Publications Published in American Meterological Society

1. ACE-ASIA: Regional Climatic and Atmospheric Chemical Effects of Asian Dust and Pollution. Seinfeld, John H; Carmichael, Gregory R; Arimoto, Richard; Conant, William C; Brechtel, Frederick J; Bates, Timothy S; Cahill, Thomas A; Clarke, Antony D.; Doherty, Sarah J..
   American Meterological Society: 2004
   Notes
   Although continental-scale plumes of Asian dust and pollution reduce the amount of solar radiation reaching the earth's surface and perturb the chemistry of the atmosphere, our ability to quantify these effects has been limited by a lack of critical observations, particularly of layers above the surface. Comprehensive surface, airborne, shipboard, and satellite measurements of Asian aerosol chemical composition, size, optical properties, and radiative impacts were performed during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) study. Measurements within a massive Chinese dust storm at numerous widely spaced sampling locations revealed the highly complex structure of the atmosphere, in which layers of dust, urban pollution, and biomass-burning smoke may be transported long distances as distinct entities or mixed together. The data allow a first-time assessment of the regional climatic and atmospheric chemical effects of a continental-scale mixture of dust and pollution. Our results show that radiative flux reductions during such episodes are sufficient to cause regional climate change.
   
   
   
2. A Micrometerological investigation of a restored California Wetland Ecosystem. Anderson, Frank E; Snyder, Richard L; Miller, Robin L; Drexler, Judith.
   American Meterological Society: 2003
   Notes
   Water flowing through the delta prevents saltwater intrusion into freshwater ecosystems. Continued subsidence, however, seriously threatens the levee system in the delta and levee breaks could result in saltwater intrusion and contamination of the freshwater supply used by 22 million southern Californians.
   
   
   
3. A Multiple-Case Analysis of Nocturnal Radiation-Fog Development in the Central Valley of California Utilizing the GOES Nighttime Fog Product. S. JEFFREY UNDERWOOD, GARY P. ELLROD, AARON L. KUHNERT.
   American Meterological Society: 2004
   Notes
   Radiation fog in the Central Valley of California has received very little attention in terms of climatological research. This study uses the Geostationary Operational Environmental Satellite (GOES) nighttime fog product to develop a sequence of images and datasets that reveal patterns of nocturnal radiation-fog development in the Central Valley. Twenty long-lived, spatially extensive radiation-fog episodes, occurring from October through January, were selected for the period of 1997–2000. Mean hourly parameters for fog cover, fog development rate, and vertical development were calculated for the 20 episodes in the Central Valley. The study region is separated into five analysis divisions oriented from south to north for spatial comparisons within the valley. Large-scale radiation fog begins developing before 1800 LST, and rates of development vary widely from south to north. Radiation fog develops earlier and covers a larger area of the southern valley as compared with the central and northern portions of t e valley. The horizontal extent of radiation fog is maximized at 0600 LST in the southern valley and near midnight in the central and northern parts of the valley. Vertical development reaches 300 m with regularity in the southern valley. Radiation-fog development of greater than 300 m occurs primarily in the early morning hours. Vertical development ‘‘bursts’’ are also observed in the southern valley during the morning hours. Climatologically important conditions for radiation-fog development in the Central Valley include cool 1600 LST surface temperatures, moisture availability as reflected by 1600 LST dewpoint temperatures, early evening surface cooling trends, the rapidity with which mean relative humidity reaches 90%, and the presence of cool, dry air aloft (700–500 hPa).
   
