Radiocarbon record of solar variability and Holocene climatic change in coastal southern California

EXTRACT (SEE PDF FOR FULL ABSTRACT): Pollen analysis and 5 radiocarbon dates for a 687-cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea level rise during the mid-Holocene, but after 4500 years BP, sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 years BP correlate global cooling events and (except the 3800-year BP event) with carbon-14 production anomalies. The coincidence of climate change and carbon-14 anomalies support a causal connection with solar variability, but regardless of the causal mechanism(s) the delta-carbon-14 curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

Validation of a semi-Lagrangian, canonical regression model of climates in the southwestern United States

EXTRACT (SEE PDF FOR FULL ABSTRACT): A local climate model (LCM) has been developed to simulate the modern and 18 ka climate of the southwestern United States. ... LCM solutions indicate summers were about 1°C cooler and winters 11°C cooler at 18 ka. Annual PREC increased 68% at 18 ka, with large increases in spring and fall PREC and diminished summer monsoonal PREC. ... Validation of simulations of 18 ka climate indicate general agreement with proxy estimates of climate for that time. However, the LCM estimates of summer temperatures are about 5 to 10°C higher than estimates from proxy reconstructions.

A numerical simulation of cool/wet and warm/wet episodes in the western United States

Wintertime precipitation in the mountains of the western United States during a warm or cool period has a pronounced influence on streamflow. During a warm year, streamflow at intermediate elevations responds more immediately to precipitation events; during a cold year, much of the discharge is delayed until the snow melts in spring and summer. Previous efforts at studying these extremes have been hampered by a limited number and length of observational analyses. In this study, we augment this limited observational record by analyzing a simplified general circulation model.

The Los Alamos General Circulation Model hydrologic cycle

As the global population has increased, so have human influences on the global environment. ... How can we better understand and predict these natural and potential anthropogenic variations? One way is to develop a model that can accurately describe all the components of the hydrologic cycle, rather than just the end result variables such as precipitation and soil moisture. If we can predict and simulate variations in evaporation and moisture convergence, as well as precipitation, then we will have greater confidence in our ability to at least model precipitation variations. Therefore, we describe here just how well we can model relevant aspects of the global hydrologic cycle. In particular, we determine how well we can model the annual and seasonal mean global precipitation, evaporation, and atmospheric water vapor transport.

High-resolution computation of isotopic processes in northern California using a local climate model

EXTRACT (SEE PDF FOR FULL ABSTRACT): We describe a coupled local climate/isotope model that can calculate Rayleigh-type processes of distillation and fractionation of hydrogen isotopes along individual air mass flowlines in the western United States.This climate model is an extension of that detailed earlier by Craig and Stamm (1990). ... Volumetric effects of evapotranspiration (ET) are included. The model allows sensitivity studies of the influence of ET recycling.

Semiempirical down-scaling of GCM output to the local scale for temperature, precipitation, and runoff

EXTRACT (SEE PDF FOR FULL ABSTRACT): An empirically derived multiple linear regression model is used to relate a local-scale dependent variable (either temperature, precipitation, or surface runoff) measured at individual gauging stations to six large-scale independent variables (temperature, precipitation, surface runoff, height to the 500-mbar pressure surface, and the zonal and meridional gradient across this surface). ...The area investigated is the western United States. ... The calibration data set is from 1948 through 1988 and includes data from 268 joint temperature and precipitation stations, 152 streamflow stations (which are converted to runoff data), and 24 gridded 500-mbar pressure height nodes.

Climatological aspects of the large-scale hydrologic cycle in the United States

We describe a 2.5-degree gridpoint atmospheric hydrology/climatology of precipitable water, precipitation, atmospheric moisture convergence, and a residual evaporation or evapotranspiration for the coterminous United States. We also describe a large-scale surface hydrology/climatology of a residual soil moisture, streamflow divergence, or runoff, as well as precipitation and evaporation. Annual and seasonal means and interrelationships among various components of the hydrologic cycles are discussed.

South American streamflow and the extreme phases of the Southern Oscillation

This study investigates the extent of the affect [sic] of the El Niño/Southern Oscillation on South American streamflow. The response of South American precipitation and temperature to the extreme phases of ENSO (El Niño and La Niña events) is well documented; but the response of South American hydrology has been barely studied. Such paucity of research contrasts sharply with that available on the response of North American streamflow to ENSO events.

Changes in the hydrometeorological regime in the Pacific Southwest [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Selected hydrometeorological (HM) data for the Pacific Northwest and atmospheric and North Pacific sea-surface temperature (SST) data are examined for three successive periods that are subsets of the historical record to estimate if their characteristics have changed.

Evidence for changes in large-scale upwelling in the California Current over the past 700 years [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Bidecadal radiocarbon measurements on tree rings provide a detailed series of carbon-14 activities at isotopic equilibrium with atmospheric carbon dioxide. ... Most marine environments do not permit development of a comparable series of carbon-14 ages with which to compare the terrestrial tree ring series. However, we have recently begun work on such a series using material from the varved sediments of the Santa Barbara Basin off southern California. ... We now have a nearly continuous record of carbon-14 dates representing the age of the water over the upper 100 meters. ... The ocean reservoir ages show an increase prior to 1450 and a progressive decrease with time after 1450. Although there may be other explanations, we believe this trend is principally the result of changes in large-scale upwelling of water from below 500 meters. These changes were probably also associated with changes in the intensity of the California Current.