bluuebunny/crossref_metadata_2025 huggingface dataset:
Bound and free infragravity waves in the nearshore zone under breaking and nonbreaking conditions
Authors: Ruessink B. G.
Published: February 2004

Recordings of near‐bottom pressure obtained at three positions in a gently sloping multiple‐bar system were analyzed with a bispectral technique to quantify the relative importance of forced motions to the total infragravity (0.004–0.04 Hz) wave field under breaking and nonbreaking conditions, both on a temporal and spatial scale. The temporal variations in the ratio of bound to total infragravity energyEbnd/Eigwere well associated with the local relative wave heightHss/h(whereHssis the significant sea‐swell wave height andhis water depth).Ebnd/Eigincreased with higherHssvalues, reaching maximum values of up to 0.8 at the onset of short‐wave breaking. With an increasing intensity of breaking the coupling between incident and infragravity waves reduced to negligible values in a saturated sea‐swell wave field. The strong phase coupling at the breakpoint with a phase relationship close to the relationship predicted by bound‐wave theory strongly supports the hypothesis that forced waves are the main source of free infragravity motions. In the cross‐shore direction,Ebndwas largest at the breakpoint. Wave breaking was associated with a rapid decrease in the ratioEbnd/Eigin the onshore direction and, consequently, with a rapid increase in the contribution of free infragravity energy to the total infragravity field. The data set indicated that free infragravity energy may also be generated in the absence of breaking waves; the reason for this is not understood.
On the upper layer circulation in the Alboran Sea
Authors: Viúdez A. , Pinot J.‐M. , Haney R. L.
Published: February 2004

We present new experimental results and assemble them with previous results in order to develop an improved picture of the upper layer circulation in the Alboran Sea. It is suggested that the key idea to understanding this upper layer circulation is the tendency of the Atlantic jet (AJ) to have negative curvature. Local interactions with the western Alboran gyre (WAG) or the African coast can, however, counterbalance this tendency and modify the anticyclonic path of the AJ. It is also proposed that the density gradients in the WAG can be maintained in part by means of an intermittent surface cross‐gyre current which results in an input, mixing, and renewal of Atlantic water. The static stability at the bottom of the gyre increases because of the mixing of Atlantic water with Western Mediterranean Deep Water which is uplifted close to the African coast. This mixing process thereby acts as a local source of potential vorticity. We also report the existence in the Alboran Sea of subsurface anticyclonic eddies (located between 100 and 400 m) of relatively cold water that appear to be detached from the Iberian shelf. Regarding the large‐scale variability of the AJ‐WAG system, we present evidence of an eastward migration of the WAG and the subsequent formation of a new anticyclonic gyre in the western Alboran basin on a timescale of 1 month. This eastward gyre migration process temporarily allows the simultaneous presence of three anticyclonic gyres in the Alboran Sea.
On continental shelf convection: The influence of an ideal coast
Authors: Coates Michael J. , Ivey Gregory N.
Published: February 2004

A series of laboratory experiments were performed in both stratified and homogeneous rotating fluids, with thermal forcing occurring over a semicircular region adjacent to a vertical coastline. The evolution of the flow followed a sequence of events similar to those observed in earlier experiments having no topographic constraints. As the fluid initially adjusts geostropically, a rim current is generated, but it becomes unstable, generating baroclinic eddies that eventually transport fluid out of the convecting region and severely disrupt its dynamics. The sequence of events observed in these laboratory experiments were also observed in a recent set of numerical experiments in a homogeneous ocean with both flat and gently sloping shelves. The magnitude of the rim current observed in both the laboratory and numerical experiments agrees with earlier results obtained in the absence of the coastline. The general shape, structure, and wavelength of the instabilities that can develop on the rim current are similar to those in the earlier unconstrained experiments, although the simulation wavelengths are a little larger. However, if the Rossby radius LR becomes large enough, the formation of the eddies appears to be suppressed so that they apparently play no role in the exchange between shelf and surrounding seas.
Dynamic behavior of natural sea surfactant films
Authors: Mass John T. , Milgram Jerome H.
Published: February 2004

The dynamic behavior of sea surfactants is studied at timescales from 0.04 to 2 seconds by generating waves on the water containing its natural surfactants in the laboratory and comparing dynamical measurements with theoretical predictions for prescribed surfactant properties. The properties considered are film pressure, elasticity and surface viscosity. For longitudinal Marangoni waves in the frequency range of 0.5 to 4.0 Hz, time‐varying film pressures are measured. For transverse waves in the frequency range of 3 to 25 Hz, spatial decay rates are measured. Prior to conducting experiments with sea water containing soluble natural surfactants, the procedures and methods of analysis are validated by experiments with clean fresh water and with an insoluble oleyl alcohol film. A notable finding is that the static film elasticity accurately predicts the dynamic behavior of both the insoluble oleyl alcohol film and the soluble natural sea surfactant films. To better understand the reasons for this finding, sea surfactant adsorption and desorption time histories were measured. The adsorption/desorption time scales ranged from 46 to 196 min. One reason for the accurate prediction of surfactant dynamic behavior by the static elasticity is that the timescales of the waves are much shorter than the adsorption/desorption timescales. The conclusion is that the static elasticity controls the interactions of surfactants with most hydrodynamic disturbances having timescales up to several min.
On the use of tide gauges to determine altimeter drift
Authors: Chambers D. P. , Ries J. C. , Shum C. K. , Tapley B. D.
Published: February 2004

