bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil organic carbon mobilization by interrill erosion: Insights from size fractions
Authors: Wang Zhengang , Govers Gerard , Oost Kristof Van , Clymans Wim , den Putte An Van , Merckx Roel
Published: December 2012

Sediments mobilized by interrill erosion are often highly enriched in soil organic carbon (SOC) in comparison to source soils. This selectivity may lead to the preferential mobilization of SOC with specific properties, e.g., SOC that is especially susceptible to decomposition. This may then have important implications with respect to the role of soil erosion in the global carbon cycle. We addressed this issue by investigating the behavior of different SOC components in field rainfall simulation experiments on arable fields in loess‐derived soils. We characterized the mobilization of mineral‐bound organic carbon (MOC) and particulate organic carbon (POC) by interrill erosion using size fractionation and we used the C:N ratio as a tracer variable to determine the composition of the SOC in eroded sediments. MOC was found to be preferentially mobilized by interrill erosion in comparison to POC. The enrichment ratio (i.e., the ratio of the concentration of a soil constituent in the eroded sediment to its concentration in the original soil) of MOC decreased with increasing sediment concentration. The enrichment ratio of POC displayed a similar pattern to that of MOC but enrichment was less pronounced. Furthermore, sediments were found to be enriched in fine POC while they were impoverished with respect to coarse POC. The selective MOC mobilization together with the dominance of MOC in the total SOC pool in the soil explained the dominance of MOC in interrill eroded sediment. The fact that it is mainly MOC that is mobilized by interrill erosion implies that the SOC in the interrill eroded sediments is on average at least as recalcitrant than that in the source soils which may have important implications for the fate of the mobilized SOC. In order to understand the role of soil erosion in C cycling, MOC and POC need to be considered separately not only because they are chemically different but also because of their different behaviors with respect to geomorphic processes.
Recurring dynamically induced thinning during 1985 to 2010 on Upernavik Isstrøm, West Greenland
Authors: Khan Shfaqat Abbas , Kjær Kurt H. , Korsgaard Niels J. , Wahr John , Joughin Ian R. , Timm Lars H. , Bamber Jonathan L. , van den Broeke Michiel R. , Stearns Leigh A. , Hamilton Gordon S. , Csatho Bea M. , Nielsen Karina , Hurkmans Ruud , Babonis Greg
Published: December 2012

Many glaciers along the southeast and northwest coasts of Greenland have accelerated, increasing the ice sheet's contribution to global sea‐level rise. In this article, we map elevation changes on Upernavik Isstrøm (UI), West Greenland, during 2003to 2009 using high‐resolution ice, cloud and land elevation satellite laser altimeter data supplemented with altimeter surveys from NASA's Airborne Topographic Mapper during 2002 to 2010. To assess thinning prior to 2002, we analyze aerial photographs from 1985. We document at least two distinct periods of dynamically induced ice loss during 1985 to 2010 characterized by a rapid retreat of the calving front, increased ice speed, and lowering of the ice surface. The first period occurred before 1991, whereas the latter occurred during 2005 to 2009. Analyses of air and sea‐surface temperature suggest a combination of relatively warm air and ocean water as a potential trigger for the dynamically induced ice loss. We estimate a total catchment‐wide ice‐mass loss of UI caused by the two events of 72.3 ± 15.8 Gt during 1985 to 2010, whereas the total melt‐induced ice‐mass loss during this same period is 19.8 ± 2.8 Gt. Thus, 79% of the total ice‐mass loss of the UI catchment was caused by ice dynamics, indicating the importance of including dynamically induced ice loss in the total mass change budget of the Greenland ice sheet.
On the reflection and transmission of low‐frequency energy at the irregular western Pacific Ocean boundary
Authors: Clarke Allan J.
Published: December 2012

The western boundary of the tropical Pacific is not continuous, and leakage of low‐frequency energy from the Pacific to the Indian Ocean is possible. At low frequencies, equatorial Kelvin and Rossby waves have very large east‐west scales compared with the east‐west scale of the land masses in the region. Consequently, these land masses may be treated as islands that are infinitesimally thin in the east‐west direction. By generalizing previous theory for a single island, the leakage and multiple reflection of low‐frequency energy through the seven major “islands” forming the boundary of the western Pacific can be studied. The results obtained depend on continuity of mass and large‐scale balances and not on the details of nonlinear and/or frictional flow near island eastern boundaries. The major results are as follows: (1) When a mode 1 low‐frequency Rossby wave is reflected at the discontinuous western Pacific boundary, the eastward reflected Kelvin wave energy flux is about one third of the incoming energy flux, or about two thirds ofthat expected for a solid meridional wall. In other words, the reflected Kelvin wave amplitude is 83% of that which would be reflected from a solid meridional wall. The reflection mainly occurs from the Indonesia/Borneo/Asia land mass and very little energy gets into the Indian Ocean. (2) Sea levels in the western equatorial Pacific and on the western boundaries of the major western Pacific land masses should be in phase and of a similar amplitude. In particular, in‐phase interannual sea levels should occur along Australia's western coast and be highly correlated with sea levels in the western equatorial Pacific. Sea level data at Truk Island and on Australia's western coastline confirm this prediction. (3) The interannual exchange of water between the Pacific and Indian oceans due to interannual oscillations in the Pacific is about 6 Sv (1 Sv = 106 m3 s−1), is highly correlated with El Niño/Southern Oscillation (ENSO) events, and bears definite phase relationships to sea level stations at locations in the western Pacific. For example, for a high sea level at Darwin, the transport is westward from the Pacific Ocean into the Indian Ocean. It seems that interannual transport may be approximately monitored using coastal sea level. (4) Strong narrow low‐frequency currents are predicted to occur westward of some island tips. (5) Interannual Indian Ocean Kelvin wave signals are largely blocked at the Indonesia/Borneo/Asia land mass. (6) In terms of net transport, reflection, and transmission properties, the seven island Pacific western boundary can be reduced to a simpler two‐island problem, in which one island is the Indonesia/Borneo/Asia land mass and the other New Guinea/Australia. (7) The comparatively small Halmahera Sea between Halmahera and New Guinea is dynamically important. Closing this sea for the incident first meridional mode Rossby wave case reduces the interannual transport between the Pacific and Indian Oceans by 40%.
The heat budget of the TOGA‐COARE domain in an ocean model
Authors: Gent Peter R.
Published: December 2012

