Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena

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Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena

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Farr T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Liu Z.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena
Water Resources Research | Year: 2017

In the San Joaquin Valley, California, recent droughts starting in 2007 have increased the pumping of groundwater, leading to widespread subsidence. In the southern portion of the San Joaquin Valley, vertical subsidence as high as 85 cm has been observed between June 2007 and December 2010 using Interferometric Synthetic Aperture Radar (InSAR). This study seeks to map regions where inelastic (not recoverable) deformation occurred during the study period, resulting in permanent compaction and loss of groundwater storage. We estimated the amount of permanent compaction by incorporating multiple data sets: the total deformation derived from InSAR, estimated skeletal-specific storage and hydraulic parameters, geologic information, and measured water levels during our study period. We used two approaches, one that we consider to provide an estimate of the lowest possible amount of inelastic deformation, and one that provides a more reasonable estimate. These two approaches resulted in a spatial distribution of values for the percentage of the total deformation that was inelastic, with the former estimating a spatially averaged value of 54%, and the latter a spatially averaged value of 98%. The former corresponds to the permanent loss of 4.14 × 108 m3 of groundwater storage, or roughly 5% of the volume of groundwater used over the study time period; the latter corresponds to the loss of 7.48 ×108 m3 of groundwater storage, or roughly 9% of the volume of groundwater used. This study demonstrates that a data-driven approach can be used effectively to estimate the permanent loss of groundwater storage. © 2017. American Geophysical Union.


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.


Song Y.T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Lee T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Qu T.,niversity of HawaiiHonolulu | Yueh S.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena
Journal of Geophysical Research C: Oceans | Year: 2015

Due to near-surface salinity stratification, it is problematic to compare satellite-measured surface salinity within the first few centimeters (skin-layer) of the ocean with Argo-measured top-level salinity at about 5 m or with ocean models that do not resolve the skin layer. Although an instrument can be designed to measure the surface salinity, a global scale measurement is currently not available. A regional model can be configured to have a vertical grid in centimeters but it would be computationally prohibited on a global scale due to time step constraints. Here we propose an extended surface-salinity layer (ESSL) within a global ocean circulation model to diagnose skin SSS without increasing the computational cost, while allowing comparable solutions with both satellite and Argo salinity at the respective depths. Using a quarter-degree global ocean model, we show that the ESSL improves near-surface salinity significantly in comparisons with the Aquarius SSS and Argo salinity at 5 and 10 m, respectively. Comparing with data-assimilated HYCOM results reveal that the ESSL provides much stronger seasonal variability of SSS, similar to the Aquarius observations. We also demonstrate that the ESSL solution can be used to constrain the global mean SSS in Aquarius SSS retrieval. © 2015. American Geophysical Union. All Rights Reserved.


Landerer F.W.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Wiese D.N.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena
Water Resources Research | Year: 2016

Basin-scale groundwater storage trends calculated from long-term streamflow records provide insight into the evolution of watershed behaviors. Our study presents the first spatially relevant validation of recession-based trend approaches by comparing three independent storage trend estimates using GRACE-derived groundwater storage, in situ groundwater elevation observations, and recession-based approaches for the time period of 2003-2015. Results documented consistent agreement between spatially interpolated groundwater observation trends and recession-based storage trends, while GRACE-derived groundwater trends were found to exhibit variable, poor comparisons. A decreasing trend in watershed storage was identified in the southeastern U.S. while increasing trends were identified in the northeast and upper Midwest estimated from recession-based approaches. Our recession-based approach conducted using nested watershed streamflow records identified variable watershed storage trends at scales directly applicable for comparative hydrology studies and for assisting in watershed-based water resources management decisions. © 2016. American Geophysical Union.


Lee T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Lagerloef G.,Earth and Space ResearchSeattle | Kao H.-Y.,Earth and Space ResearchSeattle | Mcphaden M.J.,National Oceanic and Atmospheric Administration | And 2 more authors.
Journal of Geophysical Research C: Oceans | Year: 2014

Sea surface salinity (SSS) data derived from the Aquarius/SAC-D satellite mission are analyzed along with other satellite and in situ data to assess Aquarius' capability to detect tropical instability waves (TIWs) and eddies in the tropical Atlantic Ocean and to investigate the influence that SSS has on the variability. Aquarius data show that the magnitude of SSS anomalies associated with the Atlantic TIWs is ±0.25 practical salinity unit, which is weaker than those in the Pacific by 50%. In the central equatorial Atlantic, SSS contribution to the mean meridional density gradient is similar to sea surface temperature (SST) contribution. Consequently, SSS is important to TIW-related surface density anomalies and perturbation potential energy (PPE). In this region, SSS influences surface PPE significantly through the direct effect and the indirect effect associated with SSS-SST covariability. Ignoring SSS effects would underestimate TIW-related PPE by approximately three times in the surface layer. SSS also regulates the seasonality of the TIWs. The boreal-spring peak of the PPE due to SSS leads that due to SST by about one month. Therefore, SSS not only affects the spatial structure, but the seasonal variability of the TIWs in the equatorial Atlantic. In the northeast Atlantic near the Amazon outflow and the North Brazil Current retroflection region and in the southeast Atlantic near the Congo River outflow, SSS accounts for 80-90% of the contribution to mean meridional density gradient. Not accounting for SSS effect would underestimate surface PPE in these regions by a factor of 10 and 4, respectively. © 2014. 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.


Wiese D.N.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Killett B.,Pasadena California United States | 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.


Koster R.D.,NASA | Brocca L.,CNR Research Institute for Geo-hydrological Protection | Crow W.T.,U.S. Department of Agriculture | Burgin M.S.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | De Lannoy G.J.M.,Catholic University of Leuven
Water Resources Research | Year: 2016

An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterometer (ASCAT) mission. The precipitation estimates so obtained are evaluated against in situ (gauge-based) precipitation observations from across the globe. The precipitation estimation skill achieved using the L-band SMAP and SMOS data sets is higher than that obtained with the C-band product, as might be expected given that L-band is sensitive to a thicker layer of soil and thereby provides more information on the response of soil moisture to precipitation. The square of the correlation coefficient between the SMAP-based precipitation estimates and the observations (for aggregations to ∼100 km and 5 days) is on average about 0.6 in areas of high rain gauge density. Satellite missions specifically designed to monitor soil moisture thus do provide significant information on precipitation variability, information that could contribute to efforts in global precipitation estimation. © 2016. 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.

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