bluuebunny/crossref_metadata_2025 huggingface dataset:
The detection of lightning from geostationary orbit
Authors: Christian Hugh J. , Blakeslee Richard J. , Goodman Steven J.
Published: February 2008

Lightning observations from satellites in low Earth orbit have been made over the past 25 years, producing estimates of global flash frequency by season and latitude as well as information on diurnal variations. However, these measurements have suffered from low detection efficiencies, poor spatial resolutions, and the inability to continuously monitor specific storms or storm systems. Using results of investigations with a high‐altitude NASA U‐2 aircraft and other research, a space sensor capable of mapping both intracloud and cloud‐to‐ground lightning discharges from geostationary orbit during day and night with a spatial resolution of 10 km and a detection efficiency of 90% is currently being developed. In addition, this sensor, which is called the Lightning Mapper Sensor (LMS), will monitor storms on a continual basis. The combination of modern solid state mosaic focal planes with extensive on‐board signal processing in the LMS provides a powerful technique for the detection of weak background‐contaminated signals and permits the detection of lightning during the day. The LMS has a 10.5° field of view that covers all of the continental United States, large oceanic areas, all of Central America, much of South America including the Andes and the Amazon Basin, and large regions of the intertropical convergence zone. It is anticipated that the LMS will be flown on a GOES satellite in the mid‐1990s. The characteristics and design of the LMS are presented as well as a discussion of the scientific research that will be possible with this instrument.
Atmospheric carbon dioxide measurements at Cape Matatula, American Samoa, 1976–1987
Authors: Waterman Lee S. , Nelson Donald W. , Komhyr Walter D. , Harris Thomas B. , Thoning Kirk W. , Tans Pieter P.
Published: February 2008

The U.S. National Oceanic and Atmospheric Administration (NOAA) has operated a program to continuously monitor atmospheric CO2 at Cape Matatula, American Samoa, since January 1976. This paper describes the basic operational program and reports the data through 1987. Data sets are derived from hourly means which have been selected to represent baseline conditions. All hourly mean CO2 values (with flags indicating data selection status) are archived at NOAA's Geophysical Monitoring for Climatic Change (GMCC) laboratory in Boulder, Colorado; at the Carbon Dioxide Information and Analysis Center in Oak Ridge, Tennessee; and in the microfiche version of this paper. The record from the in situ analyzer is compared with that of flask samples obtained in various ways. The overall 12‐year record shows an average increase of 1.44 parts per million by volume per year. This increase amounts to 61% of the carbon dioxide emitted into the atmosphere by fossil fuel combustion during this period. The record is also characterized by the lack of a prominent seasonal cycle. The CO2 concentrations for the first half of each year are always more variable than the second 6 months, when the wind flow is dominated by strong southeasterly trades. The interannual variability of the CO2 growth rate correlates very well with that observed at other GMCC sites.
Influence of riming on the chemical composition of snow in winter orographic storms
Authors: Mitchell David L. , Lamb Dennis
Published: February 2008

The chemical composition of surface snow and rime ice has been measured in a winter mountain setting for the purpose of identifying the principal scavenging mechanisms. The siting permitted the results to be interpreted with minimal consideration of below‐cloud scavenging processes and close comparison of the snow and rime ice compositions. The concentrations of all major ions in the snow were well below those in the rime ice and could be related to the estimated degree of snow crystal riming. The results of this study support the two‐step concept of wet removal, in which atmospheric pollutants are first incorporated into cloud droplets and then removed from the cloud through the hydrodynamical collection of the droplets by falling precipitation elements. Under some meteorological conditions, therefore, it is likely that pollutant removal from the atmosphere is mechanistically limited by the removal of cloud water.
The southern hemisphere lower stratosphere during August and September 1987: Analyses based on the United Kingdom Meteorological Office global model
Authors: McKenna D. S. , Jones R. L. , Buckland A. T. , Austin J. , Tuck A. F. , Winkler R. H. , Chan K. R.
Published: February 2008

The main object of this paper is to present in one place a series of meteorological analyses to aid the interpretation of the in situ Airborne Antarctic Ozone Experiment (AAOE) observations. Maps and sections of meteorological variables derived from the United Kingdom Meteorological Office global model are presented for ER‐2 and DC‐8 flight days. Analyzed temperatures and winds are generally in good agreement with AAOE observations at all levels. Minor discrepancies in winds and temperatures are evident, particularly at DC‐8 altitudes, and are discussed in the paper. Model analyses show temperatures at 6O°W cold enough to saturate water at 1 part per million by volume as late as September 14 and that following that date a sudden increase in the temperature at all levels within the vortex precludes further saturation at low water vapor mixing ratios. Maps of potential vorticity are presented on the 428‐K potential temperature surface for the AAOE flight days. These show that the vortex is essentially circumpolar although there are periods when major distortions are apparent. At the 428‐K potential temperature level, the area of the vortex, as defined by the areas enclosed by selected potential vorticity contours, remains approximately constant throughout the AAOE.
Space‐time structure of rain rate fields
Authors: Crane Robert K.
Published: February 2008