The annual mean heat budget of the TOGA‐COARE domain is examined in a reduced‐gravity, primitive equation model of the upper equatorial ocean that is described by Gent and Cane (1989). It is forced by the monthly winds from Rasmusson and Carpenter (1982), and the heat flux formulation is from Seager et al. (1988). It is concluded that the annual mean net heating of the ocean surface in the area 140°E‐180°E, 10°S‐10°N is between 0 and 20 W m−2. This is considerably less than the estimates given in climatic atlases which vary from about 30 W m−2 (Esbensen and Kushnir, 1981; Hsiung, 1985), about 50 W m−2 (Weare et al., 1981), to about 70 W m−2 (Reed, 1985). These estimates have no physical constraints on the analysis, whereas the model result is constrained by the ocean's ability to remove heat from the TOGA‐COARE domain.
On the variability of winds, sea surface temperature, and surface layer heat content in the western equatorial Pacific
Authors: McPhaden Michael J. , Hayes Stanley P.
Published: December 2012

In this study we examine the surface layer heat balance using wind, current, and temperature data from equatorial moorings along 165°E. The analysis focuses primarily on daily to monthly time scale variations during the 1986–1987 El Niño/Southern Oscillation event. The period is one of high mean sea surface temperatures (≳29°C) and frequent outbreaks of westerly winds. We infer that evaporative cooling related to wind speed variations accounts for a significant fraction of the observed sea surface temperature (SST) and upper ocean heat content variability. This evaporative heat flux converges nonlinearly in the surface layer, giving rise to larger temperature variations in the upper 10 m than below. Other processes examined (wind‐forced vertical advection and entrainment, lateral advection) were negligible or of secondary importance relative to evaporative cooling. A large fraction of the SST and surface layer heat content variance could not be directly related to wind fluctuations; this unexplained variance is probably related to shortwave radiative fluxes at the air‐sea interface.
An equilibrium model for the coupled ocean‐atmosphere boundary layer in the tropics
Authors: Sui C.‐H. , Lau K.‐M. , Betts Alan K.
Published: December 2012

A coupled model is used to study the equilibrium state of the ocean‐atmosphere boundary layer in the tropics. The atmospheric model is a one‐dimensional thermodynamic model for a partially mixed, partly cloudy convective boundary layer (CBL), including the effects of cloud‐top subsidence, surface momentum and heat (latent and sensible) fluxes, and realistic radiative transfer for both shortwaves and longwaves (Betts and Ridgway, 1988; 1989). The oceanic model is a thermodynamic model for a well‐mixed layer, with a closure constraint based on a one‐dimensional turbulent kinetic energy (TKE) equation following Kraus and Turner (1967). Results of several sets of experiments are reported in this paper. In the first two sets of experiments, with sea surface temperature (SST) specified, we solve the equilibrium state of the coupled system as a function of SST for a given surface wind (case 1) and as a function of surface wind for a given SST (case 2). In both cases the depth of the CBL and the ocean mixed layer (OML) increases and the upwelling below the OML decreases, corresponding to either increasing SST or increasing surface wind. The deepening of the equilibrium CBL is primarily linked to the increase of CBL moisture with increasing SST and surface wind. The increase of OML depth and decrease of upwelling are due to a decrease of net downward heat flux with increasing SST and the generation of TKE by increasing wind. In another two sets of experiments, we solve for the coupled ocean‐atmosphere model iteratively as a function of surface wind for a fixed upwelling (case 3) and a fixed OML depth (case 4). SST falls with increasing wind in both cases, but the fall is steeper in case 4, because the OML depth is fixed, whereas in case 3 the depth is allowed to deepen and the cooling is spread over a larger mass of water. The decrease of evaporation with increasing wind in case 4 leads to a very dry and shallow CBL. Results of further experiments with surface wind and SST (upwelling) prescribed as a function of longitude similar to the observed values across the Pacific show that the model gives realistic gradients of mixed‐layer depth and upwelling (SST). This work suggests that the equilibrium state of the coupled system is very sensitive to the coupling of the boundary layers. Special efforts are needed to incorporate physical processes in the CBL and OML in coupled models.
Effect of low‐latitude western boundary gaps on the reflection of equatorial motions
Authors: du Penhoat Yves , Cane Mark A.
Published: December 2012

