AVISO, 2008: SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products. Collecte Localisation Satellites,Agne, France, 39 pp.
Colbo K., R. Weller, 2007: The variability and heat budget of the upper ocean under the Chile-Peru stratus. J. Mar. Res., 65, 607- 637.10.1357/0022240077836495109a29de2de7e9cab6dacd9484887092c9http%3A%2F%2Fwww.ingentaconnect.com%2Fcontent%2Fjmr%2Fjmr%2F2007%2F00000065%2F00000005%2Fart00002http://www.ingentaconnect.com/content/jmr/jmr/2007/00000065/00000005/art00002The persistent stratus clouds found west of Chile and Peru are important for the coupling of the ocean and atmosphere in the eastern Pacific and thus in the climate of the region. The relatively cool sea-surface temperatures found west of Peru and northern Chile are believed to play a role in maintaining the stratus clouds over the region. In October 2000 a buoy was deployed at 20S, 85W, a site near the center of the stratus region, in order to examine the variability of sea-surface temperature and the temporal evolution of the vertical structure of the upper ocean. The buoy was wellinstrumented and obtained accurate time series of the surface forcing as well as time series in the upper ocean of temperature, salinity, and velocity. The variability and the extent to which local forcing explains the temporal evolution of upper ocean structure and heat content was examined. The sources of heating (primarily surface fluxes with weaker contributions from Ekman convergence and transport) are found to be balanced by cooling from the gyre-scale circulation, an eddy flux divergence and vertical diffusion. The deduced eddy flux divergence term is bounded away from zero and represents an order one source of cooling (and freshening). We postulate that the eddy flux divergence represents the effect of the cold coherent eddies formed near the coast, which propagate westward and slowly decay. Direct advection of coastal upwelled water by Ekman transport is negligible. Thus the upwelled water does influence the offshore structure, but through the fluctuating mesoscale flow not the mean transport.
de Boyer MontèGut, C., G. Madec, A. S. Fischer, A. Lazar, D. Iudicone, 2004: Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology. J. Geophys. Res,109, C12003, 481- 497.10.1029/2004JC002378549958876721e0d1668cf9a76d379a68http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2004JC002378%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2004JC002378/fullA new 2 resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed. Previous global climatologies have been based on temperature or density-gridded climatologies. The criterion selected is a threshold value of temperature or density from a near-surface value at 10 m depth (T = 0.2C or = 0.03 kg m613). A validation of the temperature criterion on moored time series data shows that the method is successful at following the base of the mixed layer. In particular, the first spring restratification is better captured than with a more commonly used larger criteria. In addition, we show that for a given 0.2C criterion, the MLD estimated from averaged profiles results in a shallow bias of 25% compared to the MLD estimated from individual profiles. A new global seasonal estimation of barrier layer thickness is also provided. An interesting result is the prevalence in mid- and high-latitude winter hemispheres of vertically density-compensated layers, creating an isopycnal but not mixed layer. Consequently, we propose an optimal estimate of MLD based on both temperature and density data. An independent validation of the maximum annual MLD with oxygen data shows that this oxygen estimate may be biased in regions of Ekman pumping or strong biological activity. Significant differences are shown compared to previous climatologies. The timing of the seasonal cycle of the mixed layer is shifted earlier in the year, and the maximum MLD captures finer structures and is shallower. These results are discussed in light of the different approaches and the choice of criterion.
Deser C., M. A. Alexand er, and M. S. Timlin, 1996: Upper ocean thermal variations in the North pacific during 1970-1991. J. Climate, 9, 1840- 1855.10.1175/1520-0442(1996)009<1840:UOTVIT>2.0.CO;286610051-77c7-4c72-b2a2-e0cf2e1e5193c149d3a1d806289914cb77607c8d2b4bhttp%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1996JCli....9.1840Drefpaperuri:(5f9d5f0523469db4bf6890e0c476f166)http://adsabs.harvard.edu/abs/1996JCli....9.1840DAbstract A newly available, extensive compilation of upper-ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400-m depth in the North Pacific during 1970-1991. A prominent decade-long perturbation in climate occurred during this time period: surface waters cooled by 651C in the central and western North Pacific and warmed by about the same amount along the west coast of North America from late 1976 to 1988. Comparison with data from COADS suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly. The vertical structure of seasonal thermal anomalies in the central North Pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400-m depth. Individual cold events descend rapidly (65100 m yr 611 ), superimposed upon a slower cooling (6515 m yr 611 ). The interdecadal climate change, while evident at the surface, is most prominent below 65150 m where interannual variations are small. Unlike the central North Pacific, the temperature changes along the west coast of North America appear to be confined to approximately the upper 200-250 m. The structure of the interdecadal thermal variations in the eastern and central North Pacific appears to be consistent with the dynamics of the ventilated thermocline. In the western North Pacific, strong cooling is observed along the axis of the Kuroshio Current Extension below 65200 m depth during the 1980s. Changes in mixed layer depth accompany the SST variations, but their spatial distribution is not identical to the pattern of SST change. In particular, the decade-long cool period in the central North Pacific was accompanied by a 6520 m deepening of the mixed layer in winter, but no significant changes in mixed layer depth were found along the west coast of North America. It is suggested that other factors such as stratification beneath the mixed layer and synoptic wind forcing may play a role in determining the distribution of mixed layer depth anomalies.