Information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems. In this study, rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of Taylor's hypothesis for relating their spatial and temporal statistics. Weather radar derived rain rate maps were employed to obtain one‐ and two‐dimensional spatial power spectra. Azimuthally averaged two‐dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two‐dimensional turbulence driven by the input of energy over a narrow band of wave numbers. One‐dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data. Temporal spectra from the gage time series were nearly identical in shape to the one‐dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate the temporal and spatial scales. For spectra corresponding to longer durations, a match could not be made.
The estimation of convective rainfall by area integrals: 2. The Height‐Area Rainfall Threshold (HART) method
Authors: Rosenfeld Daniel , Atlas David , Short David A.
Published: February 2008

Estimates of instantaneous area average rain rate (〈R〉 in millimeters per hour) are obtained with 5–10% accuracy over a large domain simply by measuring (1) the fraction of the area, F(τ), covered by rain intensity greater than a selected threshold τ and (2) the average precipitating cloud top heights. In order to achieve this high accuracy the domain has to be large enough (about 104 km2) to include a representative sample of rain cells in different stages of their life cycle, and the measurement of the threshold rain intensity (τ) has to be unbiased. This Height‐Area Rainfall Threshold (HART) method was tested with radar data of convective rains from Global Atmospheric Research Program (GARP) Tropical Atlantic Experiment (GATE) phase 3, South Africa, west Texas, and a small sample from Darwin, Australia. The results from all locations were found to be consistent and physically plausible. The cloud base temperature seems to play a major role in the determination of the constants of the HART method. The 〈R〉‐F(τ) relations were found to be rather insensitive to variations in the Z‐R relationships. However, any bias in the measurement of τ causes a similar bias in the derived 〈R〉. HART makes possible the accurate estimation of instantaneous rainfall from space when measuring the area and height of the convective rain systems with radar. Passive microwave observations may also be used over the ocean at wavelengths which allow setting a specified rain rate threshold, and when accompanied by IR measurements of storm top temperatures. Over tropical ocean domains of the order of 104 km2 or greater, the autocorrelation time of about 6 hours permits the area average instantaneous rate to represent the rate for a few hours.
Intercomparison of NO2 measurement techniques
Authors: Fehsenfeld F. C. , Drummond J. W. , Roychowdhury U. K. , Galvin P. J. , Williams E. J. , Buhr M. P. , Parrish D. D. , Hübler G. , Langford A. O. , Calvert J. G. , Ridley B. A. , Grahek F. , Heikes B. G. , Kok G. L. , Shetter J. D. , Walega J. G. , Elsworth C. M. , Norton R. B. , Fahey D. W. , Murphy P. C. , Hovermale C. , Mohnen V. A. , Demerjian K. L. , Mackay G. I. , Schiff H. I.
Published: February 2008

An intercomparison was made near Niwot Ridge, Colorado, of three different instruments for measuring NO2 at low concentrations in ambient air: (1) the photolysis/chemiluminescence (PC) instrument, (2) the tunable diode laser absorption spectrometer (TDLAS), and (3) the Luminox instrument. Calibrated mixtures of NO2 in air and NO2 with possible interferants (HNO3, peroxyacetyl nitrate (PAN), H2O2, n‐propyl nitrate, and O3) were provided in simultaneous tests. In addition, ambient air measurements were made using the three instruments. Blind procedures were followed in preparing all results. Several conclusions were reached concerning the performance of these instruments during this intercomparison: (1) For NO2 levels above 2 parts per billion by volume (ppbv), similar results were obtained for all instruments; (2) Below 2 ppbv, the expected interferences from ozone and PAN influenced the NO2 measurements made using the Luminox instruments. Those interferences were sufficiently consistent that they could be corrected for by using the measured values Of O3 and PAN down to about 0.3 ppbv NO2; (3) The ozone interference on the Luminox instruments was removed by an ozone scrubber placed in the sampled air stream of the Luminox instrument. However, this did not remove PAN. In addition, the scrubber appeared to remove about 50% of the NO2 as well; (4) Although no interferences were identified for the TDLAS technique, care must be taken in the data analysis near (or below) the detection limit for the instrument. At these levels the data reduction program provided with the TDLAS will tend to find background noise that is correlated with the reference NO2 spectrum and calculate levels of NO2 that are too high; (5) No interferences or artifacts were found for the final results reported by the PC technique. However, these results for ambient measurements were corrected by subtracting an artifact that averaged 5 parts per trillion by volume (pptv) and by calculating a correction for the effect of ambient ozone. This latter correction averaged 1.0% in magnitude.
Some properties of negative cloud‐to‐ground lightning flashes versus stroke order
Authors: Rakov Vladimir A. , Uman Martin A.
Published: February 2008