The western tropical Pacific is thought to be an important zone for generating El Niño: reflections at the boundary make it a source region of equatorial Kelvin waves. Calculations of the effect of a gappy western boundary on the reflection process are carried out in the framework of the low‐frequency limit of the shallow‐water equations and thus are highly idealized. The method is also applied to a schematic version of the flow through the Indonesian seas from the western Pacific to the Indian Oceans. The results indicate some strong sensitivities to the location of the gap and to the structure of the incoming flows. In addition, the results can be quite different, depending on whether the zonal extend of the gap is assumed to be infinite or finite. (More precisely, the latter means that the extend of the gap is short compared with the zonal wavelength of the relevant free waves at that frequency.) In view of the complexity of the results for even such a simplified model, it will be very difficult to be confident of any modeling study of the Indonesian throughflow short of a highly resolved numerical calculation with a detailed representation of the geometry and bathymetry. Nonetheless, we offer tentative conclusions concerning the efficiency of the western Pacific boundary as a reflector. Our results suggest that the realistic boundary will not greatly alter expectations based on a simple solid boundary if the reflections important for El Niño are primarily in motion, represented by low‐order Rossby modes. This is also consistent with observational evidence indicating no anomalous throughflow during El Niño events.
Air‐sea coupled modes on intraseasonal and interannual time scales over the tropical western Pacific
Authors: Kawamura Ryuichi
Published: December 2012

Dominant phase relationships between sea surface temperature (SST), high cloud cover (HCC), and zonal wind at 850 mbar on intraseasonal and interannual time scales in the warm pool region of the western Pacific are examined. Using the complex empirical orthogonal function (CEOF) analysis, two air‐sea coupled modes, that is, an intraseasonal mode and an interannual mode, are statistically extracted. It is found that in the intraseasonal mode the area of maximum SST anomaly lies to the east of the center of the active large‐scale convection area and therefore positive SST anomalies exist at the easterly anomaly area. The existence of high SST at the easterly anomaly area provides a favorable condition for a large‐scale disturbance to propagate eastward, though the evaporation‐wind feedback mechanism may also favor its eastward propagation if the mean wind is easterly. It is seen that the intraseasonal mode is very similar to the advective mode proposed by Lau and Shen (1988) with respect to the phase relationship. However, since the time evolution of the intraseasonal mode does not always coincide with the variations of east‐west SST gradient over the tropical western Pacific, this mode requires another mechanism other than the east‐west SST advection causing the advective mode. On one hand, the interannual mode has a characteristic that the phase relation of 850 mbar zonal wind (u) is different in each region of the tropical western Pacific, whereas the SST is almost in phase with HCC. The predominant growth of the mode defined in the key region (0°–10°N, 130°–160°E) corresponds to the life cycle that occurs when the El Niño/Southern Oscillation (ENSO) begins, develops, and decays. This verifies that the ENSO is one of the prominent phenomena in the air‐sea interactive system on the interannual time scale. On the other hand, the mode over the tropical Pacific around the dateline explains the air‐sea coupling when large‐scale convection is not very active. It is thus clear that evident differences of air‐sea coupling exist between the intraseasonal time scale and the interannual time scale. It is also determined that the strength of air‐sea coupling varies with year in both time scales. The above results provide a clue for understanding the mechanism of multiscale air‐sea coupling in the tropics.
Objective quality control and performance diagnostics of an oceanic subsurface thermal analysis scheme
Authors: Smith Neville R.
Published: December 2012

The burgeoning transmission and collection of real‐time and climatological ocean data has focused attention on the requirement for efficient techniques of objective quality control and analysis, amenable to both real‐time and delayed mode applications. This paper discusses the application of such techniques to analysis of Pacific Ocean temperature, using statistics and maps drawn from 12 bimonthly analyses of the 150 m temperature during 1987–1988 as a means of evaluation. It is demonstrated that for observational data of varying quality, objective standardization is an integral element of the interpolation and mapping process and provides an effective method for screening large oceanic data sets. Prechecking and cross‐validation are the center pieces of the quality control scheme, the efficacy of which depends both on the judicious choice of error tolerance levels and on the suitability of first‐guess field and statistical prescriptions. The data rejection rate is near 5%, reflecting the conservative tolerances adopted for the study. Unreasonably low rates are obtained whenever inflated signal or noise levels are used. Persistent offsets in the first‐guess field adversely affect the quality control measures and, in turn, can modify the analysis product. Using a parameter which relates to the system performance, it is shown that the analysis system is extracting close to maximum information from the available data. Degradation in system performance is chiefly linked to lack of effective quality control and poor statistical prescriptions.
Eastern equatorial Pacific response to three composite westerly wind types
Authors: Giese Benjamin S. , Harrison D. E.
Published: December 2012

