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Chris Chickadel

Principal Oceanographer

Affiliate Assistant Professor, Civil and Environmental Engineering






B.S. Oceanography, University of Washington, 1997

M.S. Oceanography, Oregon State University, 2003

Ph. D. Oceanography, Oregon State University, 2007


Inner Shelf Dynamics

The inner shelf region begins just offshore of the surf zone, where breaking by surface gravity waves dominate, and extends inshore of the mid-shelf, where theoretical Ekman transport is fully realized. Our main goal is to provide provide improved understanding and prediction of this difficult environment. This will involve efforts to assess the influence of the different boundaries — surf zone, mid and outer shelf, air-water interface, and bed — on the flow, mixing and stratification of the inner shelf. We will also gain information and predictive understanding of remotely sensed surface processes and their connection to processes in the underlying water column.

15 Dec 2015

COHerent STructures in Rivers and Estuaries eXperiment

The experiment is a four-year collaborative project that couples state-of-the-art remote sensing and in situ measurements with advanced numerical modeling to characterize coherent structures in river and estuarine flows.

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Coherent structures are generated in rivers and estuaries when the flow interacts with bathymetric and coastline features or when density stratification causes a gradient in surface properties. These coherent structures produce surface signatures that can be detected and quantified using remote sensing techniques. A second objective of this project is to determine the extent to which these remotely sensed signatures can be used to initialize and guide predictive models.

The study site selected for Year 1 and Year 2 field operations was the Snohomish River in Everett, WA. Its annual mean flow of approximately 300 cubic meters per second is the third largest discharge into Puget Sound. The mouth of the river is defined by the city of Everett to the west (man-influenced) and Jetty Island to the east (natural). The river is dredged to a nominal depth of 5 m from the mouth at the south end of Jetty Island to approximately 12 km upstream, while the undredged depth is nominally 1-3 m. Thus the river profile is a compound channel, with the full 300 m width at Jetty Island containing the dredged channel of about 50 m width. The tidal forcing is strong, with the tidal range representing up to 2/3 of the river%u2019s mean depth. There is a bypass between the north end of Jetty Island and the mainland that connects to a mudflat area. During high tides, the river flow bifurcates between the main channel and this bypass, while at low tide very little flow occurs in the bypass. A sill extends from the north tip of Jetty Island to the southeast toward the opposite bank. The depth along this sill varies from 2 m to 5 m and terminates in a large scour hole in the middle of the channel with a depth of about 10 m.

This research is being conducted by a partnership of experts in remote sensing, numerical modeling, and estuarine dynamics from the University of Washington (Applied Physics Laboratory, Civil and Environmental Engineering, and Oceanography) and Stanford University (Environmental Fluid Mechanics Laboratory). The program is funded by a Multidisciplinary University Research Initiative (MURI) grant sponsored by the Office of Naval Research.

Tidal Flats

Under an ONR-sponsored Department Research Initiative researchers are studying thermal signatures of inter-tidal sediments. The goal is to understand how sediment properties feedback on morphology and circulation, and the extent to which such properties
can be sensed remotely.



2000-present and while at APL-UW

Lobe-cleft instability in the buoyant gravity current generated by estuarine outflow

Horner-Devine, A.R., and C.C. Chickadel, "Lobe-cleft instability in the buoyant gravity current generated by estuarine outflow," Geophys. Res. Lets., 44, 5001-5007, doi:10.1002/2017GL072997, 2017.

