Summary of field activities organized by NSSL

The North American Monsoon Experiment (NAME) was carried out during the summer of 2004 over northwestern Mexico and the southwestern USA. Many different activities formed part of NAME. This summary is intended to let the participants in activities organized by NSSL know something about the project. Comprehensive information can be found in the Related Links section.

History of NAME

The NAME experiment had been in the planning stage for more than 3 years prior to the summer of 2004. NAME is part of a larger set of research activities that form a contribution to the world climate research program. The main objective of the NAME activity is to improve forecasts of the rainfall and mean climatic conditions from one to three months in advance during the warm season. The focus is on warm season precipitation because this has the greatest impact on agriculture and cattle activities, and also because over the NAME domain the rainfall occurs primarily during the warm season. At the present time there exists little skill in forecasts made this far ahead of time.

At the present time the forecasts for 1-3 months in advance are of limited value, especially during the warm season. However, even a slight improvement in the skill of such forecasts could have a large positive impact on the management of water resources (dams for example), on agricultural activities (suppose one knew the rains would be delayed 2 weeks or the summer’s rainfall would be 50% of normal), or with cattle raising activities. Thus the NAME effort.

It should be realized that the measurements made during the summer of 2004 are only one component of the NAME activity, and that there will follow a lengthy research phase. The idea is to use the observations to determine how to improve the computer models that will ultimately provide the best estimates of the future state of the atmosphere.

Although the measurements are officially justified on the basis of improving seasonal forecasting over the region, the NAME observations will also improve our understanding of phenomena from daily to weekly time scales.

Financial support for NAME and why

Most of the financial support for the NAME observations is coming from two branches of the US government: the National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation. Smaller contributions are coming from the National Aeronautics and Space Administration (NASA). In Mexico, help for the activities is being provided by the National Water Commission (CAN), the Mexican weather service (SMN), the Mexican Navy, the Civil Defense Units from various states (especially Sonora) and numerous educational institutions in the northwestern part of Mexico. A longer list is provided in the appendix.

Different components of NAME

The basic national observation networks of both countries plus special:

Radars

Ships

Radiosonde stations

Wind profilers

GPS profiles

Pilot balloons

Aircraft

Flux tower…

Our group was involved in 4 different projects related to NAME, these were:

1) A pilot balloon network consisting of about 24 sites in northwestern Mexico.

2) Activities of a CICESE research ship in the Gulf of California.

3) Flights by a research aircraft based in Mazatlan.

4) Measurements around the central Gulf of California to determine the effect of ocean temperature and vegetation changes on the rainfall over the region. (Central site at Tesopaco, Sonora).

This report describes more about three activities, and the accompanying CD includes many photos of the activities.

1) The pilot balloon network

Figure 1. Pilot balloon training in Huatabampo

Starting in early May we started to establish pilot balloon sites throughout the NAME domain. The first to be set-up were those that were part of the vegetation atmosphere feedback network, as these needed to be running well before the start of the rains in southern Sonora. The last to be established were those in the US.

The purpose of the pilot balloon network was to provide greater coverage and higher spatial density of wind observations than would be possible by the radiosonde network alone. Four additional radiosonde sites were established for NAME, and other sites that normally made one observation per day made more frequent observations. However, it was not feasible to add many more radiosonde sites over the region, so pilot balloon stations, by their simplicity and ease of establishment, were chosen as an inexpensive supplement. The pilot balloon observations also were made over a longer period than most other NAME observations; the pilot balloon measurements started from late May to late June, and ended on Sept 30 at most sites. Other NAME observations were concentrated from early July to mid-August.

