skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models

Abstract

During boreal summer, convective activity over the eastern Pacific (EPAC) inter-tropical convergence zone (ITCZ) exhibits vigorous intraseasonal variability (ISV). Previous observational studies identified two dominant ISV modes over the EPAC, i.e., a 40-day mode and a quasi-biweekly mode (QBM). The 40-day ISV mode is generally considered a local expression of the Madden-Julian Oscillation. However, in addition to the eastward propagation, northward propagation of the 40-day mode is also evident. The QBM mode bears a smaller spatial scale than the 40-day mode, and is largely characterized by northward propagation. While the ISV over the EPAC exerts significant influences on regional climate/weather systems, investigation of contemporary model capabilities in representing these ISV modes over the EPAC is limited. In this study, the model fidelity in representing these two dominant ISV modes over the EPAC is assessed by analyzing six atmospheric and three coupled general circulation models (GCMs), including one super-parameterized GCM (SPCAM) and one recently developed high-resolution GCM (GFDL HIRAM) with horizontal resolution of about 50 km. While it remains challenging for GCMs to faithfully represent these two ISV modes including their amplitude, evolution patterns, and periodicities, encouraging simulations are also noted. In general, SPCAM and HIRAM exhibit relatively superior skill inmore » representing the two ISV modes over the EPAC. While the advantage of SPCAM is achieved through explicit representation of the cumulus process by the embedded 2-D cloud resolving models, the improved representation in HIRAM could be ascribed to the employment of a strongly entraining plume cumulus scheme, which inhibits the deep convection, and thus effectively enhances the stratiform rainfall. The sensitivity tests based on HIRAM also suggest that fine horizontal resolution could also be conducive to realistically capture the ISV over the EPAC, particularly for the QBM mode. Further analysis illustrates that the observed 40-day ISV mode over the EPAC is closely linked to the eastward propagating ISV signals from the Indian Ocean/Western Pacific, which is in agreement with the general impression that the 40-day ISV mode over the EPAC could be a local expression of the global Madden-Julian Oscillation (MJO). In contrast, the convective signals associated with the 40-day mode over the EPAC in most of the GCM simulations tend to originate between 150°E and 150°W, suggesting the 40-day ISV mode over the EPAC might be sustained without the forcing by the eastward propagating MJO. Further investigation is warranted towards improved understanding of the origin of the ISV over the EPAC« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [4];  [6];  [7];  [8];  [9];  [10];  [11]
  1. Univ. of California, Los Angeles, CA (United States)
  2. California Inst. of Technology (CalTech), La Canada Flintridge, CA (United States). Jet Propulsion Lab.
  3. Columbia Univ., New York, NY (United States)
  4. Princeton Univ., NJ (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  7. Scripps Institute of Oceanography. La Jolla, California (United States)
  8. National Oceanic and Atmospheric Administration (NOAA), National Centers for Environmental Protection. Camp Springs, MD (United States)
  9. Institute for Terrestrial and Planetary Atmospheres. Stony Brook Univ., NY (United States)
  10. National Center for Atmospheric Research. Boulder, CO (United States)
  11. Ulsan National Institute for Science and Technology. Seoul (Korea)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1165825
DOE Contract Number:  
DE-AC52-07NA27344
Resource Type:
Journal Article
Journal Name:
Climate Dynamics
Additional Journal Information:
Journal Volume: 39; Journal Issue: 3-4; Journal ID: ISSN 0930-7575
Publisher:
Springer-Verlag
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Intraseasonal variability; Eastern Pacific warm pool; ITCZ

Citation Formats

Jiang, Xianan, Waliser, Duane E., Kim, Daehyun, Zhao, Ming, Sperber, Kenneth R., Stern, William F., Schubert, Siegfried D., Zhang, Guang J., Wang, Wanqiu, Khairoutdinov, Marat, Neale, Richard B., and Lee, Myong-In. Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models. United States: N. p., 2012. Web. doi:10.1007/s00382-011-1098-x.
Jiang, Xianan, Waliser, Duane E., Kim, Daehyun, Zhao, Ming, Sperber, Kenneth R., Stern, William F., Schubert, Siegfried D., Zhang, Guang J., Wang, Wanqiu, Khairoutdinov, Marat, Neale, Richard B., & Lee, Myong-In. Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models. United States. doi:10.1007/s00382-011-1098-x.
Jiang, Xianan, Waliser, Duane E., Kim, Daehyun, Zhao, Ming, Sperber, Kenneth R., Stern, William F., Schubert, Siegfried D., Zhang, Guang J., Wang, Wanqiu, Khairoutdinov, Marat, Neale, Richard B., and Lee, Myong-In. Wed . "Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models". United States. doi:10.1007/s00382-011-1098-x. https://www.osti.gov/servlets/purl/1165825.
@article{osti_1165825,
title = {Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models},
author = {Jiang, Xianan and Waliser, Duane E. and Kim, Daehyun and Zhao, Ming and Sperber, Kenneth R. and Stern, William F. and Schubert, Siegfried D. and Zhang, Guang J. and Wang, Wanqiu and Khairoutdinov, Marat and Neale, Richard B. and Lee, Myong-In},
abstractNote = {During boreal summer, convective activity over the eastern Pacific (EPAC) inter-tropical convergence zone (ITCZ) exhibits vigorous intraseasonal variability (ISV). Previous observational studies identified two dominant ISV modes over the EPAC, i.e., a 40-day mode and a quasi-biweekly mode (QBM). The 40-day ISV mode is generally considered a local expression of the Madden-Julian Oscillation. However, in addition to the eastward propagation, northward propagation of the 40-day mode is also evident. The QBM mode bears a smaller spatial scale than the 40-day mode, and is largely characterized by northward propagation. While the ISV over the EPAC exerts significant influences on regional climate/weather systems, investigation of contemporary model capabilities in representing these ISV modes over the EPAC is limited. In this study, the model fidelity in representing these two dominant ISV modes over the EPAC is assessed by analyzing six atmospheric and three coupled general circulation models (GCMs), including one super-parameterized GCM (SPCAM) and one recently developed high-resolution GCM (GFDL HIRAM) with horizontal resolution of about 50 km. While it remains challenging for GCMs to faithfully represent these two ISV modes including their amplitude, evolution patterns, and periodicities, encouraging simulations are also noted. In general, SPCAM and HIRAM exhibit relatively superior skill in representing the two ISV modes over the EPAC. While the advantage of SPCAM is achieved through explicit representation of the cumulus process by the embedded 2-D cloud resolving models, the improved representation in HIRAM could be ascribed to the employment of a strongly entraining plume cumulus scheme, which inhibits the deep convection, and thus effectively enhances the stratiform rainfall. The sensitivity tests based on HIRAM also suggest that fine horizontal resolution could also be conducive to realistically capture the ISV over the EPAC, particularly for the QBM mode. Further analysis illustrates that the observed 40-day ISV mode over the EPAC is closely linked to the eastward propagating ISV signals from the Indian Ocean/Western Pacific, which is in agreement with the general impression that the 40-day ISV mode over the EPAC could be a local expression of the global Madden-Julian Oscillation (MJO). In contrast, the convective signals associated with the 40-day mode over the EPAC in most of the GCM simulations tend to originate between 150°E and 150°W, suggesting the 40-day ISV mode over the EPAC might be sustained without the forcing by the eastward propagating MJO. Further investigation is warranted towards improved understanding of the origin of the ISV over the EPAC},
doi = {10.1007/s00382-011-1098-x},
journal = {Climate Dynamics},
issn = {0930-7575},
number = 3-4,
volume = 39,
place = {United States},
year = {2012},
month = {8}
}