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28 May 2017

Gravity currents represent a broad class of geophysical flows including turbidity currents, powder avalanches, pyroclastic flows, sea breeze fronts, haboobs, and river plumes. A defining feature in many gravity currents is the formation of three-dimensional lobes and clefts along the front and researchers have sought to understand these ubiquitous geophysical structures for decades. The prevailing explanation is based largely on early laboratory and numerical model experiments at much smaller scales, which concluded that lobes and clefts are generated due to hydrostatic instability exclusively in currents propagating over a nonslip boundary. Recent studies suggest that frontal dynamics change as the flow scale increases, but no measurements have been made that sufficiently resolve the flow structure in full-scale geophysical flows. Here we use thermal infrared and acoustic imaging of a river plume to reveal the three-dimensional structure of lobes and clefts formed in a geophysical gravity current front. The observed lobes and clefts are generated at the front in the absence of a nonslip boundary, contradicting the prevailing explanation. The observed flow structure is consistent with an alternative formation mechanism, which predicts that the lobe scale is inherited from subsurface vortex structures.

Remote measurements of tides and river slope using an airborne Lidar instrument

Hudson, A.S., S.A. Talke, R. Branch, C. Chickadel, G. Farquharson, and A. Jessup, "Remote measurements of tides and river slope using an airborne Lidar instrument," J. Atmos.Ocean.Technol., 34, 897–904, doi:10.1175/JTECH-D-16-0197.1, 2017.

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24 Apr 2017

Tides and river slope are fundamental characteristics of estuaries, but they are usually undersampled due to deficiencies in the spatial coverage of water level measurements. This study aims to address this issue by investigating the use of airborne lidar measurements to study tidal statistics and river slope in the Columbia River estuary. Eight plane transects over a 12-h period yield at least eight independent measurements of water level at 2.5-km increments over a 65-km stretch of the estuary. These data are fit to a sinusoidal curve and the results are compared to seven in situ gauges. In situ– and lidar-based tide curves agree to within a root-mean-square error of 0.21 m, and the lidar-based river slope estimate of 1.8 × 10−5 agrees well with the in situ–based estimate of 1.4 × 10−5 (4 mm km−1 difference). Lidar-based amplitude and phase estimates are within 10% and 8°, respectively, of their in situ counterparts throughout most of the estuary. Error analysis suggests that increased measurement accuracy and more transects are required to reduce the errors in estimates of tidal amplitude and phase. However, the results validate the use of airborne remote sensing to measure tides and suggest this approach can be used to systematically study water levels at a spatial density not possible with in situ gauges.

High-resolution non-hydrostatic modeling of frontal features in the mouth of the Columbia River

Shi, F., C.C. Chickadel, T.-J. Hsu, J.T. Kirby, G. Farquharson, and G. Ma, "High-resolution non-hydrostatic modeling of frontal features in the mouth of the Columbia River," Estuar. Coast., 40, 296-309, doi:10.1007/s12237-016-0132-y, 2017.

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1 Jan 2017

Airborne data measured during the recent RIVET II field experiment has revealed that horizontally distributed thermal fingers regularly occur at the Mouth of Columbia River (MCR) during strong ebb tidal flows. The high-resolution, non-hydrostatic coastal model, NHWAVE, predicts salinity anomalies on the water surface which are believed to be associated with the thermal fingers. Model results indicate that large amplitude recirculation are generated in the water column between an oblique internal hydraulic jump and the North Jetty. Simulation results indicate that the billows of higher density fluid have sufficiently large amplitudes to interrupt the water surface, causing the prominent features of stripes on the surface. The current field is modulated by the frontal structures, as indicated by the vorticity field calculated from both the numerical model and data measured by an interferometric synthetic aperture radar.

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Influence of subsurface stratification on turbulence and aeration in a tidal river

Beuzen, T., C.C. Chickadel, and A.R. Horner-Devine, "Influence of subsurface stratification on turbulence and aeration in a tidal river," IEEE Geosci. Remote Sens. Lett., 13, 1975-1978, doi:10.1109/LGRS.2016.2619680, 2016.

