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Weinheimer, AL, Cayan DR.  1997.  Radiolarian assemblages from Santa Barbara Basin sediments: Recent interdecadal variability. Paleoceanography. 12:658-670.   10.1029/97pa00986   AbstractWebsite

Santa Barbara Basin contains a sedimentary record ideal for high-resolution paleoclimate studies because of the annual varves and regional-to global-scale climate signals preserved in the sediments [Lange er al., 1990; Kennett and Ingram, 1995], even though it does not lie directly in the path of the California Current. A nearly 100-year annual time series (1909-1991) of polycystine radiolarian assemblages from Santa Barbara Basin (SBB) sediments was analyzed to the species level. Counts on a replicate SBB core, dated 1870-1987, indicate that results are reproducible and the flux of a few representative species can be extrapolated to estimate fluxes of environmentally sensitive groups. The frequency of species occurrences resembles a lognormal curve and year-by-year comparisons of species fluxes revealed only modest changes in the assemblages from 1909-1991, indicating that the assemblages represent a single oceanic province. For paleoceanographic analysis of the radiolarian record, species were combined into groups according to the water mass in which they occur. To test this method, temperature-sensitive species were identified using t-tests. This generated warm and cool classes exhibiting trends in relative flux similar to those of the water mass groups. Both total nux and relative fluxes of water mass groups relate to low-frequency, decadal-scale temperature fluctuations, but not strongly to El Nino-Southern Oscillation events. Generally, fluxes of species from different water masses covary suggesting changing carrying capacities and productivity through time, while the consistent inverse relationship in relative fluxes indicate variability in climate. The subtle, decadal-scale changes in assemblages, diversity, and increase in percent warm water-fauna are consistent with a spin-down of the California Current System suggested by other records.

Weinheimer, AL, Kennett JP, Cayan DR.  1999.  Recent increase in surface-water stability during warming off California as recorded in marine sediments. Geology. 27:1019-1022.   10.1130/0091-7613(1999)027<1019:riisws>;2   AbstractWebsite

Warming of surface waters in the California Current since the 1950s has coincided with a significant decline in zooplankton volume. This has been attributed to reduced upwelling of nutrient-rich waters caused by increased thermal stratification across the thermocline. Proxy microfossil evidence preserved in the Santa Barbara Basin suggests that stability increased early in the 1900s, intensified after the early 1940s, and became well established by 1960. Accumulation of up-welled radiolarians in the basin has steadily declined since 1900, while oxygen isotopes in surface-dwelling planktonic foraminifera reflect increasing surface temperatures. Comparison of the delta(18)O records between surface and thermocline-dwelling planktonic foraminifera reveals that the temperature difference between surface and thermocline water has increased during the twentieth century. Instrumental records of surface and thermocline temperatures, monitored since 1950, support these results. This evidence suggests that relaxation of North Pacific anticyclonic gyre circulation deepened isopycnics, causing onshore movement of warmer, less saline waters and reduced upwelling of cool, nutrient-rich waters.

Westerling, AL, Gershunov A, Brown TJ, Cayan DR, Dettinger MD.  2003.  Climate and wildfire in the western United States. Bulletin of the American Meteorological Society. 84:595-+.   10.1175/bams-84-5-595   AbstractWebsite

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.

Westerling, AL, Hidalgo HG, Cayan DR, Swetnam TW.  2006.  Warming and earlier spring increase western US forest wildfire activity. Science. 313:940-943.   10.1126/science.1128834   AbstractWebsite

Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.

