airglow observations and modeling of f region depletion zonal velocities over christmas island 1 we report image measurements of plasma depletions in the equatorial f region ionosphere over christmas island 2 1 n 157 4 w dip latitude 2 8 n in the central pacific ocean the observations were made during the equinox period september october 1995 using a utah state university ccd imaging system filtered to observe thermospheric o i 630 0 nm airglow emissions centered at 280 km altitude well defined magnetic field aligned depletions were observed on 18 nights during the campaign including strong postmidnight fossilized structures enabling detailed measurements of their morphology and dynamics the number of depletions was influenced by their initial onset times and their persistence the separations between adjacent depletions ranged from 150 to 250 km in good agreement with prior observations from other sites however measurements of their eastward zonal drift speeds indicated normal behavior peaking around 90 100 m s prior to local midnight with exceptionally high velocities 80 m s during the postmidnight period that persisted until dawn these results differ markedly from optical measurements at similar equatorial latitudes but at different longitude sectors suggesting that the zonal drift velocities can have a significant longitudinal dependence model drift velocities calculated using a simple electric field model with winds defined by the horizontal wind model hwm 07 produced an eastward drift throughout the night but their postmidnight magnitudes were much smaller than observed using a modified hwm 07 wind field a basic nighttime trend similar to the christmas island trend was successfully obtained

burial history and diagenetic reaction kinetics relations among burial histories deduced from stratigraphy thermal regimes imposed by tectonics and sedimentation and rates of diagenetic reactions extrapolated from experimental data have been explored by using sedimentation diagrams plots of burial with respect to the sediment water or sediment air interface as a function of time elapsed since deposition one can estimate paleogeotherms from such plots using assumptions on heat flow thermal conductivities compaction and cementation effects on porosity and convecting formation water systems from these one can deduce the temperature history of a sediment as a function of postdepositional time that history can be converted to the integrated value of temperature as a function of time this value which takes into ccount the total contribution of time and temperature is the relevant parameter for reaction kinetics a plot of the time temperature integral versus postdepositional time for a given formation can then be compared with the time temperature integral for specific yields of a diagenetic reaction to deduce at what stage in its history a sediment would have accumulated sufficient time and thermal energy to accomplish a given extent of reaction these deductions can be compared with petrologic information on the time of origin of diagenetic phases

images of transequatorial f region bubbles in 630 and 777 nm emissions compared with satellite measurements images of transequatorial f region bubbles were obtained from magnetic field aligned airglow observations from haleakala hawaii for 9 nights in august 1988 bubbles of scale size 10 100 km were recorded with an intensified ccd detector attached to a filter wheel imager and sequential images were made in the plasma recombination emissions at 630 nm and 777 nm and in the background emissions the observations also yield information on the large scale structure of the ionosphere in the northern appleton anomaly region particularly on the latitude variations of plasma concentration and layer height measurements from the dmsp f8 and f9 satellites extend this to include the southern anomaly region the dmsp satellites were near 830 km in altitude and in near polar orbits at about 1800 and 2120 hours local time a comparison of the bubble images and the dmsp results with plasma concentration and drift velocities obtained from the san marco satellite allows us to put the measurements along the san marco track into the larger ionospheric context one to one correspondence is found between the presence of the optical bubbles and the presence of plasma depletions measured from the san marco satellite allowing identification on consecutive orbits of the same depletions this extends for up to 5 hours of the satellite measured information for individual depletions that is their vertical and horizontal drift velocities and the plasma concentration variations the images show the shapes of the depletions in apex height and longitude and their evolution horizontal drift velocities of the bubbles were determined by a correlation analysis bubble occurrence is compared with day to day changes in the equatorial fountain electric fields and transequatorial asymmetries caused by neutral winds and with measurements of radar backscatter from centimeter scale irregularities associated with bubbles in the kwajalein sector the development of 10 100 km scale size bubbles at a given time and location is clearly a consequence of the presence of even larger wavelike corrugations in the f layer provided there is also at least a moderately strong equatorial fountain

