Michael W. Douglas, National Severe Storms Laboratory Javier Murillo, CIMMS University of Oklahoma

1
Future Trends in the Pan American Climate Studies
Sounding Network (PACS-SONET)
Michael W. Douglas, National Severe Storms
Laboratory - Javier Murillo, CIMMS / University
of Oklahoma http//www.nssl.noaa.gov/projects/pac
s/
PILOT BALLOON OBSERVATIONS Pilot balloon sounding
s, rather than radiosonde observations, have been
made throughout the PACS-SONET life span. The
main advantage of pilot balloon observations is
that they are inexpensive. Typically, a 30-gram
balloon launch, excluding labor costs, is only
5-10 that of a radionsonde launch. To date the
project has generated more than 30,000 soundings.
The graphic below shows the number of
observations per month generated by the network
from April 1997 to August 2003.
1. HISTORY AND EVOLUTION 1.1. Original network.
The original PACS-SONET configuration consisted
of 12 pilot balloon stations. The stations were
established during March and April of 1997 in
Mexico, Nicaragua, Costa Rica, Panama, Colombia,
Ecuador and Peru. The objectives of this network
included
2. SCIENTIFIC OBJECTIVES The fundamental overall
objective of the project is to establish a
long-term atmospheric sounding network for
providing baseline measurements for real-time
climate monitoring and for comparison with model
development activities over the PACS domain.
The fundamental scientific objective of
PACS-SONET is to determine both the annual cycle
and interannual variability of the lower
tropospheric windfield associated with the
monsoon circulations over and around the
Americas, with the aim of explaining the observed
variability of precipitation over the land
regions.
describing the amplitude of the diurnal variation
of the windfield at a number of sites.
Determining the circulation anomalies associated
with wet and dry spells over Central America.
Determining whether large differences existed
between the NCEP reanalysis and observations in
data sparse regions of the eastern tropical
Pacific.
2.1. Relevance to PACS PACS-SONET observations
provide the background field to the specialized
field experiments North American Monsoon Experim
ent (NAME) 2004. The observations at Puerto
Peñasco and Topolobampo in northwestern Mexico
are intended to help describe the low-level flow
along the Gulf of California and will be of
relevance for NAME. South American Low-level Jet
Experiment (SALLJEX) 2002-03. The observations at
two sites in Paraguay and 6 sites in Bolivia
served as the ramp-up network for the upper-air
component of SALLJEX. EPIC 2001. The stations dep
loyed from southern Mexico to northern Peru
provided a context for field activities related
to EPIC.
Fig. 1. Map showing the original station
configuration during mid-1997.
SCOPE The scope of PACS-SONET differs from many p
revious field programs in that
it has been expanded to a broader geographical
region from northern Mexico to Paraguay.
it has a relatively long duration for a field
program. Initially planned for 6 months, it has
since been extended for a total of almost 80
months. communication of data is in near real-tim
e via Internet.
1.2. Changes due to El Niño 1997-98
Due to the strong El Niño event of 1997-98, the
observational plan was modified to extend the
observational period at many stations through the
end of October 1998 and establish additional
stations in Ecuador and Peru to better sample
conditions in the region of anticipated heavy
rainfall. Due to financial reasons, some of the
stations actually stopped in August 1998.
Nonetheless, an unprecedented data set was
obtained to describe the wind field associated
with the developing El Niño.
4. THE FUTURE OF PACS-SONET PACS-SONET has been e
xtended for a second 3-year period, subject to a
re-evaluation of the activity and more
consensus-seeking on the part of the project.
As a first step towards renewing the direction of
the activity, a meeting has very recently been
held in Paraguay in late August 2003. The
meeting was intended to develop a consensus among
each of the participating institutions as how to
proceed to increase the effectiveness of the
PACS-SONET. All participant countries and
institutions were represented at the meeting.
Preliminary conclusions from the workshop
indicate that future activities should include
Radiosonde observations (PTU only) at key sites
such as the Galapagos Islands, Ecuador. An
optical theodolite would be used to track the
radiosonde in order to save funds by launching
inexpensive non-GPS sondes. Radiosonde
observations are feasible at locations were gas
is generated. Continue to support educational act
ivities to stimulate research with the data
collected. Different options to better utilize
the available funds were discussed during the
workshop. Work with the participating institutio
ns in designing ways to better quality control
the data. Establishment of additional sites in Pe
ru and Brazil with help from the national
meteorological services. The main benefit of the
reunion of the country coordinators has been to
create an awareness among the participants about
the necessity of optimizing the available
resources of the project to stimulate research
and applied forecasting activities throughout the
region. It was emphasized that PACS-SONET is not
a major source of resources for the countries
involved, rather it can serve as a framework for
the development of meteorological and climate
activities in the region.
The Pan American Climate Studies Sounding Network
(PACS-SONET) is a research activity funded by
the NOAAs Office of Global Programs. It has
evolved from a regional network of 6-month
duration to a hemispheric activity that has been
extended for a second 3-year period in 2003.
3. PACS-SONET DELIVERABLES 3.1 Real-time data col
lection. In addition to more observing sites, ef
forts have been made to make the network a
real-time data collection and distribution
activity. This required communications to be
upgraded at many sites, and the development of
procedures to ensure the flow of data to research
institutions and to all interested forecasting
institutions. The latter is accomplished mainly
through the development of the projects web
page, in which the observations are made
available in real time, in the form of both raw
data and synoptic maps plotted at selected
levels. The figure at right shows wind barbs from
pilot balloon soundings (blue) at 3 sites in
Bolivia and one in Asuncion, Paraguay, along with
winds obtained from the regular radiosonde
network (green).
1.3. Special Mesoscale Campaign in Bolivia
Pilot balloon observations were also made at
Santa Cruz, Bolivia, as part of the special El
Niño campaign. Although these were only made for
3 months they showed a strong and variable
low-level jet at Santa Cruz, which had not been
described from observations previously. These
observations stimulated further observations from
a more extensive network in Bolivia during 1999.
The map at right shows the pilot balloon network
in Bolivia during January-April 1999.
1.4. Extension of the PACS-SONET program
In late 1999 support was obtained for extension
of the PACS-SONET program for an additional
3-year period. In addition to an extension in
time, the network was expanded to a broader
geographical region. Pilot balloon sites have
been operating in Paraguay (2) and Bolivia (6).
The primary objective of these additional
observations was to describe the variability of
the low-level flow east of the Andes and the
circulation over the Bolivian altiplano. In
Mexico, 7 sites are being operated by the Mexican
navy, including two in northwestern Mexico to
improve the description of the low-level flow
along the Gulf of California. In March 2001, one
station was established in Venezuela at San
Fernando de Apure, a location in the very flat
llanos north of the Orinoco River. The figure at
right shows the current PACS-SONET configuration
and other stations that have been operational
with financial or logistic support from the
project.
The impact of the additional observations can be
appreciated from the figure and the quality of
the data quickly assessed by comparing neighbor
stations.
3.2 Climate monitoring Several stations have been
operating since 1997 and just now the time
series is large enough to make crude estimations
of the interannual varibility. The figures show
monthly means of the meridional wind at San
Cristobal, Galapagos for the months of May (a),
July (b) and December (c). Southerly
cross-equatorial flow at Galapagos is moderately
strong in May and has a maximum in
July-August-September. December shows the
greatest interannual variability.
(b) July
(a) May
(c) December