Westerling, AL, Cayan DR, Brown TJ, Hall B, Riddle LG.  2004.  Climate, Santa Ana winds and autumn wildfires in southern California. EOS Trans. AGU. 85:289. Abstract
Westerling, AL, Gershunov A, Cayan DR, Barnett TP.  2002.  Long lead statistical forecasts of area burned in western US wildfires by ecosystem province. International Journal of Wildland Fire. 11:257-266.   10.1071/wf02009   AbstractWebsite

A statistical forecast methodology exploits large-scale patterns in monthly U.S. Climatological Division Palmer Drought Severity Index (PDSI) values over a wide region and several seasons to predict area burned in western US. wildfires by ecosystem province a season in advance. The forecast model, which is based on canonical correlations, indicates that a few characteristic patterns determine predicted wildfire season area burned. Strong negative associations between anomalous soil moisture (inferred from PDSI) immediately prior to the fire season and area burned dominate in most higher elevation forested provinces, while strong positive associations between anomalous soil moisture a year prior to the fire season and area burned dominate in desert and shrub and grassland provinces. In much of the western US., above- and below-normal fire season forecasts were successful 57% of the time or better, as compared with a 33% skill for a random guess, and with a low probability of being surprised by a fire season at the opposite extreme of that forecast.

White, WB, Cayan DR, Niiler PP, Moisan J, Lagerloef G, Bonjean F, Legler D.  2005.  The seasonal cycle of diabatic heat storage in the Pacific Ocean. Progress in Oceanography. 64:1-29.   10.1016/j.pocean.2004.06.012   AbstractWebsite

This study quantifies uncertainties in closing the seasonal cycle of diabatic heat storage (DHS) over the Pacific Ocean from 20 degrees S to 60 degrees N through the synthesis of World Ocean Circulation Experiment (WOCE) reanalysis products from 1993 to 1999. These products are DHS from Scripps Institution of Oceanography (SIO); near-surface geostrophic and Ekman currents from Earth and Space Research (ESR); and air-sea heat fluxes from Comprehensive Ocean-Atmosphere Data Set (COADS), National Centers for Environmental Prediction (NCEP), and European Center for Mid-Range Weather Forecasts (ECMWF). With these products, we compute residual heat budget components by differencing long-term monthly means from the long-term annual mean. This allows the seasonal cycle of the DHS tendency to be modeled. Everywhere latent heat flux residuals dominate sensible heat flux residuals, shortwave heat flux residuals dominate longwave heat flux residuals, and residual Ekman heat advection dominates residual geostrophic heat advection, with residual dissipation significant only in the Kuroshio-Oyashio current extension. The root-mean-square (RMS) of the differences between observed and model residual DHS tendencies (averaged over 10 degrees latitude-by-20 degrees longitude boxes) is < 20 W m(-2) in the interior ocean and < 100 W m(-2) in the Kuroshio-Oyashio current extension. This reveals that the residual DHS tendency is driven everywhere by some mix of residual latent heat flux, shortwave heat flux, and Ekman heat advection. Suppressing bias errors in residual air-sea turbulent heat fluxes and Ekman heat advection through minimization of the RMS differences reduces the latter to < 10 W m(-2) over the interior ocean and < 25 W m(-2) in the Kuroshio-Oyashio current extension. This reveals air-sea temperature and specific humidity differences from in situ surface marine weather observations to be a principal source of bias error, overestimated over most of ocean but underestimated near the Intertropical Convergence Zone. (c) 2005 Elsevier Ltd. All rights reserved.

White, WB, Lean J, Cayan DR, Dettinger MD.  1997.  Response of global upper ocean temperature to changing solar irradiance. Journal of Geophysical Research-Oceans. 102:3255-3266.   10.1029/96jc03549   AbstractWebsite