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1 Dec 2016

Thermal infrared (IR) imagery is combined with in situ flow measurements to examine the impact of subsurface stratification on boil activity in the tidally influenced Snohomish River. Boils at the river’s surface are an expression of bottom-generated turbulence, appearing as a disruption of the cool-skin surface layer in the IR imagery. Boil activity has previously been linked to the amount of aeration occurring in river systems. A synthesis of data across an ebb tide showed that when a tidal salinity intrusion retreated, turbulent kinetic energy and dissipation rapidly increased by 700% and 575%, respectively. Additionally, the mean boil area fraction in the IR field of view increased by almost 500% across the entire ebb tide time series, with approximately half of this change occurring during the period when the stratification ceased. Using an empirical method for estimating aeration, the change in areal fraction associated with the loss of density stratification is predicted to generate a more than 300% increase in the air-water gas flux.

Inner Shelf Dynamics Science and Experiment Plan

Feddersen, F., et al., "Inner Shelf Dynamics Science and Experiment Plan," APL-UW TR 1602, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, October 2016, 35pp.

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31 Oct 2016

The deep ocean, continental shelf, and surf zone are defined by their unique physical processes and dynamics. The nearshore region from about 50 m water depth to the outer edge of the surf zone (SZ) is known as the inner shelf. This region is characterized by overlapping and interacting surface and bottom boundary layers. At the offshore side of the inner shelf, instabilities from wind-driven currents and fronts create cross-shelf meanders and eddies. In addition, energetic nonlinear internal waves (NLIWs) are ubiquitous on the inner shelf.

To understand and predict the exchange of water properties (heat, gases, sediment, pollutants, biota) across the inner shelf over a range of temporal and spatial scales, the Office of Naval Research Inner Shelf Dynamics Departmental Research Initiative (Inner Shelf DRI) is coordinating field observations (in situ and remote sensing) coupled to numerical modeling efforts on a 50-km section of coast off Vandenberg Air Force Base, California, located in the vicinity of Point Sal. The overall goal is to develop and improve the predictive capability of a range of numerical models to simulate the 3D circulation, density, and surface wave field across the inner shelf associated with a broad array of physical processes and complex bathymetry.

Infrared emissivity of seawater and foam at large incidence angles in the 3–14 μm wavelength range

Branch, R., C.C. Chickadel, and A.T. Jessup, "Infrared emissivity of seawater and foam at large incidence angles in the 3–14 μm wavelength range," Remote Sens. Environ., 184, 15-24, doi:10.1016/j.rse.2016.06.009, 2016.

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1 Oct 2016


We measured infrared emissivity of seawater and sea foam in a laboratory experiment.

We developed a method to estimate emissivity for incidence angles up to 85°.

Foam emissivity is higher than water for all wavelengths and angles > 65°.

The difference between foam and water emissivity increases with incidence angle.

Estimating wave energy dissipation in the surf zone using thermal infrared imagery

Carini, R.J. C.C. Chickadel, A.T. Jessup, and J. Thomson, "Estimating wave energy dissipation in the surf zone using thermal infrared imagery," J. Geophys. Res., 120, 3937-3957, doi:10.1002/2014JC010561, 2015.

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1 Jun 2015

Thermal infrared (IR) imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone. The foam produced in an actively breaking crest, or wave roller, has a distinct signature in IR imagery. A retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the Surf Zone Optics 2010 experiment at Duck, NC. The remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave-resolving model by Duncan (1981). The wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar, consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar. When integrated over the surf zone width, these dissipation rate estimates account for 40–69% of the incoming wave energy flux. The Duncan (1981) estimates agree with those from a dissipation parameterization by Janssen and Battjes (2007), a wave energy dissipation model commonly applied within nearshore circulation models.

Surf zone bathymetry and circulation predictions via data assimilation of remote sensing observations

Wilson, G.W., H.T. Haller-Özkan, R.A. Holman, M.C. Haller, D.A. Honegger, and C.C. Chickadel, "Surf zone bathymetry and circulation predictions via data assimilation of remote sensing observations," J. Geophys. Res., 119, 1993-2016, doi:10.1002/2013JC009213, 2014.