TOPEX measurements of sea level variability have been compared to tide gauge measurements from 40 sites and to dynamic topography measurements computed from temperatures recorded at 23 Tropical Ocean‐Global Atmosphere (TOGA)‐Tropical Atmosphere‐Ocean (TAO) buoys in the eastern Pacific and mean temperature‐salinity profiles. Buoy data in the western Pacific were not used because of large long‐term slopes in the data that appear to be due to interannual salinity variations. The relative drift between TOPEX and the two different in situ sets of data agree within 1 mm yr−1, with a weighted average of −2.6 mm yr−1 and an estimated uncertainty of 1.5 mm yr−1, if values from an internal calibration of the TOPEX altimeter are applied. The consistency of the two relative drifts suggests that the slope is due at least in part to a drift in the TOPEX measurement. A substantial portion of this drift may be due to a drift in the TOPEX microwave radiometer (TMR), since comparisons with three independent external measurements indicate a drift in sea level due to the TMR measurement of about −2 mm yr−1.
Four stages of pressure ridging
Authors: Hopkins Mark A.
Published: February 2004

The pressure ridging process is simulated using a two‐dimensional particle model. Blocks are broken from an intact sheet of relatively thin lead ice pushed against a thick, multiyear floe at a constant speed. The blocks of ice rubble accumulate to form the ridge sail and keel. During the simulations the energy consumed in ridge growth, including dissipation, is explicitly calculated. On the basis of the results of simulations performed with the model, the ridging process can be divided into four distinct stages. The first stage begins with an intact sheet of lead ice impacting a floe and ends when the sail reaches its maximum height. In the second stage the ridge keel deepens and widens. The stage ends when the maximum keel draft is reached. In the third stage the direction of growth is leadward creating a rubble field of more or less uniform thickness. The third stage ends when the supply of thin ice is exhausted. In the fourth stage the rubble field is compressed between converging floes. The results of simulations establish the dependence of ridging energetics in the first and second stages on the thickness of the ice sheet and the amount of ice pushed into the ridge. The average profiles of the simulated ridges delineate the growth process in the first, second, and third stages. The energetics and profiles of the fourth stage were described by Hopkins et al. [1991]. Lead ice extents of up to 1300 m are pushed into ridges to determine maximum sail heights, keel drafts, and ridging forces.
Ductile compressive failure of columnar saline ice under triaxial loading
Authors: Melton J. S. , Schulson E. M.
Published: February 2004

Experiments and analysis have shown that the ductile compressive yield stress (at −10°C at 4 × 10−5 s−1) of S2 saline ice, an orthotropic material whose crystallographic c axes are randomly oriented in the plane perpendicular to the long axis of the columnar grains [Michel, 1978], loaded triaxially both across and along the columnar‐shaped grains obeys Hill's [1950] criterion under low to intermediate levels of confinement. Correspondingly, the ratio of inelastic strains can be described by the attendant associated flow rule.
Inversion of pack ice elastic wave data to obtain ice physical properties
Authors: Stein Peter J. , Euerle Steven E. , Parinella James C.
Published: February 2004

Geophones mounted on floating ice sheets can potentially provide data for a robust method to monitor mechanical properties of the ice. The technique relies on the measurement and inversion of low‐frequency elastic waves propagating in the ice. To test this hypothesis, several geophone systems were deployed on the Arctic ice as part of the Office of Naval Research Sea Ice Mechanics Initiative (SIMI), including a winter‐over system of 20 triaxial geophones at the fall 1993 SIMI camp. An inversion technique is discussed here through references to the literature and by analysis of geophone data, specifically those data collected on “clean” first‐year ice off Resolute Bay, Canada, and on highly irregular multiyear ice found at the fall SIMI camp. For undeformed first‐year ice, the inversion technique gave an estimate of ice properties that agreed well with known values, although extensive work remains to determine the effects of anisotropy and inhomogeneity. The geophone data for the nonuniform ice at the SIMI camp were very complex and difficult to analyze. The inversion yielded only trends in what can, at best, be termed effective ice thickness and bending rigidity; it is uncertain how these relate to actual ice properties. The SIMI geophone system demonstrated the feasibility of performing autonomous measurements of the characteristics of propagating waves in the Arctic ice; with continued study, it seems evident that such systems can be used in clean first‐year ice to monitor ice properties. However, extensive research is required to make this technique useful in multiyear or complex first‐year ice.
Global relationships of the inherent optical properties of the oceans
Authors: Barnard A. H. , Pegau W. S. , Zaneveld J. R. V.
Published: February 2004

