New
Directions in the Pan American Climate Studies Sounding Network for Latin
America
Michael W. Douglas, NOAA/NSSL, Norman OK 73069, Jose
M. Galvez, John F. Mejia and Javier Murillo, CIMMS/University of Oklahoma
Web: http://www.nssl.noaa.gov/projects/pacs/
(A higher-quality printable version of this document
can be found here:
http://www.nssl.noaa.gov/projects/pacs/PACS-AMS04/PACS-AMS04.pdf)
Summary
The Pan American Climate Studies
(PACS) Sounding Network (SONET) evolved in response to the perceived lack of in-situ
atmospheric measurements over the inter-American region to adequately support
climate research studies. The relatively recent availability of the
global NCEP reanalyses products had stimulated a large number of studies of
climate and climate variability and it was becoming apparent that ground truth
measurements were going to be needed to validate these studies. To depend
on the individual efforts of each country in the region to enhance their own
sounding networks was not viewed as a proactive solution to the lack of
sounding data, and in 1997 the OGP supported an initial effort to establish a
temporary network to monitor the windfield in central and part of northern
South America. This has, over the succeeding 6 years, become what is now
called the PACS-SONET.
At the present time the SONET involves pilot balloon observations at some 21
sites in 8 countries in Latin America. Seven sites are operated in
Mexico, six in Bolivia, followed by two sites each in Paraguay, Venezuela and
Peru, and one each in Ecuador, Colombia and Nicaragua. About 500
observations per month continue to be made. Each site has a specific
contribution to the overall scientific objectives of the project, which have in
the past several years focused on supporting aspects of the two monsoon
experiments, SALLJEX (January 2003) and NAME (summer 2004) supported by
OGP. Observations are made daily, near 1200 UTC, except in
Mexico, where twice-daily observations are made, and in Piura, Peru where
frequent morning cloudiness forces routine afternoon soundings.
Key aspects of the SONET data set
that are potential subjects for near-term research are discussed. These
topics include the suitability of the SONET data to describe interannual
variations of 1) the cross-equatorial flow along the Peruvian coast, 2) the
warm season trade wind flow across Central America that is associated with the
mid-summer dry season, 3) the gap flow intensity across the Isthmus of
Tehuantepec, and 4) the intensity of the monsoonal flow up the gulf of
California during the warm season. Each of these is discussed as an
example of subjects that are now becoming feasible to study with multi-year
records from the PACS-SONET.
Finally, a summary of the directions in which the project intends to advance
completes this report.
1. Brief history of the PACS-SONET
The original PACS-SONET configuration consisted of 12 pilot
balloon sites (Fig. 1.1). The
stations were established during April and May of 1997 in Mexico, Nicaragua,
Costa Rica, Panama, Colombia, Ecuador and Peru, together with a combined pilot
balloon and radiosonde station on Cocos Island in the eastern Pacific Ocean.
These observations, made twice-daily, were to describe the conditions
associated with wet and dry spells over Central America (Peña and Douglas 2002)
and to help evaluate the quality of the NCEP reanalyses windfields over the
region - analyses that were (and continue to be) a mainstay of tropical climate
research activities. The intended duration of the observations was 6 months,
ideally extending through October, and close to the end of the rainy season in
much of Central America.
Fig.
1.1. PACS-SONET initial configuration.
Due to the strong El Niño of 1997-98, the observational
plan was modified to extend the period of observations at many stations through
the mid-year 1998 and to establish additional pilot balloon stations in Ecuador
and Peru to better sample conditions in the region of anticipated heavy
rainfall. This allowed an unprecedented data set to be obtained to describe the
wind field along the Ecuadorian and northern Peruvian coasts, associated with
the warm event in the eastern Pacific. In addition, more than 100 raingauges
were established throughout northwestern Peru and in western Ecuador to improve
the description of daily rainfall over the region.
Pilot balloon observations were also made at Santa Cruz,
Bolivia, as part of the special El Niño campaign. Although these observations
were only made for 3 months, they showed a strong and variable low-level jet at
Santa Cruz, which had not been well described from previous observations. These
observations indirectly stimulated further observations from a more extensive
network in Bolivia during 1999.
