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Namias, J, Cayan DR.  1981.  Large-scale air-sea interactions and short-period climatic fluctuations. Science. 214:869-876.   10.1126/science.214.4523.869   AbstractWebsite

Research during the last 15 years has shown that there is order in large-scale air-sea interactions, so that space scales of abnormalities of the lower atmosphere's circulation and the upper oceanic thermal structure are comparable. Because of this air-sea coupling, each oceanic or atmospheric pattern can be reasonably well specified by the other. Patterns of oceanic thermal anomalies are about an order of magnitude more persistent than those of atmospheric circulations, and empirical studies have had some success in using sea surface temperature patterns in long-range weather prediction. In addition to empirical studies, efforts continue in the development of numerical-dynamical models in order to understand the complex linkages of the large-scale air-sea system.

Dettinger, MD, Cayan DR.  1995.  Large-scale atmospheric forcing of recent trends toward early snowmelt runoff in California. Journal of Climate. 8:606-623.   10.1175/1520-0442(1995)008<0606:lsafor>;2   AbstractWebsite

Since the late 1940s, snowmelt and runoff have come increasingly early in the water year in many basins in northern and central California. This subtle trend is most pronounced in moderate-altitude basins, which are sensitive to changes in mean winter temperatures. Such basins have broad areas in which winter temperatures are near enough to freezing that small increases result initially in the formation of less snow and eventually in early snowmelt. In moderate-altitude basins of California, a declining fraction of the annual runoff has come in April-June. This decline has been compensated by increased fractions of runoff at other, mostly earlier, times in the water year. Weather stations in central California, including the central Sierra Nevada, have shown trends toward warmer winters since the 1940s. A series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude, suggesting that the temperature trend is sufficient to explain the runoff-timing trends. The immediate cause of the trend toward warmer winters in California is a concurrent, long-term fluctuation in winter atmospheric circulations over the North Pacific Ocean and North America that is not immediately distinguishable from natural atmospheric variability. The fluctuation began to affect California in the 1940s, when the region of strongest low-frequency variation of winter circulations shifted to a part of the central North Pacific Ocean that is teleconnected to California temperatures. Since the late 1940s, winter wind fields have been displaced progressively southward over the central North Pacific and northward over the west coast of North America. These shifts in atmospheric circulations are associated with concurrent shifts in both West Coast air temperatures and North Pacific sea surface temperatures.

Douglas, AV, Cayan DR, Namias J.  1982.  Large-scale changes in North Pacific and North American weather patterns in recent decades. Monthly Weather Review. 110:1851-1862.   10.1175/1520-0493(1982)110<1851:lscinp>;2   AbstractWebsite

This paper compares long-term seasonal means of atmospheric and oceanic fields for the recent 1969–80 period, relative to the earlier 1947–66 base period. Difference maps of North Pacific sea surface temperature (SST), 700 mb height, and United States surface temperature and precipitation are examined.An appreciable cooling of the North Pacific SST field during the 1969–80 period was found to exhibit large coherent cold pools with the maximum average cooling over the period being 1°C for the coldest locations. The center of maximum cooling varied with season; its position shifted eastward from winter to fall.The pattern of SST cooling corresponds well to the patterns of difference of 700 mb height over the North Pacific for the 1969–80 period, relative to 1947–66. The areas of cooling have generally occurred in regions of strengthened northerly wind components and/or low heights, a fact which can be rationalized by physical arguments. The winter and spring seasonal averages for 1969–80 are characterized by below normal heights in the region of the Gulf of Alaska and the Aleutians.Downstream, the field of 700 mb height over North America shows differences that are well related to those over the North Pacific, as shown by long-period teleconnections of seasonal averaged heights. The height differences over the continent are large and spatially coherent., for instance, the winter average shows a deep negative area affecting the eastern half of the United States. The patterns of height difference over the coterminous United States are easily related to those of surface temperature and precipitation. The temperature and precipitation differences also display large spatial scales, with average differences over the 1969–80 period large enough to designate them an extreme tercile class in many states.Thus, reasoning for very short period (e.g., seasonal) changes shows that climate variations may be applied to longer period (e.g., decadal) phenomena.

