Function Of Potential Temperature Research Articles

Spatiotemporal changes of ocean carbon species in the western North Pacific using parameterization technique

We constructed parameterizations for the estimation of dissolved inorganic carbon (DIC) and pH in the western North Pacific, including Japanese coastal regions. Parameterizations, determined as a function of potential temperature (θ) and dissolved oxygen (DO), provided strong correlations with direct measurements for DIC [the coefficient of determination (R2) = 0.99; the root mean square error (RMSE) = 8.49 µmol kg−1] and pH (R2 = 0.98, RMSE = 0.030). Predicted DIC and pH values were consistent with previous independent hydrographic observations, generally within 3 µmol kg−1 for DIC and 0.010 for pH. By applying these parameterizations to climatological seasonal θ and DO data and time-series θ and DO data from autonomous profiling floats (Argo) in the western North Pacific, large spatiotemporal variations in DIC and pH were demonstrated. Results indicated that the rate of increase in anthropogenic DIC above a depth of 400 m along 30° N in the western North Pacific was + 0.86 ± 0.11 µmol kg−1 year−1 between 1994 and 2004. This decreased by + 0.58 ± 0.05 µmol kg−1 year−1 after 2004 partly due to increasing anthropogenic nitrogen input, suggesting that the decrease has induced the slowdown of ocean acidification in the western North Pacific. The declining trend in anthropogenically induced ocean pH was found to be 0.0021 ± 0.0016 during 1994–2013.

Aircraft-based measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition

Abstract. The sources, chemical transformations and removal mechanisms of aerosol transported to the Arctic are key factors that control Arctic aerosol–climate interactions. Our understanding of sources and processes is limited by a lack of vertically resolved observations in remote Arctic regions. We present vertically resolved observations of trace gases and aerosol composition in High Arctic springtime, made largely north of 80∘ N, during the NETCARE campaign. Trace gas gradients observed on these flights defined the polar dome as north of 66–68∘ 30′ N and below potential temperatures of 283.5–287.5 K. In the polar dome, we observe evidence for vertically varying source regions and chemical processing. These vertical changes in sources and chemistry lead to systematic variation in aerosol composition as a function of potential temperature. We show evidence for sources of aerosol with higher organic aerosol (OA), ammonium and refractory black carbon (rBC) content in the upper polar dome. Based on FLEXPART-ECMWF calculations, air masses sampled at all levels inside the polar dome (i.e., potential temperature <280.5 K, altitude <∼3.5 km) subsided during transport over transport times of at least 10 days. Air masses at the lowest potential temperatures, in the lower polar dome, had spent long periods (>10 days) in the Arctic, while air masses in the upper polar dome had entered the Arctic more recently. Variations in aerosol composition were closely related to transport history. In the lower polar dome, the measured sub-micron aerosol mass was dominated by sulfate (mean 74 %), with lower contributions from rBC (1 %), ammonium (4 %) and OA (20 %). At higher altitudes and higher potential temperatures, OA, ammonium and rBC contributed 42 %, 8 % and 2 % of aerosol mass, respectively. A qualitative indication for the presence of sea salt showed that sodium chloride contributed to sub-micron aerosol in the lower polar dome, but was not detectable in the upper polar dome. Our observations highlight the differences in Arctic aerosol chemistry observed at surface-based sites and the aerosol transported throughout the depth of the Arctic troposphere in spring.

Temperature–Salinity Structure of the North Atlantic Circulation and Associated Heat and Freshwater Transports

Abstract This study investigates the circulation structure and relative contribution of circulation components to the time-mean meridional heat and freshwater transports in the North Atlantic, using numerical results of a high-resolution ocean model that are shown to be in excellent agreement with the observations. The North Atlantic circulation can be separated into the large-scale Atlantic meridional overturning circulation (AMOC) that is diapycnal and the subtropical and subpolar gyres that largely flow along isopycnal surfaces but also include prominent gyre-scale diapycnal overturning in the Subtropical Mode Water and Labrador Sea Water. Integrals of the meridional volume transport as a function of potential temperature θ and salinity S yield streamfunctions with respect to θ and to S, and heat functions. These argue for a significant contribution to the heat transport by the southward circulation of North Atlantic Deep Water. At 26.5°N, the isopycnic component of the subtropical gyre is colder and fresher in the northward-flowing western boundary currents than the southward return flows, and it carries heat southward and freshwater northward, opposite of that of the diapycnal component. When combined, the subtropical gyre contributes virtually zero to the heat transport and the AMOC is responsible for all the heat transport across this latitude. The subtropical gyre however significantly contributes to the freshwater transport, reducing the 0.5-Sv (1 Sv ≡ 106 m3 s–1) southward AMOC freshwater transport by 0.13 Sv. In the subpolar North Atlantic near 58°N, the diapycnal component of the circulation, or the transformation of warm saline upper Atlantic water into colder fresher deep waters, is responsible for essentially all of the heat and freshwater transports.