Table 1. Pilot balloon sites

USA		Latitude	Longitude
1	Lake Havasu City	34.57° N	114.36° W
2	Silver City	32.78° N	108.29° W
3	Gila Bend	32.96° N	112.70° W
Baja California		Latitude	Longitude
5	Cataviña	29.84° N	114.79° W
6	Bahia Tortugas	27.69° N	114.88° W
7	Santa Rosalia	27.50° N	112.29° W
8	Loreto	26.10° N	111.33° W
9	Ciudad Constitucion	25.09° N	111.68° W
10	La Paz	24.15° N	110.24° W
11	San Jose del Cabo	23.06° N	109.62° W
Mexico - Northwest		Latitude	Longitude
12	Puerto Peñasco	31.29° N	113.47° W
13	Hermosillo	29.05° N	110.98° W
14	Tesopaco	27.81° N	109.35° W
15	Huatabampo	26.84° N	109.61° W
16	Choix	26.72° N	108.31° W
17	Topolobampo	25.60° N	108.98° W
18	Empalme	27.95° N	110.76° W
Mexico - Central		Latitude	Longitude
19	Matehuala	23.65° N	100.82° W
20	Durango	24.00° N	104.60° W
21	Lerdo	25.45° N	103.46° W
22	Jimenez	27.13° N	104.86° W
Mexico - Islands		Latitude	Longitude
23	Isla Clarion	18.36° N	114.70° W
24	Isla Socorro	18.76° N	111.00° W
25	Islas Marias	21.76° N	106.54° W

Most pilot balloon sites made two observations per day, unless very low clouds or rain interfered. Two sites, Huatabampo and Tesopaco, made much more frequent observations at times, to describe the sea-land breeze circulations. These special observations were part of the vegetation-atmosphere feedback project, described below.

The overall objective of the pilot balloon network was to describe the day-to-day variability of the wind patterns over northwestern Mexico and the southwestern US with more detail than previously available. With these observations we hope to link large-scale patterns to local variations in the rainfall, and to help determine how to improve the weather forecasting models that are now being routinely run on computers in both Mexico and the US.

Figure 2. NAME upper-air network

2) The vegetation-atmosphere feedback project

We speculate that the rapid change in the vegetation over the inland foothills of Sonora and Sinaloa after the start of the summer rains would also affect the atmospheric conditions over the region, and might be partially responsible for the change in rainfall patterns as the summer progresses. For example, in July the heaviest rainfall occurs well inland from the coast in Sinaloa and Sonora. However, by August and early September the rainfall occurs frequently over the coastal regions. We sought to explain this increase in coastal rainfall by a cooling of the interior foothill region that had leafed out, as well as by increases n the gulf water temperature as the summer progresses.

To evaluate the various hypotheses that we had considered, we needed to measure the intensity of the sea-land breeze circulation throughout the summer. Since much less rain falls in Baja California and the vegetation changes there are much less than in Sonora and Sinaloa two sites (Santa Rosalia and Loreto) were operated there to see how the sea-land breeze circulation changes during the summer. Such changes would most likely be due to the difference between the ocean temperature in the gulf and the land temperature over Baja California. Two sites were operated instead of just one site to ensure than any change observed was not just due to very local conditions.

On the eastern side of the gulf more stations were operated, including Empalme, Huatabampo and Topolobampo. The radiosonde observers at Empalme made the pilot balloon observations there as well, at the same time as the other pibal sites. In Topolobampo, the Navy continued to make twice-daily observations that it had been doing for the past 4 years. In Huatabampo a special effort was made to make more frequent observations, since the site would be compared with observations at Tesopaco. Huatabampo was an ideal location, on a flat coastal plain with no hills nearby.

Together, the three sites at Empalme, Huatabampo, and Topolobampo will be used to describe the sea breeze intensity along the eastern side of the gulf and how it changes throughout the summer.

Several sites were needed well inland, away from the coast as well. The two most desirable locations were at Tesopaco and Choix. Both sites were surrounded by dry forest that rapidly turns green after the start of the rains. Both sites were at relatively low altitude and would be useful in describing the intensity of the afternoon breezes moving towards the mountains. The site at Tesopaco had been used extensively for measurements during an experiment in 1993.

Figure 3. Tethered balloon in Tesopaco

Besides the pilot balloon measurements, the vegetation-atmosphere study had other components. Frequent tethered balloon observations (and the pilot balloon measurements as well) were made from a house on the outskirts of Tesopaco to show how the atmospheric humidity and temperature profiles evolved during the day and from one day to the next (Fig. 4). These profiles usually extended to about 2000m above the surface. In Figure 4 the difference between the morning and noontime soundings is evident.

