Publications

Export 11 results:
Sort by: [ Author  (Asc)] Title Type Year
A B C D E F G H I J K L [M] N O P Q R S T U V W X Y Z   [Show ALL]
M
Mahmud, A, Tyree M, Cayan D, Motallebi N, Kleeman MJ.  2008.  Statistical downscaling of climate change impacts on ozone concentrations in California. Journal of Geophysical Research-Atmospheres. 113   10.1029/2007jd009534   AbstractWebsite

The statistical relationship between the daily 1-hour maximum ozone (O(3)) concentrations and the daily maximum upper air temperature was explored for California's two most heavily polluted air basins: the South Coast Air Basin (SoCAB) and the San Joaquin Valley Air Basin (SJVAB). A coarse-scale analysis of the temperature at an elevation of 850-mbar pressure (T850) for the period 1980-2004 was obtained from the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis data set for grid points near Upland (SoCAB) and Parlier (SJVAB). Daily 1-hour maximum ozone concentrations were obtained from the California Air Resources Board (CARB) for these locations over the same time period. The ozone concentrations measured at any given value of the Reanalysis T850 were approximately normally distributed. The 25%, 50%, and 75% quartile ozone concentrations increased linearly with T850, reflecting the effect of temperature on emissions and chemical reaction rates. A 2D Lagrangian (trajectory) form of the UCD/CIT photochemical air quality model was used in a perturbation study to explain the variability of the ozone concentrations at each value of T850. Wind speed, wind direction, temperature, relative humidity, mixing height, initial concentrations for VOC concentrations, background ozone concentrations, time of year, and overall emissions were perturbed in a realistic fashion during this study. A total of 62 model simulations were performed, and the results were analyzed to show that long-term changes to emissions inventories were the largest sources of ozone variability at a fixed value of T850. Projections of future T850 values in California were obtained from the Geophysical Fluid Dynamics Laboratory (GFDL) model under the Intergovernmental Panel on Climate Change (IPCC) A2 and B1 emissions scenarios for the years 2001 to 2100. The future temperature trends combined with the historical statistical relationships suggest that an additional 22-30 days year(-1) in California would experience O(3) >= 90 ppb under the A2 global emissions scenario, and an additional 6-13 days year(-1) would experience O(3) >= 90 ppb under the B1 global emissions scenario by the year 2050 (assuming the NO(x) and VOC emissions remained at 1990-2004 levels). These calculations help to quantify the climate "penalty" that must be overcome to improve air quality in California.

Maurer, EP, Das T, Cayan DR.  2013.  Errors in climate model daily precipitation and temperature output: time invariance and implications for bias correction. Hydrology and Earth System Sciences. 17:2147-2159.   10.5194/hess-17-2147-2013   AbstractWebsite

When correcting for biases in general circulation model (GCM) output, for example when statistically down-scaling for regional and local impacts studies, a common assumption is that the GCM biases can be characterized by comparing model simulations and observations for a historical period. We demonstrate some complications in this assumption, with GCM biases varying between mean and extreme values and for different sets of historical years. Daily precipitation and maximum and minimum temperature from late 20th century simulations by four GCMs over the United States were compared to gridded observations. Using random years from the historical record we select a "base" set and a 10 yr independent "projected" set. We compare differences in biases between these sets at median and extreme percentiles. On average a base set with as few as 4 randomly-selected years is often adequate to characterize the biases in daily GCM precipitation and temperature, at both median and extreme values; 12 yr provided higher confidence that bias correction would be successful. This suggests that some of the GCM bias is time invariant. When characterizing bias with a set of consecutive years, the set must be long enough to accommodate regional low frequency variability, since the bias also exhibits this variability. Newer climate models included in the Intergovernmental Panel on Climate Change fifth assessment will allow extending this study for a longer observational period and to finer scales.