We have collected data during eight separate research cruises from open ocean to estuarine oceanic environments. Inherent optical property data collected during these cruises were incorporated into a large database totaling 1914 vertical samples. The range of each inherent optical property within this database spans over 2 orders of magnitude. Using this database, we examine the spectral relationships of each of the inherent optical properties based on the measurements made at 488 nm. The results of this study show that there are dependencies in the individual inherent optical properties (IOP) spectra that are linearly related. The information from the regression models is used to explain the linear dependencies observed in the global data set. A separate data set collected from a recent cruise is used to compare regional relationships with the global. The implication of this research is that over a diversity of oceanic regimes, there are fundamental, first‐order relationships in the individual IOP spectra. These relationships can provide an estimate of the individual IOP spectral relationships when no information about the IOP is available, as is often the case in ocean color remote sensing. More detailed models, however, may be necessary in order to more accurately predict the IOP spectral relationships on regional scales where the expected range of variability is small.
Slow oceanic teleconnections linking the Antarctic Circumpolar Wave with the tropical El Niño‐Southern Oscillation
Authors: Peterson Ray G. , White Warren B.
Published: February 2004

A case study for the period 1982–1994 shows that a major source for the Antarctic Circumpolar Wave is in the western subtropical South Pacific, where interannual anomalies in sea surface temperature (SST) and precipitable water (PrWat) form. Once established, these interannual anomalies, in tandem with anomalies in sea level pressure (SLP), move south toward the Southern Ocean. The system then migrates east around the globe through a combination of oceanic advection with the Antarctic Circumpolar Current and ocean‐atmosphere coupling. The coincidence of interannual anomalies in SST, SLP, and PrWat indicates the extratropical ocean and atmosphere are tightly linked on these timescales. Large portions of the interannual SST anomalies branch advectively northward into the South Atlantic and Indian Oceans, ultimately reaching the tropics in each basin some 6–8 years after appearing in the low‐latitude Pacific. This constitutes a slow, oceanic teleconnection that is unique in climate dynamics, made possible by the continuity of Earth's oceans via the Southern Ocean. In the tropical Indian Ocean these interannual anomalies move east and arrive at the Indo‐Pacific transition in advance of the trans‐Pacific propagation of the respective El Niño‐Southern Oscillation (ENSO) phases. The interannual SST and PrWat anomalies that appear in the subtropical South Pacific are directly linked with the ENSO cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere, the same cell that initiates fast planetary waves in the atmosphere that carry ENSO signals around the southern hemisphere on much shorter timescales.
Formation mechanism of Japan Sea Proper Water in the flux center off Vladivostok
Authors: Kawamura Hiroshi , Wu Peiming
Published: February 2004

It is known that wintertime air‐sea interaction in the Japan Sea, enhanced by outbreaks of dry and cold air masses from the Eurasian continent, generates a characteristic water mass called Japan Sea Proper Water (JSPW) through deep convection. Using NASA scatterometer (NSCAT) wind vectors with high spatial resolution of 25 km, the role of the wind field over the Japan Sea in JSPW formation was investigated during the period of winter monsoon. It is revealed by NSCAT observations that the wintertime surface winds over the Japan Sea are strongly influenced by the upstream topography of the coastal region of the Eurasian continent. A strong wind area appears off Vladivostok, both in the snapshot and the monthly mean wind fields. The dynamics behind this strong wind flow may be attributed to the highly stratified surface wind being blocked by the coastal mountains and exiting through the narrow valley near Vladivostok into the Japan Sea. The NSCAT winds are coupled with European Centre for Medium‐Range Weather Forecasts air temperature and humidity and Japan Meteorological Agency sea surface temperature (SST) data for turbulent flux estimation. Monthly mean wind speed, momentum flux, sensible heat flux, latent heat flux, and evaporation have peak values exceeding 9 m s−1, 0.275 N m−2, 170 W m−2, 130 W m−2, and 120 mm, respectively, in the strong wind area, which has a diameter of about 150 km. Multichannel sea surface temperature (MCSST) images of the Japan Sea for late January 1997 show that the cold SST (∼0°C) area extends from the coastal region to the outer sea off Vladivostok. The MCSSTs decreased by 1°C for January in this region. The cold SST region coincides with the strong wind area, and both locations agree well with the JSPW formation region, which, according to Sudo [1986], is north of 41°N between 132° and 134°E. The spatial agreement strongly suggests that the wind, enhanced by the topographic effect around Vladivostok, causes the large turbulent heat flux and evaporation in this area, which generates the coldest SST and dense water mass, i.e., JSPW. This may be a process of coastal topography‐air‐sea interaction that leads to deep‐sea water formation in the Japan Sea. Because of the concentrated feature of turbulent fluxes and the inferred relation to the center of deep convection phenomenon, the strong wind area is called the “flux center” in this study.
A 3‐D coupled ice‐ocean model applied to Hudson Bay, Canada: The seasonal cycle and time‐dependent climate response to atmospheric forcing and runoff
Authors: Saucier François J. , Dionne Jacques
Published: February 2004