Huang R. X., 2010. Oceanic Circulation: Wind-driven and Thermohaline Processes. Cambridge University Press, Cambridge, 360- 369.
Kara A. B., P. A. Rochford, and H. E. Hurlburt, 2003: Mixed layer depth variability over the global ocean. J. Geophys. Res.: Oceans (1978-2012), 108( C3), 209.10.1029/2000JC0007363b06fed7-a1db-4491-9560-bd359f234b67abd3c64f533899a42ab5fe0dccca1c14http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2000JC000736%2Ffullrefpaperuri:(9554aced13de896e8244726590eaf470)http://onlinelibrary.wiley.com/doi/10.1029/2000JC000736/fullAbstract Top of page Abstract 1.Introduction 2.Data and Limitations 3.Mixed Layer Processes and MLD Criterion 4.Overview of Global MLD Variability 5.ILD and MLD Correspondence 6.Validation of ILD Versus MLD Correspondence 7.Conclusions Acknowledgments References Supporting Information [1] The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ocean is examined using the recently developed Naval Research Laboratory (NRL) Ocean Mixed Layer Depth (NMLD) climatologies. The MLD fields are constructed using the subsurface temperature and salinity data from the World Ocean Atlas 1994 [ Levitus et al. , 1994 ; Levitus and Boyer , 1994 ]. To minimize the limitations of these global data in the MLD determination, a simple mixing scheme is introduced to form a stable water column. Using these new data sets, global MLD characteristics are produced on the basis of an optimal definition that employs a density-based criterion having a fixed temperature difference of T = 0.8 and variable salinity. Strong seasonality of MLD is found in the subtropical Pacific Ocean and at high latitudes, as well as a very deep mixed layer in the North Atlantic Ocean in winter and a very shallow mixed layer in the Antarctic in all months. Using the climatological monthly MLD and isothermal layer depth (ILD) fields from the NMLD climatologies, an annual mean T field is presented, providing criteria for determining an ILD that is approximately equivalent to the optimal MLD. This enables MLD to be determined in cases where salinity data are not available. The validity of the correspondence between ILD and MLD is demonstrated using daily averaged subsurface temperature and salinity from two moorings: a Tropical Atmosphere Ocean array mooring in the western equatorial Pacific warm pool, where salinity stratification is important, and a Woods Hole Oceanographic Institute (WHOI) mooring in the Arabian Sea, where strongly reversing seasonal monsoon winds prevail. In the western equatorial Pacific warm pool the use of ILD criterion with an annual mean T value of 0.3鎺矯 yields comparable results with the optimal MLD, while large T values yield an overestimated MLD. An analysis of ILD and MLD in the WHOI mooring show that use of an incorrect T criterion for the ILD may underestimate or overestimate the optimal MLD. Finally, use of the spatial annual mean T values constructed from the NMLD climatologies can be used to estimate the optimal MLD from only subsurface temperature data via an equivalent ILD for any location over the global ocean.