The return stroke initial electric field peak normalized to 100 km, the probability of creating a new termination on ground, and the probability of occurrence of a dart‐stepped leader after an interstroke interval of 100 ms or less have been determined as a function of stroke order from simultaneous electric field and TV records of 76 negative cloud‐to‐ground flashes near Tampa, Florida. Fifty percent of the flashes showed multiple terminations on the ground as inferred from TV records (from 29 to 69 percent for separate thunderstorm days). For all flashes, the minimum initial electric field peak normalized to 100 km for first strokes was found to be 2.2 V/m and for subsequent strokes 0.25 V/m. The geometric mean initial electric field peak for 155 second, third and fourth strokes taken together was found to be 1.4 times larger than for 115 strokes of order 5 through 18, with the difference being statistically significant at the 0.005 significance level. The geometric mean initial electric field peak for 63 first strokes in multiple‐stroke flashes was found to be 1.3 times larger than for 13 strokes in single‐stroke flashes. The charge lowered by strokes in New Mexico was observed to exhibit behavior similar to that of the initial electric field peak in Florida described above. Subsequent strokes creating a new termination on ground showed a higher initial electric field peak than strokes following the same channel as the preceding stroke, but lower than for first strokes in a flash. Second strokes showed the maximum probability of both creating a new termination on ground (0.37) and producing a dart‐stepped leader along the channel of the previous stroke after an interstroke interval of 100 ms or less (0.36). None of the 115 strokes of order 5 and higher created a new termination on ground in spite of the fact that previous interstroke intervals for 22 of them were from 101 to 253 ms and did not contain long continuing current. The results presented and other relevant data available in the literature are consistent with the proposed hypothesis that successive strokes provide cumulative conditioning of the lightning channel.
Mesopause temperatures at 23°S
Authors: Clemesha B. R. , Takahashi H. , Batista P. P.
Published: February 2008

Observations of the OH(9,4) and O2A(0,1) atmospheric band emissions at 7750Å and 8645Å, respectively, made between 1983 and 1986, have been analyzed to give atmospheric temperatures for the corresponding emission heights. The annual mean temperatures are found to be 193 K and 198 K for the OH and O2 emissions, respectively. The OH rotational temperature shows an annual oscillation of 2.3 K amplitude with a maximum in late March, and the semiannual component shows equinoctial maxima with an amplitude of 3.0 K. The O2‐derived temperature shows a 2.5 K annual component maximizing in May.
The effect of H2O2 content on the uptake of SO2(g) by aqueous droplets
Authors: Jayne J. T. , Gardner J. A. , Davidovits P. , Worsnop D. R. , Zahniser M. S. , Kolb C. E.
Published: February 2008

The effect of H2O2 content on the uptake of SO2 by aqueous droplets has been measured. For pH < 4, SO2 gas uptake increased when the aqueous solution was doped with [H2O2] up to 2 M. The dependence of the rate of uptake on [H2O2] is consistent with the reaction rate of H2O2 with S(IV) measured in bulk aqueous solutions indicating that the droplet surface does not play a significant role in the H2O2‐S(IV) reaction.
On the Late Pleistocene ocean geochemistry and circulation
Authors: Keir Robin S.
Published: February 2008

A box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late Pleistocene may have come about. The model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric CO2, δ13C, and radiocarbon. If the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the Antarctic and if this increase is combined with a relative increase of the Atlantic sector Antarctic Bottom Water (AABW) versus North Atlantic Deep Water (NADW) source ratio from 1∶3 to about 2∶1, then the model predicts several changes that seem to be recorded in the sedimentary record, as follows: (1) A global redistribution of nutrients and 12C from the intermediate to deep water takes place with the Atlantic intermediate water phosphate decreasing 0.6 µmole kg−1 and the δ13C increasing 0.3 to 0.5‰. (2) The dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 µmole kg−1, but the intermediate water oxygen declines only a small amount. (3) The decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean. (4) The atmospheric CO2 decreases by 90 to 110 ppm. (5) Initially, a global increase in calcium carbonate dissolution occurs, which is followed by a relaxation toward better preservation than exists for the present ocean. In the model in this paper the reduction of NADW by itself does not produce these effects. Rather, the nutrient decrease that does occur is found mostly in North Pacific intermediate water, and the model atmospheric CO2 decrease is only 10 to 30 ppm. It is observed that 92% of the atmospheric CO2 change takes place according to a 200‐year time constant in the model. This corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric PCO2. Thus, according to this model, the time lag between the nutrient‐based cause and the atmospheric CO2 response is not expected to be particularly large.
Fluctuations in the composition of Late Miocene calcareous nannofossil assemblages as a response to orbital forcing
Authors: Beaufort Luc , Aubry Marie‐Pierre
Published: February 2008