interdecadal changes in the enso teleconnection to the caribbean region and the north atlantic oscillation abstract the el nino southern oscillation enso phenomenon and variability in the subtropical north atlantic high sea level pressure slp are known to affect rainfall in the caribbean region an el nino event is associated with drier than average conditions during the boreal summer of year 0 and wetter than average conditions during the spring of year 1 dry conditions during the summer of year 0 of an el nino are associated with the locally divergent surface circulation engendered by the eastward shift of deep convection in the pacific ocean wet conditions during the spring of year 1 of an el nino are associated with the lagged warming of the tropical north atlantic ocean variability in the strength of the north atlantic high is governed mainly by the north atlantic oscillation nao with a positive nao phase implying a stronger than normal high and vice versa the nao is negatively correlated with caribbean rainfall indirectly via anomalous sea surface temperatures sst associated with a

onset conditions for equatorial spread f the problem of day to day variability in the occurrence of equatorial spread f esf is addressed using multidiagnostic observations and semiempirical modeling the observational results are derived from a two night case study of esf onset conditions observed at kwajalein atoll marshall islands using the altair incoherent scatter radar and all sky optical imaging techniques the major difference between nights when esf instabilities did not occur august 14 1988 and did occur august 15 1988 in the kwajalein sector was that the northern meridional gradient of 6300 a airglow was reduced on the night of limited esf activity modeling results suggest that this unusual airglow pattern is due to equatorward neutral winds previous researchers have shown that transequatorial thermospheric winds can exert a control over esf seasonal and longitudinal occurrence patterns by inhibiting rayleigh taylor instability growth rates we present evidence to suggest that this picture can be extended to far shorter time scales namely that surges in transequatorial winds acting over characteristic times of a few hours to a day can result in a stabilizing influence upon irregularity growth rates the seemingly capricious nature of esf onset may thus be controlled in part by the inherent variability of low latitude thermospheric winds

high resolution oi 630 nm image measurements of f region depletion drifts during the guara campaign a high performance all sky imaging system has provided data on the evolution and drift motions of f region depletions above the magnetic dip equator at alc ntara brazil 2 3 s 44 5 w monochromatic images of depletions in the oi 630 nm nightglow were recorded on eight nights during 1 16 october 1994 as part of the guara campaign the drift motions of the depletions were typically 80 100 m s eastward prior to local midnight and reduced to a minimum of 30 50 m s in the morning hours in accord with previous observations however on october 2 3 and 12 13 the depletions were observed to reverse direction for 60 90 min achieving westward speeds of 30 m s before the motion reverted to eastward around 0100 lt and accelerated to 35 45 m s near dawn magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the f region dynamo rather than from shifts in the altitude of the shear in the nighttime f region plasma drift

evolution of oil generative window and oil and gas occurrence in tertiary niger delta basin assuming a simple model of delta development involving progradation and uniform burial at 500 m m y 1 640 ft m y to present depths oil genesis nomographs derived from the time temperature index tti method were constructed for geothermal gradients ranging from 2 2 to 5 1 c 100 m 1 2 2 8 f 100 ft of the niger delta and used in mapping the positions depth temperature of the top of the oil generative window ogw at various times between 40 m y b p and the present during the active subsidence phase oil generation within any megasedimentary unit was initiated at a temperature of 140 146 c 284 294 8 f and depth of 3 000 5 200 m 9 843 17 060 ft within 7 11 m y after deposition of the potential source rocks after cessation of subsidence vertical upward movement of the ogw by 800 1 600 m 2 625 5 249 ft was accompanied by a temperature lowering of 23 54 c 41 97 f producing correspondingly heavier crudes in a central belt of the delta hydrocarbon generation and expulsion from the lower part of the agbada formation predate the cessation of subsidence and structural deformation whereas in other areas it postdates the cessation of subsidence and structural deformation in this central belt the agbada is the major oil source with the akata serving as a gas source in the other areas both the agbada and akata constitute oil sources which implies that the thermal conditions rather than the kerogen type influence the oil gas mix in the niger delta basin

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

determination of paleoheat flux from vitrinite reflectance data a method is presented for determining paleoheat flux from the reflectance of vitrinite collected from wells the maturation of vitrinite is modeled using a time temperature integral that assumes pseudo first order kinetics in testing the numerical algorithm it was necessary to introduce a critical temperature of 295 k below which vitrinite does not mature this result is consistent with the latest findings of independent researchers the degree of consistency obtained from a number of wells is not perfect much of the inconsistency can be attributed to large uncertainties in the vitrinite reflectance readings to test the method heat flow history was determined for the north sea basin and the national petroleum reserve of alaska quantitative results were obtained detailing the increase and or decrease of heat flux with time and were consistent with the qualitative behavior inferred for paleoheat flow from current geologic models

