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aspects of North American climate variability, organized by the time scale of the climate feature. Section 3 covers intraseasonal variability with focus on variability in the eastern Pacific Ocean and summer drought over the southern United States and Central America. Atlantic and east Pacific tropical cyclone activity is evaluated in section 4 . Interannual climate variability is assessed in section 5 . Decadal variability and multidecadal trends are assessed in sections 6 and 7 , respectively
aspects of North American climate variability, organized by the time scale of the climate feature. Section 3 covers intraseasonal variability with focus on variability in the eastern Pacific Ocean and summer drought over the southern United States and Central America. Atlantic and east Pacific tropical cyclone activity is evaluated in section 4 . Interannual climate variability is assessed in section 5 . Decadal variability and multidecadal trends are assessed in sections 6 and 7 , respectively
of the warming and its relationship with natural climate variability. The models in phase 3 of the Coupled Model Intercomparison Project (CMIP3) were challenged in simulating this warming hole ( Kunkel et al. 2006 ). Attempts to understand the mechanism that produces the warming hole have led to several investigations in recent years (e.g., Meehl et al. 2012a ; Misra et al. 2012 ; Weaver 2013 ). While some studies have attributed the warming hole to large-scale decadal oscillations such as the
of the warming and its relationship with natural climate variability. The models in phase 3 of the Coupled Model Intercomparison Project (CMIP3) were challenged in simulating this warming hole ( Kunkel et al. 2006 ). Attempts to understand the mechanism that produces the warming hole have led to several investigations in recent years (e.g., Meehl et al. 2012a ; Misra et al. 2012 ; Weaver 2013 ). While some studies have attributed the warming hole to large-scale decadal oscillations such as the
forcing show a clear decline in snow cover since 1970 ( Fig. 2 ). The two largest short-term reversals of this longer trend in the simulations followed large volcanic eruptions (El Chichón, March 1982; Mount Pinatubo). Inspection of the smoothed time series highlights the magnitude of the post-1970 decline against the (multi)decadal variability in both observations and simulations ( Fig. 3 ). While the smoothed observations show high variability at time scales of 20–30 yr, the magnitude of the marked
forcing show a clear decline in snow cover since 1970 ( Fig. 2 ). The two largest short-term reversals of this longer trend in the simulations followed large volcanic eruptions (El Chichón, March 1982; Mount Pinatubo). Inspection of the smoothed time series highlights the magnitude of the post-1970 decline against the (multi)decadal variability in both observations and simulations ( Fig. 3 ). While the smoothed observations show high variability at time scales of 20–30 yr, the magnitude of the marked
section 5 . Changes in Atlantic and east Pacific TC activity are examined in section 6 . Multidecadal trends in interannual to decadal hydroclimate variability are analyzed in section 7 . Conclusions and a discussion are presented in section 8 . 2. CMIP5 models and experiments We use CMIP5 multimodel datasets of historical climate and climate change experiments ( Taylor et al. 2012 ). These are long-term century-scale projections of climate based on coupled simulations that include a representation
section 5 . Changes in Atlantic and east Pacific TC activity are examined in section 6 . Multidecadal trends in interannual to decadal hydroclimate variability are analyzed in section 7 . Conclusions and a discussion are presented in section 8 . 2. CMIP5 models and experiments We use CMIP5 multimodel datasets of historical climate and climate change experiments ( Taylor et al. 2012 ). These are long-term century-scale projections of climate based on coupled simulations that include a representation
generation of the atmosphere–ocean coupled general circulation models (AOGCMs). A companion paper ( Kumar et al. 2013a ) investigates east–west gradient and multidecadal aspects of the WH trends in North America as in Meehl et al. (2012) . More general results regarding North American climate in the CMIP5 models are reported in Sheffield et al. (2013a , b ). 2. Model and data The design of CMIP5 includes the new short-term decadal experiments hindcasting the interannual variability, emission
generation of the atmosphere–ocean coupled general circulation models (AOGCMs). A companion paper ( Kumar et al. 2013a ) investigates east–west gradient and multidecadal aspects of the WH trends in North America as in Meehl et al. (2012) . More general results regarding North American climate in the CMIP5 models are reported in Sheffield et al. (2013a , b ). 2. Model and data The design of CMIP5 includes the new short-term decadal experiments hindcasting the interannual variability, emission