Fluctuations in abundance between the two calcareous nannofossil species Coccolithus pelagicus and Reticulofenestra pseudoumbilica are observed in the upper Miocene sediments recovered from Deep Sea Drilling Project hole 552A. A record of these fluctuations (Cp/Rp) is established for a time interval of ∼1.35 m.y. (from 4.9 to 6.25 Ma) and is shown to yield periodicities which correspond to Milankovitch periodicities. A change in regime occurred at 5.72 Ma, as indicated by a shift from a series dominated by the 20‐kyr cycle to a series dominated by the 100‐kyr cycle. The Cp/Rp is compared with the isotopic δ18O and δ13O records from benthic and planktonic foraminifera. It is shown that a good correlation between the Cp/Rp and the isotopic records occurs only at times of major global changes. This suggests that the Cp/Rp, which reflects water masses movements, yields a complex paleoclimatic/paleoceanographic message which can help improving our understanding of the late Miocene history.
Meltwater and precipitation runoff to the North Atlantic, Arctic, and Gulf of Mexico from the Laurentide Ice Sheet and adjacent regions during the Younger Dryas
Authors: Teller James T.
Published: February 2008

Runoff from North America may have played a significant role in ocean circulation and climate change during the last deglaciation. Because the driving force behind such changes may have been related to salinity of the north flowing Atlantic Ocean conveyor circulation, it is critical to know the volume, timing, and location of fresh water entering the North Atlantic from the melting Laurentide Ice Sheet. During the Younger Dryas cold episode, 11,000–10,000 years B.P., there was a two‐fold increase in the volume of meltwater plus precipitation runoff, to more than 1700 km³ yr−1, flowing through the St. Lawrence valley to the North Atlantic, mainly because retreating ice allowed the glacial Lake Agassiz basin to drain eastward into the Great Lakes at this time. There was a corresponding decline in discharge from Lake Agassiz through the Mississippi River to the Gulf of Mexico. Runoff to the Arctic Ocean also increased at about the beginning of the Younger Dryas, from 740 to 900 km³ yr−1, because of the capture of what is now the headwater region of the Mackenzie River watershed. This, in combination with rising sea level and warming climate, may have increased the amount of pack ice reaching the North Atlantic through the Norwegian Sea from the Arctic Ocean. At 10,000 years B.P., eastward overflow from the western interior of North America was blocked by advancing ice, again forcing overflow to the Gulf of Mexico and, possibly, to the northwest into the Arctic Ocean. Although total runoff to the oceans from all regions draining from the Laurentide Ice Sheet did not vary substantially between 12,000 and 9000 years B.P., if discharge to the Gulf of Mexico is excluded, fresh water reaching the North Atlantic averaged 4000 km³ yr−1 during the Younger Dryas, in contrast to 2870 km³ yr−1 just before this cold episode and 3440 km³ yr−1 just after it.
Interpretation of heat flow anomalies 1. Contrasts in heat production
Authors: Simmons Gene
Published: February 2008

A relation between gravimetric and thermal anomalies, Q = F (A/2πGρ), where Q is the rate of heat flow, A is the rate of heat production per unit volume, G is the gravitational constant, ρ is density, and F is the gravitational attraction, is used to obtain theoretical surface heat flow anomalies for bodies from the analogous theoretical gravity anomalies. Results are collected for several geometrical shapes, and the application to digital computation of sources of arbitrary shape is indicated. The same relation may be used to verify that a gravity anomaly and a heat flow anomaly are caused by the same body.
On explaining the behavior of the ionospheric F region
Authors: Rishbeth H.
Published: February 2008

This paper reviews the current situation in ionospheric physics regarding the large‐scale behavior of the F region. Following the introduction, in which the plan of the paper is detailed, part 2 summarizes a basic physical theory of the F region and then lists the additional physical processes that are thought to influence F‐region behavior. The over‐all balance of ionization in the F region is also considered in relation to the flux of ionizing solar radiation. With currently available data, it is barely possible to account for the gross quantity of ionization present. In part 3, several phenomena of the F region are reviewed and possible explanations discussed. The phenomena include seasonal and annual variations of the F2 layer, the daily variations of peak electron density (NmF2) and the height of the peak (hmF2), the nighttime F layer, and the equatorial F2 layer. Part 4 deals with further topics of interest, though in less detail. These include the F2 layer during storms and at high latitudes, conjugate point effects, and the existence of negative ions in the F region. In the conclusion, the preceding discussion is recapitulated by listing the observed effects that are suggested to result from each physical process, and brief comments are made on possible future progress.
Dynamical aspects of lunar origin
Authors: Kaula William M.
Published: February 2008

