature anomalies (departures from a 1951--1970 reference period mean) on a 5°degree by 10°degree longitude global grid.
Abstract: This document presents land-based monthly surface air temperature anomalies (departures from a 1951--1970 reference period mean) on a 5{degree} latitude by 10{degree} longitude global grid. Monthly surface air temperature anomalies (departures from a 1957--1975 reference period mean) for the Antarctic (grid points from 65{degree}S to 85{degree}S) are presented in a similar way as a separate data set. The data were derived primarily from the World Weather Records and the archives of the United Kingdom Meteorological Office. This long-term record of temperature anomalies may be used in studies addressing possible greenhouse-gas-induced climate changes. To date, the data have been employed in generating regional, hemispheric, and global time series for determining whether recent (i.e., post-1900) warming trends have taken place. This document also presents the monthly mean temperature records for the individual stations that were used to generate the set of gridded anomalies. The periods of record vary by station. Northern Hemisphere station data have been corrected for inhomogeneities, while Southern Hemisphere data are presented in uncorrected form. 14 refs., 11 figs., 10 tabs.

Journal ArticleDOI
TL;DR: In this paper, the oceanic response to the Madden and Julian (1971, 1972) oscillation (MJO) wind stresses is studied with special attention given to the nature of the related angular momentum exchanges between the ocean and the solid earth for idealized 40-and 50-day fluctuations of Pacific winds.
Abstract: The oceanic response to the Madden and Julian (1971, 1972) oscillation (MJO) wind stresses are studied with special attention given to the nature of the related angular momentum exchanges between the ocean and the solid earth for idealized 40- and 50-day fluctuations of Pacific winds. The character of these exchanges is illustrated with the use of numerical solutions of a shallow water ocean model, which were found for a constant depth basin centered on the equator and extending over 140 deg in longitude. Solutions also suggest that even small (0.5-1.5-cm) coastal sea level fluctuations can cause variations in the length of day comparable to observed values in the 40- to 50-day band.

Journal ArticleDOI
TL;DR: In this paper, upper air data obtained from 32 equatorial stations, 1973-87, show that 70 mb wave intensity over the Maritime continent varied annually with largest amplitude in NH late winter and spring, but the seasonal cycle of intensity was not uniform in the tropics.
Abstract: Meridional wind oscillations of 3-6 day period are common in the equatorial lower stratosphere. Upper air data obtained from 32 equatorial stations, 1973-87, show that 70 mb wave intensity over the Maritime continent varied annually with largest amplitude in NH late winter and spring, but the seasonal cycle of intensity was not uniform in the tropics. Time series of meridional velocity and its spatial coherence suggest that 70 mb wave packets were local in longitude and episodic in time.

Journal ArticleDOI
TL;DR: In this article, the authors used the observations of the planetary radio astronomy (PRA) experiment aboard Voyager 2 reveal the existence of smooth and bursty radio emission, which recur in a rather regular pattern with a 16.1-hour period (the Neptunian spin period).
Abstract: The observations of the planetary radio astronomy (PRA) experiment aboard Voyager 2 reveal the existence of smooth and bursty radio emission. Both recur in a rather regular pattern with a 16.1-hour period (the Neptunian spin period). We describe the phenomenology of the smooth component in terms of frequency, polarization, and occurrence in magnetic longitude and latitude. The existence of both right-handed and left-handed polarized emissions is consistent with two sources (one in each hemisphere) which radiate independently in the TUX mode. Because Voyager passed Neptune at less than 5000 km from the surface at high northern magnetic latitudes, the radio sources were occulted by the planet near the encounter. We have taken advantage of this occultation to locate the northern hemisphere sources by calculating the radio horizon (based on the offset tilted dipole (OTD2) model) for two spacecraft positions close to the encounter. We find that the northern source is located at high magnetic latitudes δm > 40°. By using a geometrical beaming model which assumes emission in a hollow cone pattern we fit the observed PRA intensity profile. The best fit is obtained for a radio source at L=6, thus confirming δm > 40°. The longitudinal extent of the source is at least 180°, from −90° to +90° magnetic longitude. To locate the southern sources we use the large excursions of Voyager 2 to high southern magnetic latitudes. The source is found to be located also at high magnetic latitudes but is possibly more limited in longitude than the northern source. We estimate the uncertainty in source location due to the very limited knowledge of the magnetic field near the Neptunian surface, and we show that the current OTD2 model is satisfactory for the source locations for the lowest observed frequencies; however, an angular uncertainty of about 20° remains for sources in the northern hemisphere. The observed pattern of the smooth emission is strongly frequency dependent, which is in agreement with the azimuthal asymmetries of the magnetic field as predicted by the OTD2 model.

