摘要:

A realistic primitive‐equation model of the Southern Ocean at eddying spatial resolution is used to examine the effect of ocean‐surface‐velocity dependence of the wind stress on the strength of near‐inertial oscillations. Accounting for the ocean‐surface‐velocity dependence of the wind stress leads to a large reduction of wind‐induced near‐inertial energy of approximately 40% and of wind power input into the near‐inertial frequency band of approximately 20%. A large part of this reduction can be explained by the leading‐order modification to the wind stress if the ocean‐surface velocity is included. The strength of the reduction is shown to be modulated by the inverse of the ocean‐surface‐mixed‐layer depth. We conclude that the effect of surface‐velocity dependence of the wind stress should be taken into account when estimating the wind‐power input into the near‐inertial frequency band and when estimating near‐inertial energy leve

ISSN:0148-0227    

DOI:10.1002/jgrc.20198

年代:2013

数据来源: WILEY

摘要:

The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid‐depth turbulent dissipation rates are found to increase fromO(1×10−10Wkg −1)in the Southeast Pacific toO(1×10−9Wkg −1)in the Scotia Sea, typically reaching3×10−9Wkg −1within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near‐bottom flows, rough topography, and regions where the internal wavefield is found to have enhanced energy, a less‐inertial frequency content and a dominance of upward propagating energy. These results strongly suggest that bottom‐generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mW m−2in the Southeast Pacific and 14 mW m−2in the Scotia Sea. Typically, 10%–30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure‐derived estimates suggests a significant departure from wave‐wave interaction physics in t

ISSN:0148-0227    

DOI:10.1002/jgrc.20217

年代:2013

数据来源: WILEY

摘要:

The effects of solar penetration on the annual cycle of extratropical North Pacific sea surface temperature (SST) are investigated based on coupled ocean‐atmosphere model simulations. It is found that the solar penetration can significantly improve the seasonal cycle of the North Pacific SST in the model. In summer, the solar penetration can partly reduce the SST warm bias in the model by diluting the shortwave radiation to the seasonal thermocline, while in winter, it can reduce the model SST cold bias through the entrainment of the warm thermocline water into the mixed layer. The solar penetration forces significant changes not only in the ocean but also in the atmosphere. The changes in the atmospheric circulation are characterized by a baroclinic structure with ridge/trough in the lower/upper troposphere in summer and an equivalent barotropic trough in winter. As a result, the annual mean of the oceanic subtropical gyre is intensified. Our study echoes the potential importance of the ecosystem in modulating the coupled ocean‐atmosphere interaction over the extratropical oce

ISSN:0148-0227    

DOI:10.1002/jgrc.20208

年代:2013

数据来源: WILEY

摘要:

A high‐frequency asymptotics approach within the Lagrangian framework shows that some exact equatorially trapped three‐dimensional waves are linearly unstable when their steepness exceeds a specific thresh

ISSN:0148-0227    

DOI:10.1002/jgrc.20219

年代:2013

数据来源: WILEY

摘要:

The evolution of the upper Southern Ocean hydrographic structure in response to the representative concentration pathways 4.5 (RCP 4.5) forcing scenario is analyzed using model data drawn from the coupled model intercomparison project phase 5 (CMIP5) archive. A robust freshening trend is evident, associated with an increase in stratification and decoupling of the upper ocean as the mixed layer gains buoyancy at a faster rate than the underlying ocean. The magnitudes of the individual terms of the salinity and heat budgets are evaluated. Convection‐driven entrainment from the thermocline into the mixed layer is found to play a significant role in modulating the mixed layer salinity, whilst the heat budget of the mixed layer is dominated by a primary balance between atmospheric warming and the entrainment‐modulated supply of oceanic heat from below the mixed layer. The relationship between oceanic heat storage below the mixed layer, ice thickness and atmospheric temperature is investigated, and a very disparate response noted amongst the models considered here. Based on this analysis, we hypothesize that the balance between the entrainment‐modulated supply of oceanic heat from below the mixed layer and the heat supplied by the atmosphere may play an important role in determining the simulated sea ice variab

ISSN:0148-0227    

DOI:10.1002/jgrc.20226

年代:2013

数据来源: WILEY

摘要:

Analysis of data sets based on satellite measurements during 1992–2011 reveals pronounced interannual‐to‐decadal variations of the west Pacific North Equatorial Countercurrent (NECC) system, involving the intensity (INT), position (YCM), and path length (LCM) of the surface NECC jet, together with the associated recirculation gyres and mesoscale eddies. During the 1997–1998 and 2009–2010 El Niño events, the NECC jet showed increased INT before, and decreased INT, northerly position, and lengthened path after the mature phase. During the 1993–1995 and 2002–2005 central Pacific warming events, it also showed increased INT but no evident changes inYCMandLCM. The varied responses caused the different natures of individual El Niño events. In 1998 and 2010, reflected upwelling Kelvin waves south of the NECC jet, together with the downwelling Rossby waves north of it induced by the following strong La Niña events, weakened the NECC jet through geostrophy and shifted it northward. This process was however absent during the 1993–1995 and 2002–2005 events. Intensified NECC jet during warm conditions gives rise to anomalously active mesoscale eddies, which also contribute to the unstable states of the NECC system in 1998 and 2010. Hindcast with a linear Rossby wave model reveals a slow change of the western Pacific NECC system during the past 50 years. Since 1990s, low‐frequency variance of the NECC system has been dominated by quasi‐decadal signals and more closely associated with wind forcing in the western Pacific Ocean, which corresponds to the slow changes of the El Niño/Southern Oscillation (ENSO)‐r