   
   
4. Challenges in combining projections from multiple climate models. Reto Knutti, Reinhard Furrer, Claudia Tebaldi, Jan Cermak, and Gerald A. Meehl.
   American Meterological Society: 2009
   DOI: 10.1175/2009JCLI3361.1
   Notes
   Recent coordinated efforts, in which numerous general circulation climate models have been run for a common set of experiments, have produced large datasets of projections of future climate for various scenarios. Those multi-model ensembles sample initial condition, parameter as well as structural uncertainties in the model design, and they have prompted a variety of approaches to quantifying uncertainty in future climate change. International climate change assessments also rely heavily on these models and often provide equal-weighted averages as best-guess results, assuming that individual model biases will at least partly cancel and that a model average prediction is more likely to be correct than a prediction from a single model based on the result that a multi-model average of present-day climate generally out-performs any individual model. This study outlines the motivationfor using multi-model ensembles and discusses various challenges in interpreting them. Among these challenges are that the number of models in these ensembles is usually small, their distribution in the model or parameter space is unclear and the fact that extreme behavior is often not sampled. Model skill in simulating present day climate conditions is shown to relate only weakly to the magnitude of predicted change. It is thus unclear by how much our confidence in future projections should increase based on improvements in simulating present day conditions, a reduction of intermodel spread or a larger number of models. Averaging model output may further lead to a loss of signal, e.g. for precipitation change where the predicted changes are spatially heterogeneous, such that the true expected change is very likely to be larger than suggested by a model average. Finally, there is little agreement on metrics to separate ‘good’ and ‘bad’ models, and there is a concern that model development, evaluation and posterior weighting or ranking are all using the same datasets. While the multi-model average appears to still be useful in some situati ns, these results show that more quantitative methods to quantify model performance are critical to maximize the value of climate change projections from global models.
   
   
   
5. Climate and Wildfire in the Western United States. Westerling, A.L.; Gershunov, A.; Brown, T.J.; Cayan, D.R.; Dettinger, M. D..
   American Meterological Society: 2003
   Notes
   A 21-yr gridded monthly fire-starts and acres-burned dataset from U.S. Forest Service, Bureau of Land Management, National Park Service, and Bureau of Indian Affairs fire reports recreates the seasonality and interannual variability of wildfire in the western United States. Despite pervasive human influence in western fire regimes, it is striking how strongly these data reveal a fire season responding to variations in climate. Correlating anomalous wildfire frequency and extent with the Palmer Drought Severity Index illustrates the importance of prior and accumulated precipitation anomalies for future wildfire season severity. This link to antecedent seasons' moisture conditions varies widely with differences in predominant fuel type. Furthermore, these data demonstrate that the relationship between wildfire season severity and observed moisture anomalies from antecedent seasons is strong enough to forecast fire season severity at lead times of one season to a year in advance.
   
   
   
6. Climate Research and Reinsurance. Murnane, Richard J..
   American Meterological Society: 2004
   Notes
   Extreme weather events produce some of the most deadly and costly natural disasters and are a major concern of the catastrophe reinsurance industry. For example, in 1992 Hurricane Andrew caused over $20 billion (in 2002 U.S. dollars) in insured losses, the largest loss on record due to a natural disaster. In addition, 26 of the top 30 insured losses were produced by extreme weather events, mainly landfalling hurricanes and typhoons and European wind-storms. A better understanding of how extreme events vary with climate would benefit the reinsurance industry and society. The Risk Prediction Initiative hosted a workshop on Weather Extremes and Atmospheric Oscillations that examined how extreme meteorological events of interest to the reinsurance industry are influenced by the quasi-biennial oscillation (QBO), the Arctic Oscillation (AO), and the Madden–Julian oscillation (MJO). Workshop participants concluded that the stratosphere is much more relevant to predictions that aid the reinsurance industry than is generally recognized and that there is mutual interest in fostering research on the relationship between the stratospheric circulation and extreme weather events. A preliminary science–business research agenda, based on presentations and discussions during and after the workshop, highlights four areas of mutual interest to scientists and insurers. The research areas focus mainly on understanding how the QBO, AO, and MJO influence the frequency and intensity of extreme events, with particular emphasis on tropical cyclones and European windstorms. An awareness of how the catastrophe reinsurance industry operates provides insights into why specific research areas were chosen. For example, the reinsurance industry operates on the basis of annual contracts, most of which are renewed on 1 January. Thus, although skillful forecasts at any lead are of interest, skillful forecasts of extreme events are of greatest value when made in the final quarter of a calendar year.
   
