On the Front Cover
Full View of the Earth, centered on the Western Hemisphere. Taken by the NOAA GOES-8 (Geostationary Operational Environmental Satellite) on September 2, 1994, at 18:00 UT. The colors are adjusted and enhanced to provide improved contrasts by combining measurements of visible light with measurements of infrared radiation. Because the North and South Poles were not actually observed by GOES-8, observations from a GOES-7 image were used to fill in these regions. The image is available on the Internet via the NASA Goddard Space Flight Center (GSFC) Web site at <http://rsd.gsfc.nasa.gov/rsd/images/>.
Source: Image produced by M. Jentoft-Nilsen, F. Hasler, C. Chesters
(NASA/GSFC) and T. Nielsen (University of Hawaii).
Figure 1. La Niña experimental climate forecast: Global temperature forecast for January-March 1999
The International Research Institute for Climate Prediction (IRI) is a new institute sponsored by the USGCRP to focus on seasonal to interannual climate forecasting. In October, 1998, its Experimental Forecast Division issued this Climate Outlook for January-March 1999. The evolution of cooler than average conditions in the eastern and central equatorial Pacific Ocean (La Niña) and the persistence of warmer than average conditions in the western equatorial Pacific were particularly influential factors in this forecast. The sea-surface temperatures of the central and western tropical Indian Ocean were cooling from record high temperatures when this forecast was made, and this trend was expected to continue. It was assumed that the northern and tropical Atlantic Ocean would remain warmer than normal, and that sea-surface temperatures in the South Atlantic would increase during the forecast period.
This Outlook covers January-March 1999. The global map of temperature shows probabilities for expecting that the seasonal temperatures will fall into the warmest third of past years, the middle third of past years, or the coldest third of past years. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.
The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in North America. Thus, this product may differ from the official forecasts that are issued. The current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability; local variations should be expected.
Source: International Research Institute for Climate Prediction (IRI). The figure (and updated forecasts) may be accessed at the IRI web site at http://iri.ucsd.edu/forecast/net_asmt/.
Figure 2. Changes in potential distribution of Douglas Fir in western North America under 2xCO2 conditions
The U.S. Geological Survey and academic collaborators are modeling the potential effects of future climate change on plant distributions in North America. Studies of the modern relations between climatic parameters and the range boundaries of important trees and shrubs provide the basis for estimating the extents of future changes in the geographic distributions of plant species under potential future climates. The example shown here illustrates the modern distribution of Douglas-fir (Pseudotsuga menziesii) in dark green in the left panel. Light green in the right panel represents areas where this tree lives under the present climate and where it could continue to grow under an atmospheric carbon dioxide concentration of twice the pre-industrial level (a simulated "2xCO2" climate); red indicates areas where it lives today but would not survive under the simulated 2xCO2 climate; and blue represents areas where the species cannot survive today but could potentially live under the simulated 2xCO2 climate.
Source: Thompson, R.S., Hostetler, S.W., Bartlein, P.J., and Anderson, K.H., 1998: A Strategy for Assessing Potential Future Changes in Climate, Hydrology, and Vegetation in the Western United States. U.S. Geological Survey Circular 1153. The figure may be accessed on the USGS web site at http://geochange.er.usgs.gov/. This source provides a more complete description of the study.
Figure 3. Continental Scale Impact of Mexican Forest Fires: Long-range transport of smoke and dust from Mexican forest fires to the central and northeastern United States and Canada
Earth Probe satellite observations by the Total Ozone Mapping Spectrometer (TOMS) instrument have demonstrated that large forest fires in Mexico during 1998 produced plumes that were transported not only across the central part of the United States, but that the plumes actually reached the northeastern part of the U.S. (e.g., the Ohio Valley and Appalachian regions) and even penetrated well into Canada (e.g., the Hudson Bay region). The impact of these plumes, which typically exist several km off the ground, on local conditions is a subject of investigation. Potential impacts to be studied include effects on photolysis rates of chemically active species near the surface, changes in the partitioning of trace chemical species through chemical reactions that might occur on the surfaces of the particles, effects on local heating rates that could affect local meteorology, and possible contributions to the burden of particulate matter in a given area. Satellite observations of aerosol particle distributions over land have only recently become possible through the use of data from TOMS; other space-based systems for measuring aerosols produce data only over water-covered regions.