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1 Mar 2014

Bathymetry is a major factor in determining nearshore and surf zone wave transformation and currents, yet is often poorly known. This can lead to inaccuracy in numerical model predictions. Here bathymetry is estimated as an uncertain parameter in a data assimilation system, using the ensemble Kalman filter (EnKF). The system is tested by assimilating several remote sensing data products, which were collected in September 2010 as part of a field experiment at the U.S. Army Corps of Engineers Field Research Facility (FRF) in Duck, NC. The results show that by assimilating remote sensing data alone, nearshore bathymetry can be estimated with good accuracy, and nearshore forecasts (e.g., the prediction of a rip current) can be improved. This suggests an application where a nearshore forecasting model could be implemented using only remote sensing data, without the explicit need for in situ data collection.

Thermal infrared multipath reflection from breaking waves observed at large incidence angles

Branch, R., C.C. Chickadel, and A.T. Jessup, "Thermal infrared multipath reflection from breaking waves observed at large incidence angles," IEEE Trans. Geosci. Remote Sens., 52, 249-256, doi:10.1109/TGRS.2013.2238241, 2014.

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1 Jan 2014

The infrared signature of breaking waves at large incidence angles was investigated using laboratory experiments and a radiometric model. Infrared imagery of the water surface at incidence angles greater than 70° shows multipath reflections for both spilling and plunging waves generated using a programmable wave maker. For the spilling breakers, the multipath signature was initially distinct from the breaking wave front roller signature but then merged to create a single large bright distributed target. For the plunging breakers, the roller and multipath signatures overlapped from the inception of breaking. The radiance of the multipath reflection was higher than the surrounding water for simulated cold sky conditions and lower for a simulated warm sky. A specular double-reflection model successfully predicted the presence of multipath reflection but the magnitude was sensitive to small uncertainties in geometry, wave slope, and input temperatures. The results show that multipath reflection from breaking waves is characteristic of large incidence angle infrared measurements and increases the area and magnitude of the infrared signature of breaking waves compared to the background.

Turbulent kinetic energy and coherent structures in a tidal river

Talke, S.A., A.R. Horner-Devine, C.C. Chickadel, and A.T. Jessup, "Turbulent kinetic energy and coherent structures in a tidal river," J. Geophys. Res., 118, 6965-6981, doi:10.1002/2012JC008103, 2013.

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1 Dec 2013

We investigate the relationship between turbulence statistics and coherent structures (CS) in an unstratified reach of the Snohomish River estuary using in situ velocity measurements and surface infrared (IR) imaging. Sequential IR images are used to estimate surface flow characteristics via a particle-image-velocimetry (PIV) technique, and are conditionally sampled to delineate the surface statistics of bottom-generated CS, or boils. In the water column, we find that turbulent kinetic energy (TKE) production exceeds dissipation near the bed but is less than dissipation in the midwater column and that TKE flux divergence closes a significant portion of the measured imbalance. The surface boundary leads to divergence in upwelling CS, and leads to the redistribution of vertical TKE to the horizontal. Very near the surface, statistical anisotropy is observed at length scales larger than the depth H (3%u20135 m), while boil-scale motions of O(1)m are nearly isotropic and exhibit a –5/3 turbulent cascade to smaller scales. Conditional sampling suggests that TKE dissipation in boils is approximately 2 times greater on average than dissipation in ambient flow. Similarly, surface boils are marked by significantly greater velocity variance, upwelling, divergence, and TKE flux divergence than ambient flow regions. Coherent structures and their surface manifestation, therefore, play an important role in the vertical transport of TKE and the water column distribution of dissipation, and are an important component of the TKE budget.

Thermal observations of drainage from a mud flat

Rinehimer, J. P., J. Thomson, and C.C. Chickadel, "Thermal observations of drainage from a mud flat," Cont. Shelf. Res., 60, S125-S135, doi:10.1016/j.csr.2012.11.001, 2013.

