Narasimhan K. Larkin

ENSO Warm (El Niño) and Cold (La Niña) Event Life Cycles: Ocean Surface Anomaly Patterns, Their Symmetries, Asymmetries, and Implications

Abstract Previous studies by the authors have described the composite global marine surface anomalies of ENSO warm (El Nino) events and cold (La Nina) events. Here the similarities and differences in these life cycles are examined. Qualitatively different behavior between warm events and cold events exists in the tropical Indian and Atlantic Oceans and in the extratropical Pacific. Even in the tropical Pacific statistically significantly different behavior is found in some variables for particular regions and phases of the life cycles. A single-mode regression analysis of the ENSO signal is done; the patterns are very similar to those of previously published ENSO EOF and regression analyses. The authors describe how the regression patterns obscure many of the interesting life cycles and life cycle differences of cold events and warm events. Most of the regression structures outside of the tropical Pacific are not statistically significant because of such differences. ENSO models should be evaluated agains...

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

The BlueSky smoke modeling framework

Smoke from fire is a local, regional and often international issue that is growing in complexity as competition for airshed resources increases. BlueSky is a smoke modeling framework designed to help address this problem by enabling simulations of the cumulative smoke impacts from fires (prescribed, wildland, and agricultural) across a region. Versions of BlueSky have been implemented in prediction systems across the contiguous US, and land managers, air-quality regulators, incident command teams, and the general public can currently obtain BlueSky-based predictions of smoke impacts for their region. A highly modular framework, BlueSky links together a variety of state-of-the-art models of meteorology, fuels, consumption, emissions, and air quality, and offers multiple model choices at each modeling step. This modularity also allows direct comparison between similar component models. This paper presents the overall model framework Version 2.5 - the component models, how they are linked together, and the results from case studies of two wildfires. Predicted results are affected by the specific choice of modeling pathway. With the pathway chosen, the modeled output generally compares well with plume shape and extent as observed by satellites, but underpredicts surface concentrations as observed by ground monitors. Sensitivity studies show that knowledge of fire behavior can greatly improve the accuracy of these smoke impact calculations.

Climate change presents increased potential for very large fires in the contiguous United States

Very large fires (VLFs) have important implications for communities, ecosystems, air quality and fire suppressionexpenditures.VLFsoverthecontiguousUShavebeenstronglylinkedwithmeteorologicalandclimatological variability. Building on prior modelling of VLFs (.5000 ha), an ensemble of 17 global climate models were statistically downscaled over the US for climate experiments covering the historic and mid-21st-century periods to estimate potential changes in VLF occurrence arising from anthropogenic climate change. Increased VLF potential was projected across most historically fire-prone regions, with the largest absolute increase in the intermountain West and Northern California. Complementary to modelled increases in VLF potential were changes in the seasonality of atmospheric conditions conducive to VLFs, including an earlier onset across the southern US and more symmetric seasonal extension in the northern regions. These projections provide insights into regional and seasonal distribution of VLF potential under a changing climate, and serve as a basis for future strategic and tactical fire management options.

The COADS Sea Level Pressure Signal: A Near-Global El Niño Composite and Time Series View, 1946–1993

Abstract Using COADS data for the period 1946–1993, the near-global sea level pressure (SLP) patterns associated with interannual variability and the climatological seasonal march are discussed. A particular focus concerns the patterns associated with the two years before and after the South American sea surface temperatures rise (El Nino). The ten El Nino events in this record are composited, and the robustness of the features of this composite is tested. Many features of the composite are quite robust; they occur during most El Nino events and are infrequent during non-El Nino periods. The most robust feature is an area of negative SLP anomaly (SLPA) in the eastern equatorial Pacific during Year(0) of the composite. This feature exceeds significance thresholds during every El Nino year and never during non-El Nino years; it correlates better with central Pacific SST variability than does the SOI. A west-central North Pacific positive SLPA, occurring late in Year(0) and lasting into the spring of year (+...