Maurer, EP, Brekke L, Pruitt T, Thrasher B, Long J, Duffy P, Dettinger M, Cayan D, Arnold J.  2014.  An enhanced archive facilitating climate impacts and adaptation analysis. Bulletin of the American Meteorological Society. 95:1011-+.   10.1175/bams-d-13-00126.1   AbstractWebsite

We describe the expansion of a publicly available archive of downscaled climate and hydrology projections for the United States. Those studying or planning to adapt to future climate impacts demand downscaled climate model output for local or regional use. The archive we describe attempts to fulfill this need by providing data in several formats, selectable to meet user needs. Our archive has served as a resource for climate impacts modelers, water managers, educators, and others. Over 1,400 individuals have transferred more than 50 TB of data from the archive. In response to user demands, the archive has expanded from monthly downscaled data to include daily data to facilitate investigations of phenomena sensitive to daily to monthly temperature and precipitation, including extremes in these quantities. New developments include downscaled output from the new Coupled Model Intercomparison Project phase 5 (CMIP5) climate model simulations at both the monthly and daily time scales, as well as simulations of surface hydrological variables. The web interface allows the extraction of individual projections or ensemble statistics for user-defined regions, promoting the rapid assessment of model consensus and uncertainty for future projections of precipitation, temperature, and hydrology. The archive is accessible online (http://gdo-dcp.ucllnl.org/downscaled_cmip_projections).

Maurer, EP, Hidalgo HG, Das T, Dettinger MD, Cayan DR.  2010.  The utility of daily large-scale climate data in the assessment of climate change impacts on daily streamflow in California. Hydrology and Earth System Sciences. 14:1125-1138.   10.5194/hess-14-1125-2010   AbstractWebsite

Three statistical downscaling methods were applied to NCEP/NCAR reanalysis (used as a surrogate for the best possible general circulation model), and the downscaled meteorology was used to drive a hydrologic model over California. The historic record was divided into an 'observed' period of 1950-1976 to provide the basis for downscaling, and a 'projected' period of 1977-1999 for assessing skill. The downscaling methods included a bias-correction/spatial downscaling method (BCSD), which relies solely on monthly large scale meteorology and resamples the historical record to obtain daily sequences, a constructed analogues approach (CA), which uses daily large-scale anomalies, and a hybrid method (BCCA) using a quantile-mapping bias correction on the large-scale data prior to the CA approach. At 11 sites we compared three simulated daily flow statistics: streamflow timing, 3-day peak flow, and 7-day low flow. While all downscaling methods produced reasonable streamflow statistics at most locations, the BCCA method consistently outperformed the other methods, capturing the daily large-scale skill and translating it to simulated streamflows that more skillfully reproduced observationally-driven streamflows.

Maurer, EP, Stewart IT, Bonfils C, Duffy PB, Cayan D.  2007.  Detection, attribution, and sensitivity of trends toward earlier streamflow in the Sierra Nevada. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd008088   AbstractWebsite

[1] Observed changes in the timing of snowmelt dominated streamflow in the western United States are often linked to anthropogenic or other external causes. We assess whether observed streamflow timing changes can be statistically attributed to external forcing, or whether they still lie within the bounds of natural ( internal) variability for four large Sierra Nevada ( CA) basins, at inflow points to major reservoirs. Streamflow timing is measured by "center timing'' (CT), the day when half the annual flow has passed a given point. We use a physically based hydrology model driven by meteorological input from a global climate model to quantify the natural variability in CT trends. Estimated 50-year trends in CT due to natural climate variability often exceed estimated actual CT trends from 1950 to 1999. Thus, although observed trends in CT to date may be statistically significant, they cannot yet be statistically attributed to external influences on climate. We estimate that projected CT changes at the four major reservoir inflows will, with 90% confidence, exceed those from natural variability within 1 - 4 decades or 4 - 8 decades, depending on rates of future greenhouse gas emissions. To identify areas most likely to exhibit CT changes in response to rising temperatures, we calculate changes in CT under temperature increases from 1 to 5 degrees. We find that areas with average winter temperatures between -2 degrees C and -4 degrees C are most likely to respond with significant CT shifts. Correspondingly, elevations from 2000 to 2800 m are most sensitive to temperature increases, with CT changes exceeding 45 days ( earlier) relative to 1961 - 1990.

