Toshio M. Chin

Thermal wind forcing and atmospheric angular momentum: Origin of the Earth's delayed response to ENSO

[1]xa0Interannual length-of-day variations and ENSO indices such as the Southern Oscillation Index (SOI) and Nino 3.4 SST are well correlated as a consequence of angular momentum conservation. During an El Nino event, the westerly winds increase, which raises the atmospheric angular momentum (AAM); as a result, the solid Earth must slow down, which increases the duration of the day (length-of-day: LOD). However, a lag has been observed with the SOI and Nino 3.4 SST leading the LOD and AAM series by one–two months; to date no dynamical explanation has been offered. The dominant excitation mechanism of interannual LOD is the wind term, driven largely by thermal winds arising from the poleward gradient of tropical temperature (TT). We show that the TT gradient (TTG), which peaks 1–2 months after the Nino 3.4 SST anomaly, is the source of the thermal winds that drive the LOD anomaly and account for this well-known ENSO-Earth rotation lag.

JTRF2014, the JPL Kalman filter and smoother realization of the International Terrestrial Reference System

We present and discuss JTRF2014, the Terrestrial Reference Frame (TRF) the Jet Propulsion Laboratory constructed by combining space-geodetic inputs from very long baseline interferometry (VLBI), satellite laser ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite submitted for the realization of ITRF2014. Determined through a Kalman filter and Rauch-Tung-Striebel smoother assimilating position observations, Earth orientation parameters, and local ties, JTRF2014 is a subsecular, time series-based TRF whose origin is at the quasi-instantaneous center of mass (CM) as sensed by SLR and whose scale is determined by the quasi-instantaneous VLBI and SLR scales. The dynamical evolution of the positions accounts for a secular motion term, annual, and semiannual periodic modes. Site-dependent variances based on the analysis of loading displacements induced by mass redistributions of terrestrial fluids have been used to control the extent of random walk adopted in the combination. With differences in the amplitude of the annual signal within the range 0.5–0.8xa0mm, JTRF2014-derived center of network-to-center of mass (CM-CN) is in remarkable agreement with the geocenter motion obtained via spectral inversion of GNSS, Gravity Recovery and Climate Experiment (GRACE) observations and modeled ocean bottom pressure from Estimating the Circulation and Climate of the Ocean (ECCO). Comparisons of JTRF2014 to ITRF2014 suggest high-level consistency with time derivatives of the Helmert transformation parameters connecting the two frames below 0.18xa0mm/yr and weighted root-mean-square differences of the polar motion (polar motion rate) in the order of 30xa0μas (17xa0μas/d).

Comparisons of regional satellite sea surface temperature gradients derived from MODIS and AVHRR sensors

Regional sea surface temperature (SST) gradients were examined for a 6-year (2003–2008) period using data from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on two NOAA satellite platforms. Two regions, one in the California Current System and the other in the Gulf Stream, representing an eastern boundary upwelling region and strong western boundary current, respectively, were chosen to investigate the seasonal variability, statistical differences and similarities, and correlations with respect to the two sets of SST gradients. Results indicated higher gradient magnitudes using MODIS SST in relative comparison to those derived from AVHRR that are attributed to instrument and algorithm differences. These observed differences are important for any studies that employ SST gradients, such as fisheries investigations that have traditionally relied on AVHRR SST gradients only.

On Kalman filter solution of space-time interpolation

The approximate Kalman filtering algorithm presented previously (see ibid., vol.3, p.773-88, Nov. 1994) for image sequence processing can introduce unacceptable negative eigenvalues in the information matrix and can have degraded performance in some applications. The improved algorithm presented in this note guarantees a positive definite information matrix, leading to more stable filter performance.

Influence of GPS Precipitable Water Vapor Retrievals on Quantitative Precipitation Forecasting in Southern California

Abstract The effects of precipitable water vapor (PWV) retrievals from the Southern California Integrated GPS Network (SCIGN) on quantitative precipitation forecast (QPF) skill are examined over two flood-prone regions of Southern California: Santa Barbara (SB) and Ventura County (VC). Two sets of QPFs are made, one using the initial water vapor field from the NCEP 40-km Eta initial analysis, and another in which the initial Eta water vapor field is modified by incorporating the PWV data from the SCIGN receivers. Lateral boundary data for the QPFs, as well as the hydrostatic component of the GPS zenith delay data, are estimated from the Eta analysis. Case studies of a winter storm on 2 February during the 1997/98 El Nino, and storms leading up to the La Conchita, California, landslide on 10 January 2005, show notably improved QPFs for the first 3–6 h with the addition of GPS PWV data. For a total of 47 winter storm forecasts between February 1998 and January 2005 the average absolute QPF improvement is sm...

Three-Corner Hat for the assessment of the uncertainty of non-linear residuals of space-geodetic time series in the context of terrestrial reference frame analysis

We discuss the application of the Three-Corner Hat (TCH) to time series of space-geodetic station position residuals with the purpose of characterizing the uncertainties of GPS, VLBI, SLR, DORIS for the International Terrestrial Reference Frame (ITRF) determination. Adopting simulations, we show that, in the absence of time-correlated errors, TCH is able to fully recover the nominal uncertainties of groups of observations whose intrinsic precisions are remarkably dissimilar to one another, as is the case for the space-geodetic techniques. When time-correlated errors are predominant, as it happens with GPS, TCH is affected by the increased variance of the observations and its estimates are positively biased. TCH applied to 16 ITRF co-located sites confirms that GPS, albeit affected by time-correlated errors, is the most precise of the space-geodetic techniques. GPS median uncertainties are 1.1, 1.2 and 2.8xa0mm, for the north, east and height component, respectively. VLBI performs particularly well in the horizontal component, the median uncertainties being

Relationship between SST gradients and upwelling off Peru and Chile: model/satellite data analysis

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Group for High Resolution Sea Surface Temperature (GHRSST) analysis fields inter-comparisons—Part 2: Near real time web-based level 4 SST Quality Monitor (L4-SQUAM)

≈2xa0mm. The height component is