It has been suggested recently that episodes of westerly wind near the international date line in the western Pacific tend to fall into one of four types. Three of the types have enough equatorial zonal wind variation to be able to induce an eastern Pacific response by forcing equatorial waves. In this note we examine the central and eastern Pacific waveguide response to idealized representations of these three types of westerly wind episodes, using a combination of linear theory and results from an ocean general circulation model. The idealized westerly wind types are the C type (maximum anomalies centered on the equator), the N type (maximum anomalies just north of the equator), and the S type (maximum anomalies just south of the equator). The composite C‐type event excites equatorially trapped Kelvin pulses that alter sea surface temperature in the central and eastern Pacific. Warm anomalies caused by the C‐type episode have approximately equal contributions from a zonal advection of heat by the Kelvin pulses and a meridional advection of heat by an altered instability wave field. Because the center of forcing of the S‐type event is displaced off of the equator, the Kelvin pulses excited by the S‐type episode have smaller amplitude than those of the C‐type episode, even though the maximum wind anomaly is the same in the two cases. The S‐type anomaly also excites weak Rossby‐gravity waves that can propagate into the eastern Pacific. Because the Rossby‐gravity waves are dispersive, their amplitude diminishes as the waves propagate into the eastern Pacific. The N‐type episode, as observed in winds from the western tropical Pacific, is much weaker and of shorter duration than the C and S types, and therefore excites only a very weak eastern Pacific response. Although all types of westerly wind excite a local western Pacific response, only the C‐ and S‐type events excite a significant eastern Pacific response.
On the two‐phase thermodynamics of the coupled cloud‐ocean mixed layer
Authors: Chu P. C. , Garwood R. W.
Published: December 2012

The rudiments of a self‐consistent two‐phase thermodynamical theory of intraseasonal and interannual variability for the tropical cloud‐ocean mixed layer system are presented. In this paper we study some basic properties of low‐frequency phenomena in the tropical coupled cloud‐ocean mixed layer system under low mean wind speed conditions and attempt to seek a unified thermodynamical framework in which the thermodynamical oscillation can be studied and understood. In order to do so, all waves in the atmosphere and in the ocean are initially filtered out, and the coupled system is purely thermodynamic. An air‐ocean coupled model designed especially for the low wind speed condition is employed to test the basic thermodynamic feedback mechanism between clouds and the ocean mixed layer. The model has four parts: (1) a shallow‐water system for the large‐scale atmosphere motion; (2) a cloud model, (3) a marine atmospheric boundary layer, in which the physical processes are parameterized into the bulk formulae through a geostrophic drag coefficient and corresponding heat and moisture exchange coefficients; and (4) an oceanic mixed layer model. The coupled model is solved analytically as an eigenvalue problem. Three nondimensional model parameters are found to be very important in separating growing or decaying, oscillatory or nonoscillatory modes: (1) the ocean surface stability index, ϵ; (2) the surface water budget index, γ; and (3) the mean diapycnal gradient of the spiciness (χ) in the entrainment zone, δ. The sign of ϵ divides the ocean mixed layer into shallowing (ϵ > 0) and entrainment (ϵ < 0) regimes. The value of γ indicates the strength of the water budget versus the heat budget at the ocean surface. The net freshwater influx (e.g., precipitation exceeding evaporation) destabilizes the coupled cloud and ocean mixed layer. In the entrainment regime, however, the parameter δ becomes important. The unstable oscillation only appears when the entrainment zone is salinity dominated. When δ exceeds a criterion that depends upon ϵ and γ, the oscillatorily growing modes will be generated. The model results show that the criteria are: δ > 20ϵ + 11 for γ = −0.1, δ > 20ϵ + 11.8 for γ = −0.2, and δ > 20ϵ + 14.6 for γ = −0.5. The model results also demonstrate that the exchanges of heat and water across the sea surface lead to both growing and decaying modes of oscillation on two different time scales, owing to the stability of the atmosphere. For an unstable atmosphere the time scale is about 20–30 days. However, the time scale is approximately 1–3 years for a stable atmosphere. This work introduces the new concept of two‐phase thermodynamics for the coupled air‐ocean system. Both atmosphere and ocean have two important thermodynamical variables: temperature and moisture (or fractional cloudiness) for the atmosphere, and temperature and salinity for the ocean. If salinity is neglected in the ocean model, no positive feedback mechanism will be possible in the coupled air‐ocean system.
On the net surface heat flux into the western equatorial Pacific
Authors: Godfrey J. S. , Nunez M. , Bradley E. F. , Coppin P. A. , Lindstrom E. J.
Published: December 2012