Book ChapterDOI
01 Jan 1991
TL;DR: In this paper, a global coupled ocean-atmosphere general circulation climate model developed at the National Center for Atmospheric Research (NCAR) was used to simulate interannual variability of the global climate system.
Abstract: Results are presented from a global coupled ocean-atmosphere general circulation climate model developed at the National Center for Atmospheric Research. The atmospheric part of the coupled model is a global spectral (R15, 4.5° latitude by 7.5° longitude, 9 layers in the vertical) general circulation model. The ocean is a coarse-grid (5° latitude by 5° longitude, 4 layers in the vertical) global general circulation model. The coupled model includes a simple thermodynamic sea-ice model. Due mainly to inherent limitations in the ocean model, the coupled model simulates sea surface temperatures that are too low in the tropics and too high in the extratropics in the mean. In spite of these limitations, the coupled model simulates active interannual variability of the global climate system involving signals in the tropical Pacific that resemble, in some respects, the observed Southern Oscillation. These signals in the tropics are associated with teleconnections to the extratropics of both hemispheres. The implications of this model-simulated interannual variability of the coupled system relating to climate sensitivity and climate change due to an increase of atmospheric carbon dioxide are discussed.

Journal ArticleDOI
TL;DR: In this article, a model of the terrestrial plasmasphere that includes an eccentric dipole geomagnetic field has been developed and the results for L-values around 2.5 are compared with those obtained in VLF experiments at Faraday that detect whistler signals from NAA and NSS stations in the north east U.S.A.

Journal ArticleDOI
TL;DR: The results of these runs are included in Table 1 and Figs.
Abstract: The results of these runs are included in Table 1 and Figs. 1 and 2. The intrack, or longitude, error is clearly the dominant error. The error in GMAS 4 x 4 and OrbJ2 is due to the neglect of drag; the larger error in Fastorb is due to the error of order J2 in the computation of the mean motion. As an example of the resolution available in computer displays, we consider the IBM Enhanced Graphics Adaptor (EGA) board, which is widely used in personal computers. The resolution of the EGA board is 640 x 350 pixels (horizontal by vertical). Given that the entire world map is displayed (i.e., 180° longitude to 180° longitude and 90° latitude to 90° latitude) the number of pixels per degree of longitude is


Journal ArticleDOI
TL;DR: A Pacific Ocean general circulation model (horizontal resolution of 5° in longitude and 4° in latitude) is coupled with a global atmospheric general circulation (GAC) model to study the coupled atmosphere-ocean system in the tropical Pacific Ocean as discussed by the authors.

01 Sep 1991
TL;DR: In this paper, a multidimensional mapping technique is developed which determines the three dimensional electron density distribution of the ionosphere over a wide area of several thousand kilometers at any time, from sounder data recorded at the previous period just before this time.
Abstract: : A new multidimensional mapping technique is being developed which determines the three dimensional electron density distribution of the ionosphere over a wide area of several thousand kilometers at any time, from sounder data recorded at the previous period just before this time. Electron density profiles from five Digisonde stations in the northeastern regions of the North American continent are used to describe the electron distribution in a 30 deg longitude by 30 deg latitude region. The time histories over 32 hours of the profiles (the polynomial coefficients) from each station are Fourier transformed to determine the spectral components. For each spectral component a damped plane wave is fitted to amplitudes and phases at the five stations. This analysis is performed for each of the profile coefficients, and zonal maps are constructed as sums of these plane waves. This nowcasting technique can find applications in ray tracing for OTH radar, HF communication and HF direction finding.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the planetary distribution of the disturbed ion density at fixed magnetic latitudes in both hemispheres, and in the evening and morning sectors, using DE-B satellite and ground-based vertical sounding data.