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

dynamic interpretation of organic matter maturation and evolution of oil generative window two phases are recognized in the maturation of organic matter and evolution of the oil generative window ogw a a basinal subsidence phase during which potential source rocks undergo burial through a static initial ogw and maturation is due essentially to increasing temperature with depth and b a postsubsidence phase during which the ogw moves vertically upward through the static sedimentary fill and maturation is due to time effects only the final shallow position of ogw can be defined by geochemical indices of maturity the hydrocarbon generation sequence progresses from bottom to top beginning with the lighter hydrocarbons or even thermogenic gas at the initial ogw at depth followed by progressively heavier hydrocarbons as the ogw moves vertically upward this dynamic model of hydrocarbon generation permits modeling of past positions of ogw relative to basin evolution through interpretation of oil genesis nomographs it also provides genetic explanation for the increase in api gravity with depth areal variation of maturation facies variation in temperature at present tops of ogw with age of source rocks and gas oil volume ratios of sedimentary basins

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

seasonal and longitudinal variation of large scale topside equatorial plasma depletions 1 we examine the large scale properties of three classes of equatorial topside plasma depletions referred to as channels in order of increasing zonal width and internal large scale substructuring we study simple channels multichannels and superchannels we find that peaks in channel activity are centered on 0 african sector and 180 western pacific sector superchannels are found to strongly dominate in the african sector whereas simple and multichannels dominate the pacific sector within the african sector the relative proportions of the three channel classes remain stable in all seasons in the pacific sector simple and multichannels are dominant in all seasons of activity though small but significant seasonal variations in channel widths and spacings are seen structure at a zonal scale size of about 100 km is found to be present in all channels examined observational and model evidence suggests that 100 km density structure represents channels such that all multichannels and superchannels consist of multiple contiguous simple channels since seeds that initiate channel formation necessarily influence large scale channel features we utilize our data to draw conclusions regarding bottomside seeding conditions in the various seasonal and longitudinal sectors specifically we find that strong long wavelength 1000 km seeds appear much more frequently in the african sector resulting in the prevalence of superchannels there when long wavelength seeds appear in the pacific sector they result in periodic trains of simple and multichannels a bottomside preseeded at a scale size near 100 km accounts for the ubiquity of 100 km scale size in the ae e data

global positioning system measurements of the ionospheric zonal apparent velocity at cachoeira paulista in brazil ionospheric irregularities and their zonal apparent drift were studied using global positioning system gps measurements at cachoeira paulista 22 41 s 45 00 w 26 dip angle in brazil during november 6 19 1998 radio scintillations at the gps l1 frequency 1 575 ghz were monitored using four gps receivers spaced geomagnetically east west and north south total electron content tec was measured through the ionospheric advance of the gps l1 and l2 1 227 ghz phases strong amplitude scintillations coincided with tec fluctuations associated with spread f bubbles elongated along the magnetic field movement of the presnel scale 400 m ionospheric irregularity layers caused the scintillation to drift and their zonal apparent drift velocities were measured using a cross correlation technique our measurements show that the apparent eastward velocity varies from 200 m s to 150 m s at 2000 lt and then it decreases to 100 50 m s at midnight on a magnetically disturbed day reversal of the zonal apparent drift was observed just after midnight and the apparent westward velocities observed at early in the morning showed large variations with location in the sky from the receivers spaced in the geomagnetic north south direction we measured near zero time shifts from which we conclude that the correlation length of several hundred meter scale irregularities is much larger than 70 m separation between the north and south receivers

field aligned observations of transequatorial bubbles from rarotonga in 1969 70 a raster scanning photometer with 0 5 field of view was used in 1969 70 to make images in 6300 a and 5577 a emission from rarotonga of tropical f region trans equatorial bubbles or depletions from this site the f region plasma structures in the emission layer can be viewed in a magnetic field aligned configuration a spatial resolution of approximately 15 km was achieved and revealed a variety of shapes in the bubble cross sections including bifurcations and pinched off bubbles eastward drift velocities averaged 125 ms 1 tilts were usually westward at about 45 in the equatorial plane but some were near zero and some were eastward the tops reached apex heights of over 800 km the structures appeared a little less diffuse in 5577 a emission than in 6300 a owing to less diffusion of o s with its 0 75 sec lifetime than o d with its 150 sec lifetime