Downward longwave and shortwave radiation fluxes were measured for 13 days in May 1988 in the equatorial west Pacific; estimates of net radiation fluxes from these data were checked against a net radiometer over 9 days. The pyrgeometer observations were corrected to match the net radiometer measurements at night, when the latter is substantially more accurate. These measurements were compared with various empirical formulae. Three widely used empirical formulae for net longwave radiation out of the ocean consistently underestimated our observations by up to 21 ± 5 W m−2; however, the Brunt‐Budyko formula had no systematic bias. Two empirical formulae for the daily mean net shortwave radiation entering the ocean both overestimated the observations by up to 17 W m−2, although the scatter of daily estimates from observation was about ±30 W m−2. Routine ship's meteorological observations were used to estimate turbulent heat fluxes, with four empirical formulae. The 18‐day means differed by up to 28 W m−2, due to different treatment of the increase in bulk transfer coefficient at low wind speed. The Liu et al. (1979) algorithm gave the highest fluxes, and agreed well with direct measurements of turbulent fluxes reported elsewhere. A further systematic error in the measurement of air‐sea temperature difference accounted for about 11 W m−2. These systematic errors all tend to reduce the net heat flux into the ocean; their sum is as much as 60–75 W m−2 for some choices of empirical formulae. This tends to confirm the hypothesis of Godfrey and Lindstrom (1989) that ocean mixing and advection are too weak to carry a substantial heat flux away from the mixed layer of this region. Temperature profiles collected near 4°S, 150°E showed a clear warming from May 8 to May 20 in the top 20 m, equivalent to a heat storage rate of about 30 W m−2. Directly measured radiation fluxes were available for 10 days of this period of calm, sunny weather; turbulent heat fluxes were estimated for the same period with the Liu et al. (1979) algorithm. The net heat flux into the water estimated in this way averaged 38 W m−2. While the heat flux measurements were made as much as 400 km from the site of the heat storage observations, our observations provide some support, at least in calm weather, for the hypothesis that the net heat flux into this region is only of order 10 W m−2.
Measurements of sensible and latent heat flux in the western equatorial Pacific Ocean
Authors: Bradley E. F. , Coppin P. A. , Godfrey J. S.
Published: December 2012

Micrometeorological measurements, including direct eddy‐correlation measurements of heat and moisture fluxes, have been made from shipboard under light‐wind conditions in the western equatorial Pacific warm pool. Air‐sea temperature differences were typically 1.5°–2°C, that is, 1°–1.5°C larger than long‐term averages from merchant ship data. A sea surface “cool skin” of about 0.3°C was observed. Bulk transfer coefficients for both fluxes agree well with the predictions of Liu et al. (1979) in the convective wind speed regime below 4 m s−1. Between 4 and 6 m s−1 values of the neutral exchange coefficients were CEN ‐ 0.89 × 10−3; CHN = 1.03 × 10−3; CDN = 1.16 × 10−3. At zero mean wind speed, latent heat flux is maintained at about 25 W m−2 by convective exchange. Inertial dissipation estimates of the latent heat flux are about 20% lower than the directly measured eddy‐correlation values below 4 m s−1.
Simultaneous observations of sea surface temperature in the western equatorial Pacific Ocean by bulk, radiative and satellite methods
Authors: Coppin P. A. , Bradley E. F. , Barton I. J. , Godfrey J. S.
Published: December 2012

The increasing reliance on satellite observations for mapping and following changes in sea surface temperature (SST) has renewed interest in the measurement of the skin temperature of the ocean surface. In this experiment, skin surface temperature was measured with a narrow‐band radiometer over a 13‐day period in the western equatorial Pacific Ocean and compared with bulk sea temperatures and satellite‐derived estimates. A cool skin was found to be a quasi‐permanent feature in this region; its temperature averaged 0.3°C less than the bulk sea temperature. Conventional models for the cool skin were found to give a reasonable fit down to wind speeds of 1 m s−1. Satellite measurements showed some deviations from the true SST values, a result not unexpected, considering the substantial corrections required as a result of the high atmospheric water vapor content in these latitudes.
The mixed layer of the western equatorial Pacific Ocean
Authors: Lukas Roger , Lindstrom Eric
Published: December 2012

The mixed layer of the western equatorial Pacific and its thermodynamics are poorly known because of a general lack of data. Conductivity‐temperature‐depth (CTD) profiles from the recent Western Equatorial Pacific Ocean Circulation Study (WEPOCS) cruises have been analyzed for various measures of the upper layer and mixed layer thickness, using criteria which depend on vertical gradients of temperature, salinity, and density. From 434 profiles, the average mixed layer depth in the western equatorial Pacific during the two WEPOCS cruises was 29 m, which is about a factor of 3 shallower than had previously been thought. The mean depth of the top of the thermocline was found to be 64 m, so there is a nearly isothermal layer that is deeper than the mixed layer. This discrepancy is attributable to salinity stratification. It is hypothesized that the waters in this “barrier” layer between the bottom of the mixed layer and the top of the thermocline are formed to the east of the WEPOCS region, and subducted below the shallow and lighter mixed layer waters found in the west. Under light wind conditions, there was a tendency for warm and thin layers to form at the sea surface as a result of diurnal heating; however, there did not appear to be any nighttime maximum to the mixed layer depth associated with convective overturn due to cooling. This contrast with the central Pacific may be caused by the influence of salinity on the thermodynamics of the mixed layer. A strong westerly wind burst was observed during WEPOCS II, and apparently the mixed layer nearly doubled in depth while cooling by more than 1°C. Evidence of downwelling near the equator, and upwelling off the equator, was seen in the distribution of temperature, salinity, and density in the meridional section along 143°E, which was occupied immediately following the wind event. This event was apparently strong enough to erode through the salinity‐stratified layer and into the thermocline, resulting in the observed cooling. The results of this study suggest that except during strong wind events, entrainment cooling may not be an important component of the heat budget of the western Pacific warm pool. This has potentially important implications for the El Niño/Southern Oscillation (ENSO) phenomenon.
Monitoring the 1979‐1985 equatorial Pacific current transports with expendable bathythermograph data
Authors: Picaut Joël , Tournier Rolande
Published: December 2012