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15 Jun 2013

Incised channels on tidal flats create a complex flow network conveying water on and off the flat during the tidal cycle. In situ and remotely sensed field observations of water drainage and temperature in a secondary channel on a muddy tidal flat in Willapa Bay, Washington (USA) are presented and a novel technique, employing infrared imagery, is used to estimate surface velocities when the water depth in the channel becomes too shallow for ADCP measurements, i.e., less than 10 cm. Two distinct dynamic regimes are apparent in the resulting observations: ebb-tidal flow and the post-ebb discharge period. Ebb tide velocities result from the surface slope associated with the receding tidal elevation whereas the post-ebb discharge continues throughout the low tide period and obeys uniform open-channel flow dynamics. Volume transport calculations and a model of post-ebb runoff temperatures support the hypothesis that remnant water on the flats is the source of the post-ebb discharge.

Frontogenesis and frontal progression of a trapping-generated estuarine convergence front and its influence on mixing and stratification

Giddings, S.N., D.A. Fong, S.G. Monismith, C.C. Chickadel, K.A. Edwards, W.J. Plant, B. Wang, O.B. Fringer, A.R. Horner-Devine, and A.T. Jessup, "Frontogenesis and frontal progression of a trapping-generated estuarine convergence front and its influence on mixing and stratification," Estuar. Coasts, 35, 665-681, doi:10.1007/s12237-011-9453-z, 2012.

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1 Mar 2012

Estuarine fronts are well known to influence transport of waterborne constituents such as phytoplankton and sediment, yet due to their ephemeral nature, capturing the physical driving mechanisms and their influence on stratification and mixing is difficult. We investigate a repetitive estuarine frontal feature in the Snohomish River Estuary that results from complex bathymetric shoal/channel interactions. In particular, we highlight a trapping mechanism by which mid-density water trapped over intertidal mudflats converges with dense water in the main channel forming a sharp front. The frontal density interface is maintained via convergent transverse circulation driven by the competition of lateral baroclinic and centrifugal forcing. The frontal presence and propagation give rise to spatial and temporal variations in stratification and vertical mixing. Importantly, this front leads to enhanced stratification and suppressed vertical mixing at the end of the large flood tide, in contrast to what is found in many estuarine systems. The observed mechanism fits within the broader context of frontogenesis mechanisms in which varying bathymetry drives lateral convergence and baroclinic forcing. We expect similar trapping-generated fronts may occur in a wide variety of estuaries with shoal/channel morphology and/or braided channels and will similarly influence stratification, mixing, and transport.

Infrared-based measurements of velocity, turbulent kinetic energy, and dissipation at the water surface in a tidal river

Chickadel, C.C., S.A. Talke, A.R Horner-Devine, and A.T. Jessup, "Infrared-based measurements of velocity, turbulent kinetic energy, and dissipation at the water surface in a tidal river," IEEE Geosci. Remote Sens. Lett., 8, 849-853, doi:10.1109/LGRS.2011.2125942, 2011.

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1 Sep 2011

Thermal infrared (IR)-based particle image velocimetry (PIV) is used to measure the evolution of velocity, turbulent kinetic energy (TKE), and the TKE dissipation rate at the water surface in the tidally influenced Snohomish River. Patterns of temperature variability in the IR imagery arise from disruption of the cool-skin layer and are used to estimate the 2-D velocity field. Comparisons of IR-based PIV mean velocity made with a colocated acoustic velocimeter demonstrate high correlation. IR-based PIV provides detailed measurements of previously inaccessible surface velocities and turbulence statistics.

Mixing layer dynamics in separated flow over an estuarine sill with variable stratification

Talke, S.A., A.R. Horner-Devine, and C.C. Chickadel, "Mixing layer dynamics in separated flow over an estuarine sill with variable stratification," J. Geophys. Res., 115, doi:10.1029/2009JC005467, 2010.

