Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: D. J. Shea x
  • All content x
Clear All Modify Search
H. van Loon and D. J. Shea

Abstract

The year before a Warm Event takes place in the Southern Oscillation the trough in the westerlies at the surface over the South Pacific Ocean fails to amplify to its normal size in the latitudes north of 45°S during the southern fall and winter. There is therefore an anomalous northerly wind in these months over the Pacific Ocean between 15°S and 45°S, west of 140°W. In contrast, the trough's amplitude is above normal in the fall and winter of the following year when the Warm Event takes place, and one therefore observes an anomalous southerly wind where a northerly anomaly occurred the previous year. Consistent with the different wind anomalies, the temperature of the surface water is higher in the year before the Warm Event than in the year of the event between 15°S and 45°S, from Australia to 140°W.

We propose that when the South Pacific Convergence Zone expands toward the south as usual in the southern spring of the year before a Warm Event, the convection in the Convergence Zone is enhanced over the warmer water, and that this contributes to lowering the pressure over large parts of the tropical and subtropical South Pacific Ocean.

We demonstrate furthermore that a Cold Event, which is the opposite extreme of the Southern Oscillation, develops in a manner opposite to that of a Warm Event with an enhanced trough and weak trades in the year before the Cold Event, and a depressed trough and strong trades in the year of the event. The surface water over the area of interest south of 15°S therefore becomes colder than normal in the southern winter and spring of the year before the Cold Event. The colder water presumably depresses convection in the South Pacific Convergence Zone, and thus contributes to raising the pressure over large parts of the tropical and subtropical South Pacific Ocean.

Full access
H. van Loon and D. J. Shea
Full access
H. van Loon and D. J. Shea

Abstract

The paper shows the discrete, mean three-month anomalies of sea level pressure on the Southern Hemisphere during the year before and the year of a Warm Event in the Southern Oscillation, together with associated anomalies of sea surface temperature in the South Pacific 0cean. The two sets anomalies develop in a parallel and physically logical sequence over the South Pacific Ocean in conjunction with changes in the South Pacific Convergence Zone. Nearly all of the Southern Hemisphere responds to the Southern Oscillation, but the response is largest in the Australia-South Pacific sector. Large anomalies of sea level pressure form well ahead of any on the Northern Hemisphere, and this observation together with the conspicuous anomalies in the region of Australia and the South Pacific suggest that the origin of the Southern Oscillation must be sought in this region.

Full access
R. A. Madden, D. J. Shea, G. W. Branstator, J. J. Tribbia, and R. O. Weber

Abstract

A long time series of data simulated by the NCAR Community Climate Model is used to empirically determine the effects of imperfect spatial and temporal sampling on estimates of the model's global-mean surface air temperature. Results determined from a simple statistical sampling equation and those determined from a simple Monte Carlo experiment are shown to be reasonably similar to the empirically determined ones. The results provide insights into the spatial sampling problem, and it is proposed that variations of the simple models can be used in studies of real data to arrive at reasonable estimates of error that are directly applicable to the actual global-mean surface temperature.

Full access
Laura D. Riihimaki, Connor Flynn, Allison McComiskey, Dan Lubin, Yann Blanchard, J. Christine Chiu, Graham Feingold, Daniel R. Feldman, Jake J. Gristey, Christian Herrera, Gary Hodges, Evgueni Kassianov, Samuel E. LeBlanc, Alexander Marshak, Joseph J. Michalsky, Peter Pilewskie, Sebastian Schmidt, Ryan C. Scott, Yolanda Shea, Kurtis Thome, Richard Wagener, and Bruce Wielicki

Abstract

Industry advances have greatly reduced the cost and size of ground-based shortwave (SW) sensors for the ultraviolet, visible, and near-infrared spectral ranges that make up the solar spectrum, while simultaneously increasing their ruggedness, reliability, and calibration accuracy needed for outdoor operation. These sensors and collocated meteorological equipment are an important part of the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) User Facility, which has supported parallel integrated measurements of atmospheric and surface properties for more than two decades at fixed and mobile sites around the world. The versatile capability of these ground-based measurements includes 1) rich spectral information required for retrieving cloud and aerosol microphysical properties, such as cloud phase, cloud particle size, and aerosol size distributions, and 2) high temporal resolution needed for capturing fast evolution of cloud microphysical properties in response to rapid changes in meteorological conditions. Here we describe examples of how ARM’s spectral radiation measurements are being used to improve understanding of the complex processes governing microphysical, optical, and radiative properties of clouds and aerosol.

Full access