Fig.
1.2 PACS-SONET extensions due to El Niño 1997-98 (white dots), SALLJEX
pilot balloon stations (blue dots) and current PACS-SONET sites (red dots).
In late 1999 support was obtained for extension of the
PACS-SONET for a 3-year period. In addition to an extension in time of the
program, an expansion of the network took place. In terms of geographical
extension, new pilot balloon sites were established 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, three additional sites were established in
March 2000 to bring to 6 the number operating (one more was added in April
2002). The stations in northwestern Mexico were designed 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. In March 2002, a second Venezuelan station was established
in Ciudad Bolivar, a city of the eastern llanos on the Orinoco river
basin. Figure 1.2 shows the current PACS-SONET configuration and other
stations that have been operational with financial or logistic support from the
project.
In addition to more observing sites, a major effort was
made to make the network a real-time data collection and distribution activity.
This required efforts to upgrade communications at many sites, and the
development of procedures to ensure the flow of data not only to research
institutions, but also to all interested operational forecasting institutions.
The latter is accomplished mainly through the development of the project’s web
page, in which the observations are made available in near real time, in the
form of both raw data and plotted maps at select levels (See http://www.nssl.noaa.gov/projects/pacs/realtlist.shtml.)
More recently, the PACS-SONET stations in Bolivia and
Paraguay served as the ramp-up network for the upper-air component of the South
American Low Level Jet Experiment (SALLJEX), which extended from November 2002
through February 2003 and included intensive pilot balloon observations (http://www.nssl.noaa.gov/projects/pacs/web/html/salljex.html.)
Fig. 1.3. Pictures
from two special observing campaigns conducted in Bolivia during SALLJEX around
Lake Titicaca (up) and in the Salar de Uyuni (bottom).
In
2003 PACS-SONET was extended for a second 3-year period, subject to a
reevaluation of the activity and more consensus seeking on the part of the project.
2. Scientific Rationale for Each
Observing Site
While all SONET observing sites contribute to filling gaps
in the upper-air sounding network in Latin America, each observing site has one
or more specific reasons to justify its operation. In this section we summarize these objectives. Reference to the several networks map in
Fig. 2.1 would be useful.
Mexico
Puerto Peñasco. This
site is optimally suited, at the northern end of the Gulf of California, to
monitor the variability of the Gulf of California low-level jet. This shallow jet is associated with moisture
transport into the southwestern deserts of the US and variations of the flow
("surges") are a feature of interest in the 2004 North American
Monsoon Experiment (NAME).
Topolobampo. This
site, halfway between the radiosonde sites of Guaymas and Mazatlan on the east
side of the Gulf of California, is designed to measure the up-Gulf seasonal
variation of the wind at low-levels associated with the monsoonal circulation. Also, by operating two sites along the Gulf
of California the intensity and latitudinal extent of gulf surges can be more
accurately estimated. Both Puerto
Peñasco and Topolobampo make twice-daily measurements, unlike Guaymas, so the
data also provide better estimates of the mean flow, averaged over the diurnal
cycle.
Tampico. This site
is located halfway between the radiosonde sites of Brownsville, Texas and
Veracruz, Mexico, a large gap in the sounding network on the east coast of
Mexico. The original motive of the site's
selection was to describe the variability of the recurving trade-wind flow that
undergoes strong seasonal variations.
Unexpectedly high cloudiness has somewhat hampered the effectiveness of
the site.
Anton Lizardo. This site was established only recently
(2003), and it is primarily to serve as training for the cadets so that they
can supervise the rest of the network operations. The observations provide a check on the radiosonde-winds from a
nearby (~20 km away) radiosonde site of the Mexican National Weather Service.
Cd. del Carmen. This
site, moved from the nearby Naval facility at Frontera in 2000, provides winds
that describe the intensity of the trade-wind flow across the southern part of
the Yucatan peninsula. The observations
have revealed a strong diurnal variation, with an early morning low-level
jet. The observations will primarily
help to identify tropical wave passage across this part of southern Mexico
during the summer months, and provide additional estimates of variations
(intraseasonal and interannual) of the trade wind flow.