Geostrophic transports of the major equatorial currents, including the Equatorial Undercurrent and the South Equatorial Current, have been estimated on a bimonthly basis in the central and western Pacific over the 1979‐1985 period. This was made possible by a collection of carefully checked expendable bathythermograph (XBT) data and a few hydrocast and conductivity‐temperature‐depth data. This collection considerably improved the number and quality of temperature profiles of the original Institut Français de Recherche Scientifique pour le Développement en Coopération (ORSTOM)‐Scripps Institute of Oceanography tropical Pacific XBT Ship‐of‐Opportunity Program. The temperature profiles were first grouped, independently of longitude, in regions around mean XBT tracks. Dynamic heights were then calculated relative to 400 dB through a T‐S relationship deduced from the climatological Levitus file. Geostrophic currents were calculated along the roughly south‐north oriented Fiji‐Hawaii and New Caledonia‐Japan mean XBT tracks, using a specific technique. This technique, which combines Fourier filtering in the meridional direction and in time, also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field. The filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents, using the mean of data collected along 165°E during six Tropical Ocean and Global Atmosphere (TOGA)‐ORSTOM cruises. Finally, transports of the main equatorial currents were computed in a subjective way between 20°N and 20°S, 0–400 m using monthly charts of geostrophic currents along the two mean XBT tracks. The transports in the central Pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the Hawaii‐Tahiti Shuttle Experiment in 1979‐1980 and during the Line Island Profiling Project‐Pacific Equatorial Ocean Dynamics Experiment in 1982‐1983. Reasonable agreement demonstrates that it is possible to use XBT data for transport indexes of the major equatorial currents in the central and western Pacific.
Papers from the Western Pacific International Meeting and Workshop on TOGA/COARE
Authors: Lukas Roger , Webster Peter , Picaut Joël
Published: December 2012

This special issue of the Journal of Geophysical Research is remarkable in bringing together papers relating to the coupled ocean‐atmosphere system, with emphasis on the western tropical Pacific region, and in doing so, temporarily reuniting the “Oceans” and the “Atmospheres” sections of the journal. In the western Pacific, the so‐called “warm pool,” containing the world's warmest open ocean surface waters is found. Here vigorous and complex air‐sea interactions are occurring on time scales ranging from intradiurnal to interannual, and on spatial scales ranging from a few kilometers (individual convective clouds), to the westerly wind burst which interacts with the ocean over thousands of kilometers, and to the 30‐ to 60‐day oscillation, which is global in scale but which is most energetic in the warm‐pool region. Understanding these interactions is extremely important for modeling and prediction of both short‐ and long‐term climate variability [TOGA COARE Panel, 1990], since the deep convection over the warm pool provides the strongest heating source of the global upper troposphere.
Interannual fluctuations of intraseasonal variance of near‐equatorial zonal winds
Authors: Gutzler David S.
Published: December 2012

Interannual fluctuations of intraseasonal variance are investigated in zonal wind time series from six stations in the near‐equatorial eastern Indian and western Pacific Oceans, in order to document the interannual variability of the Madden‐Julian oscillation. Each time series is subjected to band‐pass filtering that retains fluctuations with periods between about 30 and 60 days. The variance of the filtered data is calculated for each season in the data record and is compared with the variance of unfiltered wind anomalies and with the interannual variance of seasonal means. The principal systematic interannual modulation of 30‐ to 60‐day wind variance occurs in time series of lower tropospheric winds (surface and 850 mbar) at the stations between 14°E and the international date line, where intraseasonal variance is enhanced during the well‐developed stages of El Niño‐Southern Oscillation warm events. No systematic interannual modulation of intraseasonal zonal wind variance is found in the records from stations west of 140°E or in 200‐mbar zonal winds.
El Niño/Southern Oscillation and Madden‐Julian (30–60 day) oscillations during 1981–1982
Authors: Weickmann K. M.
Published: December 2012

