Jon K. Eischeid

The Quality Control of Long-Term Climatological Data Using Objective Data Analysis

Abstract One of the major concerns with detecting global climate change is the quality of the data. Climate data are extremely sensitive to errant values and outliers. Prior to analysis of these time series, it is important to remove outliers in a methodical manner. This study provides statistically derived bounds for the uncertainty associated with surface temperature and precipitation measurements and yields a baseline dataset for validation of climate models as well as for a variety of other climatological uses. A two-step procedure using objective analysis was used to identify outliers. The first step was a temporal check that determines if a particular monthly value is consistent with other monthly values for the same station. The second step utilizes six different spatial interpolation techniques to estimate each monthly time series. Each of the methods is ranked according to its respective correlation coefficients with the actual time series, and the technique with the highest correlation coefficie...

Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions in the Last 50 Years

We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze changes in freezing level heights and snow cover for the past three to five decades. All the major continental mountain chains exhibit upward shifts in the height of the freezing level surface. The pattern of these changes is generally consistent with changes in snow cover, both over the course of the year and spatially. We examined different free-air temperature parameters (dry bulb temperature, virtual temperature, and 700–500 hPa thickness) using the Reanalysis grid point valueslocated over the different mountain areas as defined in this study. The different trend values were in reasonably good agreement with each other, particularly over the second half of the record.Freezing level changes in the American Cordillera are strongly modulated by the El Niño/Southern Oscillation (ENSO) phenomenon and the freezing level heights (FLH) respond to both interannual and decadal-scale change in tropical Pacific sea surface temperature (SST). The ∼ 0.5 °C increase in SST recorded in the tropical Pacific since the 1950s accounts for approximately half of the increase in FLH in tropical and subtropical latitudes of the Cordilleran region during that same time.

Present weather and climate: evolving conditions

This chapter assesses weather and climate variability and trends in the Southwest, using observed climate and paleoclimate records. It analyzes the last 100 years of climate variability in comparison to the last 1,000 years, and links the important features of evolving climate conditions to river flow variability in four of the region’s major drainage basins. The chapter closes with an assessment of the monitoring and scientific research needed to increase confidence in understanding when climate episodes, events, and phenomena are attributable to human-caused climate change.