A coupled three‐dimensional, time‐dependent ice‐ocean model is developed and applied in order to reproduce the basin‐scale ice and mixed‐layer physical properties of Hudson Bay and James Bay, Canada. Models for albedo, evaporation, storms, frazil ice production, and radiation are included. Observed monthly means of winds, temperature, precipitation, runoff, and cloudiness are used to force the model and obtain multiyear, steady state, and non‐steady state solutions. The seasonal cycle in sea ice thickness, ice concentration, ocean temperature, and salinity is first reproduced. Then we consider a set of five experiments: (1) a strong westerly event from the North Atlantic Oscillation, (2) a year with anomalously high runoff, (3) regulated runoff from hydroelectric development, (4) high autumn winds, and (5) warm conditions. We find that preconditioning of the ocean for winter, controlled by the heat transfer to the atmosphere and freshwater input rates and also related to the mixed‐layer depth attained before freezing, has a strong control over the following ice season. The results show that varying runoff has more of an effect on sea‐ice production in southeastern Hudson Bay than do temperature changes associated with the North Atlantic Oscillation but that both have a small effect on the ice cover when compared to the observed interannual variability. Regulated runoff produces a positive sea‐ice anomaly during the January‐April period which is significant (greater than 10 cm or 10%) in the southeastern part of the bay but less than 1 cm (∼1%) on average. We conclude that ∼90% of the excess winter runoff remains liquid. No significant delay is computed for breakup dates (less than 3 days in southeastern Hudson Bay and less than 1 day overall). Other controls from the atmosphere are required to explain the natural interannual variability of the ice cover. Summer and autumn winds, and air temperature (which control heat loss and winter preconditioning), spring cloud cover (which controls heat gain), and snow cover (which controls the winter insulation) can explain relatively large changes in the system. Simple climate warming by 2°C produces large impacts in the ice‐ocean system, reducing the winter ice volume by over 20%.
Bio‐optical properties of the southwestern Ross Sea
Authors: Arrigo Kevin R. , Robinson Dale H. , Worthen Denise L. , Schieber Brian , Lizotte Michael P.
Published: February 2004

The bio‐optical properties of the southwestern Ross Sea were measured as part of the Antarctic research program Research on Atmospheric Variability and Atmospheric Response in the Ross Sea (ROAVERRS). The study area contained three distinct phytoplankton blooms, distinguishable by species composition. The largest in area was located to the north of the Ross Ice Shelf and was dominated by the prymnesiophyte Phaeocystis antarctica; chlorophyll a (Chl a) ranged from 0.45 to 8.2 mg m−3. Beam attenuation and particle absorption at 435 nm were as high as 3.4 m−1 and 0.35 m−1, respectively. A bloom of diatoms was more spatially restricted, located to the north and west of the P. antarctica bloom, with Chl a generally below 4 mg m−3. Neither diatoms nor P. antarctica exhibited evidence of the level of pigment packaging measured in waters near the Antarctic Peninsula during the Research on Antarctic Coastal Ecosystem Rates (RACER) program, possibly because of their smaller sizes. A much smaller cryptophyte bloom, located south of the Drygalski Ice Tongue, displayed a lower pigment‐specific absorption spectra than did P. antarctica or diatoms, a sign of greater pigment packaging. Pigment‐specific diffuse attenuation coefficients were consistent with the pigment‐specific particle absorption coefficients (aph*), both being ∼3 times greater than similar measurements made during RACER. Spectral absorption by solutes determined through regression analysis of Kd against Chl a for the ROAVERRS data set was nearly identical to that measured during RACER. Total diffuse attenuation spectra at a given station could be reconstructed by summing the inherent optical properties of the major optical components (pure water, soluble material, detritus, phytoplankton) measured there. Differences in the absorption ratio of aph*(λ) at 490 nm to aph*(λ) at 555 nm among the three dominant phytoplankton taxa in the southwestern Ross Sea were responsible for most of the variability in the ratio of remote sensing reflectance (Rrs) at these same wavelengths. At a given concentration of Chl a, the ratio log [Rrs(490):Rrs(555)] was greatest in cryptophyte‐dominated waters, which also possessed the lowest aph*(490):aph*(555) ratio, and lowest in P. antarctica–dominated waters. These bio‐optical differences suggest that no simple empirical relationship between Chl a and log [Rrs(490):Rrs(555)] will apply to all three taxonomically distinct phytoplankton blooms in the southwestern Ross Sea.
The production of ice and dense shelf water in the Okhotsk Sea polynyas
Authors: Martin Seelye , Drucker Robert , Yamashita Kohji
Published: February 2004