Large W. G., S. G. Yeager, 2008: The global climatology of an interannually varying air-sea flux data set. Climate Dyn.,24, 341-364, doi: 10.1007/s00382-008-0441-3.10.1007/s00382-008-0441-36f6ad5b7-9ad1-4149-ae6f-befe4def052d730a7711ab2b95163dff278b8150175fhttp%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fa1868543150g2678%2Frefpaperuri:(31d84218ab793598b06e6948a1b5fa04)http://onlinelibrary.wiley.com/resolve/reference/ADS?id=2009ClDy...33..341LThe air鈥搒ea fluxes of momentum, heat, freshwater and their components have been computed globally from 194802at frequencies ranging from 6-hourly to monthly. All fluxes are computed over the 2302years f
Liu C. Y., Z. M. Wang, 2014: On the response of the global subduction rate to global warming in coupled climate models. Adv. Atmos. Sci.,31(1), 211-218, doi: 10.1007/s00376-013-2323-9.10.1007/s00376-013-2323-90adb0d71-aa10-4a5d-842b-fbdf69b862a313fef6623eccd076709e69322e54fb90http%3A%2F%2Fwww.cqvip.com%2FQK%2F84334X%2F201401%2F48212579.htmlrefpaperuri:(f3471fcc3ba0df7b8138152288846928)http://d.wanfangdata.com.cn/Periodical_dqkxjz-e201401020.aspxThe response of the global subduction rate to global warming was assessed based on a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models. It was found that the subduction rate of the global ocean could be significantly reduced under a warming climate, as compared to a simulation of the present-day climate. The reduction in the subduction volume was quantitatively estimated at about 40 Sv and was found to be primarily induced by the decreasing of the lateral induction term due to a shallower winter mixed layer depth. The shrinking of the winter mixed layer would result from intensified stratification caused by increased heat input into the ocean under a warming climate. A reduction in subduction associated with the vertical pumping term was estimated at about 5 Sv. Further, in the Southern Ocean, a significant reduction in subduction was estimated at around 24 Sv, indicating a substantial contribution to the weakening of global subduction.
Liu H. L., W. Y. Lin, and M. H. Zhang, 2010: Heat budget of the upper ocean in the south-central Equatorial Pacific. J. Climate, 23( 7), 1779- 1792. doi: 10.1175/2009JCLI3135.110.1175/2009JCLI3135.1de052b63b0e06393bc5a57ae8c4f6a80http%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20103168346.htmlhttp://www.cabdirect.org/abstracts/20103168346.htmlThe double intertropical convergence zone (ITCZ) over the tropical Pacific, with a spurious band of maximum annual sea surface temperature (SST) south of the equator between 500S and 1000S, is a chronic bias in coupled ocean09 tmosphere models. This study focuses on a region of the double ITCZ in the central Pacific from 500S to 1000S and 17000E to 15000W, where coupled models display the largest biases in precipitation, by deriving a best estimate of the mixed layer heat budget for the region. Seven global datasets of objectively analyzed surface energy fluxes and four ocean assimilation products are first compared and then evaluated against field measurements in adjacent regions. It was shown that the global datasets differ greatly in their net downward surface energy flux in this region, but they fall broadly into two categories: one with net downward heat flux of about 30 W m0903-2 and the other around 10 W m0903-2. Measurements from the adjacent Manus and Nauru sites of the Atmospheric Radiation Measurement Program (ARM), the Tropical Atmosphere Ocean (TAO) buoys, and the Tropical Ocean and Global Atmosphere Coupled Ocean09 tmosphere Response Experiment (TOGA COARE) are then used to show that the smaller value is more realistic. An energy balance of the mixed layer is finally presented for the region as primarily between warming from surface heat flux of 7 W m0903-2 and horizontal advective cooling in the zonal direction of about 5 W m0903-2, with secondary contributions from meridional and vertical advections, heat storage, and subgrid-scale mixing. The 7 W m0903-2 net surface heat flux consists of warming of 210 W m0903-2 from solar radiation and cooling of 53, 141, and 8 W m0903-2, respectively, from longwave radiation, latent heat flux, and sensible heat flux. These values provide an observational basis to further study the initial development of excessive precipitation in coupled climate models in the central Pacific.
Liu L. L., R. X. Huang, 2012: The global subduction/obduction rates: Their interannual and decadal variability. J. Climate, 25( 4), 1096- 1115.10.1175/2011JCLI4228.1408135e09061689c43b4a941d3fa4286http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2012JCli...25.1096Lhttp://adsabs.harvard.edu/abs/2012JCli...25.1096LVentilation, including subduction and obduction, for the global oceans was examined using Simple Ocean Data Assimilation (SODA) outputs. The global subduction rate averaged over the period from 1959 to 2006 is estimated at 505.8 Sv (1 Sv 09-03 106 m3 s0903-1), while the corresponding global obduction rate is estimated at 482.1 Sv. The annual subduction/obduction rates vary greatly on the interannual and decadal time scales. The global subduction rate is estimated to have increased 7.6%% over the past 50 years, while the obduction rate is estimated to have increased 9.8%%. Such trends may be insignificant because errors associated with the data generated by ocean data assimilation could be as large as 10%%. However, a major physical mechanism that induced these trends is primarily linked to changes in the Southern Ocean. While the Southern Ocean plays a key role in global subduction and obduction rates and their variability, both the Southern Ocean and equatorial regions are critically important sites of water mass formation/erosion.