McGowan, JA, Cayan DR, Dorman LM.  1998.  Climate-ocean variability and ecosystem response in the northeast Pacific. Science. 281:210-217.   10.1126/science.281.5374.210   AbstractWebsite

The role of climatic variation in regulating marine populations and communities is not well understood. To improve our knowledge, the sign, amplitude, and frequency of climatic and biotic variations should be compared as a necessary first step. it is shown that there have been large interannual and interdecadal sea-surface temperature changes off the West Coast of North America during the past 80 years. Interannual anomalies appear and disappear rather suddenly and synchronously along the entire coastline. The frequency of warm events has increased since 1977. Although extensive, serial, biological observations are often incomplete, it is clear that climate-ocean variations have disturbed and changed our coastal ecosystems.

Means, JD, Cayan D.  2013.  Precipitable Water from GPS Zenith Delays Using North American Regional Reanalysis Meteorology. Journal of Atmospheric and Oceanic Technology. 30:485-495.   10.1175/jtech-d-12-00064.1   AbstractWebsite

Precipitable water or integrated water vapor can be obtained from zenith travel-time delays from global positioning system (GPS) signals if the atmospheric pressure and temperature at the GPS site is known. There have been more than 10 000 GPS receivers deployed as part of geophysics research programs around the world; but, unfortunately, most of these receivers do not have collocated barometers. This paper describes a new technique to use North American Regional Reanalysis pressure, temperature, and geopotential height data to calculate station pressures and surface temperature at the GPS sites. This enables precipitable water to be calculated at those sites using archived zenith delays. The technique has been evaluated by calculating altimeter readings at aviation routine weather report (METAR) sites and comparing them with reported altimeter readings. Additionally, the precipitable water values calculated using this method have been found to agree with SuomiNet GPS precipitable water, with RMS differences of 2 mm or less, and are also generally in agreement with radiosonde measurements of precipitable water. Applications of this technique are shown and are explored for different synoptic situations, including atmospheric-river-type baroclinic storms and the North American monsoon.

Melville, WK, Lenain L, Cayan DR, Kahru M, Kleissl JP, Linden PF, Statom NM.  2016.  The Modular Aerial Sensing System. Journal of Atmospheric and Oceanic Technology. 33:1169-1184.   10.1175/jtech-d-15-0067.1   AbstractWebsite

Satellite remote sensing has enabled remarkable progress in the ocean, earth, atmospheric, and environmental sciences through its ability to provide global coverage with ever-increasing spatial resolution. While exceptions exist for geostationary ocean color satellites, the temporal coverage of low-Earth-orbiting satellites is not optimal for oceanographic processes that evolve over time scales of hours to days. In hydrology, time scales can range from hours for flash floods, to days for snowfall, to months for the snowmelt into river systems. On even smaller scales, remote sensing of the built environment requires a building-resolving resolution of a few meters or better. For this broad range of phenomena, satellite data need to be supplemented with higher-resolution airborne data that are not tied to the strict schedule of a satellite orbit. To address some of these needs, a novel, portable, high-resolution airborne topographic lidar with video, infrared, and hyperspectral imaging systems was integrated. The system is coupled to a highly accurate GPS-aided inertial measurement unit (GPS IMU), permitting airborne measurements of the sea surface displacement, temperature, and kinematics with swath widths of up to 800 m under the aircraft, and horizontal spatial resolution as low as 0.2 m. These data are used to measure ocean waves, currents, Stokes drift, sea surface height (SSH), ocean transport and dispersion, and biological activity. Hydrological and terrestrial applications include measurements of snow cover and the built environment. This paper describes the system, its performance, and present results from recent oceanographic, hydrological, and terrestrial measurements.

Miller, AJ, Cayan DR, White WB.  1998.  A westward-intensified decadal change in the North Pacific thermocline and gyre-scale circulation. Journal of Climate. 11:3112-3127.   10.1175/1520-0442(1998)011<3112:awidci>2.0.co;2   AbstractWebsite