Salina Cruz. The
strong and variable flow across the gap in the topography at the Isthmus of
Tehuantepec is described by measurements at Salina Cruz. Under normal conditions (northerly winds)
the skies are relatively cloud free and this site provides profiles to high
altitudes (provided the winds are not too strong). Variations in the gap flow, due to tropical wave passages in
summer or cold frontal passages in winter can be readily identified at this
site.
Puerto Madero. This
site was established to monitor tropical wave activity and tropical
cyclogenesis in the Gulf of Tehuantepec.
The wind regime is vastly different, due to the blockage of the trade
wind flow by a 2-3 km high mountain range, which is located about 40 km to the
east of the site, across a flat coastal plain.
Figure 2.1 Current radiosonde
network (blue circles), current (black dots) and proposed (stars) PACS-SONET
sites.
Nicaragua
Managua. The Managua observations, of high quality and
generally high altitudinal extent (due to the lack of frequent low cloudiness),
were intended to monitor the travel wind variability (on all time scales beyond
daily) across Central America. The low
terrain over Nicaragua is ideal to avoid the very local effects of high terrain
common to other countries in Central America, and the latitude of Nicaragua is
near the latitude where the trades are strongest.
Colombia
Cartagena. This site was one of the original 12 sites
established in 1997. The justification
for the site remains the same - to improve the description of the low pressure
that is anchored to the topography in this part of South America and which
forms part of the intertropical convergence zone. With the highly intermittent nature of the radiosonde sites in
Rio Hacha (Colombia) and Balboa (Panama), the Cartagena site becomes even more
important, as it is the only sounding site between Curacao and San Jose, Costa
Rica, a distance of 1500 km.
Isla
Malpelo (proposed). The observations
proposed for Malpelo would improve specification of the cross-equatorial flow
closer to the coast of Central America than provided by the site in the
Galapagos. In addition, as it is a very
small island there will be almost no diurnal cycle and little topographic on
the airflow, so the observations should be ideal for describing synoptic and
seasonal variations here. The site
would also fill an important gap in the sounding network, as it would be on the
equatorial side of the mean ITCZ position.
Rainfall observations are also proposed for this site, since it lies in
the region of greatest discrepancy between satellite estimation techniques for
precipitation near the ITCZ.
Banco
Serranilla (proposed). This site would
provide undisturbed trade wind measurements just north of the core of the
maximum winds. The main value of this
site is that it is flat and small, so it should be free of island-induced
diurnal or topographic effects. The
site is located almost equidistant between the radiosonde sites of Kingston
(Jamaica), San Andres (Colombia) and Grand Cayman.
Venezuela
San
Fernando de Apure. This site continues
to be important to describe the low-level flow over the wide, flat llanos of
Venezuela. The morning observations
show a strong, but shallow low-level jet during the dry season. The original intent of establishing the site
was to monitor not only the annual cycle of the trade winds across northern
South America, but to describe tropical wave propagation during the warm season
as well.
Ciudad
Bolivar. This site was established
after San Fernando, and provides redundancy in the observations, especially
during the rainy season, when cloudiness at both sites can frequently prevent
high soundings.
Isla de
Aves (proposed). We are proposing to establish
a site at Isla de Aves, located 220 km west-southwest of Guadeloupe Island in
the Lesser Antilles. This site, flat
and extremely small, will be ideal for wind profiles in the trade wind flow for
comparison with the radiosonde observations at various locations in the Lesser
Antilles. The Venezuelan Navy and
Environment Ministry has staff permanently on the island to assure sovereignty
and monitor bird and turtle nesting.
Ecuador
San
Cristobal, Galapagos Islands. This site
was originally established to monitor the cross-equatorial flow, especially for
variations associated with the ENSO cycle.
Peru
Piura.