This paper examines the ice and dense water production in the Okhotsk Sea coastal polynyas for the 1990–1995 winters. The dominant polynyas occur on the northwest and northern shelves and in Shelikhov Bay. We use an algorithm developed for the special sensor microwave/imager (SSM/I) to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production. Historic oceanographic observations show that the northwest shelf is the only North Pacific region where the σϑ = 26.8 potential density surface outcrops to the surface and is also that part of the Okhotsk shelf where the densest water is observed to occur. In support of these observations, we find that the northwest shelf polynya is the dominant ice and brine producer, contributing on average about 55% of the total production. Shelikhov Bay is the second largest producer with about 25% of the total; this region has been previously neglected by both oceanographic and remote sensing studies. Using a combination of two dense water production models, we find that the 6 year average dense water production lies between 0.2–0.4 Sv. The ice and brine production for the dominant northwest shelf vary interannually by a factor of 3, while the production from all the northern polynyas varies by factor of 2. The source of the variability for the northwest shelf comes from the fact that the southwest‐to‐northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel, which means that small variations in the wind direction yield large changes in the ice production.
Wind speed dependence of atmospheric boundary layer optical properties and ocean surface reflectance as observed by airborne backscatter lidar
Authors: Flamant Cyrille , Trouillet Vincent , Chazette Patrick , Pelon Jacques
Published: February 2004

Airborne backscatter lidar measurements made over the Azores, in clear air conditions, are analyzed using a marine aerosol model to derive the extinction coefficient in the atmospheric boundary layer and the ocean surface reflectance in connection with surface wind speed. The dependence of surface layer extinction coefficients on surface wind speed is compared to previously published results. The sensitivity of the lidar inversion procedure to the aerosol model (sea‐salt concentration in the accumulation mode, presence or absence of an accumulation mode for sulfate, vertical distribution of stationary marine components above the marine atmospheric boundary layer) is investigated. At the wavelength of the lidar (0.53 μm), the extinction coefficient is very sensitive to the sea‐salt number concentration in the accumulation mode. In the surface layer, the extinction coefficient retrieved from the lidar measurements compares well to the extinction calculated with the model (via Mie theory) for an average number concentration of 10 particles cm−3 in the sea‐salt mode at wind speeds less than 3 m s−1. The relationship between the sea surface reflectance and the atmospheric backscatter coefficient is then used to determine the optical sea surface properties as a function of wind speed. Results on reflectance are found in excellent agreement with calculated values using the model of Cox and Munk [1954] and measured wind speed. The sensitivity of the results to the aerosol model and potential application of the inversion procedure to surface wind speed retrievals from lidar measurements are also discussed.
The development and operational application of nonlinear algorithms for the measurement of sea surface temperatures with the NOAA polar‐orbiting environmental satellites
Authors: Walton C. C. , Pichel W. G. , Sapper J. F. , May D. A.
Published: February 2004

Since 1990, the NOAA National Environmental Satellite Data and Information Service (NESDIS) has provided satellite‐derived sea surface temperature (SST) measurements based on nonlinear SST algorithms, using advanced very high resolution radiometer (AVHRR) multiple‐infrared window channel data. This paper develops linear and nonlinear SST algorithms from the radiative transfer equation. It is shown that the nonlinear algorithms are more accurate than linear algorithms but that the functional dependence of the nonlinearity is data dependent. This theoretical discussion (sections 2–4) is followed with a discussion in section 5 of the accuracy over a 9‐year period of the satellite‐derived SST measurements provided by NOAA NESDIS when compared with coincident drifting buoys. Between 1989 and 1998 the global scatter of the daytime satellite SST against drifting buoy measurements has decreased from ∼0.8° to 0.5°C, while the nighttime scatter has remained fairly constant at 0.5°C. An exception to these accuracy measurements occurred after the eruption of Mount Pinatubo in June 1991.
The role of meridional flow asymmetry in the dynamics of tropical instability
Authors: Proehl Jeffrey A.
Published: February 2004

The role of asymmetry of zonally and temporally invariant, equatorial, zonal flow on the structure and dynamics of tropical instability is investigated in a continuously stratified β‐plane model. While more strongly developed flow in the northern hemisphere leads to a northern hemisphere enhancement of the instability, consistent with observational data, asymmetry is not found to dramatically change the internal dynamics of tropical instability. We find that both sides of the northern branch of the South Equatorial Current are potentially unstable, with the relative level of meridional shear on the two sides of the flow playing a role in determining the location of the dominant source region. Consideration of the structure of the energy conversions, however, demonstrates the strong dynamical importance of the surface of zero meridional, isopycnal, potential vorticity gradient in setting the phase speed and controlling the structure of the instability. This control can be clearly understood through the dynamical framework provided by the wave geometry construct.
Variability in Bering Sea ice cover as affected by a regime shift in the North Pacific in the period 1947–1996
Authors: Niebauer H. J.
Published: February 2004

