On North Pacific Multidecadal Cllimate Variability

The multidecadal climate variability in the North Pacific region is investigated by using a 2000-yr-long integration with a coupled ocean–atmosphere general circulation model. It is shown that the multidecadal variability evolves largely independent of the variations in the tropical Pacific, so that this kind of multidecadal variability may be regarded as internal to the North Pacific. The coupled model results suggest that the multidecadal variability can be explained by the dynamical ocean response to stochastic wind stress forcing. Superimposed on the red background variability, a multidecadal mode with a period of about 40 yr is simulated by the coupled model. This mode can be understood through the concept of spatial resonance between the ocean and the atmosphere

Review and assessment of latent and sensible heat flux accuracy over the global oceans

For over a decade, several research groups have been developing air-sea heat flux information over the global ocean, including latent (LHF) and sensible (SHF) heat fluxes over the global ocean. This paper aims to provide new insight into the quality and error characteristics of turbulent heat flux estimates at various spatial and temporal scales (from daily upwards). The study is performed within the European Space Agency (ESA) Ocean Heat Flux (OHF) project. One of the main objectives of the OHF project is to meet the recommendations and requirements expressed by various international programs such as the World Research Climate Program (WCRP) and Climate and Ocean Variability, Predictability, and Change (CLIVAR), recognizing the need for better characterization of existing flux errors with respect to the input bulk variables (e.g. surface wind, air and sea surface temperatures, air and surface specific humidities), and to the atmospheric and oceanic conditions (e.g. wind conditions and sea state). The analysis is based on the use of daily averaged LHF and SHF and the asso- ciated bulk variables derived from major satellite-based and atmospheric reanalysis products. Inter-comparisons of heat flux products indicate that all of them exhibit similar space and time patterns. However, they also reveal significant differences in magnitude in some specific regions such as the western ocean boundaries during the Northern Hemisphere winter season, and the high southern latitudes. The differences tend to be closely related to large differences in surface wind speed and/or specific air humidity (for LHF) and to air and sea temperature differences (for SHF). Further quality investigations are performed through comprehensive comparisons with daily-averaged LHF and SHF estimated from moorings. The resulting statistics are used to assess the error of each OHF product. Consideration of error correlation between products and observations (e.g., by their assimilation) is also given. This reveals generally high noise variance in all products and a weak signal in common with in situ observations, with some products only slightly better than others. The OHF LHF and SHF products, and their associated error characteristics, are used to compute daily OHF multiproduct-ensemble (OHF/MPE) estimates of LHF and SHF over the ice-free global ocean on a 0.25° × 0.25° grid. The accuracy of this heat multiproduct, determined from comparisons with mooring data, is greater than for any individual product. It is used as a reference for the anomaly characterization of each individual OHF product

Coral δ18O evidence for Pacific Ocean mediated decadal variability in Panamanian ITCZ rainfall back to the early 1700s

In Central America, seasonal and interannual shifts in the position of the Intertropical Convergence Zone (ITCZ) control the hydrologic budget. To better understand long-term changes in regional ITCZ-driven precipitation we re-examined a coral δ18O record from a Porites lobata coral head near Secas Island (Core ID: S1) (7°59′ N, 82°3′ W) in the Gulf of Chiriquí on the Pacific side of Panamá. Linsley et al., (1994) originally published the 277-year time series and first described the presence of a narrow-band decadal cycle (period near 9–12 years) in δ18O. The original study did not present potential drivers for the decadal cycle, although they ruled out the influence of the sun spot cycle. Our re-analysis of this record supports the original interpretation that coral δ18O is largely responding to variations in precipitation and associated river discharge, but with a new proposed mechanism to explain the decadal mode. There is no similar decadal cycle in gridded instrumental sea surface temperature from the area, suggesting that the decadal coral δ18O signal results from hydrologic changes that influence coastal δ18O seawater. The decadal component in S1 δ18O is also coherent with a decadal mode embedded in the Pacific Decadal Oscillation (PDO) Index that we suggest has tropical origins. We speculate that the coral's temporary δ18O deviation (1900–1930) in the decadal mode from the corresponding bands in rainfall and the PDO can be ascribed to a weak PDO in addition to local Panama gap wind variability and its effect on moisture transport from the Atlantic to the Pacific. Ultimately, the Secas Island coral δ18O series records ITCZ-driven precipitation dictated by both the Atlantic and Pacific basins

What determines the spatial pattern in summer upwelling trends on the U.S. West Coast?

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C08012, doi:10.1029/2012JC008016.Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434.2013-03-0

Satellite-based Cloudiness and Solar Energy Potential in Texas and Surrounding Regions

Global horizontal irradiance (i.e., shortwave downward solar radiation received by a horizontal surface on the ground) is an important geophysical variable for climate and energy research. Since solar radiation is attenuated by clouds, its variability is intimately associated with the variability of cloud properties. The spatial distribution of clouds and the daily, monthly, seasonal, and annual solar energy potential (i.e., the solar energy available to be converted into electricity) derived from satellite estimates of global horizontal irradiance are explored over the state of Texas, USA and surrounding regions, including northern Mexico and the western Gulf of Mexico. The maximum (minimum) monthly solar energy potential in the study area is 151–247 kWhm−2 (43–145 kWhm−2) in July (December). The maximum (minimum) seasonal solar energy potential is 457–706 kWhm−2 (167–481 kWhm−2) in summer (winter). The available annual solar energy in 2015 was 1295–2324 kWhm−2. The solar energy potential is significantly higher over the Gulf of Mexico than over land despite the ocean waters having typically more cloudy skies. Cirrus is the dominant cloud type over the Gulf which attenuates less solar irradiance compared to other cloud types. As expected from our previous work, there is good agreement between satellite and ground estimates of solar energy potential in San Antonio, Texas, and we assume this agreement applies to the surrounding larger region discussed in this paper. The study underscores the relevance of geostationary satellites for cloud/solar energy mapping and provides useful estimates on solar energy in Texas and surrounding regions that could potentially be harnessed and incorporated into the electrical grid