Luo Y. Y., Q. Y. Liu, and L. M. Rothstein, 2011: Increase of South Pacific eastern subtropical mode water under global warming. Geophys. Res. Lett., 38, L01601.10.1029/2010GL0458789f9d7a49b10f4b0af30817eb2880b400http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2010GL045878%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2010GL045878/full[1] The response of South Pacific Eastern Subtropical Mode Water (SPESTMW) to global warming is investigated by comparing solutions from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled models between a present-day climate and a future, warmer climate. Under the warmer climate scenario, the SPESTMW extends southwestward and is significantly increased in volume. This is because all the local surface forcing mechanisms (i.e., wind stress, heat and freshwater fluxes) in the eastern subtropical South Pacific tends to de-stratify the upper ocean and thus deepen the mixed layer. Further, a suite of process-oriented experiments with an ocean general circulation model suggest that it is the intensified southeast trade winds under the warmer climate that promotes more heat flux from the ocean into the atmosphere that then results in a deepening of the mixed layer in the eastern subtropics of the South Pacific.
Nishikawa S., A. Kubokawa, 2012: Mixed layer depth front and subduction of low potential vorticity water under seasonal forcings in an idealized OGCM. Journal of Oceanography, 68( 1), 53- 62.10.1007/s10872-011-0086-4c0064573-4ed8-446a-9cdf-586742dd2c7850778201268153-62Abstract<br/>The mixed layer depth (MLD) front and subduction under seasonal variability are investigated using an idealized ocean general circulation model (OGCM) with simple seasonal forcings. A sharp MLD front develops and subduction occurs at the front from late winter to early spring. The position of the MLD front agrees with the curve where <span class="a-plus-plus inline-equation id-i-eq1"><span class="a-plus-plus equation-source format-t-e-x">${\rm D}T_{\rm s}/{\rm D}t = \partial T_{\rm s} /\partial t + {\user2{u}}_{\rm g} \cdot \nabla T_{\rm s} = 0$</span></span> is satisfied (<em class="a-plus-plus">t</em> is time, <span class="a-plus-plus inline-equation id-i-eq2"><span class="a-plus-plus equation-source format-t-e-x">${\user2{u}}_{\rm g}$</span></span> is the upper-ocean geostrophic velocity, <span class="a-plus-plus inline-equation id-i-eq57"><span class="a-plus-plus equation-source format-t-e-x">$T_{\rm s}$</span></span> is the sea surface temperature (SST), and <span class="a-plus-plus inline-equation id-i-eq58"><span class="a-plus-plus equation-source format-t-e-x">$\nabla$</span></span> is the horizontal gradient operator), indicating that thick mixed-layer water is subducted there parallel to the SST contour. This is a generalization of the past result that the MLD front coincides with the curve <span class="a-plus-plus inline-equation id-i-eq3"><span class="a-plus-plus equation-source format-t-e-x">${\user2{u}}_{\rm g} \cdot \nabla T_{\rm s} = 0$</span></span> when the forcing is steady. Irreversible subduction at the MLD front is limited to about 1 month, where the beginning of the irreversible subduction period agrees with the first coincidence of the MLD front and <span class="a-plus-plus inline-equation id-i-eq59"><span class="a-plus-plus equation-source format-t-e-x">${\rm D}T_{\rm s}/{\rm D}t =0$</span></span> in late winter, and the end of the period roughly corresponds to the disappearance of the MLD front in early spring. Subduction volume at the MLD front during this period is similar to that during 1 year in the steady-forcing model. Since the cooling of the deep mixed-layer water occurs only in winter and SST can not fully catch up with the seasonally varying reference temperature of restoring, the cooling rate of SST is reduced and the zonal gradient of the SST in the northwestern subtropical gyre is a little altered in the seasonal-forcing case. These effects result in slightly lower densities of subducted water and the eastward shift of the MLD front.<br/>
Pan A. J., Q. Y. Liu, and Z. Y. Liu, 2008: Formation mechanism of the "Stability Gap" and the North Pacific central mode water. Chinese Journal of Geophysics, 51( 1), 77- 87. (in Chinese)10.1002/cjg2.11954204b447-ca8f-4a85-9092-195362973783982fa326560e41d3ceed9842f7a68a8fhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fcjg2.1195%2Fcitedbyhttp://en.cnki.com.cn/Article_en/CJFDTotal-DQWX200801012.htmLocal feature of the formation region (165E-160W,38N-42N) of the North Pacific Central Mode Water (NPCMW) is first put forward from data analysis, and for which, the external atmospheric forcing (solar shortwave radiation, net heat flux and wind stress curl) could not give acceptable explanation. Further analysis on the seasonal variability of the upper ocean stratification shows that a special weak zone of the ocean stratification in the upper ocean (75 m)-the "stability gap" is detected in (165E-160W,38N-42N) in autumn (September-October). As "Precondition Mechanism", the "stability gap" provides a reliable answer for the "local feature" of the formation of the NPCMW. Based on a heat balance equation of the upper ocean mixed layer, diagnostic analysis suggests that the formation of the "stability gap" is the cooperative product of the surface heat flux forcing, vertical entrainment, Ekman advection and geostrophic advction. Among which, the latitudinal differences of the surface heat flux forcing, the cold Ekman advection and the warm geostrophic advection play the crucial roles on determining the critical eastern and western bound of the "stability gap".