Integral descriptors of the vertical structure of the ocean

We propose a simple polynomial expression for neutral density and nutrients as a function of potential temperature, pressure and salinity. The expression is applied to the 1988 North Atlantic A16N WOCE meridional section and the polynomial coefficients are calculated using an inverse technique. The resulting polynomials show good skill in reproducing the nutrients and density structure, as verified through an analysis of variance (ANOVA) test. The large-scale changes in the polynomial coefficients occur between equatorial (E), tropical (T), subtropical (ST), and subpolar (SP) waters. The temperature and pressure coefficients experience substantial changes at all transitions (E-T, T-ST, and ST-SP), while the salinity ones only have major variations at the T-ST transition. Mesoscale-like oscillations occur all along the section but are relatively small, except between about 40 and 50°N, in a region of rough bottom topography. The density field is reconstructed using individual and group coefficients, and the contribution of each coefficient is identified. The method is also applied to analyze the neutral density distribution in a nearly identical 2003 section, removing near-surface density values that may be related to different warming/cooling of the surface layer. The results show close resemblances but also some significant variations, which are discussed in terms of interdecadal variability. Hence, we argue that the set of calculated coefficients provides good integral descriptors for the vertical structure of the ocean.

Formation and pathways of North Atlantic Deep Water in a coupled ice–ocean model of the Arctic–North Atlantic Oceans

We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation. Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models, owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water) leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar convection is found in other models, we discuss broader implications.

Refinements in the use of equivalent latitude for assimilating sporadic inhomogeneous stratospheric tracer observations, 2: Precise altitude-resolved information about transport of Pinatubo aerosol to very high latitude

Abstract. From high latitude lidar observations, quite precise information is extracted about the temporal evolution and vertical distribution of volcanic aerosol in the high latitude lower stratosphere following the eruption of Mount Pinatubo. Irreversible mixing of lower stratospheric aerosol, to the arctic pole during early 1992, is demonstrated, as a function of potential temperature and time. This work complements previous studies, which either identify vortex intrusions - without demonstrating irreversible transport, or use lower resolution satellite observations. The observed transport is associated tentatively with the vortex disturbance during late January, 1992. A very large number of high resolution lidar observations of Mount Pinatubo aerosol are analysed, without any data averaging. Averaging in measurement or analysis can cause tracer mixing to be overestimated. Averaging in the analysis can also require assumptions about which quantity has the dominant error (in this case, the equivalent latitude coordinate or the measurement), and which part of the data contains real structure. The method below attempts to avoid such assumptions.

A climatology of stratospheric polar vortices and anticyclones

United Kingdom Meteorological Office global analyses from 1991 to 2001 are used to create a global climatology of stratospheric polar vortices and anticyclones. New methodologies are developed that identify vortices in terms of evolving three‐dimensional (3‐D) air masses. A case study illustrates the performance of the identification schemes during February and March of 1999 when a merger of anticyclones led to a stratospheric warming that split the Arctic polar vortex. The 3‐D structure and temporal evolution of the Arctic vortex and identified anticyclones demonstrates the algorithm's ability to capture complicated phenomena. The mean geographical distribution of polar vortex and anticyclone frequency is shown for each season. The frequency distributions illustrate the climatological location and persistence of polar vortices and anticyclones. A counterpart to the Aleutian High is documented in the Southern Hemisphere: the “Australian High.” The temporal evolution of the area occupied by polar vortices and anticyclones in each hemisphere is shown as a function of potential temperature. Large polar vortex area leads to an increase in anticyclone area, which in turn results in a decrease in the size of the polar vortex. During Northern winter and Southern spring, 9 years of daily anticyclone movement are shown on the 1200 K (36 km, 4 hPa) isentropic surface. Preferred locations of anticyclogenesis are related to cross‐equatorial flow and weak inertial stability. Regimes of traveling and stationary anticyclones are discussed.

Interpolation of TC0 2 data on a 1° × 1° grid throughout the water column below 500 m depth in the Atlantic Ocean

We have combined the available total CO 2, temperature, salinity and oxygen data from the TTO, SAVE and WOCE programs in the Atlantic Ocean to parameterize TCO 2 below 500 m depth as a function of potential temperature, salinity and apparent oxygen utilization. We then use the Levitus data set of temperature, salinity and oxygen to compute the TCO 2 profiles at the resolution of the Levitus data set on a 1° × 1° grid with a vertical resolution of 33 layers, more densely spaced in the upper 1500 m than below. Depending on the method used to interpolate the data (along isopycnals or vertically by station), the estimated random uncertainty of the computed TC0 2 values in the Atlantic Ocean throughout the water column below the wintertime mixed layer depth ranges from ± 7.1 μmol kg −1 to t 5.9 μmol kg −1.