By focusing on time sequences of basin-average and global-average upper ocean temperature (i.e., from 40 degrees S to 60 degrees N) we find temperatures responding to changing solar irradiance in three separate frequency bands with periods of >100 years, 18-25 years, and 9-13 years. Moreover, we find them in two different data sets, that is, surface marine weather observations from 1990 to 1991 and bathythermograph (BT) upper ocean temperature profiles from 1955 to 1994. Band-passing basin-average find each frequency component in phase across the Indian, Pacific, and Atlantic Oceans, yielding global-average records with maximum amplitudes of 0.04 degrees +/- 0.01 degrees K and 0.07 degrees 0.01 degrees K on decadal and interdecadal scales, respectively. These achieve maximum correlation with solar irradiance records (i.e., with maximum amplitude 0.5 W m(-2) at the top of the atmosphere) al phase lags ranging from 30 degrees to 50 degrees. From the BT data set, solar signals in global-average temperature penetrate to 80-160 m, confined to the upper layer above the main pycnocline. Operating a global-average heat budget for the upper ocean yields sea surface temperature responses of 0.01 degrees-0.03 degrees K and 0.02 degrees-0.05 degrees K on decadal and interdecadal scales, respectively, from the 0.1 W m(-2) Penetration of solar irradiance to the sea surface. Since this is of the same order as that observed (i.e., 0.04 degrees-0.07 degrees K), we can infer that anomalous heat from changing solar irradiance is stored in the upper layer of the ocean.

White, WB, Cayan DR.  2000.  A global El Nino-Southern Oscillation wave in surface temperature and pressure and its interdecadal modulation from 1900 to 1997. Journal of Geophysical Research-Oceans. 105:11223-11242.   10.1029/1999jc900246   AbstractWebsite

Zonal wavenumber frequency spectra of sea surface temperature (SST) anomalies along the equator in the Indo-Pacific basin For the 98 years from 1900 to 1997 and of surface temperature (ST) and sea level pressure (SLP) anomalies extending around the globe along 10 degrees N for the 48 years from 1950 to 1997 display significant peak spectral energy density for standing and eastward propagating waves of 3-7 year periods and 120 degrees-360 degrees zonal wavelengths, The global standing wave is the familiar Southern Oscillation, but the global propagating wave represents a new paradigm for the El Nino-Southern Oscillation (ENSO). Global distributions of the phase velocities for this global ENSO wave finds covarying SLP and ST anomalies propagating eastward along the mean path of the Intertropical Convergence Zone (ITCZ), with the global zonal wavenumber 1 (2) component taking similar to 4 (6) years to cross the tropical Indian, Pacific, and Atlantic Oceans at a zonal average speed of 90 degrees (60 degrees) longitude per year. Along this path the interannual SST acid SLP anomalies are directly out of phase. Since thermocline depth anomalies underneath the ITCZ in the Pacific Ocean propagate westward [White et al. 1985], we view the global ENSO wave as a slow coupled SST wave trapped onto the ITCZ. Separating the global ENSO wave from the Southern Oscillation using complex empirical orthogonal function analysis finds the amplitude of the propagating wave to be half that of the standing wave, with the former (latter) accounting for one third (two thirds) of the interannual variability in Nino-3 SST and SLP indices during the 1980s. The global ENSO wave is shown to be responsible for the eastward propagation of covarying zonal surface wind and thermocline depth anomalies across the equatorial Pacific Ocean and through this mechanism is able to influence both the phasing and intensity of El Nino. Examining the persistence of the global ENSO wave from 1900 to 1997 finds it and the intensity of El Nino in the eastern equatorial Pacific Ocean modulated by interdecadal change, Both were strong (weak or absent) during decades of global tropical cooling (warming).

White, WB, Cayan DR.  1998.  Quasi-periodicity and global symmetries in interdecadal upper ocean temperature variability. Journal of Geophysical Research-Oceans. 103:21335-21354.   10.1029/98jc01706   AbstractWebsite

