Surface Potential Temperature Research Articles

A New Surface Model for β-Plane Turbulence

Abstract This paper introduces a new numerical model for studying wave–turbulence interactions in a continuously stratified rotating flow, having a uniform potential vorticity and a rigid boundary. The meridional variation in the Coriolis parameter (β effect), a channel geometry, and the first-order nonlinear terms in a small Rossby number expansion are included into the surface quasigeostrophic dynamics. The model contains important dynamical characteristics of three-dimensional flows such as advection by ageostrophic winds, and stretching and tilting of relative vorticity. Nevertheless, it has the computational economy of two-dimensional flows. Long-term direct numerical simulations are performed for decaying turbulence arising from random initial conditions. In addition to the formation of steady zonal jets, frequently reported as a possible end state under the β effect, this model exhibits several other realistic physical effects that were lacking in the previously studied β-plane models for wave–turbulence interactions. There is a significant contrast in the spatial and time scales of the formed eddies, resulting in high meridional asymmetry of the flow. Mean surface cooling and persistent large-scale blocking eddies are observed as well. The surface potential temperature variance spectrum exhibits a well-resolved k−5/3 inertial range.

A calibration method of Argo floats based on multiple regression analysis

Argo floats are free-moving floats that report vertical profiles of salinity, temperature and pressure at regular time intervals. These floats give good measurements of temperature and pressure, but salinity measurements may show significant sensor drifting with time. It is found that sensor drifting with time is not purely linear as presupposed by Wong (2003). A new method is developed to calibrate conductivity data measured by Argo floats. In this method, Wong’s objective analysis method was adopted to estimate the background climatological salinity field on potential temperature surfaces from nearby historical data in WOD01. Furthermore, temperature and time factors are taken into account, and stepwise regression was used for a time-varying or temperature-varying slope in potential conductivity space to correct the drifting in these profiling float salinity data. The result shows salinity errors using this method are smaller than that of Wong’s method, the quantitative and qualitative analysis of the conductivity sensor can be carried out with our method.

Some characteristics of the atmosphere during an adiabatic process*

Abstract Some important characteristics of the atmosphere during an adiabatic process are investigated, which include the invariability of atmospheric entropy range and local surface potential temperature, the conservation of the atmospheric mass intervened between any isentropic surface and the ground, and the isentropic surface intersecting with the ground. The analysis shows that the atmospheric reference state (ARS) for investigation on available potential energy (APE) should be defined objectively as the state which could be approached from the existing atmosphere by adiabatic adjustment, and be related to initial atmospheric state before adjustment. For the initial atmosphere state at any time, its corresponding ARS is different from the one at another time. Based on the above-mentioned total conclusions, the reference state proposed by Lorenz cannot be obtained physically, so a new conception, the conditional minimum total potential energy, is put forward in order to objectively investigate atmosph...

Measurements of NO, NO<sub>y</sub>, N<sub>2</sub>O, and O<sub>3</sub> during SPURT: implications for transport and chemistry in the lowermost stratosphere

Abstract. We present measurements of NO, NOy, O3, and N2O within the lowermost stratosphere (LMS) over Europe obtained during the SPURT project. The measurements cover all seasons between November 2001 and July 2003. They span a broad band of latitudes from 30° N to 75° N and a potential temperature range from 290 to 380 K. The measurements represent a comprehensive data set of these tracers and reveal atmospheric transport processes that influence tracer distributions in the LMS. Median mixing ratios of stratospheric tracers in equivalent latitude-potential temperature coordinates show a clear seasonal cycle related to the Brewer-Dobson circulation, with highest values in spring and lowest values in autumn. Vertical tracer profiles show strong gradients at the extratropical tropopause, suggesting that vertical (cross-isentropic) mixing is reduced above the tropopause. Pronounced meridional gradients in the tracer mixing ratios are found on potential temperature surfaces in the LMS. This suggests strongly reduced mixing along isentropes. Concurrent large gradients in static stability in the vertical direction, and of PV in the meridional direction, suggest the presence of a mixing barrier. Seasonal cycles were found in the correlation slopes ΔO3/ΔN2O and ΔNOy/ΔN2O well above the tropopause. Absolute slope values are smallest in spring indicating chemically aged stratospheric air originating from high altitudes and latitudes. Larger values were measured in summer and autumn suggesting that a substantial fraction of air takes a "short-cut" from the tropical tropopause region into the extratropical LMS. The seasonal change in the composition of the LMS has direct implications for the ozone chemistry in this region. Comparisons of measured NO with the critical NO value at which net ozone production changes from negative to positive, imply ozone production up to 20 K above the local tropopause in spring, up to 30 K in summer, and up to 40 K in autumn. Above these heights, and in winter, net ozone production is negative.

