Corrigendum to “Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation gyre” [Deep-Sea Res. II 85 (2013) 62–74]

This paper is not subject to U.S. copyright. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 132 (2016): 263–264, doi:10.1016/j.dsr2.2016.08.001

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

This paper is not subject to U.S. copyright. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 85 (2013): 62-74, doi:10.1016/j.dsr2.2012.07.018.Data from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3×10−4 m2/s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.N. Bond and L. Rainville were supported by NSF Grant OCE-0827125. T. Farrar and S. Jayne were supported by NSF Grant OCE-0825152. B. Qiu was supported by NSF Grant OCN-0220680

Low-Cost GNSS-R Altimetry on a UAV for Water-Level Measurements at Arbitrary Times and Locations

Together with direct Global Navigation Satellite System (GNSS) signals, the signals reflected at the water surface can be received by an unmanned aerial vehicle (UAV). From the range difference between two GNSS signal paths, the height of the UAV above the water level can be geometrically estimated using the weighted least squares method, called GNSS reflectometry (GNSS-R) altimetry. Experimental low-cost GNSS-R altimetry flights with a UAV were conducted at the coast of Lake Biwa, Japan. Although the height estimated by the GNSS-R altimeter included large short-term noises up to 8 m amplitude, it agreed well with the UAV altitude measured by the post-processed kinematic positioning. By selecting better weight functions in the least square method and using sufficient temporal averaging, the GNSS-R altimetry achieved accuracy in the order of 0.01 m if a sufficient number of GNSS satellites with high elevation angles were available. The dependency of the results on the weight functions is also discussed

1990年代のインド洋ダイポールモードにおける大気海洋間相互作用の果たす役割の弱さについて

観測データと4次元結合同化システムの結果を用いて，インド洋ダイポールモード(IOD)発生時の東極の水温構造の変化を調べた．熱収支解析の結果，インドネシア沿岸域の水温偏差が湧昇の影響で変動している可能性が強まった．正のダイポール年において海上風偏差は全域で正偏差であったにも関わらず，沿岸域の海面熱フラックスが水温偏差を解消する方向に働いていた．これは沿岸湧昇による水温変動が潜熱フラックスに支配的に働いたためと考えられ，ダイポールモード発生時の実際の水温変動過程は領域平均の解析から得られた描像とは異なっている．IODの発生機構については，沿岸湧昇に加えて潜熱フラックスによって生じる海面水温偏差の重要性が特に指摘されてきたが，このような大気海洋が非断熱的に結合した正のフィードバック過程の働きは，従来考えられていたよりも弱い可能性が出てきたといえる．We analyze the temporal and spatial variation of the thermal structure of the eastern tropical Indian Ocean associated with Indian Ocean Dipole Mode (IOD), mainly using the water temperature of 10 years (1990-1999) of the World Ocean Circulation Experiment (WOCE) repeat IX1 expendable bathythermograph (XBT) section between Java and Western Australia together with the product of the air-sea coupled four-dimensional variational analysis (4D-VAR) system. The temperature anomaly of the XBT section reveals that the subsurface ocean temperature changes earlier than the surface before the surface IOD pattern starts to grow up. From May to August, a marked subsurface temperature anomaly is also found as well as the sea surface temperature (SST) that is formed primarily by the anomalous coastal upwelling along the south Java coast. Heat budget analysis along IX1 shows that the surface heat flux does not work to enhance the mixed layer temperature anomaly in the eastern pole region.観測データと4次元結合同化システムの結果を用いて，インド洋ダイポールモード(IOD)発生時の東極の水温構造の変化を調べた．熱収支解析の結果，インドネシア沿岸域の水温偏差が湧昇の影響で変動している可能性が強まった．正のダイポール年において海上風偏差は全域で正偏差であったにも関わらず，沿岸域の海面熱フラックスが水温偏差を解消する方向に働いていた．これは沿岸湧昇による水温変動が潜熱フラックスに支配的に働いたためと考えられ，ダイポールモード発生時の実際の水温変動過程は領域平均の解析から得られた描像とは異なっている．IODの発生機構については，沿岸湧昇に加えて潜熱フラックスによって生じる海面水温偏差の重要性が特に指摘されてきたが，このような大気海洋が非断熱的に結合した正のフィードバック過程の働きは，従来考えられていたよりも弱い可能性が出てきたといえる．We analyze the temporal and spatial variation of the thermal structure of the eastern tropical Indian Ocean associated with Indian Ocean Dipole Mode (IOD), mainly using the water temperature of 10 years (1990-1999) of the World Ocean Circulation Experiment (WOCE) repeat IX1 expendable bathythermograph (XBT) section between Java and Western Australia together with the product of the air-sea coupled four-dimensional variational analysis (4D-VAR) system. The temperature anomaly of the XBT section reveals that the subsurface ocean temperature changes earlier than the surface before the surface IOD pattern starts to grow up. From May to August, a marked subsurface temperature anomaly is also found as well as the sea surface temperature (SST) that is formed primarily by the anomalous coastal upwelling along the south Java coast. Heat budget analysis along IX1 shows that the surface heat flux does not work to enhance the mixed layer temperature anomaly in the eastern pole region