This site, about 60 km inland from the coast, on a flat coastal plain, is
useful for monitoring variations of the flow near the coast associated with
ENSO variations. It has become more
useful with time, as the site has the most complete record for interannual
variability studies. The site is almost
7 degrees north of the only coastal radiosonde site, Lima. A radiosonde site has been established at
Piura as part of ENSO monitoring activities, but this site is not operating
every day and the observations are not routinely transmitted.
Arequipa. This site was established in November 2002
as part of SALLJEX. Because of its
drier and more cloud-free climate, this site routinely provides wind profiles
to higher altitudes than does La Paz.
The observations should be useful for monitoring flow over the northern
altiplano and the subtle variability of the Bolivian high. Peruvian motivation for the site's operation
also is due to the desire to monitor winds for the prediction of ash or fumes
from nearby Volcano Misti (Arequipa is Peru's second largest city).
Pucallpa
(proposed). The Pucallpa site proved
very useful during the SALLJEX, and provided a surprising number of relatively
high soundings. This site is feasible
to maintain, as good logistical support exists, and the observations provide
data well upstream of the Bolivian site at Cobija for monitoring LLJ
variability.
Iquitos
(proposed). This site currently makes
radiosonde observations every other day, and pilot balloon observations are
proposed for the site to provide more frequent wind profiles. This site will
extend monitoring of low-level flow east of the Andes from Paraguay to nearly
the Equator. The observations should be
useful for describing the equatorward extent of cold surges during the cool
season and the longer-period variations associated with the seasonal cycle. The observations at Iquitos will compliment
those at Leticia (Colombia) located some 400 km to the east. The latter observations have been erratic.
Puerto
Maldonado (proposed). This site is
currently an ENSO-monitoring radiosonde site and pilot balloon observations are
proposed to increase the frequency of the wind observations. The site is partially redundant with Cobija,
but the future status of Cobija is not known with certainty, and the Puerto
Maldonado observations will insure observations between Pucallpa (~8˚S) and Trinidad, Bolivia (~15˚S). Fundamentally, the site will contribute to monitoring the
variability of the East Andean low-level jet.
Bolivia
La
Paz. This site, and the site at Uyuni
provide altiplano-level measurements for more precisely describing the flow
over the Bolivian and Peruvian altiplano.
The position of the Bolivian high typically is found between these two
sites and subtle shifts in the position can be quantified more accurately
through the use of these station's data.
There is typically a considerable N-S gradient in the zonal wind during
the winter between these two sites.
Uyuni. See comments above. The Uyuni site is more cloud-free than La
Paz, thus helping to provide measurements over the altiplano more often that
would be possible from only one site.
Cobija. This site was intended to measure wind
conditions somewhat upstream (~11˚S) from the region of maximum winds (~18˚S) associated with the LLJ.
Trinidad. This site, located in a very flat region
more than 100 km form the Andes, provides less-cloud contaminated soundings
near the core of the LLJ over eastern Bolivia.
Robore. This site describes the LLJ flow at
considerable distance from the Andes, providing information on the horizontal
extent of the LLJ flow. It is also
useful for describing the zonal extent of the flow during cold surges, which
typically is more closely confined to the topography.
Santa
Cruz. This site, at Viru-Viru
International Airport, is near the region of strongest winds associated with
LLJ east of the Andes. However, it is a
relatively cloudy site.
Paraguay
Mariscal
Estigarribia. This site is located very
close to the mean position of the low level jet over the Chaco, and as such it
frequently reports the strongest winds of the low-level jet SONET sites. The primary objective of this site is to
provide estimates of the wind speed and vertical structure of the jet near its
core. This site is much less cloudy
than Santa Cruz, Bolivia and offers better possibilities of frequent soundings
to high altitudes.
Asuncion. This site provides measurements near the
exit region of the East Andean low-level jet.
Chile
San Felix
Island (proposed). We are proposing
this island (26˚S, 80˚W), about 1000 km west of the coast
of Chile, as a future SONET site because of its unique position to describe the
flow over the stratocumulus region of this area. Currently there are no soundings made from this island, though
VEPIC enhancements are being considered.