Figure 4. Morning (08:08 local time) and afternoon (14:44 local time) temperature profiles in Tesopaco

Also, near the Tesopaco site was a “micrometeorological” tower (Fig. 5) that was instrumented with special sensors to measure the moisture and heat fluxes at the top of the forest canopy and other sensors from the soil to the top of the tower to measure other atmospheric conditions. This tower will be operated through the rainy season of the next year (2006). The tower is 18 meters tall, and stands well above the top of the surrounding forest.

Figure 5. Flux tower near Tesopaco

Finally, but certainly not least of the activities, a special raingauge network was established prior to the onset of the rains in the southernmost 9 municipalities of Sonora and also around Choix in Sinaloa. About 250 raingauges were distributed. A few other raingauges were distributed in Baja California as well. (Another project, with many more raingauges, also deployed raingauges over northwest Mexico, but started after the beginning of the rains).

Figure 6. Raingauge network training

3. NOAA P-3 operations from Mazatlan

A research aircraft from the NOAA (National Oceanic and Atmospheric Administration) of the US government, one of two research aircraft that is used to study hurricanes, was based in Mazatlan from July 6^th through August 4^th. Ten flights were carried out over this period, for a total of 70 flight hours. Although the aircraft carried special meteorological radars, most of the flights were in conditions free of storms, either west of Baja California or over the Gulf of California. The purpose of the flights was to describe the atmospheric conditions associated with variations in the flow over the Gulf of California and to help determine the source of moisture for the summer rains over the region. The CD contains some photos taken from the P-3 during the different flights.

Figure 7. NOAA P-3 research aircraft in Mazatlan

4. CICESE research ship operations in the Gulf of California

We were associated with the oceanographic cruises of the RV Ulloa, a shrimp boat that has been converted to a research vessel and is operated by CICESE in Ensenada. Radiosonde and some pilot balloon and tethered balloon observations were made from the ship during two 17-day cruises (June 6-22 and August 5-22). The primary purpose of the cruise was however to release drifters to describe oceanographic currents in the lower part of the gulf and to make related oceanographic profiles. The CD shows some of the activities carried out aboard ship.

The scientific rational for the cruises was to help determine the processes responsible for the increase in the gulf’s temperature during the summer months and to identify a suspected current that was transporting warm water from the mouth of the gulf to higher up the gulf in early summer. The temperature of the gulf waters is suspected to be important in modulating the onset of the rains over Sonora and Sinaloa.

Figure 8. CICESE's research ship "Francisco de Ulloa"

Other activities not supervised by NSSL

Mexican Navy research ship

A large research ship of the Mexican navy was stationed at the same location for 35 days in the middle of the lower Gulf of California. This ship had a wind profiler, and made frequent radiosonde and surface observations with the aim of estimating evaporation from the gulf.

Radar S-Pol

A large meteorological radar was brought from Colorado and installed in a corn field about 90km north of Mazatlan. This radar operated for about 6 weeks to describe the precipitation and storm development in the region. Other meteorological radars from the Mexican National Weather Service were modified to record more precisely the radar data at each site in northwest Mexico.

Profilers and special radiosondes

At 3 locations there were special radars, called wind profilers that nearly continuously measure the winds at levels up to about 3 to 4 km. These systems were intended to describe the changes associated with sea-land breezes and so-called “surges”, strong wind events over the Gulf of California that seem to be associated with thunderstorm complexes from the previous night.

GPS-met (Tesopaco)

Small automatic weather stations were installed in a half-dozen locations in Sonora to continuously describe water vapor in the atmosphere. These use GPS signals to estimate the total water vapor present above the site, though they cannot infer accurately at what level it occurs. One such site is at an Internet café in Tesopaco.

Special radiosonde observations

More frequent radiosonde launches were made at most of the SMN sites in northern Mexico. Also, 7 us sites in the southwest made special radiosonde observations. The wind profiles sites, and another site at Loreto, also made special radiosonde observations.