Cayan, DR.  1980.  Large-scale relationships between sea-surface temperature and surface air temperature. Monthly Weather Review. 108:1293-1301.   10.1175/1520-0493(1980)108<1293:lsrbss>;2   AbstractWebsite

Empirical relationships between the sea surface temperature (SST) and surface air temperatures (SAT) are examined on monthly, seasonal and annual time scales for Marsden square areas in the North Pacific and the North Atlantic. On these time scales SST and SAT have roughly the same variance throughout the sample region. They are well correlated (contemporaneously) with warm seasons and months having slightly higher correlations than cold ones. For the most part, the spatial patterns and temporal changes in these statistics are similar between the North Atlantic and North Pacific.

Cayan, DR.  1992.  Latent and sensible heat flux anomalies over the Northern Oceans: Driving the sea surface temperature. Journal of Physical Oceanography. 22:859-881.   10.1175/1520-0485(1992)022<0859:lashfa>;2   AbstractWebsite

A part of the large-scale thermodynamic forcing of the upper ocean is examined by relating monthly anomalous latent and sensible heat flux to changes in sea surface temperature (SST) anomalies over the North Atlantic and North Pacific. The fluxes are estimated using bulk formulas from a set of about four decades of marine observations from the COADS dataset from 1946 to 1986. Monthly anomalies are constructed by removing the long-term monthly means. The latent and sensible flux anomalies are strongly correlated over most of the ocean, so they are considered together as a sum. The heat flux estimates contain large spatial-scale anomalies consistent with both atmospheric circulation anomalies and with month-to-month changes (tendencies) in monthly SST anomalies. The monthly flux anomalies and the SST anomaly tendency are significantly con-elated over much of the oceans, with anomalous positive/negative fluxes associated with anomalous cooling/warming. The connection between the flux and the SST tendency anomalies is strongest in the extratropics during the cool season when the latent and sensible fluxes and their variability are greatest, and the radiative fluxes are weakest. While the heat flux forcing of the SST anomalies operates locally, the flux and SST tendency anomalies are organized over spatial scales that often span major portions of the North Atlantic and North Pacific. For each basin, canonical correlations expose large-scale, collocated anomaly patterns in the two fields. These patterns reflect the control exerted by the large-scale atmospheric circulation, inferred from sea level pressure (SLP) modes. Evidence for this result is the strong similarity in the configuration of anomalous flux and SST tendency patterns in their association with major SLP modes. Typical flux anomalies of 50 W m-2 are associated with monthly SST anomaly changes of order 0.2-degrees-C. The surface-layer thickness inferred from a simplified model relating the flux anomalies to the temperature anomalies of a slab ocean is consistent in magnitude and seasonal cycle with the observed mixed-layer depth in middle latitudes.

Cayan, DR.  1992.  Latent and sensible heat flux anomalies over the Northern Oceans: the connection to monthly atmospheric circulation. Journal of Climate. 5:354-369.   10.1175/1520-0442(1992)005<0354:lashfa>;2   AbstractWebsite

The influence of the atmospheric circulation on monthly anomalies of ocean surface latent and sensible heat fluxes is explored. The fluxes are estimated using bulk formulas applied to a set of about four decades of marine observations over 1946-1986. Monthly averaging over 5-degrees "squares" reduces errors contained in individual observations. The focus is on behavior of the flux anomalies over the relatively well-sampled North Atlantic and North Pacific oceans during winter, when the latent and sensible components are large and the incoming shortwave radiative flux is low. In the North Atlantic and North Pacific (north of about 15-degrees-N), flux anomalies are partially caused by local variations in the monthly mean wind direction. In these extratropical regions, largest positive anomalies occur during northerly to northwesterly winds in response to advection of humidity and temperature from north to south and also to favored directions experiencing strong wind speeds. In the tropics, there is little relationship between the direction and the latent and sensible flux anomalies, since horizontal gradients of humidity and temperature are weak and the wind direction is relatively steady. The most convincing connection between the wind and the flux anomalies is not local, but rather has basin scales associated with the monthly atmospheric circulation. In the North Atlantic and North Pacific, dominant atmospheric circulation modes, represented as empirical orthogonal functions of the sea level pressure (SLP) anomaly, have systematic patterns of the anomalies of wind speed (w), surface saturation humidity-air humidity difference (DELTA-q), and sea surface temperature-air temperature difference (DELTA-T); these produce large-scale patterns in the latent and sensible fluxes. In the extratropics, a major negative SLP anomaly tends to have positive w anomalies to its south and negative w anomalies to its north, while DELTA-q (and DELTA-T) anomalies lie to the west and east of the low, apparently because of meridional air advection. The resultant flux anomalies are shifted meridionally and zonally about the SLP centers, with enhanced sea-to-air fluxes to the southwest and diminished fluxes to the east of an anomalous low. Regions of increased monthly mean fluxes tend to have larger than normal intramonthly variability in the fluxes. Months with strong monthly atmospheric circulation anomalies frequently exhibit combined latent and sensible flux anomalies with magnitudes exceeding 50 W m-2 over several hundred kilometer regions.