Wind soundings from the island would allow estimates of the divergence
to be made (monthly mean at least), using sites on the coast of Chile and
southern Peru. These observations, if
successful, could be eventually developed into inexpensive radiosonde
observations, or powersonde observations.
3.
Current status of the network
Despite the budget-related issues that affected the network
during the last fiscal year, most of the stations managed to operate almost
regularly and most interruptions were ultimately related to problems particular
to each country, as explained in the following paragraphs.
3.1
Summary of station operation and performance by country.
Mexico
There are 7 stations currently operating in Mexico. The most
recent addition is the site operating from the Naval Academy in Anton Lizardo,
Veracruz. The Mexican Navy (Secretaria de Marina Armada de Mexico, SEMAR)
requested the station to be established primarily for educational purposes (all
officers in the Mexican Navy are trained there), but observations are also made
there routinely and the data is transmitted in real time from the site. At least 5 of the Mexican stations rely on
PACS-SONET to cover communications and other expenses; due to the lack of funds
to repair a computer, one station (Salina Cruz) has not been able to process
and transmit data in real time in the last two months. Other stations had problems with
intermittent gas supply caused by delays in transfer of funds for gas purchase
from SEMAR to the Naval bases that operate the sites. Most of the gas problems were rapidly solved after a letter was
sent to SEMAR explaining the relevance of the observations for NAME, especially
those made in northwestern Mexico.
The observations in Mexico are made twice daily, contrasting
with most PACS-SONET sites. The reason
for this is that the Naval personnel at these sites are dedicated to this
activity and it was suggested by the Mexican Navy senior staff that these
individuals be more fully utilized. The
Navy covers the cost of personnel and hydrogen gas for all sites, SONET covers the
balloons and costs associated with data communications (PC's at each site,
internet connectivity and some phone line costs). Although the twice-daily observations are an additional cost, the
afternoon observations provide information on the diurnal cycle that is missing
from most other SONET sites.
Nicaragua
Nicaragua had been operating one station in the airport of
Managua since 1997. This site was reliable, and has generated a very good data
set, especially during the period 2000-2002.
However, Managua is not currently operating because SONET has not been
able to transfer funds to INETER, the institution in charge of making the
observations. This institution is very
strict in regards to payment, and will not make any observations if money is
not available from the project to pay for the observers. The forecasters at the
airport recognize the value of the observations for the forecast, but this
interest has not been able to change the attitudes of senior INETER personnel. This lack of interest on the part of the
institution responsible for geophysical observations in Nicaragua is not new,
and is motivation for a planned trip to Central America early next year. This travel will seek additional sources of
support for observations in the region and provide lectures to broader the
awareness of the SONET (and related activities) in the Central American region.
Venezuela
Venezuela has been operating two pilot balloon stations, at
San Fernando de Apure and in Ciudad Bolivar.
These sites are operated by the Venezuelan Air Force Weather Service,
which is the main weather forecasting institution in the country. Both sites are in the flat llanos region
along the Orinoco River drainage. San
Fernando is reliable and provides good quality data. On the other hand, unreliable gas supply and communication
problems at Ciudad Bolivar are causes of this station’s poorer performance.
Several motivated individuals from Venezuela participated in the PACS-SONET
short course in Panama in 2001 and good communication between the project and
the country has existed ever since. The
person in charge of the stations attended the PACS-SONET coordination meeting
in Paraguay. The willingness and collaboration
is highlighted by the relatively inexpensive operations in this country, with
labor being provided at no cost to the project and transport of balloons
effected through Venezuelan Air Force flights from Miami to Venezuela. Hydrogen gas for balloon inflation is also
inexpensive in the country.
In addition to the high level of interest shown by the
Venezuelan Air Force in the SONET activities, faculty members at the
Universidad de Los Andes in Merida, Venezuela have shown interest in SONET
activities. Future activities may
involve a joint field program and associated follow-on research related to the
mesoscale meteorology around Lake Maracaibo.
