Bates C.M.,Arnold and Mabel Beckman Laboratories for Chemical SynthesisCalifornia Institute of TechnologyPasadena |
Chang A.B.,Arnold and Mabel Beckman Laboratories for Chemical SynthesisCalifornia Institute of TechnologyPasadena |
Momcilovic N.,Arnold and Mabel Beckman Laboratories for Chemical SynthesisCalifornia Institute of TechnologyPasadena |
Jones S.C.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena |
Grubbs R.H.,Arnold and Mabel Beckman Laboratories for Chemical SynthesisCalifornia Institute of TechnologyPasadena
Journal of Polymer Science, Part B: Polymer Physics | Year: 2015
The structure, rheological response, and ionic conductivity of ABA brush block copolymer (BBCP) ion gels containing 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMI][TFSI]) at polymer concentrations spanning 5-50 wt % (Φgel) were studied by small angle X-ray scattering, dynamic mechanical analysis, and AC impedance spectroscopy. Application of a hard sphere form factor and Percus-Yevick structure factor reveals trends in gel micellar structure as a function of BBCP molecular weight, A block volume fraction (ΦA), and Φgel. Viscoelastic properties are strongly dependent on end-block molar mass, with storage moduli ≤103 Pa at 25 °C. Impedance measurements reveal near liquid-like dynamics in the matrix phase as evidenced by conductivities near 1 mS/cm at 25 °C that decrease with increasing Φgel and ΦA. © 2015 Wiley Periodicals, Inc.
Song Y.T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena
Journal of Geophysical Research C: Oceans | Year: 2015
The Indonesian throughflow (ITF) from the Pacific to the Indian Ocean plays an important role in global ocean circulation and climate. Yet, continuous ITF measurement is difficult and expensive. The longest time series of in situ measurements of the ITF to date were taken in the Makassar Strait, the main pathway of the ITF. Here we have demonstrated a plausible approach to derive the ITF transport proxy using satellite altimetry sea surface height (SSH), gravimetry ocean bottom pressure (OBP) data, in situ measurements from the Makassar Strait from 1996 to 1998 and 2004 to 2011, and a theoretical formulation. We first identified the optimal locations of the correlation between the observed ITF transport through the Makassar Strait and the pressure gradients, represented by the SSH and OBP differences between the Pacific and Indian Oceans at a 1° × 1° horizontal resolution. The optimal locations were found centered at 162°E and 11°N in the Pacific Ocean and 80°E and 0° in the Indian Ocean, then were used in the theoretical formulation to estimate the throughflow. The proxy time series follow the observation time series quite well, with the 1993-2011 mean proxy transport of 11.6±3.2 Sv southward, varying from 5.6 Sv during the strong 1997 El Niño to 16.9 Sv during the 2007 La Nina period, which are consistent with previous estimates. The observed Makassar mean transport is 13.0±3.8 Sv southward over 2004-2011, while the SSH proxy (for the same period) gives an ITF mean transport of 13.9±4.1 Sv and the SSH+OBP proxy (for 2004-2010) is 15.8±3.2 Sv. © 2015. American Geophysical Union. All Rights Reserved.