Source: NASA Goddard Space Flight Center
Figure 4. Notable past droughts in the United States reconstructed from tree rings
Severe droughts and wet periods in the United States can have enormous social and economic consequences. While much research has been done to improve understanding of the causes of these unusual climatic events in the 20th century, less research has been done on characterizing their long-term variability and patterns of occurrence over the U.S. In order to better estimate this variability and place some notable 20th century dry and wet years in an improved historical perspective, a network of long, climatically sensitive tree-ring chronologies has been examined to reconstruct past drought and wetness over the continental U.S. since 1700. This has been done at 154 grid point locations, which provides considerable spatial detail. The measure of drought used for these reconstructions is the Palmer Drought Severity Index (PDSI), a widely used measure of relative drought and wetness. Moderate-to-extreme droughts fall in the -2 to -6 PDSI range. Equivalent wet periods fall in +2 to +6 PDSI range. Presented here are some examples of notable past dry and wet years over the United States as reconstructed by tree rings.
The figure shows the PDSI maps for eight drought years since 1700. In terms of both severity and areal extent, the 1934 Dust Bowl drought year, which plunged almost 80% of the United States into some level of moisture deficit, stands out clearly as the worst drought to hit the United States in the past ~300 years. If the range of future drought variability over the U.S. remains as it has since 1700, then another "Dust Bowl" event in the near term is unlikely. However, the other less severe and less pervasive droughts are still quite remarkable and would have a severe impact on the U.S. were they to occur today. Note that each drought has a distinct spatial pattern, although there is a tendency for serious droughts to occur in the Great Plains. All of this spatial variability obviously complicates making accurate regional forecasts of drought.
Source: Edward Cook, Lamont-Doherty Earth Observatory, Columbia University. Maps were downloaded from the National Geophysical Data Center, World Data Center-A for Paleoclimatology North American Drought web site (www.ngdc.noaa.gov/paleo/drought.html), where they are available to the public.
Figure 5. Land-cover change in the Tensas River basin
EPA has completed an ecological assessment in the Tensas River Basin, Louisiana, in partnership with the Louisiana Department of Environmental Quality and other stakeholder groups. By examining landscape ecology and water quality issues, this assessment provides an evaluation of the impact of current land-use practices. Because many riparian vegetation areas throughout the United States are being restored, the GIS and landscape methods developed here can be used to help make better decisions on the restoration sites, thereby enhancing environmental quality at lowest cost.
The Tensas River Basin, one of 2,099 individual watersheds located across the United States, encompasses approximately 930,000 acres of Mississippi River alluvial flood plain in Northeast Louisiana. The freshwater marshes, stream bank areas, and bottomland swamps of the Tensas River Basin have been under strong development pressures. Large portions of forest near streams and in backwater swamp areas have been converted to agriculture.
Land cover is the product of past land uses on the backdrop of the biophysical setting. A map of land cover is essentially a picture of the dominant vegetative, water, or urban cover in an area. The images of land cover in the Tensas River Basin for 1972 and 1991 are based primarily on images taken by the Landsat Multispectral Scanner satellite since the early 1970s. The land-cover map was based on the North American Landscape Characterization (NALC) data, a Federal effort to create similar data for the entire country. The resolution of the land-cover data is 60 by 60 meters, so each pixel (picture element) represents an area about the size of a football field. Although individual pixels are far too small to be rendered accurately here, the visual impression of broadscale regional patterns is readily apparent. Forest vegetation shows up on the image as red in color, agriculture shows up as light red, grey, light blue and white and almost always shows a pattern with rows or right angles typical of farm fields. The data in these images were then used to categorize land use. Through these computerized Landscape analyses, the 1972 image was compared to the 1991 image and changes in forest areas and human use areas were determined. As the images show, there was substantial forest loss over that time period, with forest cover dropping from 34% of the area in 1972 to 22% in 1991. Where forests were removed, agriculture and urban land covers became more dominant. The images also show how the forest, agriculture, and urban land cover vary across the landscape of the Tensas River Basin. Understanding the variation of land cover with respect to landscape features, such as cities, roads, lakes and streams, has formed the foundation for this assessment.
Source: U.S. Environmental Protection Agency
Figure 6. Hurricane Bonnie storm cloud
This scientific visualization of Hurricane Bonnie shows a cumulonimbus storm cloud, towering like a skyscraper, 59,000 feet (18 kilometers) into the sky from the eyewall. By comparison, the highest mountain in the world, Mt. Everest, is 29,000 feet (9 kilometers) and the average commercial jet flies at one-half to two-thirds the height of the Bonnie's cloud tops. These images were obtained on Saturday, August 22, 1998, by the world's first spaceborne rain radar aboard the Tropical Rainfall Measuring Mission (TRMM), a joint U.S.-Japanese mission.