PACS-SONET might contribute expertise in the design of the activity and
procedures for analyzing the data.
One possible complication related to the Venezuelan SONET
activities is that Venezuela is currently undergoing a major modernization
activity that eventually will include the establishment of a number of
radiosonde stations. One site will be
at Cd. Bolivar, which may obviate the need for the pilot balloon observations
there. As these sites will be sustained
by an international loan, the long-term sustainability of this network is not
assured, complicating decisions about the potential long-term data to be
obtained from the sites. We are following this activity, as it may suggest
revisions to at least one (Cd. Bolivar) of the Venezuelan station's operations.
Colombia
The Colombian Navy has been operating one station in
Cartagena since 1997. However, this station has had a poor performance in the
last two years, with an average of only 5 observations per month. The apparent
reason for this is not only the lack of personnel at this research facility
(CIOH), but also the perceived value of the SONET observations, that keeps them
from assigning more people to this activity.
We are planning travel to Colombia in early 2004, where we expect to
meet with senior-level Navy officials, and to provide a short course related to
the meteorology and climate of the region, and the project's objectives. Details of possible observations (Malpelo
and Serranilla) on the islands administered by Colombia and staffed by
Colombian Navy personnel will also be conducted.
During the past few months, contacts have been initiated
with IDEAM, the Colombian institution in charge of Environmental affairs (and
the official weather and climate service).
As part of planned travel to Colombia we intend to visit the IDEAM
office in Bogota with the objective on ensuring collaboration with the
establishment of observations (including raingauge) on the islands mentioned
above. The IDEAM has asked for help
during this past year in maintaining its upper-air network (under budgetary
pressure at the moment) and we will provide ideas on what might be feasible
(short course possibility).
Ecuador
San Cristobal, in the Galapagos Islands, is the only site
in operation in Ecuador. The site at ESPOL in Guayaquil was stopped in May 2002
due to the low number of observations caused by frequent cloudiness at the site
(not a problem with the observers or institution). The San Cristobal site performed well during a 5-month period in
2003, but very few observations have been received in the last two months. We have been informed that the reason is
lack of personnel in Quito to process and transmit the observations.
Because of the difficulty in maintaining a reliable data
stream from the Galapagos site, despite the availability of observers, gas, and
communications, we plan a visit to Quito to discuss the feasibility of
maintaining this site. It is currently
the most expensive site to operate, and if we do not receive strong assurances
that it will operate effectively, we are likely to see other institutions on
the islands to make the observations.
Since our perception is that Ecuador, like Nicaragua, has a weak
meteorological infrastructure and lack of appreciation for meteorological and
climate information, we are anticipating giving a short course in Quito early
in 2004, as part of travel to northwestern South America.
Peru
Two different institutions currently operate pilot
balloon stations in Peru. The longest times series, and indeed the best
SONET time series of any stations, is from the site at the University of
Piura. This site, established in 1997, continues to operate at a high
level of efficiency. It is one of the
few sites that makes afternoon observations - a fact required by the relatively
high frequency of morning low clouds along the coastal plain of northern
Peru. Some analyses of these observations are shown in Section 5.
The National Meteorological
Service in Peru (Servicio Nacional de Meteorologia e Hidrologia, SENAMHI)
operated four stations during the SALLJEX at Pucallpa, Ica, Arequipa and
Puno. These sites were established in
November 2002, and were reliable during SALLJEX. The site at Arequipa became
part of the PACS-SONET in July 2003, and has operated very reliably since. SENAMHI has agreed to operate pilot balloon
stations also at Pucallpa, Iquitos, and Puerto Maldonado. The latter two sites are currently special
El Niño radiosonde sites that make soundings every other day. Arrangements are being made to make pilot
balloon observations at these sites; the exact protocol (number of observations
per week etc.) has yet to be worked out.
The Pucallpa and Iquitos sites are potentially valuable as they describe
the currently poorly-monitored conditions upstream of the low-level jet axis
over eastern Bolivia.
SENAMHI has also expressed interest in obtaining information
on the costs and detailed specifications of recoverable radiosonde systems that
were partially demonstrated during the recent workshop in Paraguay. This information is being forwarded to them.
