Tezopaco, Sonora:

Tezopaco is situated in a broad valley about 10-15km wide, the last such valley before the main foothills of the Sierra Madre Occidental are reached. and one travels inland. The observing site was about 410m above sea level, and was flat, except for a several hundred m high hill about 1.5km to the NE of the observing site. This site was chosen as a major EMVER meteorological observatory for many reasons. First, it was the closest site, at low elevations, to the area shown from satellite imagery to be the most convectively active region of northwestern Mexico during the summer. The low-level southerly flow was relatively unobstructed by major hills as it flowed up from the south and southwest. Thus tethersonde and radiosonde soundings would provide a good depiction of the flow that was entering the convective region. Secondly, Tezopaco was close (~90 km) to Obregon, which allowed for personnel from the forecast center to frequently visit the observing site. This was essential for running the tethersonde system, since there were inadequate facilities for staying overnight in Tezopaco. Observing teams typically left Obregon near 0400, arriving in time for a tethersonde sounding near sunrise.

The observations in Tezopaco were made at Colegio Juarez, a Seventh Day Adventist school. For religious reasons no observations could be made by anyone on Saturday. Thus, no Saturday observations are generally available from Tezopaco (with a few exceptions). Several students were trained to make the observations, and generally performed very well. EMVER personnel operated the tethersonde system, which was housed in the school's Chapel. The tethersonde system was an A.I.R. system, using regular AIR radiosondes with carbon strip hygristors for the most part. No wind observations were made by the tethersonde system; pilot balloons were used for wind soundings.

A network of simple plastic raingauges was established along the roads near Tezopaco. These gauges were spaced every 1-2km and were read once daily in the morning, by driving along the roads. Initially, 27 gauges were available, but because these were mounted on fence posts and sometimes quite visible, some were lost to tampering by the local population. About 20 were available at the end of EMVER.

The observing schedule was disorganized initially, but eventually the following schedule was developed:

File name Time Type of sounding

A 6:00AM: 100gm pilot balloon (by students at Colegio Juarez)

1 9:00AM: 30gm pilot balloon by EMVER-93 personnel

2 12:00 PM: 30 gm pilot balloon by EMVER-93 personnel

3 3:00 PM: 30gm pilot balloon by EMVER-93 personnel

P 5:30PM 100gm pilot balloon (by Colegio Juarez students)

Tethersonde soundings were made near 6:00AM, 10PM, and 1:00PM, though this was more variable than the pilot balloon schedule. Many problems with the winches and other arrangements made the tethersonde operation less routine. One balloon was lost, the winch mechanism failed on numerous occasions, and frequent lack of electricity at Colegio Juarez required the presence of an electrical generator.

In addition to tethersonde soundings, free radiosonde launches were made at Tezopaco, especially near the end of EMVER. These soundings were made in the afternoon, and were done in advance of storms. The objective was to make "proximity soundings" to sample the atmosphere in the environment of storms developing northeast of Tezopaco. The free radiosondes end with "R".

The 30gm pilot balloons were generally tracked until 40min, or until they were lost in clouds or the sun. The 100gm balloons were tracked to 52 min, and were intended to be comparable with all other EMVER pilot balloon network observations.

The reason for making 30gm balloon observations was to compared the diurnal wind cycle at Tezopaco with that at Empalme, where similar observations were also being made.

On the last day of observations at Tezopaco (August 15-16), observations were made with tethersonde all night, and free radiosonde and pilot balloon soundings were made at night as well. The numbering of the soundings on these two days is slightly different than on other days, with the numbers going from 1-9, and then s, to depict the additional soundings.

Special pilot balloons were made at the Empalme Observatorio, where the regular SMN radiosonde observations were made. This site was about 3km from the Gulf of California, and well exposed to the prevailing southerly winds. The pilot balloons were (after the first two days, when tracking of the 4:15AM radiosonde with balloon lights was unsuccessfully attempted) launched at 6:00AM, 9:00AM and 12:00 Noon. The 4:15PM radiosonde sounding was tracked by a theodolite, to compare with the Omega-windfinding system of the radiosonde. The radiosonde provides accurate ascent rate information (altitude, calculated from the hydrostatic equation, every 10s) that can be merged with the angle measurements from the theodolites, for the computation of accurate wind profiles.

Observers travelled from Obregon, to stay at Empalme for several days before rotating. There were inadequate hotel facilities in Empalme, and the crews generally slept in the offices at the radiosonde station.

This site did not make pilot balloon soundings, but it did track the twice-daily radiosonde soundings make at the radiosonde station. At this site, the afternoon radiosonde sounding was tracked by optical theodolite, to obtain higher-vertical resolution winds than provided by the radiosonde's windfinding system (Omega, with about a 3-4 minute average of the balloon drift). During the early morning, pilot balloon lights were attached to the radiosonde 350gm balloons. In order to calculate the winds using the theodolite angles, the radiosonde ascent rate for each afternoon sounding has been obtained from the radiosonde's height and time after launch information.

There were no radiosonde launches from 29 June to 6 July because of equipment failure at the site.

This site was one of the more difficult to maintain functioning and to establish initially, as there were few personnal at the site. Jorge Sanchez of IMTA flew to La Paz, then was driven to Loreto, where training was conducted. For most of the time, there was personnel available for only one launch a day, and observations did not start until later than most stations. These data may be potentially especially valuable, since they are the only special EMVER observations made on the Baja California peninsula.

This station's personnel had observers experienced from the 1990 SWAMP/TRAVASON, and provided generally complete data sets. The site is well away from the nearest mountains of substantial height.

There were not enough operators at this site to provide a sounding record without many missed observations, but after initial difficulties with incorrect ascent rates (serious underinflated balloons until ________?????)

Observers at this site had experience from 1990 and generally made very reliable observations.

This site was new for EMVER, being in a very isolated location on the coast (about 300km from Hermosillo by road). The observers were engineers at the Thermoelectric power plant operated by the CFE. The launch site was at about 10m above sea level, a few hundred meters from the Gulf, and about 1km west of the generating plant. There were some difficulties in getting gas and balloons to the site that resulted in some delays in starting the observations.

This site was operated by personnel at CEDO (Centro de Estudios de Desiertos y Oceanos), about 5 km east of Puerto Peñasco. The launch site was situated atop a coastal dune, about 200m from the shore. Observers made twice-daily pilot balloon soundings (100gm) from June 15 until 18 July, when an AIR radiosonde system was established there. Thereafter the radiosondes were made twice daily, but with 200gm balloons. The ascent rate for the balloons was obtained from the radisonde data, and winds were calculated from the theodolite angles. There was no independent windfinding associated with the AIR radiosonde system.

When comparing the Peñasco radiosonde data with other sites such as Empalme it is important to realize that the radiosondes are different. The AIR radiosonde data was not calibrated above 250mb, and the data is frequently bad at and above this level. Also, the morning radiosonde launch at Peñasco was made after sunrise, and radiation errors affect the data that do not affect the other morning radiosonde observations in the region. The magnitude of this error is about .5û to 1ûC (Pe˜ãsco is warmer). The moisture sensor of the AIR sonde did not report relative humidities below 20%.

This site had some experience with pilot balloon soundings in 1990, and after delays in receiving the theodolites for EMVER, observations generally appeared to go smoothly.

As with Nuevo Casas Grandes, this site had some experience with pilot balloon soundings in 1990, and received the theodolites late during EMVER, but thereafter the observations generally appeared to go smoothly.