Real Front or Baroclinic Trough?

In a recent study, Sanders and Hoffman (2002, hereafter SH) found that only about half of the cold-front segments appearing on surface maps of the National Centers for Environmental Prediction (NCEP) from December 1999 through February 2000 were associated, even loosely, with a moderately strong surface baroclinic zone. In an earlier study (Sanders and Kessler 1999), some extreme examples had been identified in which an abrupt nocturnal temperature rise was analyzed as the passage of a cold front. These features are clearly not the type of structure described by Bjerknes (1918). To enlarge the sample of comparisons between analyzed fronts and baroclinic zones reported by SH, a comparison was made for the period between 7 February and 29 March 2002. The fronts were again taken from analyses prepared by the Hydrometeorological Prediction Center (HPC) of NCEP. The maps of surface potential temperature were prepared at the Department of Atmospheric Science, The University of Arizona, and were manually analyzed without knowledge of the concurrent frontal analysis. As in SH, the times were 0000 and 1200 UTC and the area of analysis was the same. The analysis consisted of isotherms at intervals of 8°C. Areas of moderate or intense gradient, representing an 8°C contrast of potential temperate over distances of no more than 220 or 110 km, respectively, were marked. These distances represent values of the gradient close to those used by SH. Edges of frontal segments occurred where the analyzed notation changed, generally at centers of low pressure, or where indicated in the analyses, or at the edge of the analyzed area. Warm fronts, cold fronts, and stationary fronts were separately considered. A small number of occluded segments occurred but were considered as extended portions of cold or warm fronts, depending on whether the air following the frontal wind shift was colder or warmer than the air ahead. Whereas SH considered each segment as associated or not associated with a baroclinic zone, in this study the total length of each segment was measured, as was the length associated with a baroclinic zone. Association was considered to occur if the analyzed front lay within 220 km of the warm edge of a zone, or was within it. Where the orientations of the front and of the zone differed by nearly 90°, the two were considered associated if the air on the cold side of the front was significantly colder than the air on the warm side, but not otherwise. The length and proportions of frontal segments associated with baroclinic zones are presented in Table 1. In the table the fractional length of segments associated with baroclinic zones was around one-half for both times and for all frontal types. Cold frontal segments were not less associated, as in the study by SH (seen in their Table 3). The lengths of stationary and cold fronts is understated because in many instances the segment was terminated when it reached the limits of the area of analysis of potential temperature, usually over the ocean. If the temperature analysis had extended over the oceanic regions, the association would have likely been weaker because of the lack of prominent contrasts in these regions. Warm fronts were fewer and shorter than other types, representing in many cases stubs ahead of an analyzed cold front with less than compelling indications. In the earlier study a decision was made whether the segment as a whole was or was not associated with a baroclinic zone. The present study may be less subjective. In an attempt to mimic the procedure used in the earlier study, we determined whether each individual frontal segment was or was not associated with a baroclinic zone over at least 50% of its length. The proportions of each frontal type meeting this criterion were 0.53, 0.43, and 0.45 for stationary, cold, and warm segments, respectively. In both studies it is apparent that many analyzed fronts are not assoCorresponding author address: Dr. Frederick Sanders, 9 Flint Street, Marblehead, MA 01945-3716. E-mail: fnmisander@comcast.net AUGUST 2005 F O R E C A S T E R S ’ F O R U M 647