Recent studies find interannual (i.e., 3 to 7 year), decadal (i.e., 9 to 13 year), and interdecadal (i.e., 18 to 23 year) periodicities, and a trend dominating global sea surface temperature (SST) and sea level pressure (SLP) variability over the past hundred years, with the interdecadal signal dominating sub-El Nino-Southern Oscillation (ENSO) frequencies. We isolate interdecadal frequencies in SST and SLP records by band passing with a window admitting 15 to 30 year periods. From 1900 to 1989, the rms of interdecadal-filtered SST and SLP anomalies is largest in the extratropics and eastern boundaries. First-mode empirical orthogonal functions (EOFs) explain about half the interdecadal variance in both variables, with the tropical warn phase peaking near 1900, 1920, 1940, 1960, and 1980. From 1955 to 1994, EOF spatial patterns of interdecadal SST, SLP, and 400m temperature (T400) anomalies reveals global reflection symmetries about the equator and global translation symmetries between ocean basins, with tropical and eastern ocean SSTs warmer (cooler) than normal, covarying with stronger (weaker) extratropical westerly winds, cooler (warmer) SSTs in western-central subarctic and subantarctic frontal zones (SAFZs), stronger (weaker) subtropic and subarctic gyre circulations in North Pacific and North Atlantic Oceans, and warmer (cooler) basin and global average SSTs of 0.1 degrees C or so. Evolution of interdecadal variability from the tropical warm phase to the tropical cool phase is propagative, also characterized by reflection and translation symmetries. During the tropical warm phase, cool SST anomalies along western-central SAFZs are advected slowly eastward to the eastern boundaries and subsequently advected poleward and equatorward by the mean gyre circulation, the latter conducting extratropical SST anomalies into the tropics. A delayed action oscillation model is constructed that yields the quasiperiodicity of interdecadal variability in a manner consistent with these global symmetries in both pattern and evolution.

White, WB, Dettinger MD, Cayan DR.  2003.  Sources of global warming of the upper ocean on decadal period scales. Journal of Geophysical Research-Oceans. 108   10.1029/2002jc001396   AbstractWebsite

[1] Recent studies find global climate variability in the upper ocean and lower atmosphere during the twentieth century dominated by quasi-biennial, interannual, quasi-decadal and interdecadal signals. The quasi-decadal signal in upper ocean temperature undergoes global warming/cooling of - 0.1degreesC, similar to that occurring with the interannual signal (i. e., El Nino-Southern Oscillation), both signals dominated by global warming/cooling in the tropics. From the National Centers for Environmental Prediction troposphere reanalysis and Scripps Institution of Oceanography upper ocean temperature reanalysis we examine the quasi-decadal global tropical diabatic heat storage (DHS) budget from 1975 to 2000. We find the anomalous DHS warming tendency of 0.3-0.9 W m(-2) driven principally by a downward global tropical latent-plus-sensible heat flux anomaly into the ocean, overwhelming the tendency by weaker upward shortwave-minus-longwave heat flux anomaly to drive an anomalous DHS cooling tendency. During the peak quasidecadal warming the estimated dissipation of DHS anomaly of 0.2-0.5 W m(-2) into the deep ocean and a similar loss to the overlying atmosphere through air-sea heat flux anomaly are balanced by a decrease in the net poleward Ekman heat advection out of the tropics of 0.4-0.7 W m(-2). This scenario is nearly the opposite of that accounting for global tropical warming during the El Nino. These diagnostics confirm that even though the global quasi-decadal signal is phase-locked to the 11-year signal in the Sun's surface radiative forcing of -0.1 W m(-2), the anomalous global tropical DHS tendency cannot be driven by it directly.

White, WB, Cayan DR, Dettinger MD, Auad G.  2001.  Sources of global warming in upper ocean temperature during El Nino. Journal of Geophysical Research-Oceans. 106:4349-4367.   10.1029/1999jc000130   AbstractWebsite