In the late 1970s, a “regime shift” or “step” occurred in the climate of the North Pacific, causing, among many other effects, a 5% reduction in the ice cover in the eastern Bering Sea as well as shifts in the position of the Aleutian low. Analyses of the Aleutian low from monthly mean northern hemisphere sea level pressure for winters (December‐March) for 1947–1996 are presented and compared with monthly mean ice cover from the Bering Sea for 1952–1996, the Southern Oscillation Index, and the western Pacific oscillation. Before the regime shift, below normal ice cover in the Bering Sea was typically associated with El Niño conditions, which caused the Aleutian low to move eastward of normal, carrying warm Pacific air over the Bering Sea. Conversely, above normal ice cover was associated with La Niña conditions, which caused the Aleutian low to move westward of normal, allowing higher pressure to move over the Bering Sea. Since the regime shift, during El Niños the Aleutian low has been moving even farther east, causing winds to blow from the east and north off Alaska and resulting in above normal ice in the Bering Sea. Before the regime shift the occurrence of El Niño and La Niña conditions was about even. Since the regime shift, El Niño conditions are about 3 times more prevalent. In recent work [e.g., Mantua et al., 1997; Minobe, 1997] there is evidence that this regime shift is the latest in a series of climate shifts going back to at least the late 1800s and may be due to a 50‐ to 70‐year oscillation in a North Pacific atmospheric‐ocean coupled system.
Collision of anticyclonic, lens‐like eddies with a meridional western boundary
Authors: Sansón L. Zavala , Graef F. , Pavía E. G.
Published: February 2004

The collision of anticyclonic, lens‐like eddies with a meridional western boundary is investigated as a function of two independent, nondimensional numbers: β = β0R/f0 and ε = ω/f0, where f0 and β0 are the Coriolis parameter and its rate of change with latitude, respectively, both evaluated at the reference latitude. R is the eddy's radius, and ω is its angular frequency. The numerical experiments show that in all cases there is a southward expulsion of mass proportional to both β and ε. which is estimated during the eddy‐boundary interaction. The eddies are invariably deformed with the initial collision, but afterward, they reacquire a new circular shape. There is a meridional translation of the eddy along the boundary which depends exclusively on the initial ratio r = ε/β. If r>1, the eddy goes southward, but if r<1, the eddy goes northward first and then southward. As the eddy loses mass and reacquires a new circular shape, there is a readjustment of β and ε such that β decreases because its radius becomes smaller and ε increases by energy conservation. This implies that the eddies ultimately migrate southward. A formula, derived for the meridional speed of the center of mass of the eddy is consistent with the numerical results. A physical interpretation shows that after collision a zonal force is exerted on the eddy by the wall which is balanced by a meridional migration. Nonlinearities induce a southward motion, while high β values could produce northward motion, depending on the mass distribution along the wall.
A balloon‐borne cloud condensation nuclei counter
Authors: Delene David J. , Deshler Terry , Wechsler Perry , Vali Gabor A.
Published: February 2004

A balloon‐borne instrument was constructed for observations of vertical profiles of cloud condensation nucleus (CCN) concentrations, active at 1% supersaturation. Droplet concentration in the static thermal‐gradient diffusion chamber is deduced from the amount of scattered laser light detected by a photodetector. The photodetector is calibrated using a video camera and computer system to count the number of droplets produced from NaCl aerosol. Preliminary data are available from nine early morning profiles obtained at Laramie, Wyoming, between June 1995 and January 1997. To complement the CCN measurements, instruments that measure condensation nuclei (CN) and aerosols with diameter greater than 0.30 μm (D0.3) were also included on the balloon package. CCN concentrations exhibited a general decrease from the surface to the top of the boundary layers, were generally uniform through well‐mixed layers, and show variability above well‐mixed layers. In general, the structure of the CCN profile appears to be closely related to the structure in the CN and D0.3 profiles. Summer profiles generally have CCN concentration greater than 200 cm−3 up to 500 mbar, whereas winter profiles are less than 200 cm−3 at all levels.
Environmental controls on soil respiration in the Eurasian and Greenlandic Arctic
Authors: Christensen T. R. , Jonasson S. , Michelsen A. , Callaghan T. V. , Havström M.
Published: February 2004

Arctic regions contain large amounts of stored soil carbon and comprise huge areas of discontinuous vegetation. The potential for feedback effects on possible changing climatic conditions through altered source/sink action for atmospheric CO2 is therefore an important issue in tundra regions. In this study we investigate environmental controls on CO2 evolution rates in Arctic soils through observations along a Eurasian transect of tundra sites and comparative experiments in northern Sweden and northeast Greenland. Among factors potentially controlling decomposition rates in Eurasian wet and mesic tundra temperature and depth of the water table significantly influenced the CO2 efflux, while thaw depth, soil nitrogen, and organic matter concentrations explained very little of the variation in fluxes. The minor importance of the soil N status in controlling decomposition rates was confirmed in experiments in which N and P was added in a factorial manner at a subarctic heath and a high‐Arctic drained fen. Phosphorus decreased the CO2 emissions, while the combined N and P treatment increased the emissions in the subarctic. These effects were not reproduced in the high Arctic. The results support most assumptions in current decomposition models on the soil climatic controls on decomposition rates in the Arctic.
Clustering, randomness, and regularity in cloud fields: 5. The nature of regular cumulus cloud fields
Authors: Nair U. S. , Weger R. C. , Kuo K. S. , Welch R. M.
Published: February 2004