POAM II ozone observations in the Antarctic ozone hole in 1994, 1995, and 1996

We present an overview of Polar Ozone and Aerosol Measurement (POAM) II satellite‐based observations of ozone in the Antarctic ozone hole in 1994, 1995, and 1996. The POAM II observations are consistent with previous observations suggesting that ozone loss in the ozone hole is confined to the polar vortex. Ozone concentrations are observed to decrease by nearly a factor of 10 near 20 km during the ozone hole formation period, and a reduction in ozone was observed up to 24 km. The timing of ozone loss and recovery was similar in each year. Ozone concentrations begin to decrease in July, and the period of largest depletion observed by POAM II occurs between early September and early October, when the observations are obtained at high southern latitudes (82°–88°S) near the vortex center. However, ozone concentrations were consistently lower (by about 10%) in 1996, throughout the ozone hole altitude region and time period, than in the other two years. We have also used the POAM II observations to compute vertical profiles of monthly averaged ozone photochemical loss rates as a function of potential temperature in August (450–800 K) and September (450–700 K) of each year, incorporating a correction for diabatic descent. We find that the ozone loss rates are not significantly different from zero in August 1994 at any potential temperature level. However, we do find significant chemical loss in August 1995 below 600 K, and in August 1996 at all levels up to 700 K. Maximum monthly averaged ozone chemical loss rates occurred in September near 500 K in each year (1994: 0.1±0.004 parts per million by volume per day (ppmv/d); 1995 and 1996: 0.08±0.004 ppmv/d). Generally, in September, loss rates were larger in 1994 than in 1995 and 1996 below 550 K, and above 550 K the largest loss rates occurred in 1996. We find significant chemical loss up to at least 700 K in September in all three years. Finally, the POAM II observations show that in late spring, after the ozone hole chemical processing has been completed, ozone mixing ratios are lower inside the Antarctic vortex (relative to outside the vortex) at all levels between at least 450 K and 1500 K, presumably resulting from a combination of dynamical and chemical effects.

An Equation of State for Use in Ocean Models: Eckart’s Formula Revisited

Abstract Approximate formulas for in situ density as a function of potential temperature, salinity, and pressure are determined for use in numerical models. The approach taken is similar to that of Mellor, but use of the Tumlirz equation of state results in formulas that are somewhat simpler and more computationally efficient. Comparison is made with results obtained from the full United Nations Educational, Scientific and Cultural Organization equation of state and with the results obtained from the sound speed equation of Del Grosso. The corresponding formulas relating in situ density to the in situ temperature are also given.

Temporal variation in primary magma compositions in the northeast Japan Arc

Abstract A remarkable temporal variation in primary magma compositions has been found in the Northeast Japan arc. The trench‐side magmas have become more enriched in FeO* and the backarc‐side magmas have become more depleted in FeO* while retaining almost constant SiO, levels for the last ∼20 million years. In order to understand the origin of the temporal variation, FeO* and SiO, contents in partial melts are modeled for an adiabatically‐rising mantle as a function of potential temperature and original composition of the mantle material. The result demonstrates that the primary magmas that are more depleted in FeO* were derived from the mantle materials either at lower potential temperatures or with compositions more depleted in basaltic components. A possible mechanism for the inferred primary magma variability is the change in depth intervals with time of magma production in a compositionally‐layered mantle wedge; greater degrees of depletion at a greater depth is reconciled with a probable thermal regime in the mantle wedge.

Distribution of ozone laminae during EASOE and the possible influence of inertia‐gravity waves

The distribution of laminae in ozone has been determined from the EASOE ozonesonde archive as a function of potential temperature and potential vorticity. Results confirm previous studies that laminae are absent above ∼450K within the vortex, and are most abundant near its edge. Observations of inertia‐gravity waves in the lower stratosphere appear to suggest that such waves are not of sufficiently large amplitude to cause the kinds of laminae that are observed.

Boundary layer structure in two fronts passing a tower

The atmospheric boundary layer in an ana-cold front and in a kata-cold front is investigated using measurements at a 200 m high tower near Karlsruhe, Germany. In the ana-cold front the wind speed decreased, whereas the passage of the kata-cold front was accompanied by strong gusts. The frontogenesis function of potential temperature was only weak. Turbulence increased at the fronts as expressed by the turbulent kinetic energy. However, the turbulent vertical momentum flux was relatively inefficient at the passage of the fronts. Also it is attempted to calculated flux profiles and friction in the cold air.