Modelling smoke transport from wildland fires: a review

Among the key issues in smoke management is predicting the magnitude and location of smoke effects. These vary in severity from hazardous (acute health conditions and drastic visibility impairment to transportation) to nuisance (regional haze), and occur across a range of scales (local to continental). Over the years a variety of tools have been developed to aid in predicting smoke effects. This review follows the development of these tools, from various indices and simple screening models to complex air quality modelling systems, with a focus on how each tool represents key processes involved in smoke transport.

Modeling very large-fire occurrences over the continental United States from weather and climate forcing

Very large-fires (VLFs) have widespread impacts on ecosystems, air quality, fire suppression resources, and in many regions account for a majority of total area burned. Empirical generalized linear models of the largest fires (>5000 ha) across the contiguous United States (US) were developed at ∼60 km spatial and weekly temporal resolutions using solely atmospheric predictors. Climatefire relationships on interannual timescales were evident, with wetter conditions than normal in the previous growing season enhancing VLFs probability in rangeland systems and with concurrent long-term drought enhancing VLFs probability in forested systems. Information at sub-seasonal timescales further refined these relationships, with short-term fire weather being a significant predictor in rangelands and fire danger indices linked to dead fuel moisture being a significant predictor in forested lands. Models demonstrated agreement in capturing the observed spatial and temporal variability including the interannual variability of VLF occurrences within most ecoregions. Furthermore the model captured the observed increase in VLF occurrences across parts of the southwestern and southeastern US from 1984 to 2010 suggesting that, irrespective of changes in fuels and land management, climatic factors have become more favorable for VLF occurrence over the past three decades in some regions. Our modeling framework provides a basis for simulations of future VLF occurrences from climate projections. S Online supplementary data available from stacks.iop.org/ERL/9/124009/mmedia

Climate and very large wildland fires in the contiguous western USA

Very large wildfires can cause significant economic and environmental damage, including destruction of homes, adverse air quality, firefighting costs and even loss of life. We examine how climate is associated with very large wildland fires (VLWFs

Tropical Pacific ENSO Cold Events, 1946–95: SST, SLP, and Surface Wind Composite Anomalies*

50 000 acres, or ,20 234 ha) in the western contiguous USA. We used composite records of climate and fire to investigate the spatial and temporal variability of VLWF-climatic relationships. Results showed quantifiable fire weather leading up and up to 3 weeks post VLWF discovery, thus providing predictors of the probability that VLWF occurrence ina given week. Models were created for eight National Interagency Fire Center Geographic Area Coordination Centers (GACCs). Accuracy was good (AUC.0.80) for all models, but significant fire weather predictors of VLWFs vary by GACC, suggesting that broad-scale ecological mechanisms associated with wildfires also vary across regions. These mechanisms are very similar to those found by previous analyses of annual area burned, but this analysis provides a means for anticipating VLWFs specifically and thereby the timing of substantial area burned within a given year, thus providing aquantifiable justification forproactive firemanagement practices tomitigatethe risk andassociated damage of VLWFs. Additional keywords: AUC, GACC, logistic regression, niche space, precision, rare events, recall, wildland fire.

Grassland and forest understorey biomass emissions from prescribed fires in the south-eastern United States – RxCADRE 2012

Abstract ENSO cold (La Nina) events are shown to exhibit a distinctive life cycle. The first near-global description of ENSO cold (La Nina)–event anomaly features is described using ocean surface data. It is found that cold-event anomalies are not simply the mirror image of warm (El Nino) events. The Comprehensive Ocean–Atmosphere Data Set marine surface record [SST, sea level pressure (SLP), and wind] is used to identify the statistically significant features of the nine cold-event periods during 1946–95 and to focus on the large-scale elements that are typical of most events. By examining time series, the most robust features of the composite that have occurred during nearly all of the post–World War II cold events are identified. These robust cold-event features are more numerous and cover more of the globe than their warm-event counterparts. Of the 90 composite features examined, 57 (63%) are found to be robust. Most of these are located in the Tropics (70%) and in the Pacific (65%). However, robust e...