Kwok R.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena |
Morison J.,Applied Physics LaboratoryUniversity of Washington Seattle 98105
Journal of Geophysical Research: Oceans | Year: 2016
We examine 4 years (2011-2014) of sea surface heights (SSH) from CryoSat-2 (CS-2) over the ice-covered Arctic and Southern Oceans. Results are from a procedure that identifies and determines the heights of sea surface returns. Along 25 km segments of satellite ground tracks, variability in the retrieved SSHs is between ∼2 and 3 cm (standard deviation) in the Arctic and is slightly higher (∼3 cm) in the summer and the Southern Ocean. Average sea surface tilts (along these 25 km segments) are 0.01±3.8 cm/10 km in the Arctic, and slightly lower (0.01±2.0 cm/10 km) in the Southern Ocean. Intra-seasonal variability of CS-2 dynamic ocean topography (DOT) in the ice-covered Arctic is nearly twice as high as that of the Southern Ocean. In the Arctic, we find a correlation of 0.92 between 3 years of DOT and dynamic heights (DH) from hydrographic stations. Further, correlation of 4 years of area-averaged CS-2 DOT near the North Pole with time-variable ocean-bottom pressure from a pressure gauge and from GRACE, yields coefficients of 0.83 and 0.77, with corresponding differences of <3 cm (RMS). These comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the Arctic Ocean. Broadly, the mean DOT from CS-2 for both poles compares well with those from the ICESat campaigns and the DOT2008A and DTU13MDT fields. Short length scale topographic variations, due to oceanographic signals and geoid residuals, are especially prominent in the Arctic Basin but less so in the Southern Ocean. Key Points:: Time-varying dynamic topography of ice-covered oceans from CryoSat-2 Assessment with dynamic height from hydrographic stations and ocean bottom pressure Relative length scale and amplitude of baroclinic and barotropic signals in Arctic Ocean © 2015. American Geophysical Union. All Rights Reserved. January 2016 10.1002/2015JC011357 Research Article Research Articles © 2015. American Geophysical Union.
Zeng L.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology |
Liu W.T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena |
Xue H.,University of Chinese Academy of Sciences |
Xiu P.,University of Chinese Academy of Sciences |
Wang D.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research C: Oceans | Year: 2014
Newly available sea surface salinity (SSS) data from the Aquarius together with in situ hydrographic data are used to explore the spatial and temporal characteristics of SSS in the South China Sea (SCS). Using in situ observations as the reference, an evaluation of daily Aquarius data indicates that there exists a negative bias of 0.45 psu for the version 3.0 data set. The root-mean-square difference for daily Aquarius SSS is about 0.53 psu after correcting the systematic bias, and those for weekly and monthly Aquarius SSSs are 0.45 and 0.29 psu, respectively. Nevertheless, the Aquarius SSS shows a reliable freshening in the SCS in 2012, which is larger than the Aquarius uncertainty. The freshening of up to 0.4 psu in the upper-ocean of the northern SCS was confirmed by in situ observations. This freshening in 2012 was caused by a combined effect of abundant local freshwater flux and limited Kuroshio intrusion. By comparing the Kuroshio intrusion in 2012 with that in 2011, we found the reduction as a relatively important cause for the freshening over the northern SCS. In contrast to the northern SCS, reduced river discharge in 2012 played the leading role to the saltier surface in the region near the Mekong River mouth with respect to 2011. © 2014. American Geophysical Union. All Rights Reserved.
Wiese D.N.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena |
Watkins M.M.,University of Texas at AustinAustin |
Yuan D.-N.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena
Journal of Geophysical Research: Oceans | Year: 2016
The extended length of the GRACE data time series (now 13.5 years) provides the unique opportunity to estimate global mass variations due to ocean tides at large (∼300 km) spatial scales. State-of-the-art global tide models rely heavily on satellite altimetry data, which are sparse for latitudes higher than 66°. Thus, the performance of the models is typically worse at higher latitudes. GRACE data, alternately, extend to polar latitudes and therefore provide information for both model validation and improvement at the higher latitudes. In this work, 11 years of GRACE inter-satellite range-acceleration measurements are inverted to solve for corrections to the amplitudes and phases of the major solar and lunar ocean tidal constituents (M2, K1, S2, and O1) from the GOT4.7 ocean tide model at latitudes south of 50°S. Two independent inversion and regularization methods are employed and compared against one another. Uncertainty estimates are derived by subtracting two independent solutions, each spanning a unique 5.5 years of data. Features above the noise floor in the derived solutions likely represent errors in GOT4.7. We find the GOT4.7 amplitudes to be generally too small for M2 and K1, and too large for S2 and O1, and to spatially correlate with geographic regions where GOT4.7 predicts the largest tidal amplitudes. In particular, we find GOT4.7 errors to be dominant over the Patagonia shelf (M2), the Filchner-Ronne Ice Shelf (M2 and S2), the Ross Ice Shelf (S2), and the Weddell and Ross Seas (K1 and O1). © 2016. American Geophysical Union. All Rights Reserved.