According to tidal friction calculations in which estimates of the current dissipation factor are used, the moon was close to the earth less than two billion years ago. The most plausible solution to this ‘time scale’ problem appears to be a much lesser extent of shallow seas in the past; a coupling of the moon's orbit with Venus is also a possibility. The same calculations indicate that the moon had an inclination of at least 10° to the equator, and that the earth's rotation period was five hours. Fission hypotheses, of which the most carefully developed is by O'Keefe, have not yet dealt successfully with these constraints. Fission theories are also unsatisfyingly episodic: matter must first lose angular momentum to fall into the earth, and then regain it to separate. All capture hypotheses are inherently improbable, particularly if the moon came from a different enough part of the solar system to account for the moon's density difference. The least implausible capture hypothesis, by Urey and MacDonald, entails collision with a pre‐existing earth satellite at 30–40 earth radii, but the reasoning behind it is not compelling. Most compatible with the idea that formation of the moon is closely connected to the formation of the earth are hypotheses that the moon formed out of a geocentric swarm of matter to which matter from heliocentric orbit was continually added. The theory of Ruskol seems to incorporate most of the dynamical essentials. However, the model needs to be developed further to include gas drag and other effects of the severe heating associated with chemical fractionation between the earth and moon, as well as to account for the inclination of the lunar orbit. A possibly severe constraint on the distance from the earth at which the moon's formation was completed is a systematic ellipticity of lunar craters pointed out by Öpik; it should be re‐examined after oriented metric photographs from Apollo 15–17 flights are obtained.
General circulation of the tropical lower stratosphere
Authors: Wallace John M.
Published: February 2008

The zonally symmetric flow in the tropical lower stratosphere exhibits three types of variability: (1) an annual cycle that has odd symmetry about the equator with easterlies in the summer hemisphere and westerlies in the winter hemisphere, (2) a semiannual oscillation with a rather complex distribution of amplitude and phase, and (3) irregular long‐period fluctuations with an average period of somewhat >2 years and even symmetry about the equator, successive easterly and westerly wind regimes of this so‐called quasi‐biennial oscillation being observed to propagate downward at a rate of ∼1 km month−1. Superposed on the zonally symmetric circulation are two types of planetary scale wave disturbances which propagate both zonally and vertically with periods of 10–15 days and 4–5 days, respectively. These have been identified with the gravest modes of the family of forced zonally propagating waves on a rotating sphere. The first type is an atmospheric ‘Kelvin wave,’ which bears some similarity to the shallow water wave that propagates along coastlines. The second type is a ‘mixed Rossby‐gravity wave.’ Both waves transport energy upward which suggests a tropospheric energy source. The waves are capable of modifying the zonally symmetric flow in the stratosphere through the vertical transport of zonal momentum. Consideration of the interactions between the waves and the zonal flow suggests a plausible mechanism for producing the observed quasi‐biennial oscillation in zonal wind.
Energy and momentum theorems in magnetospheric processes
Authors: Carovillano Robert L. , Siscoe George L.
Published: February 2008

This review deals with the several energy and momentum theorems that relate to magnetospheric processes that have been developed. The region of primary consideration in this paper is the magnetospheric domain that extends between the ionosphere and the interplanetary medium, although, for studying certain phenomena, ionospheric and solar wind properties are of central importance and must be included. Both energy theorems and momentum theorems with their applications are presented. Since energy is an integral property of the system variables, analytical results can be found without knowledge of detailed dynamical processes. Thus, relations are derived between particle and magnetic system energies, and application is made to the shape of the magnetopause and various phases of a magnetic storm. Particular attention is given to symmetric and asymmetric ring currents, including energy and momentum equilibrium conditions; a review of nonlinear self‐consistent models and a discussion of how charge exchange and energy diffusion participate in the recovery phase are presented. Comprehensive expressions for the storm time disturbance field are given in terms of both ring current and boundary current energies, and changes that occur during magnetospheric compressions are discussed. The momentum theorems center around the requirement of static force balance during geomagnetically quiet intervals. Whereas the energy theorems give expressions for the average disturbance field over the earth, the momentum theorems give the gradient in the disturbance field across the earth. The forces between earth and the boundary current, the ring current, and the tail current are derived for various models. It is noted that existing vacuum models of the geomagnetic tail are deficient in meeting the combined requirements of energetics and dynamics of the quiet time tail. Introducing the plasma sheet removes the difficulty by allowing an extra degree of freedom in adjusting the force between the earth and the tail. The role of the plasma sheet in making force adjustments is shown to be consistent with the observed thinning of the plasma sheet before sub storms.
New evidence for effects of variable solar corpuscular emission on the weather
Authors: Roberts Walter Orr , Olson Roger H.
Published: February 2008

New evidence supports some earlier findings of connections between solar activity and weather that involve streams of solar corpuscular emission. The time lag between the arrival of the solar streams and their first lower stratospheric or tropospheric response is about three days, and the effects appear to be most pronounced in winter. No fully plausible physical explanation is known, but some speculations are advanced regarding a possible heating mechanism for the upper troposphere that results from aurora‐induced cirrus clouds over the relatively warm Gulf of Alaska.
Theory of the magnetic viscosity of lunar and terrestrial rocks
Authors: Dunlop David J.
Published: February 2008