Zonal Momentum Balance, Potential Vorticity Dynamics, and Mass Fluxes on Near-Surface Isentropes

AbstractWhile it has been recognized for some time that isentropic coordinates provide a convenient framework for theories of the global circulation of the atmosphere, the role of boundary effects in the zonal momentum balance and in potential vorticity dynamics on isentropes that intersect the surface has remained unclear. Here, a balance equation is derived that describes the temporal and zonal mean balance of zonal momentum and of potential vorticity on isentropes, including the near-surface isentropes that sometimes intersect the surface. Integrated vertically, the mean zonal momentum or potential vorticity balance leads to a balance condition that relates the mean meridional mass flux along isentropes to eddy fluxes of potential vorticity and surface potential temperature. The isentropic-coordinate balance condition formally resembles balance conditions well known in quasigeostrophic theory, but on near-surface isentropes it generally differs from the quasigeostrophic balance conditions. Not taking the intersection of isentropes with the surface into account, quasigeostrophic theory does not adequately represent the potential vorticity dynamics and mass fluxes on near-surface isentropes—a shortcoming that calls into question the relevance of quasigeostrophic theories for the macroturbulence and global circulation of the atmosphere.

A Mesoscale Analysis Method for Surface Potential Temperature in Mountainous and Coastal Terrain

Abstract A technique is developed to anisotropically spread surface observations in steep valleys. The goal is to create an improved objective analysis for the lowest, terrain-following numerical weather prediction (NWP) model level in mountainous terrain. The method is a mother–daughter (MD) approach, where the amount of information transferred from one grid point (the mother) to all neighboring grid points (the daughters) depends on elevation differences. The daughters become mothers and further share information with their neighboring grid points. This iterative method allows information to follow valleys around ridges, while reducing spread over the ridge top. The method is further refined to account for land–sea anisotropy. This approach is tested in the objective analyses of surface potential temperatures over the steep mountainous and coastal terrain of southwestern British Columbia, Canada. Analysis results are compared with other existing schemes using the Advanced Regional Prediction System Data Assimilation System (ADAS). It is found that the MD approach outperforms the other schemes over mountainous and coastal terrain.

Optimal Perturbations in the Eady Model: Resonance versus PV Unshielding

Abstract Using a nonmodal decomposition technique based on the potential vorticity (PV) perspective, the optimal perturbation or singular vector (SV) of the Eady model without upper rigid lid is studied for a kinetic energy norm. Special emphasis is put on the role of the continuum modes (CMs) in the structure of the SV, and on the importance of resonance to the SV evolution. The basis for the SV is formed by a number of nonmodal structures, each consisting of a superposition of one CM and one edge wave, such that the initial surface potential temperature (PT) is zero. These nonmodal structures are used as PV building blocks to construct the SV. The motivation for using a nonmodal approach is that no attempt has been made so far to include the CM residing at the steering level of the surface edge wave in the perturbation, although it is known that this CM is in linear resonance with the surface edge wave. Experiments with one PV building block in the initial disturbance show that the SV growth is dominated by the resonance effect except for small optimization times (less than 1 day), in which case the unshielding of PV and surface PT dominates the growth of the SV. The PV–PT unshielding provides additional growth to the SV and this explains the observation that the PV resides above the resonant level. More PV building blocks are added to include PV unshielding as a third growth mechanism. Which of the three mechanisms dominates during the SV evolution depends on the region of interest (interior or surface), as well as on the optimization time and on the number of building blocks used. At the surface, resonance plays a dominant role even when a large number of building blocks is used and relatively small optimization times are used. For the interior of the domain, PV unshielding becomes the dominant growth mechanism when more than two PV building blocks are used. With increasing optimization times, the PV distribution of the SV becomes increasingly more concentrated near the steering level of the edge wave. This concentration of PV is explained by the enhanced importance of resonance for long optimization times as compared to short optimization times.