01 Oct 1991
TL;DR: A significant enhancement in infrared emission from hydrocarbon constituents of Jupiter's stratosphere was observed at a north polar hot spot (60 degrees latitude, 180 degrees longitude) as discussed by the authors.
Abstract: A significant enhancement in infrared emission from hydrocarbon constituents of Jupiter's stratosphere was observed at a north polar hot spot (60 degrees latitude, 180 degrees longitude). A unique probe of this phenomena is ethylene (C2H4), which has not been observed previously from the ground. The profile of the emission line from ethylene at 951.742 cm-1, measured near the north pole of Jupiter, was analyzed to determine the morphology of the enhancement, the increase in C2H4 abundance and local temperature, as well as possible information on the altitude (pressure regions) where the increased emission is formed. Measurements were made using infrared heterodyne spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii in December 1989. At 181 degrees longitude a very strong emission line was seen, which corresponds to a 13-fold increase in C2H4 abundance or a 115K increase in temperature in the upper stratosphere, compared to values outside the hot spot. The hot spot was found to be localized to approx. 10 degrees in longitude; the line shape (width) implied that the enhanced emission originated very high in the stratosphere.

Journal ArticleDOI
TL;DR: In this article, the DE-2 data were used to define a global spectral model of electron temperature and density for the fixed altitudes of 300, 500, and 850 km, using measurements obtained during intervals short compared to a season.

Journal Article
TL;DR: In this article, a comparison of the monthly median value of the f0F2 for two stations with similar geomagnetic latitude but different longitude has been made, which can be used to investigate the longitudinal variation of the equatorial anomaly in East Asia.
Abstract: The comparison of the monthly median value of the f0F2 for two stations with similar geomagnetic latitude but different longitude has been made. The differences of the monthly median value of- the f0F2 in the ionosphere observation chains in the east of China and in Japan have been found. All of these can be used to investigate the longitudinal variation of the equatorial anomaly in East Asia. The results are these: In winter, the equatorial anomaly in east of China sector is weaker than that in Japan sector; but in summer, the equatorial anomaly in east of China sector is stronger than that in Japan sector; The end latitude of the northern crest for two sectors in summer are larger than that in winter.

Journal ArticleDOI
TL;DR: In this article, a theoretical model, describing the longitude variations of O/N 2 ratio, has been constructed to explain the vertical wind-induced motions of the F layer accompanied by upwelling or downwelling of the neutral particles -the result of the ion neutral coupling.

01 Jan 1991
TL;DR: The Meteorological Measurement System (MMS) on the high altitude ER-2 aircraft was developed specifically for atmospheric research as discussed by the authors, which provides accurate measurements of pressure, temperature, wind vector, position (longitude, latitude, altitude), pitch, roll, heading, angle of attack, angles of sideslip, true airspeed, aircraft eastward velocity, northward velocity and vertical acceleration, at a sample rate of 5/s.
Abstract: The Meteorological Measurement System (MMS) on the high altitude ER-2 aircraft was developed specifically for atmospheric research. The MMS provides accurate measurements of pressure, temperature, wind vector, position (longitude, latitude, altitude), pitch, roll, heading, angle of attack, angle of sideslip, true airspeed, aircraft eastward velocity, northward velocity, vertical acceleration, and time, at a sample rate of 5/s. MMS data products are presented in the form of either 5 or 1 Hz time series. The 1 Hz data stream, generally used by ER-2 investigators, is obtained from the 5 Hz data stream by filtering and desampling. The method of measurement of the meteorological parameters is given and the results of their analyses are discussed.

Journal ArticleDOI
TL;DR: The conclusions drawn in the 1990 Congress Paper "Longitude 129 Degrees East, and Why it isn't the Longest, Straight Line in the World" may well be the correct interpretation as discussed by the authors.
Abstract: The conclusions drawn in the 1990 Congress Paper “Longitude 129 Degrees East, and Why it isn't the Longest, Straight Line in the World” may well be the correct interpretation. However, in the absence of litigation to establish this, other interpretations equally may be correct. One such alternative is offered here.