Global average sea surface temperature (SST) from 40 degreesS to 60 degreesN fluctuates +/-0.3 degreesC on interannual period scales, with global warming (cooling) during El Nino (La Nina). About 90% of the global warming during El Nino occurs in the tropical global ocean from 20 degreesS to 20 degreesN, half because of large SST anomalies in the tropical Pacific associated with El Nino and the other half because of warm SST anomalies occurring over similar to 80% of the tropical global ocean. From examination of National Centers for Environmental Prediction [Kalnay et al., 1996] and Comprehensive Ocean-Atmosphere Data Set [Woodruff et al., 1993] reanalyses, tropical global warming during El Nino is associated with higher troposphere moisture content and cloud cover, with reduced trade wind intensity occurring during the onset phase of EI Nino. During this onset phase the tropical global average diabatic heat storage tendency in the layer above the main pycnocline is 1-3 Wm(-2) above normal. Its principal source is a reduction in the poleward Ekman heat flux out of the tropical ocean of 2-5 Wm(-2). Subsequently, peak tropical global warming during El Nino is dissipated by an increase in the flux of latent heat to the troposphere of 2-5 W m(-2), with reduced shortwave and longwave radiative fluxes in response to increased cloud cover tending to cancel each other. In the extratropical global ocean the reduction in poleward Ekman heat flux out of the tropics during the onset of El Nino tends to be balanced by reduction in the flux of latent heat to the troposphere. Thus global warming and cooling during Earth's internal mode of interannual climate variability arise from fluctuations in the global hydrological balance, not the global radiation balance. Since it occurs in the absence of extraterrestrial and anthropogenic forcing, global warming on decadal, interdecadal, and centennial period scales may also occur in association with Earth's internal modes of climate variability on those scales.

White, AB, Anderson ML, Dettinger MD, Ralph FM, Hinojosa A, Cayan DR, Hartman RK, Reynolds DW, Johnson LE, Schneider TL, Cifelli R, Toth Z, Gutman SI, King CW, Gehrke F, Johnston PE, Walls C, Mann D, Gottas DJ, Coleman T.  2013.  A twenty-first-century California observing network for monitoring extreme weather events. Journal of Atmospheric and Oceanic Technology. 30:1585-1603.   10.1175/jtech-d-12-00217.1   AbstractWebsite

During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for the water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. To improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, are required. Here, the authors describe how California is addressing their most important and costliest environmental issue-water management-in part, by installing a state-of-the-art observing system to better track the area's most severe wintertime storms.

White, WB, Cayan DR, Lean J.  1998.  Global upper ocean heat storage response to radiative forcing from changing solar irradiance and increasing greenhouse gas/aerosol concentrations. Journal of Geophysical Research-Oceans. 103:21355-21366.   10.1029/98jc01477   AbstractWebsite

We constructed gridded fields of diabatic heat storage changes in the upper ocean from 20 degrees S to 60 degrees N from historical temperature profiles collected from 1955 to 1996. We filtered these 42 year records for periods of 8 to 15 years and 15 to 30 years, producing depth-weighted vertical average temperature (DVT) changes from the sea surface to the top of the main pycnocline. Basin and global averages of these DVT changes reveal decadal and interdecadal variability in phase across the Indian, Pacific, Atlantic, and Global Oceans, each significantly correlated with changing surface solar radiative forcing at a lag of 0 +/- 2 years. Decadal and interdecadal changes in global average DVT are 0.06 degrees +/- 0.01 degrees K and 0.04 degrees K +/- 0.01 degrees K, respectively, the same as those expected from consideration of the Stefan-Boltzmann radiation balance (i.e., 0.3 degrees K per W m(-2)) in response to 0.1% changes in surface solar radiative forcing of 0.2 W m(-2) and 0.15 W m(-2), respectively. Global spatial patterns of DVT changes are similar to temperature changes simulated in coupled ocean-atmosphere models, suggesting that natural modes of Earth's variability are phase-locked to the solar irradiance cycle. A trend in global average DVT of 0.15 degrees K over this 42 year record cannot be explained by changing surface solar radiative forcing. But when we consider the 0.5 W m(-2) increase in surface radiative forcing estimated from the increase in atmospheric greenhouse gas and aerosol (GGA) concentrations over this period [Intergovernmental Panel on Climate Change, 1995], the Stefan-Boltzmann radiation balance yields this observed change. Moreover, the sum of solar and GGA surface radiative forcing can explain the relatively sharp increase in global and basin average DVT in the late 1970's.