Search Results

You are looking at 1 - 5 of 5 items for :

  • Author or Editor: Baird Langenbrunner x
  • Refine by Access: All Content x
Clear All Modify Search
Baird Langenbrunner
and
J. David Neelin

Abstract

The accurate representation of precipitation is a recurring issue in climate models. El Niño–Southern Oscillation (ENSO) precipitation teleconnections provide a test bed for comparison of modeled to observed precipitation. The simulation quality for the atmospheric component of models in the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) is assessed here, using the ensemble of runs driven by observed sea surface temperatures (SSTs). Simulated seasonal precipitation teleconnection patterns are compared to observations during 1979–2005 and to the ensemble of CMIP phase 3 (CMIP3). Within regions of strong observed teleconnections (equatorial South America, the western equatorial Pacific, and a southern section of North America), there is little improvement in the CMIP5 ensemble relative to CMIP3 in amplitude and spatial correlation metrics of precipitation. Spatial patterns within each region exhibit substantial departures from observations, with spatial correlation coefficients typically less than 0.5. However, the atmospheric models do considerably better in other measures. First, the amplitude of the precipitation response (root-mean-square deviation over each region) is well estimated by the mean of the amplitudes from the individual models. This is in contrast with the amplitude of the multimodel ensemble mean, which is systematically smaller (by about 30%–40%) in the selected teleconnection regions. Second, high intermodel agreement on teleconnection sign provides a good predictor for high model agreement with observed teleconnections. The ability of the model ensemble to yield amplitude and sign measures that agree with the observed signal for ENSO precipitation teleconnections lends supporting evidence for the use of corresponding measures in global warming projections.

Full access
J. David Neelin
,
Baird Langenbrunner
,
Joyce E. Meyerson
,
Alex Hall
, and
Neil Berg

Abstract

Projections of possible precipitation change in California under global warming have been subject to considerable uncertainty because California lies between the region anticipated to undergo increases in precipitation at mid-to-high latitudes and regions of anticipated decrease in the subtropics. Evaluation of the large-scale model experiments for phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests a greater degree of agreement on the sign of the winter (December–February) precipitation change than in the previous such intercomparison, indicating a greater portion of California falling within the increased precipitation zone. While the resolution of global models should not be relied on for accurate depiction of topographic rainfall distribution within California, the precipitation changes depend substantially on large-scale shifts in the storm tracks arriving at the coast. Significant precipitation increases in the region arriving at the California coast are associated with an eastward extension of the region of strong Pacific jet stream, which appears to be a robust feature of the large-scale simulated changes. This suggests that effects of this jet extension in steering storm tracks toward the California coast constitute an important factor that should be assessed for impacts on incoming storm properties for high-resolution regional model assessments.

Full access
Justin Sheffield
,
Suzana J. Camargo
,
Rong Fu
,
Qi Hu
,
Xianan Jiang
,
Nathaniel Johnson
,
Kristopher B. Karnauskas
,
Seon Tae Kim
,
Jim Kinter
,
Sanjiv Kumar
,
Baird Langenbrunner
,
Eric Maloney
,
Annarita Mariotti
,
Joyce E. Meyerson
,
J. David Neelin
,
Sumant Nigam
,
Zaitao Pan
,
Alfredo Ruiz-Barradas
,
Richard Seager
,
Yolande L. Serra
,
De-Zheng Sun
,
Chunzai Wang
,
Shang-Ping Xie
,
Jin-Yi Yu
,
Tao Zhang
, and
Ming Zhao

Abstract

This is the second part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal to multidecadal variability and teleconnections with North American climate. Overall, the multimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of the models examined can reproduce observed variability in the eastern Pacific and most models capture the midsummer drought over Central America. The multimodel mean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among the models. On the other hand, the coarse resolution of the models means that tropical cyclone frequencies are underpredicted in the Atlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influence on continental temperature and West Coast precipitation but less well for the wintertime precipitation. The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central–southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.