Franco, G, Cayan D, Luers A, Hanemann M, Croes B.  2008.  Linking climate change science with policy in California. Climatic Change. 87:S7-S20.   10.1007/s10584-007-9359-8   AbstractWebsite

Over the last few years, California has passed some of the strongest climate policies in the USA. These new policies have been motivated in part by increasing concerns over the risk of climate-related impacts and facilitated by the state's existing framework of energy and air quality policies. This paper presents an overview of the evolution of this increased awareness of climate change issues by policy makers brought about by the strong link between climate science and policy in the state. The State Legislature initiated this link in 1988 with the mandate to prepare an assessment of the potential consequences of climate change to California. Further interactions between science and policy has more recently resulted, in summer of 2006, in the passage of Assembly Bill 32, a law that limits future greenhouse gas emissions in California. This paper discusses the important role played by a series of state and regional climate assessments beginning in 1988 and, in particular, the lessons learned from a recently completed study known as the Scenarios Project.

Cayan, DR, Roads JO.  1984.  Local relationships between United States west coast precipitation and monthly mean circulation parameters. Monthly Weather Review. 112:1276-1282.   10.1175/1520-0493(1984)112<1276:lrbusw>;2   AbstractWebsite

Monthly accumulations of area-averaged precipitation along the West Coast of the United States are related to estimates of local circulation parameters. The annual cycle as well as anomalous components of these quantities are compared. A strong annual cycle in most of the circulation parameters reflects the influence of the large-scale circulation on the annual variation of the precipitation field. For the anomalous monthly components, especially in winter, high correlations are found between precipitation and sea-level pressure or 70 kPa height. Other circulation parameters are also significantly correlated with the precipitation. These include the zonal and meridional wind components and the advection of relative vorticity.

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.

Chen, SC, Cayan DR.  1994.  Low-frequency aspects of the large-scale circulation and West Coast United States temperature/precipitation fluctuations in a simplified general circulation model. Journal of Climate. 7:1668-1683.   10.1175/1520-0442(1994)007<1668:lfaotl>;2   AbstractWebsite

Behavior of regional precipitation and temperature over the West Coast of the United States was examined in a long perpetual winter simulation from a simplified global general circulation model. The model, a simplified version of the U.S. National Weather Service global operational forecast model, was run over a series of 568 winters, complete with geopotential, precipitation, and near-surface temperature. In spite of the fixed climatological boundary conditions, the simulated winter-mean precipitation and temperature anomalies have a fairly realistic low-frequency regional variability. Both synoptic-scale events and seasonal average behavior are produced quite realistically by the model. Like observations, the regional surface variations can be related to the large-scale low-frequency circulation. Four regional temperature/precipitation extremes-namely, warm/dry, cool/wet, cool/dry, and warm/wet-can be identified from the simulated winter-mean time series over the West Coast. Associated with these four regional extremes, model Northern Hemisphere 500-mb height composites exhibit distinct planetary-scale circulation patterns. An empirical orthogonal function analysis further reveals that the first and third modes of the 500-mb height anomalies are primary contributors to these four regional extremes. The first mode largely governs the regional temperature variation, whereas the third mode largely determines the precipitation variation.