An important issue in understanding the low‐frequency oscillations of the atmosphere and the ocean‐atmosphere system concerns the role of transients during individual events. This question is examined from an observational point of view for the period from September 1981 to April 1982, which includes the transitional phase of the 1982–1983 El Niño/Southern Oscillation (ENSO) cycle, as well as six Madden‐Julian (30–60 day) oscillations (MJO). For the developing ENSO, it is shown that interannual transitions in the anomalous atmospheric circulation and in the sea surface temperatures in the western‐central Pacific coincide with the passage of strong MJOs from the Indian to Pacific oceans. For a MJO during December 1981, evidence is provided that the shift of convection from the eastern Indian Ocean to the western Pacific Ocean involves transients having periods around 10 days. The role of transients is discussed from the perspective of these interannual and intraseasonal modes.
Temporal and compositional diversity in seafloor hydrothermal fluids
Authors: Von Damm K. L.
Published: December 2012

Within the last 4 years a number of discoveries have significantly improved our understanding of the processes occurring in seafloor hydrothermal systems, and their net effects on the chemical and physical properties of the fluids. Prior to the 1990's time series samplings of vent fluids suggested that they were characterized by great temporal stability in their chemistry [e.g., Campbell et al, 1988]. In the late 1980's, the discoveries of megaplumes in the water column over the Juan de Fuca Ridge provided evidence for the episodicity of hydrothermal processes [Baker et al, 1987]. We therefore had a basic contradiction in our observations ‐ astounding temporal stability in the vent systems that had been sampled numerous times (primarily 21°N East Pacific Rise (EPR), Guaymas Basin, South Cleft on the Juan de Fuca Ridge) (Figure 1) versus the water column evidence for temporal variability. The observation of volcanic eruptions at three sites on the world ridge crest system has provided the resolution to this apparent contradiction, and provided new insights into the evolution of seafloor hydrothermal systems. Direct information on the third dimension of a hydrothermal system became available for the first time, with the successful drilling of an active hydrothermal site at Middle Valley by the Ocean Drilling Program (ODP). Evaluating the hydrothermal input to the ocean (i.e., the flux) has become more problematic, but progress in understanding the underlying processes responsible for controlling vent chemistry, and in defining the flux of chemicals from the ocean ridge flanks, are important steps to eventual resolution of the flux question.
Lightning research: 1991–1994
Authors: Beasley William H.
Published: December 2012

The guidelines request that articles include three principal sections: (i) fundamental process science (basic or “curiosity” research), (ii) applied science (that is, directed or “mission‐oriented” research) and (iii) implementation (research in support of commercial use or operational application of the results of basic or directed research). The ends of basic research on lightning are, to understand the processes of electrical discharges in the atmosphere, to understand the effects of lightning on and relation of lightning to other physical processes in the atmosphere, and to gain insights into the processes whereby thunderstorms become electrically charged. The principal means to these ends are observations, mainly of the electromagnetic emissions (radio‐frequency, infrared, visible, ultraviolet, and occasionally x‐ray) associated with lightning. Often the observational results are interpreted or extended through use of mathematical models. Because it is very difficult to obtain good observational data on natural lightning, the community has been making increasing use of rockets with trailing wires to trigger lightning when and where it is desired. Interferometric and time‐of‐arrival observations of radio‐frequency emissions, intended to elucidate the temporal and spatial structure of discharge channels within storm clouds, show considerable promise for significant advancements in our basic understanding of lightning discharges. Applied, or mission‐oriented, lightning research is concerned with meteorological and climatological application of lightning data and with the effects of lightning on electrical and electronic systems, property, and living things, humans in particular. It is not easy to draw the line between the category of applied research and the third category, “implementation”. Commercial use and operational applications of lightning data are well underway, but not necessarily as a result of research dedicated to bridging the gap between basic and applied science, on the one hand, and commercial or operational application, on the other. Indeed, it appears that many papers that address commercially important issues or operational application, at least in part, easily fall under the more traditional category of applied research. This suggests that perhaps the distinction is an. artificial one. Nevertheless, the author has attempted to address the intent of the guidelines with a section on work that most directly relates to commercial and operational applications.
Helium‐3 in the Guaymas Basin: Evidence for injection of mantle volatiles in the Gulf of California
Authors: Lupton John E.
Published: December 2012

Helium isotope measurements in six major basins in the Gulf of California show that the deep Guaymas Basin has 3He/4He 65–70% higher than atmospheric helium, clear evidence of mantle helium injection. Smaller 3He excesses observed in the Carmen and Farallon basins may be derived from this Guaymas Basin anomaly. The 3He concentrations in the Mazatlan Basin in the mouth of the Gulf of California are similar to average eastern Pacific values, indicating that the Gulf does not provide a significant flux of 3He into the general Pacific circulation. On the basis of temperature and salinity measurements an upper limit of 0.28°C can be placed on the amount of geothermal heating observed in any of the basins. The isotopic ratio of the injected Guaymas Basin helium is found to be 3He/4He = (1.10±0.06) × 10−5, almost identical to the helium signature observed at the Galapagos Rift but somewhat lower than the average ratio in oceanic basalt glasses.
Geology of a submarine hydrothermal field, Mid‐Atlantic Ridge, 26°n latitude
Authors: Temple Darcy G. , Scott Robert B. , Rona Peter A.
Published: December 2012