From the early 1970s to the mid-1980s, the main thermocline of the subarctic gyre of the North Pacific Ocean shoaled with temperatures at 200-400-m depth cooling by 1 degrees-4 degrees C over the region. The gyre-scale structure of the shoaling is quasi-stationary and intensified in the western part of the basin north of 30 degrees N, suggesting concurrent changes in gyre-scale transport. A similar quasi-stationary cooling in the subtropical gyre south of 25 degrees N is also observed but lags the subpolar change by several years. To explore the physics of these changes, the authors examine an ocean model forced by observed wind stress and heat flux anomalies from 1970-88 in which they find similar changes in gyre-scale thermocline structure. The model current fields reveal that the North Pacific subpolar and subtropical gyres strengthened by roughly 10% from the 1970s to the 1980s. The bulk of the eastward Row of the model Kuroshio-Oyashio Extension returned westward via the subpolar gyre circuit, while the subtropical gyre return flow along 20 degrees N lags the subpolar changes by several years. The authors demonstrate that the model thermocline cooling and increased transport occurred in response to decadal-scale changes in basin-scale wind stress curl with the quasi-stationary oceanic response being in a time-dependent quasi-Sverdrup balance over much of the basin east of the date line. This wind stress curl driven response is quasi-stationary but occurs in conjunction with a propagating temperature anomaly associated with subduction in the central North Pacific that links the subpolar and subtropical gyre stationary changes and gives the appearance of circumgyre propagation. Different physics evidently controls the decadal subsurface temperature signal in different parts of the extratropical North Pacific.

Miller, AJ, Cayan DR, Barnett TP, Graham NE, Oberhuber JM.  1994.  Interdecadal variability of the Pacific Ocean: model response to observed heat flux and wind stress anomalies. Climate Dynamics. 9:287-302.   10.1007/bf00204744   AbstractWebsite

Variability of the Pacific Ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux, wind stress and turbulent kinetic energy (TKE) over the period 1970-88. The model captures the 1976-77 winter time climate shift in sea surface temperature, as well as its monthly, seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses. Examination of the surface mixed-layer heat budget reveals that the 1976-77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi-month period preceding the shift in both the central Pacific region (where cooling occurred) and the California coastal region (where warming occurred). In the central Pacific, the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux (TKE input) into the mixed layer (which deepens in the model after the shift) from the early 1970s to the late 1970s and 1980s. Since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976-77 shift, it appears that the midlatitude part of the shift was driven by the atmosphere, although effects of midlatitude ocean-atmosphere feedback are still possible. The surface mixed-layer heat budget also reveals that, in the central Pacific, the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size. In the California coastal region, in contrast, where wind variability is much weaker than in the central Pacific, horizontal advection and vertical mixing effects on the mixed-layer heat budget are only one-quarter the size of typical heat flux input anomalies.

Miller, AJ, White WB, Cayan DR.  1997.  North Pacific thermocline variations on ENSO timescales. Journal of Physical Oceanography. 27:2023-2039.   10.1175/1520-0485(1997)027<2023:nptvoe>2.0.co;2   AbstractWebsite

The North Pacific thermocline (250 to 400 m) is studied using XBT observations acquired during the 1970s and 1980s. Interannual variations (3-5 yr timescales) in thermocline temperature, with O(0.1 degrees C) amplitude at 400 m, are found to exhibit westward propagation throughout the extratropical North Pacific up to 45 degrees N. Southward of 30 degrees N, the features propagate intact across the basin from the eastern boundary to the western boundary. Northward of 30 degrees N, the features can be observed to propagate only as far as the date line. The observed midlatitude thermocline anomalies are often related to tropical ENSO events in that they occur most strongly after the development of tropical El Nino or La Nina conditions and propagate westward from near the eastern boundary in the midlatitudes. But it is found that the observed midlatitude thermocline anomalies have larger phase speeds than theoretically predicted free baroclinic Rossby waves. Also, the observed anomalies have larger wavelength and faster propagation speeds than baroclinic Rossby waves that radiate from coastal Kelvin-like waves near the eastern boundary in well-known high-resolution models. Large-scale thermocline fluctuations that have spatial scale and phase speeds similar to the observations are also found in a coarse-resolution model of the Pacific Ocean forced by observed wind and heat Aux anomalies over the 1970-88 period. In the midlatitudes, north of 30 degrees N, large-scale Ekman pumping by interannual wind stress curl variations provides a significant driving mechanism for the modeled large-scale thermocline anomalies. The modeled ocean response is a combination of the static thermocline response to large-scale Ekman pumping plus a train of westward traveling Rossby waves, which accounts for part of the propagating temperature fluctuations. A tropical, remotely forced component is prominant near the eastern boundary, but this only contributes weakly in the model open ocean.