The Tropopause and the Thermal Stratification in the Extratropics of a Dry Atmosphere

A dynamical constraint on the extratropical tropopause height and thermal stratification is derived by considerations of entropy fluxes, or isentropic mass fluxes, and their different magnitudes in the troposphere and stratosphere. The dynamical constraint is based on a relation between isentropic mass fluxes and eddy fluxes of potential vorticity and surface potential temperature and on diffusive eddy flux closures. It takes baroclinic eddy fluxes as central for determining the extratropical tropopause height and thermal stratification and relates the tropopause potential temperature approximately linearly to the surface potential temperature and its gradient. Simulations with an idealized GCM point to the possibility of an extratropical climate in which baroclinic eddy fluxes maintain a statically stable thermal stratification and, in interaction with large-scale diabatic processes, lead to the formation of a sharp tropopause. The simulations show that the extratropical tropopause height and thermal stratification are set locally by extratropical processes and do not depend on tropical processes and that, across a wide range of atmospheric circulations, the dynamical constraint describes the relation between tropopause and surface potential temperatures well. An analysis of observational data shows that the dynamical constraint, derived for an idealized dry atmosphere, can account for interannual variations of the tropopause height and thermal stratification in the extratropics of the earth's atmosphere. The dynamical constraint implies that if baroclinic eddies determine the tropopause height and thermal stratification, an atmosphere organizes itself into a state in which nonlinear interactions among eddies are inhibited. The inhibition of nonlinear eddy–eddy interactions offers an explanation for the historic successes of linear and weakly nonlinear models of large-scale extratropical dynamics.

A Numerical Study of a Mesoscale Convective System during TOGA COARE. Part II: Organization

In Part I, the authors presented a successful numerical simulation of the life cycle of a warm-pool mesoscale convective system (MCS) that occurred on 15 December 1992 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. In this study, the simulation results of Part I are diagnosed to investigate the organization of the MCS and the convective onsets that occurred during the growing and mature stages of the MCS. During the life cycle of the MCS, four convective onsets occur in the presence of large-scale ascent, convective available potential energy (CAPE), and surface potential temperature drop-off (SPTD). It is found that the first convective onset is caused by the existence of upward motion, CAPE, and SPTD in the model initial conditions. The second convective onset is regulated by the favorable occurrence of SPTD. The third and fourth convective onsets arise from the development of upward motion associated with the westward propagation of the quasi-2- day wave. The four mesoscale precipitation features clustered together to form the MCS in response to the evolution of the vertical motion field. The organization of the MCS is characterized by the presence of a midtropospheric mesovortex situated near the position of the first convective onset. Analysis of the relative vorticity (RV) budget indicates that the mesovortex originates and intensifies largely from vortex stretching induced by deep convective heating. A decrease in RV above (below) the mesovortex arises because of the combined effects of the tilting and horizontal advection terms (the tilting, stretching, and solenoidal terms). Our results suggest that the mesovortex played little role in the subsequent onsets (i.e., second, third, and fourth) and that other warm-pool MCSs occurring near the transequatorial flow are likely to be associated with mesovortices.

VALIDATION OF ARGO DATA IN THE INDIAN OCEAN

ARGO -salinity data from the Indian Ocean are validated using salinity from floatversus-float match-ups and also using CTD observations from three cruises. Validation data sets are selected in such a way that the float and the match-up data are collocated with tolerable space-time difference. For validation a time difference of less than 10 days and space difference less than 100 Km have been considered. The evaluation is done using salinity data on theta (potential temperature) surfaces from deeper observations. One of the significant observation of float-versus-float validation is the large random error observed in the initial profiles of the float-salinity compared to later profiles. While the float salinity data is found to be largely in good agreement with the ship based CTD observations, there are cases where the salinity error exceeds the desired 0.01 PSU.