Qiu B., R. X. Huang, 1995: Ventilation of the North Atlantic and North Pacific: Subduction versus obduction. J. Phys. Oceanogr., 25, 2374- 2390.2fa79fd7ce9aac653661a58184a0be93http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1995jpo....25.2374q/s?wd=paperuri%3A%28b80d133fabb514fdf3e3383bda174649%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1995jpo....25.2374q&ie=utf-8
Sato K., T. Suga, 2009: Structure and modification of the South Pacific eastern subtropical mode water. J. Phys. Oceanogr., 39, 1700- 1714.10.1175/2008JPO3940.1f59a0a7d3666709922da986ba122942fhttp%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2009JPO....39.1700Shttp://adsabs.harvard.edu/abs/2009JPO....39.1700SUsing all available temperature and salinity profiles obtained by Argo floats from July 2004 to June 2007, this study investigated the structure and modification of the South Pacific Eastern Subtropical Mode Water (SPESTMW). Based on the observed characteristics of the vertical minima of potential vorticity over the subtropical South Pacific, SPESTMW is defined as water with potential vorticity magnitude less than 2.5 01- 10-10 m-1 s-1 and thickness exceeding 40 m. It is found between 350009/500S and 1600009/7000W and has a temperature of 130009/2600C, salinity greater than 34.0, and density of 24.509/25.8 kg m-3 at its core. This study confirmed that vertical changes in temperature and salinity tend to compensate for each other in terms of density changes, resulting in favorable salt fingering conditions, as previously reported. By analyzing many profiles of Argo data in spring immediately after the SPESTMW formation period, its temperature and salinity are vertically uniform in the formation region, but large vertical gradients of temperature and salinity are found downstream from that region, even in the SPESTMW core. Consequently, the low potential vorticity signature of SPESTMW spread much wider than its signature as a thermostad. The Argo data also captured the seasonal changes of the vertical gradients of temperature and salinity at the SPESTMW core; these gradients increased as the seasons progressed, even in the formation region. Therefore, SPESTMW is truly vertically uniform water (i.e., thermostad, halostad, and pycnostad simultaneously) only immediately after the formation period. Afterward, it is only pycnostad. This seasonal evolution is related to temperature and salinity diffusion due to salt fingering in a manner similar to the rapid modification of interannual anomalies as shown by previous research. The temperature and salinity near the SPESTMW core and lower region decreased soon after its formation.
Williams R. G., 1991: The role of the mixed layer in setting the potential vorticity of the main thermocline. J. Phys. Oceanogr., 21, 1803- 1814.10.1175/1520-0485(1991)021<1803:TROTML>2.0.CO;2f3264ce549c80ecf19d7da305ce3a768http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1991JPO....21.1803Whttp://adsabs.harvard.edu/abs/1991JPO....21.1803WAbstract A steady ventilation model is used to assess the effect of the mixed layer on the structure of the main thermocline; the potential vorticity is found in a subtropical gyre after imposing the thickness and density of the mixed layer, the Ekman pumping, and the hydrography on the eastern boundary. The modeled potential vorticity becomes comparable in value to observations in the North Atlantic if the mixed layer deepens poleward as is observed in winter. The isopycnal gradients in potential vorticity are reduced on the denser ventilated surfaces if the mixed-layer outcrops deviate from latitude circles and, more realistically, sweep southward along the eastern boundary; the age of the subducted fluid is also in reasonable agreement with observations of the tritium-helium age by Jenkins. This study suggests that ventilation may form much of the extensive region of nearly uniform potential vorticity observed on the = 26.75 surface in the North Atlantic, with lateral mixing by eddies being required only in the unventilated pool on the western side of the gyre.