ISSN:0148-0227    

DOI:10.1002/jgrc.20196

年代:2013

数据来源: WILEY

摘要:

A variational data assimilation system based on an incremental 4D‐Var approach is proposed for use with a zero‐dimensional model of the diurnal cycle of sea surface temperature (SST). Traditional 4D‐Var, which seeks to find the initial state of a system, is not appropriate for diurnal SST which is a wind and heat flux driven system that has only a limited memory of its prior state. Instead the proposed assimilation system corrects both the initial SST and the heat and wind fluxes applied throughout the day. The assimilation system is tested using ensembles in a set of idealized twin experiments. In these tests controlling parameters are varied around reasonable “default” values with the quality of the analyses assessed against a known “truth”. Within our tests data assimilation is shown to improve diurnal SST under most circumstances. Analyzed heat fluxes are also sometimes improved, although the improvement is much less than that observed for diurnal SST. The system was not found to improve the wind stress. The only circumstances where diurnal SST was not found to be improved by the assimilation were where either observational errors were large (greater than 0.5 K in our tests), or biases in the observations were too big (less than −0.3 K or greater than 0.2 K). The non‐Gaussian behavior of the wind stress was found to have an impact on the assimilation in low‐wind conditions and under these conditions the best analyses were obtained by artificially inflating th

ISSN:0148-0227    

DOI:10.1002/jgrc.20215

年代:2013

数据来源: WILEY

摘要:

The response of the Bay of Fundy and Gulf of Maine to large‐scale tidal power plants and future sea‐level rise is investigated using an established numerical tidal model. Free stream tidal turbines were simulated within the Bay of Fundy by implementing an additional bed friction term,Kt. The present‐day maximum tidal power output was determined to be 7.1 GW, and requiredKt = 0.03. Extraction at this level would lead to large changes in the tidal amplitudes across the Gulf of Maine. With future SLR implemented, the energy available for extraction increases with 0.5–1 GW per m SLR. SLR simulations without tidal power extraction revealed that the response of the semidiurnal tides to SLR is highly dependent on how changes in sea level are implemented in the model. When extensive flood defenses are assumed at the present‐day coast line, the response to SLR is far larger than when land is allowed to (permanently) flood. For example, within the Bay of Fundy itself, the M2amplitude increases with nearly 0.12 m per m SLR without flooding, but it changes with only 0.03 m per m SLR with flooding. We suggest that this is due to the flooding of land cells changing the resonant properties

ISSN:0148-0227    

DOI:10.1002/jgrc.20221

年代:2013

数据来源: WILEY

摘要:

The source of the Canary Current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre (29–37°N, 9–24°W). The Portugal Current is observed between 13.5 and 14.8°W at 37°N carrying1.8±0.4Sv southward. This current presumably merges with the eastward transport of the Azores Current System and partly contributes to the Mediterranean inflow and partly to the northward recirculation of the Azores Current through the Gulf of Cadiz. The Azores Current System is located in the meridional range 33.50–36.25°N at 24.50°W. This System transports eastward7.2±0.5Sv in the thermocline layers and1.1±0.8Sv at intermediate layers. The Azores Current intermediate water mass has the highest portion of Sub‐Arctic intermediate water (SAIW) in the region, while the Azores Countercurrent intermediate waters mass is mainly Mediterranean water. The Canary Current extends from 22.25° to 18.50°W at 29°N, the westernmost position ever observed. This current transports southward−6.2±0.6Sv in the thermocline layers and−2.0±0.8Sv in the intermediate layers. This intermediate flow shows a relative maximum of oxygen and a relative minimum in nutrient concentration, indicating the presence of SAIW. The study concludes that, at least in fall 2009, the Canary Current extends to the intermediate waters (γn≤27.9220approximately 1600 dbar) and that Azores Current feeds the Canary Current at sur

ISSN:0148-0227    

DOI:10.1002/jgrc.20227

年代:2013

数据来源: WILEY

摘要:

Snow depth on sea ice (SD) is a key geophysical variable, knowledge of which is critical for calculating the energy and mass balance budgets. Moreover, accurate knowledge of the SD distribution is important to retrieve sea‐ice thicknesses from altimetry data. So far, only space‐based microwave radiometers (e.g., Advanced Microwave Scanning Radiometer for Earth Observing System; AMSR‐E) provide operational SD on seasonal sea‐ice retrievals. A thorough assessment of these retrievals is needed on a large scale and on a variety of sea‐ice types. Our study presents such an assessment on Arctic sea ice using NASA's airborne Operation IceBridge (OIB) SDs, retrieved from radar measurements. Between 2009 and 2011, ∼610 12.5 km satellite grid cells were covered by seasonal sea ice where both satellite SD retrievals and OIB data were available. Using all the available data, the difference between the AMSR‐E product and the averaged OIB snow‐radar‐derived SD is 0.00±0.07 m. Satellite‐derived SD was accurate in the Beaufort Sea and the Canadian Archipelago but underestimated (∼0.07 m) in the Nares Strait. The RMSE between the two products ranges between 0.03 and 0.15 m. The RMSE is less than 0.06 m over a shallow snow cover (0.10 m) have been identified and related to the presence of either low ice concentration or significant fraction of multiyear ice within the grid ce

ISSN:0148-0227    

DOI:10.1002/jgrc.20228

年代:2013

数据来源: WILEY