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

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.

Publication type: 
Author: 
Xianan Jiang
Duane E. Waliser
Daehyun Kim
Ming Zhao
Kenneth R. Sperber
William F. Stern
Siegfried D. Schubert
Guang J. Zhang
Wanqiu Wang
Marat Khairoutdinov
Richard B. Neale
Myong Lee-In
Subjects: 
Atmospheric sciences
Title string: 
Simulation of the intraseasonal variability over the Eastern Pacific ITCZ in climate models
GUID update: 
http://academiccommons.columbia.edu/catalog/ac:133665

Romania, Bulgaria, The United States and the European Union: The Rules of Empowerment at the Outskirts of Europe

After the collapse of the Soviet Union, the United States came to Eastern Europe spreading the gospel of democracy and the American Rule of Law. In addition to encouraging Western ideology, the United States was there to forge new economic relationships and, following the terrorist attacks of September 11, 2001, to accelerate the creation of military alliances through membership in the North Atlantic Treaty Organization (NATO) and the newly-formed "coalition of the willing." Romania and Bulgaria, among other former Soviet satellites, welcomed the invitation. Romania and Bulgaria are small countries which share similar economic pressures as they attempt to emerge from troubled political histories. When the United States, with its military budget of $ 399 billion, approached Romania and Bulgaria seeking support for its global war against terror, both countries experienced a major transformation on a local and international level. In what seems like a perfect example of Andy Warhol's notoriety allotment, for fifteen minutes the West gazed at them in disbelief.

Topic: 
Publication type: 
Author: 
Elena Dana Neacsu
Subjects: 
International relations
Title string: 
Romania, Bulgaria, The United States and the European Union: The Rules of Empowerment at the Outskirts of Europe
GUID update: 
http://academiccommons.columbia.edu/catalog/ac:133647

Ultrapassando o debate entre convergência e divergência urbanas: a arquitetura e o urbanismo em um contexto global

UNI: 
Publication type: 
Author: 
Clara Irazabal
Subjects: 
Urban planning
Title string: 
Ultrapassando o debate entre convergência e divergência urbanas: a arquitetura e o urbanismo em um contexto global
GUID update: 
http://academiccommons.columbia.edu/catalog/ac:132199

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