Full access
Eric D. Maloney
,
Suzana J. Camargo
,
Edmund Chang
,
Brian Colle
,
Rong Fu
,
Kerrie L. Geil
,
Qi Hu
,
Xianan Jiang
,
Nathaniel Johnson
,
Kristopher B. Karnauskas
,
James Kinter
,
Benjamin Kirtman
,
Sanjiv Kumar
,
Baird Langenbrunner
,
Kelly Lombardo
,
Lindsey N. Long
,
Annarita Mariotti
,
Joyce E. Meyerson
,
Kingtse C. Mo
,
J. David Neelin
,
Zaitao Pan
,
Richard Seager
,
Yolande Serra
,
Anji Seth
,
Justin Sheffield
,
Julienne Stroeve
,
Jeanne Thibeault
,
Shang-Ping Xie
,
Chunzai Wang
,
Bruce Wyman
, and
Ming Zhao

Abstract

In part III of a three-part study on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) models, the authors examine projections of twenty-first-century climate in the representative concentration pathway 8.5 (RCP8.5) emission experiments. This paper summarizes and synthesizes results from several coordinated studies by the authors. Aspects of North American climate change that are examined include changes in continental-scale temperature and the hydrologic cycle, extremes events, and storm tracks, as well as regional manifestations of these climate variables. The authors also examine changes in the eastern North Pacific and North Atlantic tropical cyclone activity and North American intraseasonal to decadal variability, including changes in teleconnections to other regions of the globe. Projected changes are generally consistent with those previously published for CMIP3, although CMIP5 model projections differ importantly from those of CMIP3 in some aspects, including CMIP5 model agreement on increased central California precipitation. The paper also highlights uncertainties and limitations based on current results as priorities for further research. Although many projected changes in North American climate are consistent across CMIP5 models, substantial intermodel disagreement exists in other aspects. Areas of disagreement include projections of changes in snow water equivalent on a regional basis, summer Arctic sea ice extent, the magnitude and sign of regional precipitation changes, extreme heat events across the northern United States, and Atlantic and east Pacific tropical cyclone activity.

Full access
Justin Sheffield
,
Andrew P. Barrett
,
Brian Colle
,
D. Nelun Fernando
,
Rong Fu
,
Kerrie L. Geil
,
Qi Hu
,
Jim Kinter
,
Sanjiv Kumar
,
Baird Langenbrunner
,
Kelly Lombardo
,
Lindsey N. Long
,
Eric Maloney
,
Annarita Mariotti
,
Joyce E. Meyerson
,
Kingtse C. Mo
,
J. David Neelin
,
Sumant Nigam
,
Zaitao Pan
,
Tong Ren
,
Alfredo Ruiz-Barradas
,
Yolande L. Serra
,
Anji Seth
,
Jeanne M. Thibeault
,
Julienne C. Stroeve
,
Ze Yang
, and
Lei Yin

Abstract

This is the first part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the historical simulations of continental and regional climatology with a focus on a core set of 17 models. The authors evaluate the models for a set of basic surface climate and hydrological variables and their extremes for the continent. This is supplemented by evaluations for selected regional climate processes relevant to North American climate, including cool season western Atlantic cyclones, the North American monsoon, the U.S. Great Plains low-level jet, and Arctic sea ice. In general, the multimodel ensemble mean represents the observed spatial patterns of basic climate and hydrological variables but with large variability across models and regions in the magnitude and sign of errors. No single model stands out as being particularly better or worse across all analyses, although some models consistently outperform the others for certain variables across most regions and seasons and higher-resolution models tend to perform better for regional processes. The CMIP5 multimodel ensemble shows a slight improvement relative to CMIP3 models in representing basic climate variables, in terms of the mean and spread, although performance has decreased for some models. Improvements in CMIP5 model performance are noticeable for some regional climate processes analyzed, such as the timing of the North American monsoon. The results of this paper have implications for the robustness of future projections of climate and its associated impacts, which are examined in the third part of the paper.

Full access