Paraguay
The pilot balloon site at Asuncion has a good record of
observations, spanning a 4-year period.
The second Paraguayan site, Mariscal Estigarribia is at a location far
(500 km) northwest Asuncion with poorly motivated individuals and little
supervision. The two sites in Paraguay performed well during SALLJEX, when the
Mariscal Estigarribia site was staffed by additional personnel. M. Estigarribia stopped making observations
shortly after SALLJEX ended, and has just resumed operations (October 1st) with
motivated and more capable observers.
Efforts to modernize the meteorological infrastructure and emergency
management capabilities in Paraguay have led to the acquisition of a radiosonde
system that has been installed in Mariscal Estigarribia. However, shortly after
its installation the hydrogen generator failed and, for this reason,
radiosondes have not been launched since the equipment was put in place more
than one year ago. Now, with closer
supervision by DINAC senior staff, we expect the Paraguayan PACS-SONET
observations to continue without significant problems for the foreseeable
future.
Bolivia
Gas availability and gas costs continue to be the main
issues in Bolivia. The gas company (Praxair) in Bolivia has been unable to
satisfy the demand of gas despite of the high prices they charge for it. Gas is imported from Brazil and the supply and
transport has not been reliable. Also,
gas is delivered only at two stations (La Paz and Santa Cruz) and AASANA has to
arrange for transportation to the other 4 relatively remote sites. Bad road
conditions in Bolivia complicate transportation and recycling of the gas
cylinders. The station at Robore has not been making observations for the last
2 months because they ran out of gas.
AASANA has been unable to send them gas because of new regulations that
prohibit transportation of gas by train.
Civil unrest also complicates transport throughout the country; strikes
and road blockages are currently common.
We will attempt to have lower-cost gas (either hydrogen or
helium) imported from Peru during the coming year. Currently we are using gas purchased as part of SALLJEX
activities but which was not delivered until after the experiment ended.
On the positive side, the AASANA observers and other
personnel remain committed to the activity and continue interested in spite of
some of the difficulties.
3.2
Performance statistics over the past year.
The overall performance of
the network appears to be stable in terms of the number of observations per
month (Figure 3.1). However, the average number of observations per month is
below 500 for the months following SALLJEX; this average is somewhat lower than
that in the previous 3 years. On the other hand, the average is higher than
expected given the problems with the transfers of funds.
Figure
3.1. Pilot balloon
soundings per month (PACS-SONET and SALLJEX combined) from April 1997 to
September 2003.
To
date, PACS-SONET has generated more than 30,000 observations - more than 5,000 per year in the period
2000-2003 (Fig. 4.2). This calendar year a total of 8,000 soundings are
expected, including ~2,000 soundings made at Argentine and Brazilian stations
that operated only during SALLJEX months.
Figure
3.2. Pilot balloon
observations per year (PACS-SONET and SALLJEX combined) in the period
1997-2003. For year 2003, only 9 months are shown (Jan-Sep).
3.3 Concerns related to the
network
Hardware
The theodolites in use are old Warren Knight units, which
were obtained from the US National Weather Service warehouse in Kansas City
over the past 6 years. This source of
theodolites has now been exhausted, and the remnants of the theodolites all
reside at NSSL and in the countries where they are in use. Data loss has occurred because of faulty
theodolites, and the inability to repair them rapidly in the field. Our SONET web site now has detailed information
on the use of the theodolites, but still lack some information of maintenance,
though individuals in each institution have been trained in basic maintenance
procedures.
At some point in the not distant future replacement
theodolites will be needed, especially since many were used during SALLJEX and
are expected to be used during NAME. To
some degree it may be possible to use theodolites that exist in Peru and
Venezuela; those in Peru are of the same type (Warren-Knight) as used in SONET,
while those of Venezuela are a different type, but still usable.