   
   
7. Drought Reconstructions for the Continental United States. Cook, Edward R.; Meko, David M.; Stahle, David W.; Cleaveland, Malcom K..
   American Meterological Society: 1999
   Notes
   The development of a 2° lat × 3° long grid of summer drought reconstructions for the continental United States estimated from a dense network of annual tree-ring chronologies is described. The drought metric used is the Palmer Drought Severity Index (PDSI). The number of grid points is 154 and the reconstructions cover the common period 1700–1978. In producing this grid, an automated gridpoint regression method called “point-by-point regression” was developed and tested. In so doing, a near-optimal global solution was found for its implementation. The reconstructions have been thoroughly tested for validity using PDSI data not used in regression modeling. In general, most of the gridpoint estimates of drought pass the verification tests used. In addition, the spatial features of drought in the United States have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design. The drought reconstructions show that the 1930s “Dust Bowl” drought wa the most severe such event to strike the United States since 1700. Other more local droughts are also revealed in the regional patterns of drought obtained by rotated principal component analysis. These reconstructions are located on a NOAA Web site at the World Data Center-A in Boulder, Colorado, and can be freely downloaded from there.
   
   
   
8. Examination of Potential Biases in Air Temperature Caused by Poor Station Locations. Peterson, Thomas C.
   American Meterological Society: 2006
   
   
9. Influence of Cloud Condensation Nuclei on Orographic Snowfall. STEPHEN M. SALEEBY, WILLIAM R. COTTON, DOUGLAS LOWENTHAL, RANDOLPH D. BORYS, MELANIE A. WETZEL.
   American Meterological Society: 2009
   DOI: 10.1175/2008JAMC1989.1
   Notes
   Pollution aerosols acting as cloud condensation nuclei (CCN) have the potential to alter warm rain clouds via the aerosol first and second indirect effects in which they modify the cloud droplet population, cloudlifetime and size, rainfall efficiency, and radiation balance from increased albedo. For constant liquid water content, an increase in CCN concentration (NCCN) tends to produce an increased concentration of droplets with smaller diameters. This reduces the collision and coalescence rate, and thus there is a local reduction in rainfall. While this process applies to warm clouds, it does not identically carry over to mixed-phase clouds in which crystal nucleation, crystal riming, crystal versus droplet fall speed, and collection efficiency play active roles in determining precipitation amount. Sulfate-based aerosols serve as very efficient cloud nuclei but are not effective as ice-forming nuclei. In clouds where precipitation formation is dominated by the ice phase, NCCN influences precipitation growth by altering the efficiency of droplet collection by ice crystals and the fall trajectories of both droplet and crystal hydrometeors. The temporal and spatial variation in both crystal and droplet populations determines the resultant snowfall efficiency and distribution. Results of numerical simulations in this study suggest that CCN can play a significant role in snowfall production by winter, mixedphase, cloud systems when liquid and ice hydrometeors coexist. In subfreezing conditions, a precipitating ice cloud overlaying a supercooled liquid water cloud allows growth of precipitation particles via the seeder– feeder process, in which nucleated ice crystals fall through the supercooled liquid water cloud and collect droplets. Enhanced NCCN from sulfate pollution by fossil fuel emissions modifies the droplet distribution and reduces crystal riming efficiency. Reduced riming efficiency inhibits the rate of snow growth, producing lightly rimed snow crystals that fall slowly and advect farther downstream prior o surface deposition. Simulations indicate that increasing NCCN along the orographic barrier of the Park Range in north-central Colorado results in a modification of the orographic cloud such that the surface snow water equivalent amounts are reduced on the windward slopes and enhanced on the leeward slopes. The inhibition of snowfall by pollution aerosols (ISPA) effect has significant implications for water resource distribution in mountainous terrain.
   
   
   
10. RAIN-ON-SNOW EVENTS IN THE WESTERN UNITED STATES. GREGORY J. MCCABE, MARTYN P. CLARK, LAUREN E. HAY.
    American Meterological Society: 2007
    DOI: 10.1175/BAMS-88-3-319