Wong A. P. S., G. C. Johnson, 2003: South Pacific eastern subtropical mode water. J. Phys. Oceanogr., 33( 7), 1493- 1509.ab3a6bf0d644d4cf082c87066a01d7a8http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2003JPO....33.1493W/s?wd=paperuri%3A%289ea36b14be1c1e9376426ad380c08244%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2003JPO....33.1493W&ie=utf-8
Xie P. P., P.A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc., 78, 2539- 2558.10.1175/1520-0477(1997)078<2539:GPAYMA>2.0.CO;2b11e9f6a-e0a7-42f9-a97b-a26069da3c8d3039680de89ffc852c3d9b6b72a9b3dbhttp%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1997BAMS...78.2539Xrefpaperuri:(f637afb56e50553202efc8c31489db4c)http://adsabs.harvard.edu/abs/1997BAMS...78.2539XAbstract Gridded fields (analyses) of global monthly precipitation have been constructed on a 2.5 latitude ongitude grid for the 17-yr period from 1979 to 1995 by merging several kinds of information sources with different characteristics, including gauge observations, estimates inferred from a variety of satellite observations, and the NCEPCAR reanalysis. This new dataset, which the authors have named the CPC Merged Analysis of Precipitation (CMAP), contains precipitation distributions with full global coverage and improved quality compared to the individual data sources. Examinations showed no discontinuity during the 17-yr period, despite the different data sources used for the different subperiods. Comparisons of the CMAP with the merged analysis of Huffman et al. revealed remarkable agreements over the global land areas and over tropical and subtropical oceanic areas, with differences observed over extratropical oceanic areas. The 17-yr CMAP dataset is used to investigate the annual and interannual variability in large-scale precipitation. The mean distribution and the annual cycle in the 17-yr dataset exhibit reasonable agreement with existing long-term means except over the eastern tropical Pacific. The interannual variability associated with the El Ni09o鈥揝outhern Oscillation phenomenon resembles that found in previous studies, but with substantial additional details, particularly over the oceans. With complete global coverage, extended period and improved quality, the 17-yr dataset of the CMAP provides very useful information for climate analysis, numerical model validation, hydrological research, and many other applications. Further work is under way to improve the quality, extend the temporal coverage, and to refine the resolution of the merged analysis.
Xie S. P., L. X. Xu, Q. Y. Liu, and F. Kobashi, 2011: Dynamical role of mode water ventilation in decadal variability in the central subtropical gyre of the North Pacific. J. Climate, 24, 1212- 1225.10.1175/2010JCLI3896.1132699c5078a1bfc35667ede9e7a7029http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2011JCli...24.1212Xhttp://adsabs.harvard.edu/abs/2011JCli...24.1212XAbstract Decadal variability in the interior subtropical North Pacific is examined in the Geophysical Fluid Dynamics Laboratory coupled model (CM2.1). Superimposed on a broad, classical subtropical gyre is a narrow jet called the subtropical countercurrent (STCC) that flows northeastward against the northeast trade winds. Consistent with observations, the STCC is anchored by mode water characterized by its low potential vorticity (PV). Mode water forms in the deep winter mixed layer of the Kuroshio yashio Extension (KOE) east of Japan and flows southward riding on the subtropical gyre and preserving its low-PV characteristic. As a thick layer of uniform properties, the mode water forces the upper pycnocline to shoal, and the associated eastward shear results in the surface-intensified STCC. On decadal time scales in the central subtropical gyre (15-35N, 170E-130W), the dominant mode of sea surface height variability is characterized by the strengthening and weakening of the STCC because of variations in mode water ventilation. The changes in mode water can be further traced upstream to variability in the mixed layer depth and subduction rate in the KOE region. Both the mean and anomalies of STCC induce significant sea surface temperature anomalies via thermal advection. Clear atmospheric response is seen in wind curls, with patterns suggestive of positive coupled feedback. In oceanic and coupled models, northeast-slanted bands often appear in anomalies of temperature and circulation at and beneath the surface. The results of this study show that such slanted bands are characteristic of changes in mode water ventilation. Indeed, this natural mode of STCC variability is excited by global warming, resulting in banded structures in sea surface warming.