Mesoscale diagnostics of prefrontal and frontal precipitation in the Southeast Alps during MAP IOP 5

In terms of heavy precipitation, the MAP IOP 5 was a two-phase event. During the first phase – on 3 October 1999 – there was strong precipitation in the Lago Maggiore MAP target area, while the prefrontal precipitation was mainly limited to the mountain ranges of the MAP mission area in the Julian and the Karnic Alps involving a series of thunderstorms developing continuously for about 15 hours and contributing most to precipitation levels. During the second phase – on 4 October – the main precipitation was limited to the Julian and the Karnic Alps where a frontal passage was noted by a squall line moving from Veneto region towards the east, accompanied by a strong SW upper-level jet. At the same time, a strong low-level cold flow invaded the region to the north of Adriatic Sea from the east as a significant amount of cold air moving ageostrophically around the eastern edge of the Alps was arriving in the area. To study MAP IOP 5 in detail, we describe the development for mesoscale features of the event’s radar images, time-height cross-sections and estimates of Convective Available Poteintial Energy (CAPE) based on radio-sounding data, and how surface-measured precipitation offers some smaller scale information. Surface potential temperature and winds are also studied. Very large precipitation accumulation gradients are diagnosed (150 mm per day/25 km in S–N direction) and time distributions of hourly precipitation shows completely diverse regimes in the Friuli plain and in the Alps with peak intensities in the Julian Alps. The mesometeorological mechanisms for high precipitation rate in the SE Alps are diagnosed and some characteristics of the squall line are discussed.

Climatology of the stratospheric BrO vertical distribution by balloon‐borne UV–visible spectrometry

A balloon‐borne UV–visible spectrometer, the SAOZ‐BrO, has been designed for the measurement of BrO on small and relatively low‐cost balloons. It allows the retrieval of the vertical BrO profile with a resolution of 1 km, a precision of 0.5–2 pptv (below 25 km), and a +5/−10% accuracy during the daytime balloon ascent. Fifteen successful flights have been carried out since 1997. Significant BrO amounts were observed at all latitudes and seasons, with a peak concentration altitude varying from 15 km in the winter vortex to 22 km in the tropics. The mixing ratio increases steadily from the tropopause to 25–30 km, depending on the latitude, above which it remains constant up to 30 km. The latitudinal and seasonal changes (maximum at high latitude and in the winter) are largely controlled by the vertical transport of total inorganic bromine and to a smaller extent by photochemistry. Photochemical changes are primarily related to NO2 abundances. On a constant potential temperature surface, the BrO mixing ratio is the largest in Polar Regions in the winter, where NO2 is nearly absent. In contrast, BrO is the smallest during the polar day and in the summer at midlatitude. The presence of activated chlorine in the cold vortex has little impact on BrO abundances. Finally, significant amounts were observed in the upper troposphere: (1) in the summer at midlatitude where it was the result of a stratosphere–troposphere exchange (STE) event advecting bromine from the stratosphere and (2) at the tropics where its presence is likely due to the conversion of organic bromine at lower altitude.

Role of NOy as a diagnostic of small‐scale mixing in a denitrified polar vortex

Observations of three stratospheric species (N2O, CH4, and NOy) are examined for their suitability as mixing tracers in the inner Arctic vortex region between late February and mid‐March 2000. NOy is highly inhomogeneous on isentropic surfaces and has little systematic vertical gradient between the 420 and 470 K potential temperature surfaces due to severe and extensive denitrification. Probability distribution functions of NOy calculated from in situ measurements do not show systematic and significant change as a function of time, indicating that mixing was too slow to substantially homogenize NOy distribution and therefore to strongly affect photochemical O3 destruction rates during the period. We propose that the NOy inhomogeneity is useful for diagnosing small‐scale, irreversible mixing rates during the measurement period. A simple kinematic model is used to show that the NOy standard deviation on an isentropic level in the vortex has desirable properties for quantifying these rates. A practical method for deriving mixing rates for chemistry and transport models has been proposed for future studies.

