Pan-American Climate Studies

Project Description
Esecutive Summary of Project:

Over its ten-year lifetime, the Tropical Ocean-Global Atmosphere
(TOGA) program (1985-1995) made major strides toward
understanding the El Ni?o Southern Oscillation (ENSO)
phenomenon, which impacts surface air temperature and rainfall
over many regions of the globe. In particular, TOGA
demonstrated the feasibility of operational
seasonal-to-interannual climate prediction of equatorial
Pacific sea surface temperature anomalies based on numerical
models that simulate, in a rudimentary manner, the physics of
the coupled tropical ocean-atmosphere system, and it clarified
the nature of the remote, planetary-scale atmospheric response
to these anomalies. The U.S. Global Ocean-Atmosphere-Land
System (GOALS) program is predicated on the belief that the
skill of operational climate prediction can be further
increased by continued research on ENSO and by efforts to
understand other elements of the climate system that contribute
to the observed seasonal-to-interannual variability. The ! Pan
American Climate Studies (PACS) program is a component of the
U.S. GOALS program in the 1995-2005 time frame, and PACS
provides a phenomenological context for some of the GOALS

The overall goal of PACS is to extend the scope and improve the
skill of operational seasonal-to-interannual climate prediction
over the Americas. Particular emphasis is placed on warm season
rainfall, which is not yet predictable. In the context of PACS,
climate prediction is concerned not only with seasonal mean
rainfall and temperature, but also with the frequency of
occurrence of significant weather events such as hurricanes or
floods over the course of a season or seasons.

The scientific objectives of PACS are to promote a better
understanding and more realistic simulation of (1) the boundary
forcing of seasonal-to-interannual climate variations over the
Americas, (2) the evolution of tropical sea surface temperature
anomalies, (3) the seasonally varying mean climate over the
Americas and adjacent ocean regions, (4) the time-dependent
structure of the Intertropical Convergence Zone (ITCZ)/cold
tongue complex, and (5) the relevant land surface processes.

To state these objectives more explicitly:

Boundary forcing: The atmospheric circulation, in isolation, is
not predictable beyond a week or two. Hence, prospects for
improved climate prediction on the seasonal-to-interannual time
scale hinge on the ability to exploit the relationships between
the planetary-scale atmospheric circulation and the slowly
evolving and potentially predictable boundary forcing; i.e.,
the fields of sea surface temperature, vegetation, and soil
moisture, in which the season-to-season "memory" of the coupled
ocean-atmosphere-land system resides. Improved understanding of
boundary-forced atmospheric anomalies is of central importance,
not only to PACS, but to the entire GOALS program.

Evolution of tropical sea surface temperature anomalies: For
climate prediction of a season or more in advance, it is
necessary to take into account the evolution of the boundary
forcing of the atmosphere. In keeping with the general strategy
of GOALS, PACS will seek to advance the state-of-the-art of the
prediction of sea surface temperature anomalies in the tropical
Atlantic and Pacific, both of which are known to influence
climate variability over parts of the Americas.

Seasonally varying mean climate: Regional rainfall anomalies
over the Americas are largely a reflection of the
intensification or weakening, or subtle displacements in
positions of the climatological-mean features that organize the
rainfall, i.e., the monsoons, the oceanic ITCZs, and the
tropical and extratropical cyclone tracks. An understanding of
these robust climatological-mean features and their seasonal
evolution is a prerequisite for the interpretation and
prediction of the anomalies.

Structure of the ITCZ/cold tongue complex: A major stumbling
block in the validation of the models used to simulate tropical
atmosphere-ocean interaction in ENSO is the lack of
observational data for defining the structure of the ocean
mixed layer and the overlying atmosphere in the ITCZ/cold
tongue complex. PACS will address this deficiency through its
field projects and the related modeling studies that will make
use of these data.

Land surface processes: The distribution of rainfall over the
Americas is shaped, not only by sea surface temperature patterns
but also by land surface processes, particularly during the warm
season, when vegetation and soil moisture are highly
influential. Orography and coastal geometry mediate these
effects and leave a distinctive mesoscale imprint upon the
rainfall patterns. These issues will be addressed in
collaboration with the Global Energy and Water Experiment
(GEWEX) and its regional programs, with PACS supplying the
atmospheric modeling expertise and GEWEX the hydrological
expertise. Much of this research will require the use of
mesoscale models, applied in a climatological setting.

PACS scientific objectives (1) and (2) directly address the
scientific objectives of the GOALS program: (1) relates to
atmospheric prediction and (2) to prediction of tropical sea
surface temperature; in this sense they may be viewed as
primary. Objectives (3)-(5) play a supportive role by advancing
understanding of the mechanisms that give rise to and limit the
predictability of the coupled global ocean-atmosphere-land
system: (3) and (4) relate to the prediction of ENSO and other
phenomena that give rise to tropical sea surface temperature
anomalies, and (5) relates to the prediction of continental

PACS encompasses a broad range of activities, including
empirical studies, data set development, modeling, climate
monitoring, and more intensive, limited-term field
experiments. In order to avoid being spread too thin, the field
studies will focus on different regions of the Pan-American
climate system in sequence. During the first five years they
will focus on atmosphere-ocean interaction in the tropical
eastern Pacific, in association with the ENSO cycle and the
climatological-mean annual march. During the second half of
PACS the emphasis will shift to the tropical Atlantic Ocean
where the sea surface temperature anomalies are more subtle and
more diverse in terms of horizontal structure than in the
Pacific, but no less important in terms of their influence upon
precipitation in the adjacent continental regions.

This scientific prospectus/implementation plan provides the
motivation and scientific basis for PACS and describes the
research that will be carried out in pursuit of PACS scientific
objectives. Section 1 gives a scientific description of
phenomena in the ocean-atmosphere system that are likely to be
of importance for understanding and predicting
seasonal-to-interannual climate variations over the
Americas. The climate and weather variations over the Americas
that provide the practical and scientific motivation for PACS
are discussed in Section 2, while Sections 3-5 describe the
empirical studies, data set development, and modeling that will
be conducted under its auspices. Section 6 describes field
studies envisioned for PACS, starting with projects already
funded and going on to describe activities likely to be
proposed for the 1997-2000 time frame. Section 7 discusses
linkages with GEWEX and its regional programs and NASA's
Tropical Rainfall Measurement Mission (TRMM). Se! ction 7 also
describes the anticipated linkages with emerging national and
international programs, including the Scripps-Lamont Consortium
for the Ocean's Role in Climate (CORC), the Pilot Research
Moored Array in the Tropical Atlantic (PIRATA), the anticipated
World Climate Research Programme (WCRP) Climate Variability and
Predictability (CLIVAR) international programs on the
Variability of the American Monsoon Systems (VAMOS), and
Pacific and Atlantic basinwide extended climate studies
(BECS). Program management is discussed in Section 8. Within
the U.S., interagency support is being sought for PACS, with
coordination by the GOALS Project Office. The Inter-American
Institute for Global Change Research serves as a vehicle for
coordinating international cooperation.

Contact Person:

Candance Gudmundson

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[Summary provided by JISAO]