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Clemesha, RES, Gershunov A, Iacobellis SF, Cayan DR.  2017.  Daily variability of California coastal low cloudiness: A balancing act between stability and subsidence. Geophysical Research Letters. 44:3330-3338.   10.1002/2017gl073075   AbstractWebsite

We examine mechanisms driving daily variability of summer coastal low cloudiness (CLC) along the California coast. Daily CLC is derived from a satellite record from 1996 to 2014. Atmospheric rather than oceanic processes are mostly responsible for daily fluctuations in vertical stability that dictate short-period variation in CLC structure. Daily CLC anomalies are most strongly correlated to lower tropospheric stability anomalies to the north. The spatially offset nature of the cloud-stability relationship is a result of the balancing act that affects low cloudiness wherein subsidence drives increased stability, which promotes cloudiness, but too much subsidence limits cloudiness. Lay explanations claim that high inland temperatures pull in CLC, but such a process presumably would have the high temperatures directly inland. Rather, we find that the spatially offset associations between CLC and atmospheric circulation result in positive correlations between CLC and inland surface temperature anomalies to the north.

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.

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.

Polade, SD, Gershunov A, Cayan DR, Dettinger MD, Pierce DW.  2013.  Natural climate variability and teleconnections to precipitation over the Pacific-North American region in CMIP3 and CMIP5 models. Geophysical Research Letters. 40:2296-2301.   10.1002/grl.50491   AbstractWebsite

Natural climate variability will continue to be an important aspect of future regional climate even in the midst of long-term secular changes. Consequently, the ability of climate models to simulate major natural modes of variability and their teleconnections provides important context for the interpretation and use of climate change projections. Comparisons reported here indicate that the CMIP5 generation of global climate models shows significant improvements in simulations of key Pacific climate mode and their teleconnections to North America compared to earlier CMIP3 simulations. The performance of 14 models with simulations in both the CMIP3 and CMIP5 archives are assessed using singular value decomposition analysis of simulated and observed winter Pacific sea surface temperatures (SSTs) and concurrent precipitation over the contiguous United States and northwestern Mexico. Most of the models reproduce basic features of the key natural mode and their teleconnections, albeit with notable regional deviations from observations in both SST and precipitation. Increasing horizontal resolution in the CMIP5 simulations is an important, but not a necessary, factor in the improvement from CMIP3 to CMIP5.

Rodo, X, Ballester J, Cayan D, Melish ME, Nakamura Y, Uehara R, Burns JC.  2011.  Association of Kawasaki disease with tropospheric wind patterns. Scientific Reports. 1   10.1038/srep00152   AbstractWebsite

The causal agent of Kawasaki disease (KD) remains unknown after more than 40 years of intensive research. The number of cases continues to rise in many parts of the world and KD is the most common cause of acquired heart disease in childhood in developed countries. Analyses of the three major KD epidemics in Japan, major non-epidemic interannual fluctuations of KD cases in Japan and San Diego, and the seasonal variation of KD in Japan, Hawaii, and San Diego, reveals a consistent pattern wherein KD cases are often linked to large-scale wind currents originating in central Asia and traversing the north Pacific. Results suggest that the environmental trigger for KD could be wind-borne. Efforts to isolate the causative agent of KD should focus on the microbiology of aerosols.

Dettinger, MD, Cayan DR, Meyer M, Jeton AE.  2004.  Simulated hydrologic responses to climate variations and change in the Merced, Carson, and American River basins, Sierra Nevada, California, 1900-2099. Climatic Change. 62:283-317.   10.1023/B:CLIM.0000013683.13346.4f   AbstractWebsite

Hydrologic responses of river basins in the Sierra Nevada of California to historical and future climate variations and changes are assessed by simulating daily streamflow and water-balance responses to simulated climate variations over a continuous 200-yr period. The coupled atmosphere-ocean-ice-land Parallel Climate Model provides the simulated climate histories, and existing hydrologic models of the Merced, Carson, and American Rivers are used to simulate the basin responses. The historical simulations yield stationary climate and hydrologic variations through the first part of the 20th century until about 1975 when temperatures begin to warm noticeably and when snowmelt and streamflow peaks begin to occur progressively earlier within the seasonal cycle. A future climate simulated with business-as-usual increases in greenhouse-gas and aerosol radiative forcings continues those recent trends through the 21st century with an attendant + 2.5 degreesC warming and a hastening of snowmelt and streamflow within the seasonal cycle by almost a month. The various projected trends in the business-as-usual simulations become readily visible despite realistic simulated natural climatic and hydrologic variability by about 2025. In contrast to these changes that are mostly associated with streamflow timing, long-term average totals of streamflow and other hydrologic fluxes remain similar to the historical mean in all three simulations. A control simulation in which radiative forcings are held constant at 1995 levels for the 50 years following 1995 yields climate and streamflow timing conditions much like the 1980s and 1990s throughout its duration. The availability of continuous climate-change projection outputs and careful design of initial conditions and control experiments, like those utilized here, promise to improve the quality and usability of future climate-change impact assessments.

Cayan, DR, Riddle LG, Aguado E.  1993.  The influence of precipitation and temperature on seasonal streamflow in California. Water Resources Research. 29:1127-1140.   10.1029/92wr02802   AbstractWebsite

We examine the influence of climate parameters on seasonal streamflow in watersheds over a range of elevations in California and Oregon. Effects of precipitation, temperature, and snow water content (SWC) are diagnosed using linear regression models and categoric composites. Most of the models explain over 60-80% of the seasonal streamflow variability. The models and the composites provide insight into the climate influences which drive the individual watersheds. Low (warmer) basins have little snow and little memory of prior seasons' climate variability. High (cooler) basins, with more snow, have longer memories. Precipitation has the greatest influence on streamflow variations in spring. Temperature is important in spring in the mid and high elevations. By late spring, SWC accounts for nearly all of the summer streamflow variation at mid and high elevations, but earlier in the runoff season, precipitation and temperature add variance. The variations in surface climate parameters, including streamflow, are generally controlled by atmospheric circulation anomalies with a spatial scale much larger than those in watersheds. This explains why little skill was lost by broadening the scale of temperature and precipitation predictors to regional climate areas.