Clouds this tall are rarely observed in the core of Atlantic hurricanes. This huge cloud probably happened because at the time the data was collected, Bonnie was moving very slowly. The lack of movement kept funneling warm moist air into the upper atmosphere, thus raising the entire height of the tropopause, which is normally at around 45,000-52,000 feet (14-16 kilometers). The tropopause marks the upper limits of the layer of atmosphere within which the weather occurs. The vast amount of warm, moist air being raised high into the atmosphere, and the subsequent release of latent energy as raindrops form in this tropical airmass, is believed by many scientists to be the precursor of hurricane intensification, which was observed in Bonnie in the 24-to-48 hours after these data were collected.
TRMM has flown over 100 tropical cyclones since its launch in November of 1997. This collection of data enormously enhances our information about cloud structures within tropical storms during their growth and decay phases. The TRMM spacecraft fills an enormous void in the ability to observe world-wide precipitation because so little of the planet is covered by rain gauges or ground-based radars. By studying rainfall regionally and globally, and the difference between ocean and land-based storms, TRMM is providing scientists the most detailed information to date on the processes creating these powerful storms, leading to new insights on how they affect global climate patterns.
Source: NASA Goddard Space Flight Center, via Greg Williams, NASA Earth Science Program. The image may be downloaded from the TRMM web site at http://trmm.gsfc.nasa.gov/archive.html. Text courtesy of NASA Headquarters and Goddard Space Flight Center release, September 1, 1998.
Figure 7. Soil organic carbon in the United States
The amount of carbon sequestered as soil organic carbon is an important component of the global carbon budget. Soils can either contribute carbon dioxide to the atmosphere or remove it, depending on local conditions of moisture, temperature, and land management. The map shows amounts of soil organic carbon, as calculated from the USDA State Soil Geographic data base. The USGS Mississippi Basin Carbon Project is investigating the influence of erosion and sedimentation on the processes that could sequester atmospheric carbon in the soil, or conversely contribute to the release of soil carbon to the atmosphere. Model simulations are being started to show how soil organic carbon can change in response to land management changes over time and space.
Source: Courtesy of Norman Bliss, U.S. Geological Survey. Information about the Mississippi Basin Carbon Project may be found on the USGS web site at http://geochange.er.usgs.gov.
Figure 8. Ocean circulation profiling floats
The figure shows the trajectories of an array of about 400 Profiling Autonomous Lagrangian Circulation Explorer (PALACE) floats deployed at a depth of 1500 meters in the North Atlantic Ocean between 1996 and 1998. This measurement program has been a major component of the Atlantic Circulation and Climate Experiment (ACCE), which is a component of the World Ocean Circulation Experiment (WOCE). Vertical profiles of temperature and salinity are collected when floats rise to the surface at approximately 10-day intervals. These instruments have been deployed to explore specific scientific questions about the nature of convection in the Labrador Sea and the overturning at high latitudes, the production and circulation of mode water in the subtropics, and the circulation and fluxes of heat and fresh water in the Tropics. In addition, this successful deployment of a large number of PALACE floats has shown for the first time that it is feasible to observe changes in ocean heat and fresh water content in near-real time over an ocean basin. A proposal for a global Array for Real-time Geostrophic Oceanography (ARGO) is a new FY 2000 USGCRP initiative.
Source: Courtesy of Eric Itsweire, National Science Foundation, Division of Ocean Sciences
Figure 9. Ocean circulation: Comparison of modeling and observation
Many elements of a global ocean observing network are either in place now or the technology exists with which to develop and implement them. Progress in ocean modeling and computer architecture has enabled realistic, eddy-resolving models of ocean circulation to be constructed. (By eddy-resolving, we mean able to actually simulate the most natural scale of motions in the oceans, typically tens of kilometers in size.) The figure shows a comparison of an eddy-resolving simulation of Sea Surface Height variance from the Miami Isopycnal Ocean Model (MICOM), compared with sea-level variance from TOPEX altimetric measurements.
Source: Courtesy of Eric Chassignet, University of Miami, Rosenstiel School
of Marine and Atmospheric Science, Miami, FL. The figure may be accessed
on the web site of the Miami Isopycnic Coordinate Ocean Modeling Group
at the University of Miami, at the link titled "Very-high-resolution (1/12
deg.) North Atlantic MPP simulation" (http://panoramix.rsmas.miami.edu/micom/micom_highres.html).