This study focuses on the nature of regularity in cumulus cloud fields at the spatial scales suggested by Weger et al. [1993]. We analyzed cumulus cloud fields from Landsat, advanced very high resolution radiometer, and GOES satellite imagery for regularity, using nearest‐neighbor cumulative distribution statistics. We found that the spatial scales over which regularity is observed vary from 20 km to 150 km in diameter. Clouds involved in regularity range in radius from about 300 m to 1.5 km. For the cases analyzed, we observed regularity in about 20% of the scenes, while randomness was the dominant spatial distribution for cumulus cloud fields; in addition, we frequently observed a tendency toward regularity. For regions in which we observed either regularity or randomness with a tendency toward regularity, small clouds were inhibited up to a distance of 3 cloud radii from the center of the large cloud. We also determined the size distributions of clouds, using a power law. For clouds larger than 1.5 km radius the exponent of the power law was correlated to the type of spatial distribution of the clouds. The exponent has largest values for regular spatial distributions, smallest values for clustered distributions, and in‐between values for random spatial distributions. Analysis of GOES scenes shows that the spatial distribution tends to be clustered in the early stages of the cloud field. During the mature phase it becomes either random, regular, or random with tendency toward regularity. During the later stages of cloud field development the spatial distribution once again becomes clustered.
Expected retrieval accuracies of bidirectional reflectance and albedo from EOS‐MODIS and MISR angular sampling
Authors: Lucht Wolfgang
Published: February 2004

This paper reports expected accuracies of bidirectional reflectance and albedo retrievals from the angular sampling provided by NASA's upcoming moderate resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR) on the EOS‐AM‐1 satellite platform. A numerical discrete ordinates method radiative transfer model by Myneni is used to simulate bidirectional reflectances for combined MODIS and MISR angular sampling as a function of latitude and time of year for six different bidirectional reflectance distribution function (BRDF) types (land cover types) in the red and near‐infrared wave bands. These simulated observations are then inverted using three different simple BRDF models scheduled for use in the future operational MODIS and MISR BRDF/Albedo Products: the reciprocal Ambrals, the modified Rahman‐Pinty‐Verstraete (RPV), and the modified Walthall BRDF models. Bidirectional reflectance and albedo retrievals are studied not only at the mean solar zenith angle of observation but extrapolated to arbitrary other Sun zenith angles as well. The influence of loss of observations to clouds is also examined. Results show that albedo may be retrieved with 2 to 8% median accuracy using either the Ambrals or the modified RPV model for any solar zenith angle for any MODIS/MISR sampling and that the accuracy of predicted nadir view reflectance is also mostly within a 10% error margin. For the Myneni forward model used, the Ambrals model may be slightly more accurate. The empirical modified Walthall model clearly performs worse than the two semiempirical models. Error distribution histograms allow assessing the overall accuracy to be expected from the planned MODIS BRDF/Albedo Product.
Processes controlling dimethylsulfide over the ocean: Case studies using a 3‐D model driven by assimilated meteorological fields
Authors: Chin Mian , Rood Richard B. , Allen Dale J. , Andreae Meinrat O. , Thompson Anne M. , Lin Shian‐Jiann , Atlas Robert M. , Ardizzone Joseph V.
Published: February 2004

This study investigates the processes that influence dimethylsulfide (DMS) concentrations over the ocean using a global three‐dimensional chemistry and transport model (CTM). The model is driven by assimilated meteorological data from the Goddard Earth Observing System Data Assimilation System (GEOS‐I DAS). Results from the model are compared with DMS measurements from two marine sites, a ship cruise, and an aircraft campaign. When observed seawater DMS concentrations and meteorological conditions are used, the model reproduces the observed daily and diurnal variations of DMS concentrations at a tropical Pacific station. The model also predicts the observed changes of DMS concentrations across the Atlantic, although it overestimates the DMS level by a factor of 2. The calculated vertical DMS concentrations off Tasmania are more than 4 times higher than the measured data. The model simulates day‐to‐day fluctuations and interannual variations observed at Amsterdam Island but underpredicts the magnitude of the variations. Sensitivities for DMS concentrations to the parameters used in DMS emission, oxidation, boundary layer mixing, and cloud convective transport are tested. The limitations of the current model in interpreting the observations are due to (1) the uncertainties in parameterization of DMS emission from the ocean, (2) the simplistic boundary layer mixing scheme, (3) the inaccurate spatial distribution and intensity of deep convective clouds in the GEOS‐I DAS, and (4) the uncertainties in DMS oxidation rates.
Satellite estimation of spectral surface UV irradiance in the presence of tropospheric aerosols: 1. Cloud‐free case
Authors: Krotkov N. A. , Bhartia P. K. , Herman J. R. , Fioletov V. , Kerr J.
Published: February 2004