Stokes Diffusion by Atmospheric Internal Gravity Waves

Abstract Owing to the stochastic action of Stokes drift induced by a spectrum of noninteracting gravity waves, a parcel of air subject to a spectrum of randomly superposed waves will be displaced, on average, an increasing distance from an initial position as time goes on. The effect of this drift on an ensemble of parcels is to induce a diffusive-like growth in time of the mean-square separation between parcels. We refer to this process as Stokes diffusion. We have calculated trajectories for an ensemble of parcels moving under the influence of a spectrum of gravity waves and have found vertical diffusion coefficients inferred from the dispersion of parcels on the order of 102 m s−2, which is comparable to the values usually attributed to turbulence. If a constituent is distributed as a function of potential temperature, the dispersion due to conservative waves is not apt to accomplish a significant vertical transport. However, if the constituent has a significant gradient on wave-perturbed potential tem...

The Vertical Motion of Submesoscale Coherent Vortices across Neutral Surfaces

Abstract Submesoscale coherent vortices (SCVs, “meddies” or “bullets”) are shown not to move along either potential density surfaces or neutral surfaces, due to the compressibility of sea water being a function of potential temperature and salinity. While it has been recognized that SCVs may make an important contribution to lateral property fluxes in the ocean, it is shown in this paper that they can also cause significant vertical fluxes across neutral surfaces. Since they represent the slow vertical translation of macroscopic water masses, these fluxes are not measurable with microstructure measurements of the dissipation of kinetic energy, but are nonetheless real. These vertical fluxes of heat and salt can be either down-gradient or up-gradient, corresponding to either a positive or a negative vertical diffusivity. The magnitude of the effective diffusivity for salt is different from that for heat. Formulae are derived for estimating the mean vertical velocity of SCVs through neutral surfaces.

An oceanographic variable for the characterization of intrusions and water masses

An oceanographic variable ideally suited for characterizing the amount of mixing between water masses and also for quantifying the strength of intrusions is defined as a function of potential temperature and salinity. Previous attempts to derive a variable with such a property have led to functions which are (a) not mathematically well-defined and (b) not independent of the scales chosen for the potential temperature-salinity diagram. Our new variable does not suffer these problems. Variations of our variable τ along isopycnal surfaces are defined to be porportional to the contraction coefficient of salt, times the corresponding variation of salinity along the isopycnal surfaces. This property ensures that the difference in τ along an isopycnal surface between two water parcels is a meaningful measure of water property differences along iisopycnals. A polynomial expression is given for τ in terms of potential temperature and salinity and comparison are made, using oceanographic data, between the anomalies of τ, salinity, and Veronis' (1972, Journal of Marine Research, 30, 227–255) variable. This comparison indicates that for most purposes, the anomaly between water masses can be adequately found by multiplying the salinity anomaly (along isopycnals) by twice the local value of the haline contraction coefficient.

A Standard Analytic Curve of Potential Temperature versus Salinity for the Western North Atlantic

Abstract An algorithm is described for computing salinity as a continuous function of potential temperature for the western North Atlantic. The algorithm uses historical data compiled by Worthington and Melcalf (1961) for the deep western North Atlantic, and Iselin (1936) for shallow and intermediate waters of the same region.

Oxygen-Total Inorganic Carbon Dioxide Relationship in the Pacific Ocean*

The total inorganic carbon dioxide-oxygen relationship in the ocean has been studied previously using two different approaches, one of which is theoretical and the other is statistical. Discrepancies between the two sets of results have been solved in this work by applying multiple linear regression analysis to express total inorganic carbon dioxide, normalized to constant S‰, as a function of potential temperature and total alkalinity and oxygen normalized to constant S ‰. Results of the regression are in agreement with the assumption that total alkalinity changes in the open ocean are only due to S ‰ changes and calcium carbonate dissolution or precipitation; and with Redfield's model for the prediction of the total inorganic carbon dioxide-oxygen ratio for the biochemical oxidation.

Oxygen-total inorganic carbon dioxide relationship in the Pacific Ocean

The total inorganic carbon dioxide-oxygen relationship in the ocean has been studied previously using two different approaches, one of which is theoretical and the other is statistical. Discrepancies between the two sets of results have been solved in this work by applying multiple linear regression analysis to express total inorganic carbon dioxide, normalized to constant S‰, as a function of potential temperature and total alkalinity and oxygen normalized to constant S ‰. Results of the regression are in agreement with the assumption that total alkalinity changes in the open ocean are only due to S ‰ changes and calcium carbonate dissolution or precipitation; and with Redfield's model for the prediction of the total inorganic carbon dioxide-oxygen ratio for the biochemical oxidation.