). The dark green shade indicates topography above 1500 m, and the gray shade bar indicates mean daily precipitation rate (mm day −1 ) calculated for the entire historic period of the simulations (1951–2005). The majority of the CMIP5 models simulate well the pattern of warming over tropical SA, in particular the remarkable expansion of T850 p85 in the 1996–2005 decade in spite of the large intermodel variability of the pattern of daily precipitation ( Figs. 1c–m ). The eastward enlargement of the T
). The dark green shade indicates topography above 1500 m, and the gray shade bar indicates mean daily precipitation rate (mm day −1 ) calculated for the entire historic period of the simulations (1951–2005). The majority of the CMIP5 models simulate well the pattern of warming over tropical SA, in particular the remarkable expansion of T850 p85 in the 1996–2005 decade in spite of the large intermodel variability of the pattern of daily precipitation ( Figs. 1c–m ). The eastward enlargement of the T
the relevant ocean changes may be potentially predictable on decadal time scales (e.g., Griffies and Bryan 1997a , b ; Pohlmann et al. 2004 ; Collins et al. 2006 ; Pohlmann et al. 2009 ; Msadek et al. 2010 ; S10 ; Teng et al. 2011 ; Chikamoto et al. 2013 ; van Oldenborgh et al. 2012 ; A. Rosati et al. 2012, unpublished manuscript; Yang et al. 2012; Yeager et al. 2012 ). As decadal variability and the associated predictability can result from both internally and externally forced
the relevant ocean changes may be potentially predictable on decadal time scales (e.g., Griffies and Bryan 1997a , b ; Pohlmann et al. 2004 ; Collins et al. 2006 ; Pohlmann et al. 2009 ; Msadek et al. 2010 ; S10 ; Teng et al. 2011 ; Chikamoto et al. 2013 ; van Oldenborgh et al. 2012 ; A. Rosati et al. 2012, unpublished manuscript; Yang et al. 2012; Yeager et al. 2012 ). As decadal variability and the associated predictability can result from both internally and externally forced
Fig. 10c ), four models simulate the significant multidecadal bands: GFDL CM3, HadGEM2-CC, MPI-ESM-LR, and MRI-CGCM3. In category II (shown in Fig. 10d ), three models simulate the interannual band and multidecadal bands: GFDL-ESM2G, GFDL-ESM2M, and HadCM3 at the 95% significance level. In category III six models ( Fig. 10e ), consisting of GISS-E2H, GISS-E2R, INM-CM4, IPSL-CM5A-MR, MPI-ESM-P, and NorESM1-M, simulate significant variability for the decadal and multidecadal bands. In category IV
Fig. 10c ), four models simulate the significant multidecadal bands: GFDL CM3, HadGEM2-CC, MPI-ESM-LR, and MRI-CGCM3. In category II (shown in Fig. 10d ), three models simulate the interannual band and multidecadal bands: GFDL-ESM2G, GFDL-ESM2M, and HadCM3 at the 95% significance level. In category III six models ( Fig. 10e ), consisting of GISS-E2H, GISS-E2R, INM-CM4, IPSL-CM5A-MR, MPI-ESM-P, and NorESM1-M, simulate significant variability for the decadal and multidecadal bands. In category IV
1. Introduction During boreal summer, convective activity over the eastern North Pacific Ocean (ENP) along the intertropical convergence zone (ITCZ) exhibits significant intraseasonal variability (ISV). Through its associated large-scale circulation and thermodynamical variations, the ISV exerts broad impacts on regional weather and climate systems, including the North American monsoon (NAM), midsummer drought over Central America, and Caribbean rainfall and low-level jet, as well as tropical
1. Introduction During boreal summer, convective activity over the eastern North Pacific Ocean (ENP) along the intertropical convergence zone (ITCZ) exhibits significant intraseasonal variability (ISV). Through its associated large-scale circulation and thermodynamical variations, the ISV exerts broad impacts on regional weather and climate systems, including the North American monsoon (NAM), midsummer drought over Central America, and Caribbean rainfall and low-level jet, as well as tropical
produce reductions in precipitation in the subtropics and precipitation increases at mid-to-high latitudes, and California is located in the region between these opposing tendencies ( Meehl et al. 2007 ). California's precipitation is also influenced by large-scale climate variability patterns such as El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation. To address the effects of complex topography and other locally variable effects on precipitation, a common approach is to
produce reductions in precipitation in the subtropics and precipitation increases at mid-to-high latitudes, and California is located in the region between these opposing tendencies ( Meehl et al. 2007 ). California's precipitation is also influenced by large-scale climate variability patterns such as El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation. To address the effects of complex topography and other locally variable effects on precipitation, a common approach is to