The algorithm for determining spectral UVA (320–400 nm) and UVB (290–320 nm) flux in cloud‐free conditions is discussed, including estimates of the various error sources (uncertainties in ground reflectivity, ozone amount, ozone profile shape, surface height, and aerosol attenuation). It is shown that the Brewer‐measured spectral dependence of UV flux can be accurately reproduced using just total column ozone amount and the solar flux spectrum. The presence of aerosols tends to reduce the logarithm of the absolute UV flux linearly with aerosol optical depth. Using Brewer measurements of UV flux and aerosol optical depth on clear days at Toronto, the estimated slope falls in the range 0.2 to 0.3 (aerosol single‐scattering albedo about 0.95). The Brewer measurements of UV flux can be reproduced using the aerosol model derived within uncertainties of the instrument calibration. We have applied the algorithm to the data collected by the total ozone mapping spectrometer (TOMS) instruments that have been flown by NASA since November 1978. It was demonstrated that in the absence of clouds and UV‐absorbing aerosols, TOMS measurements of total column ozone and 380 nm (or 360 nm) radiances can be used in conjunction with a radiative transfer model to provide estimates of surface spectral flux to accuracies comparable to that of typical ground‐based instruments. A newly developed technique using TOMS aerosol index data also allows estimation of UV flux transmission by strongly absorbing aerosols. The results indicate that over certain parts of the Earth, aerosols can reduce the UV flux at the surface by more than 50%. Therefore the most important need for reducing errors in TOMS‐derived surface UVB spectra is to improve the understanding of UV aerosol attenuation.
Biomass burning aerosol size distribution and modeled optical properties
Authors: Remer L. A. , Kaufman Y. J. , Holben B. N. , Thompson A. M. , McNamara D.
Published: February 2004

Satellite remote sensing of smoke aerosol and estimates of aerosol forcing of climate require knowledge of the aerosol optical properties. A smoke aerosol physical and optical model is developed from a database of over 800 volume size distributions inverted from sky radiance data measured by the AERONET radiometer network in Brazil over a 3‐year period. The model represents total column, ambient conditions during the burning season in the Amazon Basin and cerrado region of Brazil. The mean volume size distributions are bimodal and can be represented by two lognormals. Accumulation mode modal radius is 0.13±0.02 μm with σ = 0.60 ± 0.04, and coarse‐mode modal radius ranges from 6 to 40 μm, with a mean of 11.5 μm and σ = 1.26 ± 0.23. The volume of each mode varies with optical thickness, causing the ratio of accumulation mode and coarse mode to vary as well, but the effect on the optical properties is negligible. Refractive index is taken to be 1.43‐0.0035i, and single scattering albedo is assumed to be 0.90, which is modeled with an external mixing of black carbon. The optical properties in the visible are dominated by the accumulation mode. Accumulation mode characteristics do not vary from year to year, from forest to cerrado region, with optical thickness or with precipitable water vapor. At one test location, accumulation mode characteristics do vary with air mass trajectory origin. The model is tested with independent data and can accurately predict the scattering phase function and path radiance in the backscattering direction that determines remote sensing properties and is responsible for scattering sunlight back to space.
Analytic forms of bidirectional reflectance functions for application to Earth radiation budget studies
Authors: Manalo‐Smith N. , Smith G. L. , Tiwari S. N. , Staylor W. F.
Published: February 2004

Analytic expressions for the bidirectional reflectance functions are formulated and fit to the Earth Radiation Budget Experiment (ERBE) operational models, which were developed using Nimbus 7 ERB data. The analytic bidirectional reflectance distribution functions (BRDFs) are based on theoretical considerations and are functions of viewing geometry and scene type. The models consist of a Rayleigh scattering term and a term for scattering due to clouds and surface. The darkness of the ocean permits the empirical determination of the Rayleigh component of scattering from the atmosphere. The models have the advantage that they are smooth in terms of view and solar zenith angles and relative solar azimuth angle and satisfy reciprocity. Results are presented for the ERBE scene types. The analytic functions closely model the reflectances in the forward scatter direction, but in the backscatter direction, the analytic models are slightly more limb brightened than the ERBE operational models. The model was also fit to the Dlhopolsky/Cess BRDF for clear ocean, which provides a finer angular resolution than the ERBE BRDFs. The results of this study provide a set of BRDFs for ERBE scene types in terms of a set of simple equations and few coefficients for each scene type. These models can be used for mission planning and interpretation of data from future Earth radiation budget missions such as the Clouds and Earth's Radiant Energy System (CERES).
Bias of atmospheric shortwave absorption in the NCAR Community Climate Models 2 and 3: Comparison with monthly ERBE/GEBA measurements
Authors: Zhang M. H. , Lin W. Y. , Kiehl J. T.
Published: February 2004

A direct comparison is made of collocated shortwave reflection at the top of the atmosphere and insolation at the surface between the National Center for Atmospheric Research Community Climate Models 2 and 3 (CCM2 and CCM3) and monthly Earth Radiation Budget Experiment/Global Energy Balance Archive (ERBE/GEBA) measurements. It is shown that atmospheres in the models are brighter at the top of the atmosphere than ERBE measurements and meanwhile transmit more solar radiation to the surface than GEBA measurements. As a consequence, the models underestimate atmospheric shortwave absorption. The amount of this underestimation is about 20 W m−2 in CCM2 and 17 W m−2 in CCM3. It is emphasized that regardless of whether the bias is in clear sky or in clouds, this underestimation has important implications for the intensity of the hydrological cycle and thus circulation in the models.