PACS-SONET Annual Report 2003

 

Prepared by Michael Douglas of the National Severe Storms Laboratory (NSSL) and Javier Murillo, John Mejia and Jose Galvez of the Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) and the University of Oklahoma

 

 

 

Contents

 

 

Summary

 

1.    Brief history of the project

 

2.    Current status of the PACS-SONET

 

3.    Scientific Rationale for each observing site

 

4.    Educational activities and annual meetings

 

5.    Next Year’s Activities

 

6.    Some aspects of the PACS-SONET data that suggest avenues of future research

 

 

 

 

 


Summary

 

This is the first official annual report of the PACS-SONET project, after some 7 years of operation.  This surprising statement is a consequence of our using the web site of the project as the source of primary information for the activity, rather than printed material.  However, there are advantages to printed documents over web sites and these advantages, together with the need to satisfy a now-official requirement, are the impetus for this report. 

 

The PACS-SONET project 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. 

 

The PACS-SONET continually strives to maintain the network operations against a number of factors that tend to reduce the efficiency of the activity.  This year, delays in the availability of funds from NOAA, due to government-wide budget delays, had a major adverse impact on the SONET, with one station ceasing operations for the past 9 months.  Changes in the procedures involved in making funds transfers to participating countries also delayed the reception of funds to maintain the network operations.  These procedural difficulties are now slowly being sorted out, but were a source of considerable consternation and delay during 2003.

 

During the past year the first meeting involving representatives from all institutions involved in the SONET took place in Paraguay.  The summary of this 6-day workshop is described in an appendix to this annual report.  The objective of the workshop was to seek input on the direction that the SONET should take during its 3- year current extension.  Issues covered included what stations should be operated, which new sites might be valuable, how to maintain the budget of the activity, what educational activities could stimulate use of the data, including research activities. Finally, the use of radiosonde observations was evaluated as a possible component of a future SONET design.

 

Although a number of presentations related to SONET were given during the past year, no publications appeared.  In lieu of this, we are presenting, as part of this report, key aspects of the SONET data set that are potential subjects for near-term research.  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 Istmus 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 the report.


 

1. Brief history of the PACS-SONET

The Pan American Climate Studies Program - Sounding Network (PACS-SONET) is a network of pilot balloon stations in Latin America funded by NOAA to help monitor the climate variability through measurement of lower-middle tropospheric winds in data sparse regions. The observations, transmitted in near real-time, can also be used for weather forecasting activities.

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 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 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.

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 has been 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 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/).

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) that started on November 15, 2002.

 


Fig. 1.3. Pictures from two special observing campaigns conducted in Bolivia

during SALLJEX around Lake Titicaca (left) and in the Salar de Uyuni (right).

 

In 2003 a second extension of the PACS-SONET was approved for an additional 3 years. Additional changes in the network configuration and mode of operation are expected.

 

 

 

2. Current status of the network

 

2.1 Introduction.

 

Several budget-related issues affected the network’s performance during the past 12 months. The transition from the end of the previously funded period towards the new 3-year extension presented a challenge to the project. During this transition several stations were left unfunded for a lapse of 3-4 months, due to the delay in transferring funds from Washington to NSSL.  The reason for this, it appeared, was a financial cycle change for all NOAA-funded projects.  Finally, the problem that impacted the most our attempt at a smooth transition was related to changes in payment procedures and delays in money transfers to the foreign countries.  These are now being made through the NOAA MASC Office in Boulder, instead of the Washington Finance Office previously. The problem is so serious that at the time this report was written we were still struggling to complete a large number of transfers.  For reasons that remain unclear to us, MASC refused to make electronic transfers to a number of countries and decided to send checks instead. This method of payment wasn't acceptable to some of the institutions participating in PACS-SONET, and this has introduced delays in the availability of funds to many network sites.  

 

Despite the long delays in transferring funds to the countries, most of the stations managed to operate almost regularly and most interruptions were ultimately related to problems particular to each country, as is explained in the following paragraphs. The stations in Peru, Bolivia and Paraguay were part of the SALLJEX upper-air network and were operated during the first quarter of the year primarily from SALLJEX funds.

                   

 

2.2 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, specially 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 areshown in Section 6.

 

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.

 

 

 

2.3 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 2.1). 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 2.1. 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 2.2. 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).

 

 

 

2.4 Concerns related to the network

 

2.4.1 Hardware

 

The theodolites in use are old Warren Knight units, which were obtained from the US NWS 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.

 

 

2.4.2. Sustainability, gas supplies

 

The major topic of the Paraguayan workshop 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.

 

 

 

 

 


3. 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 various networks map (Fig. 3.1) 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 Istmus 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 2.3 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 Serrannilla (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.

 

 

Figure 2.4 Zoom on the northern end of the Panamerican radiosonde network (blue circles), current  (black dots) and proposed (stars) PACS-SONET sites.

 

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 a 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.