role of temperature and time on organic metamorphism geologic notes organic metamorphism kerogen to hydrocarbon transformation is a function of both temperature and exposure time the effect of temperature is exponential of that of time linear at very low temperatures 266 f 130 c the reaction proceeds at such a high rate that time also plays no important role the effect of time is noticeable in the range of 158 to 212 f 70 to 100 c where intermediate conversion rates prevail stopping the heating process termination of burial freezes the rate constant of the reaction and allows organic metamorphism to continue at a linear rather than exponential rate this effect is demonstrated with the help of a simple geologic model for the first example a source rock was subjected to continuous linear heating whereas for the second the heating was terminated at a certain temperature level the model was analyzed by using the oleum scale a modified lopatin approach

the subsidence and thermal history of the bass basin southeastern australia abstract the bass basin located offshore between mainland australia and tasmania contains an unknown thickness of continental sediments of cretaceous and lower paleocene age overlain by up to 3 km of eocene to recent marine sediments it has been postulated that the basin resulted from tensional stress due to the relative movement of mainland australia and tasmania stratigraphic data from petroleum exploration wells indicate a basin subsidence in tertiary times proportional to the square root of time after beginning of subsidence t 1 2 early and middle tertiary subsidence appears to have occurred under block wise isostatic compensation geothermal gradients in the basin are typically 35 c km 1 three mechanisms of subsidence 1 a thermal contraction of the lithosphere 2 b stretching of the lithosphere 3 c deep crustal metamorphism are discussed in relation to the formation of the basin mechanisms a and c produce subsidence proportional to t 1 2 and mechanism b approximates this condition the deep crustal metamorphism mechanism is most consistent with observed subsidence thermal history and depositional environments

enhancement of atmospheric radiation by an aerosol layer the presence of a stratospheric haze layer may produce increases in both the actinic flux and the irradiance below this layer such haze layers result from the injection of aerosol forming material into the stratosphere by volcanic eruptions simple heuristic arguments show that the increase in flux below the haze layer relative to a clear sky case is a consequence of photon trapping we explore the magnitude of these flux perturbations as a function of aerosol properties and illumination conditions with a new radiative transfer model that can accurately compute fluxes in an inhomogeneous atmosphere with nonconservative scatterers having arbitrary phase function one calculated consequence of the el chichon volcanic eruption is an increase in the midday surface actinic flux at 20 n latitude summer by as much as 45 at 2900 a this increase in flux in the uv b wavelength range was caused entirely by aerosol scattering without any reduction in the overhead ozone column

dynamic interpretation of organic matter maturation and evolution of oil generative window discussion two principal elements of the hydrocarbon generation model proposed by ejedawe and coker 1984 are as follows 1 organic matter maturation occurs in two phases the first phase corresponds to basinal subsidence with essentially constant burial rate and geothermal gradient therefore the oil generative window ogw is fixed in space the second phase is the postsubsidence phase when all materials remain at constant temperatures appropriate to their depths p 1028 and the ogw moves vertically upward through the static sedimentary fill and maturation is due to time effects p 1024 2 hydrocarbon generation begins with the lighter hydrocarbons or even thermogenic gas at the initial ogw at depth followed by progressively heavier hydrocarbons as the ogw moves vertically upward p 1024

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

equatorial spread f found in 5577 a and 6300 a airglow observations from hawaii 1 we have searched for f region ionospheric disturbances in a database of airglow observations from mt haleakala hawaii the airglow scan observations were made with narrowband filters of oi 5577 a and oi 6300 a for 164 nights in the period of april 1965 through october 1968 the oi 6300 emissions are produced mostly via recombination of o2 in the f region whereas the oi 5577 emissions are generated both in the e and f regions the database has unique significance since it covers more than three years of observations in the 1960s when there was no other program that systematically monitored ionospheric airglows we find disturbances in the oi airglow brightness from which we constructed projected maps of airglow distributions at the f region altitude the projected maps clearly show wavelike disturbances whose crests are mostly aligned along a north south direction structures seen even in the raw scan data the disturbances were found exclusively in the southerly azimuth toward the equator implying that they are one of the equatorial ionospheric irregularities known as equatorial spread f esf the esf disturbances occurred 19 nights out of a total of 161 nights of azimuth scanning observations with a maximum in september the disturbances seem to arise regardless of geomagnetic activities the seasonal variation of the occurrence is consistent with recent analyses of satellite data in which esf is suggested to be caused by gravity waves from the troposphere where they are generated by strong convection in intertropical convergence zone