Lunar materials exhibit two distinct types of viscous or time‐dependent magnetic behavior. Igneous rocks and largely recrystallized breccias, whose magnetic properties are due to multidomain iron, typically have weak magnetic viscosity, but decay persists for very long times following even a brief exposure to a field. Lunar soils and low metamorphic grade breccias, which contain an important fraction of metallic iron of single‐domain and superparamagnetic size, generally acquire an anomalously strong viscous remanence, whose decay time is about equal to the time of exposure to the field. Four theories of magnetic viscosity are reviewed in this paper in an attempt to interpret the very different viscous properties of these two types of rocks. The Richter (1937) and Néel (1949) theories are appropriate to soils and low‐grade breccias, whereas igneous and recrystallized rocks are better described by the multidomain theories of Néel (1950) and Stacey (1963). Both the Stacey and Néel theories correctly predict logarithmic magnetic viscosity, in spite of the fact that the central role played by the internal demagnetizing field in multidomain grains is ignored in Néel's formulation. This apparent paradox has been resolved. Analysis of the particularly simple case of a two‐domain particle shows that the distribution of asymmetrical nonidentical potential barriers required by Néel is automatically generated from the simpler distribution of symmetrical identical barriers proposed by Stacey through the action of the demagnetizing field. Experimental evidence on many facets of viscous magnetization, from terrestrial as well as lunar materials, is reviewed in detail before a final evaluation of the various theories is made. One interesting conclusion is that the magnetic viscosity of multidomain particles, although relatively weak, is still too strong to be explained by displacements of entire domain walls. Either displacements of small wall segments or rotation of pseudo‐single‐domain moments could account for the enhancement of magnetic viscosity in these particles.
Cosmic‐ray‐produced electrons and gamma rays in the atmosphere
Authors: Daniel R. R. , Stephens S. A.
Published: February 2008

The propagation of the primary cosmic radiation through the earth's atmosphere is a phenomenon of considerable intrinsic complexity stemming from the large number and variety of parameters involved and their dependence on energy, latitude, and atmospheric depth. Although in the past the study of the hadronic component in the atmosphere has received appreciable attention, not much interest has been focused on the electron‐photon component until very recent years. As a consequence, the observational data now available on the latter are meager and fragmentary; such information as is available is reviewed here, and the existing gaps in our knowledge are highlighted. Because of the very complexity of the problem, it has been recognized that extensive and refined calculations are needed to understand the observations and to provide new motivation to experimenters. In the present article the limited theoretical calculations so far attempted are first reviewed; a summary of detailed calculations recently carried out by the present authors follows. Finally, the results from the calculations are compared with those available from experiments; wherever it is necessary, attempts are made to identify the areas in which further work is needed.
Observations of interactions between interplanetary and geomagnetic fields
Authors: Burch J. L.
Published: February 2008

Magnetospheric effects associated with variations of the north‐south component of the interplanetary magnetic field (IMF) are examined in light of recent experimental and theoretical results. Although the occurrence of magnetospheric substorms is statistically related to periods of southward IMF, the details of the interaction are not understood. In particular, attempts to separate effects resulting directly from the interaction between interplanetary and geomagnetic fields from those associated with substorms have produced conflicting results. One can, however, say with some assurance that the transfer of magnetic flux from the day side to the night side magnetosphere, as evidenced by equatorward motion of the polar cusp and increases of the magnetic energy density in the lobes of the geomagnetic tail, is a direct consequence of the southward IMF. On the other hand, the formation of a macroscopic X‐type neutral line at tail distances less than 35 RE appears to be a substorm phenomenon. Although other plasma and field phenomena in the outer magnetosphere and at low altitudes may be directly associated with the southward IMF, the evidence is less convincing. The quantitative results that have been obtained are compared with current theoretical models of the reconnection process.
Structure of the Moon
Authors: Toksöz M. Nafi , Dainty Anton M. , Solomon Sean C. , Anderson Kenneth R.
Published: February 2008