Xu L. X., S. P. Xie, J. L. McClean, Q. Y. Liu, and H. Sasaki, 2014: Mesoscale eddy effects on the subduction of North Pacific mode waters. J. Geophys. Res.-Oceans,119, 4867-4886, doi: 10.1002/2014JC009861.10.1002/2014JC009861c36cb47bf8cc6fc905ae1856eba81c45http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2F2014JC009861%2Fabstracthttp://onlinelibrary.wiley.com/doi/10.1002/2014JC009861/abstractAbstract Mesoscale eddy effects on the subduction of North Pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved. The eddy-resolving models produce results closer to observations than the noneddy-resolving model. There are large discrepancies in subduction patterns between eddy-resolving and noneddy-resolving models. In the noneddy-resolving model, subduction on a given isopycnal is limited to the cross point between the mixed layer depth (MLD) front and the outcrop line whereas in eddy-resolving models and observations, subduction takes place in a broader, zonally elongated band within the deep mixed layer region. Mesoscale eddies significantly enhance the total subduction rate, helping create remarkable peaks in the volume histogram that correspond to North Pacific subtropical mode water (STMW) and central mode water (CMW). Eddy-enhanced subduction preferentially occurs south of the winter mean outcrop. With an anticyclonic eddy to the west and a cyclonic eddy to the east, the outcrop line meanders south, and the thermocline/MLD shoals eastward. As eddies propagate westward, the MLD shoals, shielding the water of low potential vorticity from the atmosphere. The southward eddy flow then carries the subducted water mass into the thermocline. The eddy subduction processes revealed here have important implications for designing field observations and improving models.
Yu L. S., 2007: Global variations in oceanic evaporation (1958-2005): The role of the changing wind speed. J. Climate, 20( 21), 5376- 5390.10.1175/2007JCLI1714.17c5dd972-fc32-4abb-8652-3efe3da52001528d04042991cf1eef016e690ab7ecbahttp%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2007JCli...20.5376Yrefpaperuri:(116174cc574f783c4fcd02bf6f4eddc1)http://adsabs.harvard.edu/abs/2007JCli...20.5376YAbstract Global estimates of oceanic evaporation (Evp) from 1958 to 2005 have been recently developed by the Objectively Analyzed Airea Fluxes (OAFlux) project at the Woods Hole Oceanographic Institution (WHOI). The nearly 50-yr time series shows that the decadal change of the global oceanic evaporation (Evp) is marked by a distinct transition from a downward trend to an upward trend around 1977-78. Since the transition, the global oceanic Evp has been up about 11 cm yr 611 (6510%), from a low at 103 cm yr 611 in 1977 to a peak at 114 cm yr 611 in 2003. The increase in Evp was most dramatic during the 1990s. The uncertainty of the estimates is about 卤2.74 cm yr 611 . By utilizing the newly developed datasets of Evp and related airea variables, the study investigated the cause of the decadal change in oceanic Evp. The decadal differences between the 1990s and the 1970s indicates that the increase of Evp in the 1990s occurred over a global scale and had spatially coherent structures. Larger Evp is most pronounced in two key regionsne is the paths of the global western boundary currents and their extensions, and the other is the tropical Indo-Pacific warm water pools. It is also found that Evp was enlarged primarily during the hemispheric wintertime (defined as the mean of Decemberebruary for the northern oceans and June ugust for the southern oceans). Despite the dominant upward tendency over the global basins, a slight reduction in Evp appeared in such regions as the subtropical centers of the Evp maxima as well as the eastern equatorial Pacific and Atlantic cold tongues. An empirical orthogonal function (EOF) analysis was performed for the yearly winter-mean time series of Evp and the related airea variables [i.e., wind speed ( U ) and airea humidity differences ( dq )]. The analysis suggested a dominant role of the wind forcing in the decadal change of both Evp and dq . It is hypothesized that wind impacts Evp in two ways. The first way is direct: the greater wind speed induces more evaporation by carrying water vapor away from the evaporating surface to allow the airea humidity gradients to be reestablished at a faster pace. The second way is indirect: the enhanced surface wind strengthens the wind-driven subtropical gyre, which in turn drives a greater heat transport by the western boundary currents, warms up SST along the paths of the currents and extensions, and causes more evaporation by enlarging the airea humidity gradients. The EOF analysis performed for the time series of the global annual-mean Evp fields showed that the first three EOF modes account for nearly 50% of the total variance. The mode 1 variability represents the upward trend in Evp after 1978 and is attributable to the increased U , and the mode 2 variability explains much of the downward trend in Evp before 1978 and is correlated to the global dq variability. The EOF mode 3 of Evp captures the interannual variability of Evp on time scales of the El Ni09oouthern Oscillation, with the center of action over the eastern equatorial Pacific.