A Climatology of Surface Baroclinic Zones

Analyses of surface potential temperature for one year over the contiguous United States, southern Canada, northern Mexico, and adjacent oceanic areas showed three regions of relatively high frequency of strong gradients. These were the Atlantic and Gulf coasts, the Pacific coast, and the eastern slopes of the North American Cordillera. The Atlantic and Gulf zone was most pronounced at 1200 UTC during winter. The Pacific coast zone was most frequent at 0000 UTC in summer. The zone on the eastern slopes was present at both times and during all seasons but was most pronounced at 1200 UTC in winter. The locations of the maxima and the pronounced diurnal changes provide circumstantial evidence that the horizontal variation of diabatic heating and cooling due to surface heat flux is a more important physical mechanism than confluence is in the creation of surface baroclinic zones. An example is shown of the importance of the East Coast zone for weather forecasting during the cold season. In January of 2000 a low pressure center propagated along the surface baroclinic zone, separating cold air over land from warm air over the water, rather than following the deep baroclinic zone in the troposphere. During the warm season, the ‘‘backdoor cold front,’’ separating cool air over the water from hot air over land, presents a challenging forecast problem. Many analyzed fronts are not associated with significant horizontal density gradients. Because of these and other surface analysis issues, short-range forecasting might benefit from routine analysis of the surface temperature field.

Global tracer modeling during SOLVE: High‐latitude descent and mixing

We compare tracer observations made during the northern winter of 1999/2000 with the results of simulations with a three‐dimensional chemical transport model, driven by assimilated winds. During the course of the winter, very low concentrations of tracers of tropospheric origin (such as N2O) descend into the lower stratosphere within the polar vortex. The altitude of origin of this air has been a matter of debate in the literature; by midwinter, both observations and model results indicate a significant fraction of mesospheric air in the lower stratosphere. Observations from aircraft and balloon flights reveal markers of mesospheric air within the Arctic vortex in the lower and middle stratosphere. An artificial tracer introduced into the model mesosphere at the start of winter descends (being diluted as it does so) all the way down to the 450 K potential temperature surface by March. Modeled tracer‐tracer relationships evolve through the winter in a way similar to observations, but the separation between vortex and extravortex curves is exaggerated, suggesting that the model exhibits excessive horizontal mixing within and into the vortex. The tracer‐tracer relationships are used to identify partly mixed air as lying, in tracer‐tracer space, in a region intermediate between the characteristic vortex and midlatitude relationships. Air lying in a collar region just inside the vortex edge is thus identified as being mixed, and this indicates excessive horizontal mixing in the model across the vortex edge.

Fluoroquinolone−Biomembrane Interaction at the DPPC/PG Lipid−Bilayer Interface

The interaction of two fluoroquinolones, ciprofloxacin (CPX) and its N-4-butylpiperazinyl derivative (BCPX), with liposomes bearing negative surface charge was studied by fluorescence methods. Binding of 1-anilino-8-naphthalenesulfonate to the liposome surface and diphenylhexatriene (DPH) and diphenylhexatriene−propionic (DPH−AP) acid fluorescence anisotropy measurements were differently affected by the two. On the basis of the variations of the surface potential and phase transition temperature (Tm) of the phospholipids studied, it was concluded that (i) both drugs interact electrostatically at the lipid membrane interface and (ii) the butyl side chain of BCPX led to a different interaction with the lipid headgroups. This behavior is then related to the activity of an efflux pump Serratia marcescens NIMA, which appear to be affected by the ability of CPX and BCPX to interact with the inner surface of the plasma membrane.

