Sharon Zhong

A Multiscale and Multidisciplinary Investigation of Ecosystem- Atmosphere CO2 Exchange over the Rocky Mountains of Colorado

A significant fraction of Earth consists of mountainous terrain. However, the question of how to monitor the surface–atmosphere carbon exchange over complex terrain has not been fully explored. This article reports on studies by a team of investigators from U.S. universities and research institutes who carried out a multiscale and multidisciplinary field and modeling investigation of the CO2 exchange between ecosystems and the atmosphere and of CO2 transport over complex mountainous terrain in the Rocky Mountain region of Colorado. The goals of the field campaign, which included ground and airborne in situ and remote-sensing measurements, were to characterize unique features of the local CO2 exchange and to find effective methods to measure regional ecosystem–atmosphere CO2 exchange over complex terrain. The modeling effort included atmospheric and ecological numerical modeling and data assimilation to investigate regional CO2 transport and biological processes involved in ecosystem–atmosphere carbon exch...

Ozone, nitric acid, and ammonia air pollution is unhealthy for people and ecosystems in southern Sierra Nevada, California.

Two-week average concentrations of ozone (O3), nitric acid vapor (HNO3) and ammonia (NH3) were measured with passive samplers during the 2002 summer season across the central Sierra Nevada Mountains, California, along the San Joaquin River drainage. Elevated concentrations of the pollutants were determined with seasonal means for individual sites ranging between 62 and 88 ppb for O3, 1.0-3.8 microg m(-3) for HNO3, and 2.6-5.2 microg m(-3) for NH3. Calculated O3 exposure indices were very high, reaching SUM00-191 ppm h, SUM60-151 ppm h, and W126-124 ppm h. Calculated nitrogen (N) dry deposition ranged from 1.4 to 15 kg N ha(-1) for maximum values, and 0.4-8 kg N ha(-1) for minimum values; potentially exceeding Critical Loads (CL) for nutritional N. The U.S., California, and European 8 h O3 human health standards were exceeded during 104, 108, and 114 days respectively, indicating high risk to humans from ambient O3.

Comparative visualization of ensembles using ensemble surface slicing

By definition, an ensemble is a set of surfaces or volumes derived from a series of simulations or experiments. Sometimes the series is run with different initial conditions for one parameter to determine parameter sensitivity. The understanding and identification of visual similarities and differences among the shapes of members of an ensemble is an acute and growing challenge for researchers across the physical sciences. More specifically, the task of gaining spatial understanding and identifying similarities and differences between multiple complex geometric data sets simultaneously has proved challenging. This paper proposes a comparison and visualization technique to support the visual study of parameter sensitivity. We present a novel single-image view and sampling technique which we call Ensemble Surface Slicing (ESS). ESS produces a single image that is useful for determining differences and similarities between surfaces simultaneously from several data sets. We demonstrate the usefulness of ESS on two real-world data sets from our collaborators.

A North American regional reanalysis climatology of the Haines Index

A warm-season (May through October) Haines Index climatology is derived using 32-km regional reanalysis temperature and humidity data from 1980 to 2007. We compute lapse rates, dewpoint depressions, Haines Index factors A and B, and values for each of the low-, mid- and high-elevation variants of the Haines Index. Statistical techniques are used to investigate the spatial and temporal variability of the index across North America. The new climatology is compared with a previous climatology derived from 2.5° (~280 km) global reanalysis data. Maps from the two climatologies are found to be very similar for most of North America. The largest differences appear along the eastern coastline and in regions of large elevation gradients, where the orography in the 32-km climatology is better resolved than that of the 2.5° climatology. In coastal areas of eastern North America and where there is steeply sloping terrain, the new climatology can augment the information from the 2.5° climatology to help analyse the performance and interpret the results of the Haines Index in these regions. A linear trend analysis of the total number of high-Haines Index days occurring in each warm season reveals no significant linear trends over the 28-year data period.

Analysing the effects of the 2002 McNally fire on air quality in the San Joaquin Valley and southern Sierra Nevada, California

Smoke from wildfires can expose individuals and populations to elevated levels of particulate matter (PM) and ozone (O3). Between 21 July and 26 August 2002, the McNally Fire burned over 150000 acres (61000 ha). The fire occurred in the Sequoia National Forest, in the southern Sierra Nevada of California. This study evaluated the effects of the McNally Fire on air quality, specifically particles <10 μm in diameter (PM10) and O3. Downwind of the fire on the eastern side of the Sierra Nevada, 24-h concentrations of PM10 more than doubled. The PM10 federal standard was exceeded four times during the fire. Violations of the California PM10 standard increased drastically during the fire. The California PM10 standard was violated six times before the fire and 164 times during the fire. Most of the PM10 exceedances occurred at the Kernville Work Center and sites east of the fire. Compared with the other sites, the highest 2-week average O3 concentrations occurred in the eastern part of the Sierra Nevada and north of the fire, where O3 increased by a factor of two at two locations.

Influence of the Antarctic Oscillation, the Pacific–South American modes and the El Niño–Southern Oscillation on the Antarctic surface temperature and pressure variations

Abstract In this study, the impacts of the Antarctic Oscillation (AAO), the Pacific–South American teleconnection (PSA) and the El Niño–Southern Oscillation (ENSO) on Antarctic sea level pressure and surface temperature are investigated using surface observational data, European Centre for Medium-Range Weather Forecasts (ECMWF) 40 Year Re-analysis (ERA-40) and the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) re-analysis data from 1958–2001. There is the most significant correlation between PSA and Antarctic sea level pressure and surface temperature in the northern Antarctic Peninsula during four seasons. But the correlation between Southern Oscillation Index and surface temperature and sea level pressure is significant at some stations only in spring. The three indices can explain a large portion of the trends found in sea level pressure and temperature at some stations, but not at all stations. Among the three indices the most important contribution to the trends in the two surface variables comes from AAO, followed by PSA, and finally by ENSO. The two re-analysis datasets show great similarity for the trends in surface temperature and sea level pressure in April–May and October–November, but not December–February. In summer the trends in surface temperature and sea level pressure in East Antarctica for ERA-40 re-analysis are opposite to those of NCEP re-analysis.