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4 Sep 2010

We investigate the generation of a mixing layer in the separated flow behind an estuarine sill (height H ~4 m) in the Snohomish River, Washington as part of a larger investigation of coherent structures using remote and in situ sensing. During increasing ebb flows the depth and stratification decrease and a region of sheared flow characterized by elevated production of turbulent kinetic energy develops. Profiles of velocity and acoustic backscatter exhibit coherent fluctuations of order 0.1 Hz and are used to define the boundaries of the mixing layer. Variations in the mixing layer width and its embedded coherent structures are caused by changes to both the normalized sill height H/d and to a bulk Richardson number Rih defined using the depth of flow over the sill. Entrainment ET and the mixing layer expansion angle increase as stratification and the bulk Richardson number decrease; this relationship is parameterized as ET = 0.07Rih-0.5 and is valid for approximately 0.1 < Rih < 2.8.

Available comparisons with literature for inertially dominated conditions (Rih < 0.1) are consistent with our data and validate our approach, though lateral gradients may introduce an upwards bias of approximately 20%. As the ratio H/d increases over the ebb, the free surface boundary pushes the mixing layer trajectory downward, reduces its expansion angle, and produces asymmetry in the acoustic backscatter (coherent structures). Three-dimensional divergence, as imaged by infrared video and transecting data, becomes more prominent for H/d > 0.8 due to blocking of flow by the sill.

Remotely sensed river surface features compared with modeling and in situ measurements

Plant, W.J., R. Branch, G. Chatham, C.C. Chickadel, K. Hayes, B. Hayworth, A. Horner-Devine, A. Jessup, D.A. Fong, O.B. Fringer, S.N. Giddings, S. Monismith, and B. Wang, "Remotely sensed river surface features compared with modeling and in situ measurements," J. Geophys. Res., 114, doi:10.1029/2009JC005440, 2009.

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3 Nov 2009

Images of river surface features that reflect the bathymetry and flow in the river have been obtained using remote sensing at microwave, visible, and infrared frequencies. The experiments were conducted at Jetty Island near the mouth of the Snohomish River at Everett, Washington, where complex tidal flow occurs over a varied bathymetry, which was measured as part of these experiments. An X band (9.36 GHz) Doppler radar was operated from the river bank and produced images of normalized radar cross sections and radial surface velocities every 20 min over many tidal cycles. The visible and infrared instruments were flown in an airplane. All of these techniques showed surface evidence of frontal features, flow over a sill, and flow conditioned by a deep hole. These features were modeled numerically, and the model results correspond well to the remote observations. In situ measurements made near the hole showed that changes in measured velocities correlate well with the occurrence of the features in the images. In addition to tidal phase, the occurrence of these features in the imagery depends on tidal range. The surface roughness observed in the imagery appears to be generated by the bathymetry and flow themselves rather than by the modulation of wind waves.

Vertical boil propagation from a submerged estuarine sill

Chickadel, C.C., A.R. Horner-Devine, S.A. Talke, and A.T. Jessup, "Vertical boil propagation from a submerged estuarine sill," Geophys. Res. Lett., 36, doi:10.1029/2009GL037278, 2009.

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20 May 2009

Surface disruptions by boils during strong tidal flows over a rocky sill were observed in thermal infrared imagery collected at the Snohomish River estuary in Washington State. Locations of boil disruptions and boil diameters at the surface were quantified and are used to test an idealized model of vertical boil propagation. The model is developed as a two-dimensional approximation of a three-dimensional vortex loop, and boil vorticity is derived from the flow shear over the sill. Predictions of boil disruption locations were determined from the modeled vertical velocity, the sill depth, and the over-sill velocity. Predictions by the vertical velocity model agree well with measured locations (rms difference 3.0 m) and improve by using measured velocity and shear (rms difference 1.8 m). In comparison, a boil-surfacing model derived from laboratory turbulent mixed-layer wakes agrees with the measurements only when stratification is insignificant.

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