Onset, extent, and duration of dehydration in the southern hemisphere polar vortex

Satellite observations of water vapor and aerosol extinction along with temperature trajectory calculations are analyzed for the Southern Hemisphere winter of 1992 in order to determine the onset, extent, and duration of dehydration within the polar vortex. Our investigation uses measurements of water vapor from the Microwave Limb Sounder (MLS) and aerosol extinction from the Cryogenic Limb Array Etalon Spectrometer (CLAES), both on board the Upper Atmosphere Research Satellite (UARS). Evidence of persistent ice cloud formation, supported by temperature statistics obtained from air parcel trajectories, suggests that the onset of the dehydration process occurs between late June and early July. By late August‐early September water vapor depleted areas within the vortex no longer coincide with high aerosol extinctions, indicating that severe dehydration has occurred with the irreversible removal of water vapor over vast areas. Areas with depleted levels of water vapor, below the prewinter values, persist well into November. Evidence for dehydration is found on potential temperature surfaces from 420 K (the lower limit of the MLS measurements) to 520 K (approximately 16 to 22 km). The horizontal extent of the dehydrated area at 465 K encompasses up to 35% of the total vortex area equatorward of 80°S. A comparison of CLAES aerosol extinction measurements and model calculations of aerosol extinction suggests an average ice particle number concentration and size of 10−2–10−3 cm−3 and 10–30 μm, respectively. We show that the difference between the timing of the onset of dehydration found here and that in a recent analysis of Polar Ozone and Aerosol Measurement III (POAM) observations can be explained by the latitudinal sampling pattern of the POAM instrument.

A Numerical Study of a Mesoscale Convective System during TOGA COARE. Part I: Model Description and Verification

Abstract A 16-h numerical simulation of the growing and mature stages of the 15 December 1992 Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) mesoscale convective system (MCS) is performed to demonstrate the predictability of tropical MCSs when initial conditions and model physical processes are improved. The MCS began with two entities S1 and S2, which developed and eventually merged to form a large anvil cloud. To obtain a realistic simulation of the MCS, the initial moisture field in the operational European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is improved, based on previous findings. The deep column ascent and surface potential temperature dropoff (SPTD) are implemented into the initiation mechanism of the Kain–Fritsch cumulus parameterization scheme (KF CPS). Other refinements to the KF CPS include the introduction of the accretion process in the formation of convective rain and the detrainment of rain and ice particles at the cloud top...

Systematic Adjustments of Hydrographic Sections for Internal Consistency*

A significant legacy of the World Ocean Circulation Experiment (WOCE) is the large number of high quality, high-resolution, full-depth, transoceanic hydrographic sections occupied starting in the mid-1980s. The section data provide an unprecedented survey of World Ocean water properties. Most stations sampled pressure, temperature, salinity, dissolved oxygen, and nutrients (nitrate, phosphate, and silicic acid) at up to 36 depths. While the WOCE Hydrographic Program (WHP) strenuously advocated employing standardized measurement techniques on all sections, small but significant systematic differences among cruise legs are found. A simple method for adjusting measurements to maximize internal consistency is presented and applied to available WOCE data in the Pacific Basin. First, the sections are broken into distinct cruise legs between port stops. Then, crossovers are identified where two different cruise legs cross or approach each other. Using hydrographic data from each cruise leg near each crossover, linear fits are made of properties on potential temperature surfaces against distance along cruise track. These fits are then used to evaluate property differences and their uncertainties at crossovers. A set of least squares models are used to generate sets of adjustments, with related uncertainties, for all the properties of each cruise leg. These adjustments minimize differences of water properties among cruise legs at the crossovers in a least squares sense. The adjustments can be weighted by difference uncertainties, and damped by a priori estimates of the expected differences. Initial standard deviations of crossover differences are 0.0028 for salinity, 2.1% for oxygen, 2.8% for nitrate, 1.6% for phosphate, and 2.1% for silicic acid. The adjustments roughly halve these values, bringing cruise legs into agreement within WHP target accuracies.