A comparison of structural and lithologic features observed from two stereophotographic traverses of the Trans‐Atlantic Geotraverse (TAG) hydrothermal field, 26°N, Mid‐Atlantic Ridge, with features of the French‐American Mid‐Ocean Undersea Study (Famous) hydrothermal site and the Mounds hydrothermal field of the Galapagos spreading center shows that all three areas have hydrothermal deposits with restricted and patchy lateral extent and are associated with closely spaced normal faults commonly of small displacement. No one lithology characterizes either the rocks or the sediments that underlie the hydrothermal deposits. Regions without hydrothermal manganese oxide deposits such as the rift valley at 37°N in the Famous area exhibit larger and fewer faults and lack the abundant permeable semiconsolidated breccia seen at 26°N. Thus structural factors which facilitate hydrothermal circulation by enhancing permeability appear critical to hydrothermal deposition. Structural features of the rift valley wall at 26°N include inward facing normal faulting, outward facing normal faulting, and outward tilting by rotation of fault blocks. These observations support a viscous drag mechanism of uplift of the rift valley walls.
Acoustic fluidization: A new geologic process?
Authors: Melosh H. Jay
Published: December 2012

A number of geologic processes, particularly seismic faulting, impact crater slumping, and long runout landslides, require the failure of geologic materials under differential stresses much smaller than expected on the basis of conventional rock mechanics. This paper proposes that the low strengths apparent in these phenomena are due to a state of ‘acoustic fluidization’ induced by a transient strong acoustic wave field. The strain rates possible in such a field are evaluated, and it is shown that acoustically fluidized debris behaves as a newtonian fluid with a viscosity in the range 105–107 P for plausible conditions. Energy gains and losses in the acoustic field are discussed, and the mechanism is shown to be effective if internal dissipation in the field gives a Q ≳ 100. Whether such values for Q are realized is not known at present. However, acoustic fluidization provides a qualitatively correct description of the failure of rock debris under low differential stresses in the processes of faulting, crater slumping, and long runout landslides. Acoustic fluidization thus deserves serious consideration as a possible explanation of these phenomena.
On the structure of two‐phase hydrothermal flows in permeable media
Authors: Sheu J. P. , Torrance K. E. , Turcotte D. L.
Published: December 2012

Numerical solutions are obtained for the ascending convection of ground water with boiling. The results are applicable to geothermal reservoirs above cooling igneous intrusions. The steady vertical flow of water in a uniform permeable medium is assumed. Pressure release boiling results in a two‐phase, steamwater zone. Within this zone, steam percolates upward relative to water. Near the surface is a water zone due to conductive cooling. The conductive cooling prevents boiling at low water flow rates. Calculated results are compared with temperature and pressure logs from drill holes in the thermal systems of Steamboat Springs, Nevada, and Yellowstone National Park, Wyoming.
Release adiabat measurements on minerals: The effect of viscosity
Authors: Jeanloz Raymond , Ahrens Thomas J.
Published: December 2012

The current inversion of pressure‐particle velocity data for release from a high‐pressure shock state to a pressure‐density path usually depends critically upon the assumption that the release process is isentropic. It has been shown by Kieffer and Delaney that for geological materials below stresses of ∼150 GPa, the effective viscosity must be ≲103kg m−1 s−1 (104 P) in order that the viscous (irreversible) work carried out on the material in the shock state remains small in comparison to the mechanical work recovered upon adiabatic rarefaction. The available data pertaining to the offset of the Rayleigh line from the Hugoniot curve for minerals, the magnitude of the shear stress in the high‐pressure shock state for minerals, and the direct measurements of the viscosities of several engineering materials shocked to pressures below 150 GPa yield effective viscosities of ∼103kg m−1 s−1 or less. We infer that this indicates that the conditions for isentropic release of minerals from shock states are achieved, at least approximately, and we conclude that the application of the Riemann integral to obtain pressure‐density states along the release adiabats of minerals in shock experiments is valid.
Interrelation of flow or fracture and phase transition in the deformation of carbonate rock
Authors: Grady D. E.
Published: December 2012

Shock wave, ultrasonic, hydrostatic, and triaxial compression data for carbonate rock are considered in terms of the mechanisms of yielding. The results suggest that yielding by flow or fracture can be replaced by phase transformation for selected stress paths. For certain calcite rocks, these stress paths include uniaxial strain loading. The results further suggest that when initial yielding is by flow or fracture, behavior is strain rate dependent. This is apparently the case for Vermont marble and Blair dolomite, as comparison of the dynamic and quasi‐static stress‐strain paths and yield stress under uniaxial‐strain loading indicates. In contrast, similar comparisons for Solenhofen limestone and Oakhall limestone show little rate dependence, suggesting that the apparent initial yielding is dominated by onset of the calcite I‐II phase transition. Both static and dynamic studies show that the I‐II transition in calcite rock is largely rate independent, reversible, continuous (gradual), and shear stress sensitive. Rate independence and reversibility are apparently the consequence of a displacive and coherent phase transformation. Continuous transformation appears to be due to rock microstructure which leads to stress concentrations and hence a spread in the macroscopic stress region over which the transition occurs. Shear stress sensitivity can be due to both microscopic dependence of the transition on local shearing stresses and shear stress dependence of the microstructural stress inhomogeneities.