Yu L. S., R. A. Weller, 2007: Objectively analyzed air-sea heat fluxes for the global ice-free oceans (1981-2005). Bull. Amer. Meteor. Soc., 88( 4), 527- 539.10.1175/BAMS-88-4-527e1d266f6-da9d-4447-9ea8-46e3e0cd317e13f000d1e05099b83ea6218aa70a28f8http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2007BAMS...88..527Yrefpaperuri:(6110649686cf0990540db0110f7812f8)http://adsabs.harvard.edu/abs/2007BAMS...88..527YAbstract A 25-yr (1981-2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air ea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset. The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m 612 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.
Yu L. S., X. Z. Jin, and R. A. Weller, 2006: Role of net surface heat flux in seasonal evolutions of sea surface temperature in the tropical Atlantic Ocean. J. Climate, 19, 6153- 6169.10.1175/JCLI3970.11f7ff90c-7a5e-46c0-8cfd-c234c48225d3026bea503a13f7778f3a9cfcf13a6182http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F49245594_Role_of_net_surface_heat_flux_in_the_seasonal_evolution_of_sea_surface_temperature_in_the_Atlantic_Oceanrefpaperuri:(33c69410c2aad0530942cb4216409dee)http://www.researchgate.net/publication/49245594_Role_of_net_surface_heat_flux_in_the_seasonal_evolution_of_sea_surface_temperature_in_the_Atlantic_OceanABSTRACT The present study used a new net surface heat flux (Qnet) product obtained from the Objective Analyzed Air&ndash;Sea Fluxes (OAFlux) project and the International Satellite Cloud Climatology Project (ISCCP) to examine two specific issues&mdash;one is to which degree Qnet controls seasonal variations of sea surface temperature (SST) in the tropical Atlantic Ocean (20&ndash;20, east of 60), and the other is whether the physical relation can serve as a measure to evaluate the physical representation of a heat flux product. To better address the two issues, the study included the analysis of three additional heat flux products: the Southampton Oceanographic Centre (SOC) heat flux analysis based on ship reports, and the model fluxes from the National Centers for Environmental Prediction&ndash;National Center for Atmospheric Research (NCEP&ndash;NCAR) reanalysis and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The study also uses the monthly subsurface temperature fields from the World Ocean Atlas to help analyze the seasonal changes of the mixed layer depth (hMLD). The study showed that the tropical Atlantic sector could be divided into two regimes based on the influence level of Qnet. SST variability poleward of 5 and 10 is dominated by the annual cycle of Qnet. In these regions the warming (cooling) of the sea surface is highly correlated with the increased (decreased) Qnet confined in a relatively shallow (deep) hMLD. The seasonal evolution of SST variability is well predicted by simply relating the local Qnet with a variable hMLD. On the other hand, the influence of Qnet diminishes in the deep Tropics within 5 and 10 and ocean dynamic processes play a dominant role. The dynamics-induced changes in SST are most evident along the two belts, one of which is located on the equator and the other off the equator at about 3 in the west, which tilts to about 10 near the northwestern African coast. The study also showed that if the degree of consistency between the correlation relationships of Qnet, hMLD, and SST variability serves as a measure of the quality of the Qnet product, then the Qnet from OAFlux + ISCCP and ERA-40 are most physically representative, followed by SOC. The NCEP&ndash;NCAR Qnet is least representative. It should be noted that the Qnet from OAFlux + ISCCP and ERA-40 have a quite different annual mean pattern. OAFlux + ISCCP agrees with SOC in that the tropical Atlantic sector gains heat from the atmosphere on the annual mean basis, where the ERA-40 and the NCEP&ndash;NCAR model reanalyses indicate that positive Qnet occurs only in the narrow equatorial band and in the eastern portion of the tropical basin. Nevertheless, seasonal variances of the Qnet from OAFlux + ISCCP and ERA-40 are very similar once the respective mean is removed, which explains why the two agree with each other in accounting for the seasonal variability of SST. In summary, the study suggests that an accurate estimation of surface heat flux is crucially important for understanding and predicting SST fluctuations in the tropical Atlantic Ocean. It also suggests that future emphasis on improving the surface heat flux estimation should be placed more on reducing the mean bias. Author Posting. American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 19 (2006): 6153&ndash;6169, doi:10.1175/JCLI3970.1. This study is support by the NOAA CLIVAR Atlantic under Grant NA06GP0453 and NOAA Climate observations and Climate Change and Data Detection under Grant NA17RJ1223.