Seismic data from the four stations of the Apollo passive seismic network have been analyzed to obtain the velocity structure of the moon. The long reverberating train of seismic energy observed in lunar seismograms may be explained by scattering in a near‐surface zone. The earliest parts of the seismogram correspond to body wave phases and may be interpreted by conventional methods. There are no clearly identifiable dispersed surface wave trains present on lunar seismograms. This absence can be explained by scattering of surface waves by near‐surface heterogeneities. Analysis of body wave phases from artificial impacts of known impact time and position yields a crustal section. In the Mare Cognitum region the crust is about 60 km thick and is layered. In the 20‐km‐thick upper layer, velocity gradients are high and microcracks may play an important role. The 40‐km‐thick lower layer has a nearly constant 6.8‐km/s velocity. There may be a thin high‐velocity layer present beneath the crust. The determination of seismic velocities in the lunar mantle is attempted by using natural impacts and deep moonquakes. The simplest model that can be proposed for the mantle consists of a ‘lithosphere’ overlying an ‘asthenosphere.’ Shear waves are attenuated in the ‘asthenosphere,’ and this zone may be partially molten. No seismic data contradict this model. The best value for the compressional wave velocity of the lithosphere is 8.0 → 8.3 km/s, but this may be an average over several differing regions. Density models are calculated for the moon by using the latest value for the moment of inertia (C/MR² = 0.395±0.005), mean density, and temperature and pressure dependence of density for likely lunar models. The mean density in the lunar mantle, corrected to standard (surface temperature, zero pressure) conditions, is 3.4–3.5 g/cm³. These values together with the mean compressional wave velocities are consistent with an olivine‐pyroxene (olivine‐rich) lunar mantle but do not exclude other compositions. On the basis of the density models, some limitations can be placed on the maximum allowable radius of an iron‐rich lunar core. If the lunar mantle is chemically and mineralogically homogeneous, the maximum radius of such a core is about 700 km for an FeS composition and about 450 km for pure Fe composition. There are no geophysical data that indicate whether the moon does or does not have an iron‐rich core.
Magnetotelluric deep electrical sounding and resistivity
Authors: Bennett D. J. , Filloux J. H.
Published: February 2008

Since the previous report to the IUGG in this field [Hermance, 1971], geoelectromagnetic induction studies have steadily increased in importance as a means of delineating tectonic structure in the upper few hundred kilometers of the earth. Such an advance is due especially to (1) the development of various computational techniques of modeling, (2) the accumulation of further data in tectonically interesting regions, (3) the increase in our knowledge of the relationships between the electrical conductivity of crustal and upper mantle materials and other parameters such as temperature, physical state, free water content, and seismic velocity, and (4) the ability to interpret many studies in terms of terrestrial conductivity structures which not only provide useful tectonic information not obtainable by other means but also are generally consistent with other relevant geological and geophysical data. Further stimulus has been provided by the availability of good electromagnetic sounding data for the moon obtained by the Apollo series of lunar landings.

An outstanding problem remains the limited resolution of these studies as compared to seismology, for example. In consequence, average conductivity‐depth profiles of the upper few hundred kilometers still remain quite poorly determined for most of the earth, and a corresponding level of nonuniqueness is passed on to the models of two or three‐dimensional terrestrial conductivity structure.
The geology of Mars: A brief review of some recent results
Authors: Mutch T. A. , Head J. W.
Published: February 2008

Most of what we know about the geology of Mars derives from the data of the Mariner 9 mission. This dramatically successful orbital reconnaissance of the planet continued for almost an entire year, from November of 1971 to October of 1972. Although many of the Mariner 9 data remain unanalyzed, the initial phase of intensive study is complete.

An international colloquium on Mars was held in November 1973 in Pasadena, California, under the sponsorship of the American Geophysical Union, the American Astronomical Society, and the National Aeronautics and Space Administration. The objective of the colloquium was to synthesize Mariner results and to identify important problems for additional study. Most of the papers presented at the colloquium have since been published, particularly in Icarus [22(2, 3), 1974] and in the Journal of Geophysical Research [79(24, 26), 1974]. An attractive summary of Mariner 9 results has been prepared by Hartmann and Raper [1974].
Climate modeling through radiative‐convective models
Authors: Ramanathan V. , Coakley J. A.
Published: February 2008

We present a review of the radiative‐convective models that have been used in studies pertaining to the earth's climate. After familiarizing the reader with the theoretical background, modeling methodology, and techniques for solving the radiative transfer equation the review focuses on the published model studies concerning global climate and global climate change. Radiative‐convective models compute the globally and seasonally averaged surface and atmospheric temperatures. The computed temperatures are in good agreement with the observed temperatures. The models include the important climatic feedback mechanism between surface temperature and H2O amount in the atmosphere. The principal weakness of the current models is their inability to simulate the feedback mechanism between surface temperature and cloud cover. It is shown that the value of the critical lapse rate adopted in radiative‐convective models for convective adjustment is significantly larger than the observed globally averaged tropospheric lapse rate. The review also summarizes radiative‐convective model results for the sensitivity of surface temperature to perturbations in (1) the concentrations of the major and minor optically active trace constituents, (2) aerosols, and (3) cloud amount. A simple analytical model is presented to demonstrate how the surface temperature in a radiative‐convective model responds to perturbations.
Some physical processes in the solar wind
Authors: Hollweg Joseph V.
Published: February 2008

The ‘standard physics’ of the solar wind is reviewed, and arguments that this standard physics is inadequate are summarized. A variety of suggestions for modifying the physics of the solar wind are then reviewed, with emphasis on effects of MHD waves of solar origin and collisionless or instability‐limited electron heat conduction. The basic effects of the modified physics are demonstrated in a two‐fluid model of the solar wind flow. The predictions of this model are carefully compared with observations, and the need for further observations is emphasized. The review concludes with suggestions for future theoretical efforts.
Jovian magnetosphere‐Satellite interactions: Aspects of energetic charged particle loss
Authors: Thomsen M. F.
Published: February 2008