Sustainability, gas supplies
The
major topic of the recent SONET workshop in Paraguayan was the sustainability
of the network and means to reduce the costs of operations. One means was to use hydrogen gas in some of
the countries where helium is currently being used. The importation of less expensive helium or hydrogen into Bolivia
in particular could save thousands of dollars per year.
4.
Educational activities and annual meetings
PACS-SONET has had, as part of its activities, educational
activities throughout its existence.
During the first two years 8 visitors participated in 1-3 month visits
to NSSL, and carried out applied research activities with the recently started
SONET data. Prior to the SALLJEX
activities, 6 visitors from South America participated in similar visits to
NSSL during the summer of 2002.
In addition to these activities, SONET has supported, or
helped support a series of multi-week workshops in Bolivia, Panama, and shorter
series of lectures in Mexico, Peru, and most recently Paraguay.
During the recent SONET workshop in Paraguay the concept of
SONET-supported educational activities was discussed at length. The principal concern was not that these
activities were not a good activity, but rather that the cost involved consumed
a significant percentage of the available SONET funds that might otherwise be
used for observations. A major workshop
or course, involving international participants, has typically incurred an expense
of approximately $25K. This is about
20% of the funds available for observations.
Much discussion centered on what was the best way to invest the
available funds in educational activities.
The options discussed included 1) multi-month visits to NSSL, short
(several week) courses, sponsoring students at selected educational
institutions, funding SONET research activities in certain countries, and
having NSSL personnel provide short courses in selected countries (just for
members of the particular country).
Some of these activities are not feasible, while others will require
careful evaluation.
The participants in the SONET
workshop prepared a document, which summarizes the discussions that took place
during the meetings and presents the participants’ views and suggestions about
different aspects of the project. Much emphasis was put in the network’s design
and in the planning of future educational activities. Although many of the
changes proposed may not be feasible or may lack sound scientific
justification, those highlight the level of motivation of the PACS-SONET
coordinators. Their input is much appreciated and we will continue to encourage
this kind of participation. The document will be made available in the
project’s web page through the following URL:
http://www.nssl.noaa.gov/projects/pacs/laquinta/
5. Some aspects of the PACS-SONET data that suggest avenues of
further research
In this
section we present some aspects of the PACS-SONET data that have shown promise
for further work. These analyses are
preliminary, mostly because some of these data are not yet
quality-controlled. However, the results
are unlikely to change in a qualitative sense.
These results are presented to suggest areas of further work.
5.1 Observations along the northern coast of
Peru. Piura interannual variations
The best
SONET data set to describe interannual variability and the mean annual cycle at
a particular locality is to be found with the observations from Piura,
Peru. This site, at 5.5˚S and
about 60 km inland from the coast in northern Peru, has nearly 6 complete years
of afternoon soundings.
The mean
annual cycle for the afternoon Piura meridional winds (Fig. 5.1) show a northward flow near the surface of between 3 and 7
m/s, with weakest winds during the February/March time frame when the SST are
highest in the eastern Pacific off the coast of northern Peru and the ITCZ is
farthest south. The southerly flow
increases from March to May, and then again from July to November, when it
reaches a peak of about 7 m/s at about 300m above the surface. This southerly flow is very shallow, with
near zero meridional flow at the 1.5km level throughout the year. The zonal wind is relatively weak compared
with the meridional wind, though it is stronger and deeper during the warm
season (time of highest SST's), around February-March.
By
subtracting the annual mean values at each level, we can display the monthly
evolution of the anomalies of the meridional winds at Piura (Fig. 5.2). The zonal wind anomalies are interesting in that they are
relatively deep - the period October through April is characterized by westerly
wind anomalies of about 1 m/s, while the period from May through September
shows easterly wind anomalies. The
layer between 1500 and 2000 m shows an inverse relationship with the layer
beneath it. It is possible that when
the onshore flow (positive zonal) is stronger in February-March the return flow
above the afternoon sea-breeze is also stronger (negative zonal wind
anomaly). Likewise, when the sea-breeze
circulation is weaker than the annual mean (in June-July), the return flow of
the sea-breeze, centered at 1.5 km altitude, is anomalous in the opposite
sense.