ALBERT

Description: Submarine canyons are common features of the coastal ocean. Although they are known to be hotspots of turbulence that enhance diapycnal transport in their stratified waters, the dynamics of canyon mixing processes are poorly understood. Most studies of internal wave dynamics within canyons have focused on a handful of canyons with along-axis slopes less steep than semidiurnal (D 2 ) internal wave characteristics (subcritical). Here, we present the first tidally-resolving observations within a canyon with a steeply sloping axis (supercritical). A process study consisting of two 24-hour shipboard stations and a profiling mooring was conducted in the La Jolla Canyon off the coast of La Jolla, CA. Baroclinic energy flux is oriented up-canyon and decreases from 182 ± 18 W m −1 at the canyon mouth to 46 ± 5 W m −1 near the head. The ratio of horizontal kinetic energy to available potential energy and the observed group speed of each mode are lower than expected for freely propagating D 2 internal waves at each station, indicating partial reflection. Harmonic analysis reveals that variance is dominated by the D 2 tide. Moving up-canyon, the relative importance of D 2 decreases and its higher harmonics are needed to account for a majority of the observed variance, indicating steepening. Steep internal tides cause large isopycnal displacements (∼50 m in 100m water depth) and high strain events. These events coincide with enhanced O(10 −7 -10 −5 m 2 s −3 ) dissipation of turbulent kinetic energy at mid-depths.

Description: Weighted mean temperature ( T m ) and pressure ( P s ) are two parameters of great relevance to precipitable water vapor (PWV) retrieval from global positioning system (GPS) data. However, information about the T m and P s cannot be available for those GPS stations that are not co-located with meteorological sensors. To investigate the optimal GPS-PWV retrieval method for China, two enhanced T m models, GM- T m (temperature dependent) and GH- T m (temperature independent), are developed. Additionally, the potentials of the P s data from the two reanalysis datasets, the NCEP-DOE Reanalysis II (NCEP II) and ERA-Interim, and from the empirical model GPT2w, for GPS-PWV retrieval are investigated over China. To evaluate the performances of multi-sources T m and P s data for GPS-PWV retrieval, GPS data (2011-2013) collected from 22 stations of the Crustal Movement Observation Network of China (CMONOC) were processed by using the precise point positioning (PPP) technique, estimating the zenith tropospheric delay (ZTD) so as to be subsequently converted to GPS-PWV. The retrieved GPS-PWVs are compared with their counterparts derived from NCEP II and radiosonde data over China. The results show that (1) the GM- T m model consistently shows the highest accuracy (with root mean square error of 2.3 K), and the GH- T m model should be selected when temperature observations are not available, and that (2) the performances of P s from NCEP II and ERA-Interim differ marginally for GPS-PWV retrieval, and significant seasonal variations are found in the agreement between the GPS-PWVs and the PWVs derived from NCEP II and radiosonde data over China.