Observations of energetic charged particles obtained by Pioneers 10 and 11 near the orbits of the inner Jovian satellites are reviewed with particular emphasis on the implications of these observations with regard to possible models of the access of charged particles to the satellite surfaces. The observed effects on particle pitch angle distributions and the observed energy dependence of the intensity depletions seen at the satellite orbits are compared with predictions of satellite sweepup based on several different access models. The two major uncertainties which hamper the comparisons are those associated with the satellite conductivities and the ionospheric dynamo electric field power spectrum. The satellite conductivity is important because it governs the access of the particles to the satellite surface and therefore the lifetime τ; the dynamo power spectrum is important because it controls the magnitude and energy dependence of the radial diffusion coefficient. In spite of these uncertainties we can nevertheless make the following conclusions. (1) The electron pitch angle distributions at Io's orbit are compatible with expectations based on sweeping. (2) The energy dependences of the observed electron depletions at all three inner satellites (Amalthea, Io, and Europa) are incompatible with expectations based on a perfect conductor model of a satellite and its flux tube but are compatible with the energy dependence expected for perfectly insulating or partially conducting satellites; the energy dependences of the proton losses at all three satellites also appear to be compatible with absorption by an insulating or partially conducting satellite but only if certain forms of the dynamo power spectrum are assumed. (3) However, the proton losses at Io are observed to be much stronger than the electron losses, in contradiction to expectations based on sweeping. (4) The most attractive explanation for the proton‐electron discrepancy at Io is that the large proton losses at Io's orbit are principally due to enhanced pitch angle scattering in the region of higher plasma density and probably greater turbulence associated with the satellite rather than to satellite sweeping alone.
F‐region dynamics
Authors: Mayr H. G. , Harris I.
Published: February 2008

Problems of upper atmosphere dynamics represent a challenge that in itself attracts and deserves considerable attention. In a broader picture, dynamic processes are manifestations of energization processes that we seek to understand. An attempt is made here to report primarily on the U.S. research effort over the last 4 years that directly or indirectly relates to an understanding of upper atmosphere and F‐region dynamics.

The upper atmosphere or thermosphere is referred to as the region above the mesopause (80—90 km) where the neutral gas temperature begins increasing with height to values as high as 2000°K. It harbors a relatively dense plasma population—the ionosphere—which, controlled by electric and magnetic fields, affects the energetics and dynamics of the neutral atmosphere. Through current loads, the ionospheric plasma distribution can also affect the electric fields across the magnetosphere which in turn penetrate into the lower atmosphere. The distribution of this plasma, is in turn influenced by atmospheric mass and energy transport. In the lower thermosphere, winds are a source for dynamo electric fields.
The dynamics of the Jovian magnetosphere
Authors: Goertz C. K. , Thomsen M. F.
Published: February 2008

The current status of our understanding of the dynamics of Jupiter's magnetosphere is reviewed. First, a brief summary is presented of the concepts and processes which were identified as being of probable importance by pre‐Pioneer 10 and 11 work (both theoretical and observational). The insights provided by the in situ Pioneer flights are then discussed. The Jovian magnetosphere consists of several relatively distinct regions: the inner magnetosphere, the intermediate magnetosphere, the outer magnetosphere, a transition region just inside the magnetopause, and the magnetosheath. The basic particle and magnetic field characteristics of these regions are summarized, and the dynamical processes which are currently thought to be significant in each of them are reviewed. Finally, some outstanding questions and problems are identified for future treatment based on Pioneer data or on data from the upcoming Voyager and Galileo missions.
Ultra‐high‐pressure experimental mantle mineralogy
Authors: Bell Peter M.
Published: February 2008

This review is focused on ultra‐high‐pressure mineralogical research done during the period of the quadrennium. Where possible, reference to review articles and books have been substituted for discussion. Static‐pressure experiments are the theme of the review because of the breakthroughs in technique and discovery during the period. Shock‐pressure experimental results during the period, of equal importance, have also contributed to the gains in understanding of the mineralogy of the mantle and core.
Relativistic solar cosmic rays
Authors: Duggal S. P.
Published: February 2008

This paper reviews the present state of knowledge concerning the relativistic particles of solar origin. The analytic techniques for obtaining information regarding the distribution of particles in the interplanetary space from ground‐based observations are described. The general features of pitch angle anisotropy of high‐energy particles are outlined. The concepts of relativistic particle propagation in the corona and interplanetary space are discussed with special reference to the relevant new ideas that have emerged from studies of energetic particle events. The experimental and theoretical arguments that indicate that particles can be accelerated to high energies by shock waves in the heliomagnetosphere are reviewed. Finally, a brief summary of the well‐established ideas and unsolved problems is presented.