CEMRC operates two identical meteorological towers at sampling sites in the vicinity of the WIPP (Fig. 2). The Near Field site is located approximately 1 km northwest of the WIPP site at an elevation of 1088 m (latitude 32°
22'40.385"N; longitude 103°
47'55.425"W). The Cactus Flats site is located approximately 19 km southeast of the WIPP site at an elevation of 1041 m (latitude 32°
13'05.451"N; longitude 103°
41'42.583"W).
Each station consists of a 10-meter tower equipped with sensors for temperature, relative humidity, barometric pressure, solar radiation, Ultra-Violet B (UVB) radiation, wind speed and direction and vertical wind speed. Data are collected every second, with averaging times of ten minutes. In addition, the maximum wind speed and total precipitation occurring over the ten-minute averaging period are recorded.
Temperature, relative humidity and all wind parameters are measured at a height of
10 m above the surface. Precipitation, barometric pressure solar radiation and UVB are measured at heights of 0.4, 1, 2 and 3 m, respectively. The barometric pressure sensors are adjusted for temperature, but are not referenced to mean sea level. The solar radiation sensors (pyranometers) measure the energy flux per unit area (Wm-2) of both direct and diffuse sky radiation. The UVB sensor measures direct and diffuse UVB in the 280-320 nm band.
The data are stored in electronic dataloggers and downloaded twice weekly. Once downloaded, the data are screened for outliers and other anomalies and uploaded to a main database. Performance checks of the sensors are conducted quarterly, and sensors are re-calibrated at least annually.
This report summarizes meteorological data collected over the 12 month period from December 1998 through November 1999. In addition, data collected at the sites from
1 December 1997 through 30 November 1998 (12 month period) are compared with data from the same time interval during 1998-1999.
For the 1999 sampling period, data recovery exceeded 97% for all sensors, except the UVB sensor at Cactus Flats. Data recovery was slightly lower at Cactus Flats during the month of June when a nearby lightning strike disabled several of the sensors. In addition, the Cactus Flats UVB sensor failed in April and was undergoing repairs and recalibration during April through July. Other short-term (typically less than two hours) data losses occurred throughout the year due to sensor maintenance, repair, performance testing and malfunction.
Averaged over the year, winds were from a southeasterly direction (E, ESE, SE and SSE quadrants, inclusive) 49% and 48% of the time at the Cactus Flats and Near Field sites, respectively (Fig. 3). However, there were some distinctive seasonal variations in wind direction (Fig. 4 and Fig. 5). Wind direction was highly variable during the winter and spring (December through May) when compared with the summer and fall (June through November). During summer, wind from the southeastern quadrant occurred over 50% of the time, but dropped to less than 40% during the winter. The inter-annual and intra-annual variability in wind direction are important parameters in modeling dispersion pathways for potential airborne releases from the WIPP.
Wind velocities were very similar between sites. Wind velocities (10-minute means) were less than 5.4 m s-1 over 72% of the time, with speeds frequently from 3.1 to 5.4 m s-1. Calm periods (wind velocities < 0.1 m s-1) occurred less than 1% of the time over the year. Wind velocities > 5.4 m s-1 occurred less than 28% of the time, but were more frequent during the spring, and typically came from west and west-northwest. The highest wind velocities recorded at each site were 27.1 m s-1 (62 mph) on 5 September, and 28.0 m s-1 (64 mph) on 24 May, at the Near Field and Cactus Flats sites, respectively.
Air temperatures at Near Field ranged from -10.9 to 41.5 oC and from -10.9 to
41.0 oC at Cactus Flats. The maximum temperatures were recorded on 30 June at Cactus Flats, and 1 July at Near Field. The lowest temperatures were recorded on 26 December 1998 at both locations. The annual mean temperatures were 18.5 oC and 18.0 oC at Near Field and Cactus Flats, respectively. At both locations, December was the coldest month (mean = 7.5 oC at Near Field; mean = 7.2 oC at Cactus Flats) and August was the hottest month (mean = 28.4 oC at Near Field; mean = 28.1 oC at Cactus Flats) (Fig. 6).
The annual mean relative humidity at Near Field was 43% and ranged from 4 to 101%. Humidity at the Cactus Flats site was very similar to Near Field, averaging 44% and ranging from 4 to 101%. Mean relative humidities were lowest when temperatures peaked in late spring and early summer (Fig. 7). It should be noted that the accuracy of the relative humidity sensors declines at relative humidities below 12% and above 94%, and readings outside these ranges should be interpreted with caution.
Barometric pressure did not exhibit an obvious seasonal trend at either site (Fig. 8). The annual mean was 893.6 mb at Cactus Flats and 898.3 mb at the Near Field site. The apparent 4.7 mb difference between the sites can be attributed to a 41 m difference in elevation, and this difference is not significant if corrected using standard barometric conversions that incorporate elevation (U.S. Department of Commerce Weather Bureau, 1963, Manual of Barometry, Vol. 1, Washington D.C.).
Solar radiation flux (Wm-2) was integrated over daily intervals to calculate total energy received per unit area (MJm-2). As is typical, solar radiation received at the sites peaked in the summer and was lowest during the winter months (Fig. 9). This pattern is due to a combination of increasing solar radiation intensity, less cloud cover and additional hours of daylight during the summer months. Over the year, the daily total solar radiation ranged from 2.5 to 33 MJ m-2 at Near Field and 3 to 32 MJ m-2 at Cactus Flats.
Solar UVB flux (Wm-2) was integrated over daily intervals to calculate total energy received per unit area (MJ m-2). The UVB radiation followed a pattern similar to that of the total solar radiation (Fig 10).
Over the year, a total of 19.66 cm of precipitation was measured on 43 days at Cactus Flats and 22.88 cm of precipitation was measured on 54 days at Near Field (Fig. 11). At both sites, the month of July had the highest number of days (9 at Near Field, 7 at Cactus Flats) on which precipitation was recorded. At Cactus Flats, December was the month with the highest total precipitation (3.96 cm). In contrast, at the Near Field site, July was the month with the highest total amount of precipitation (5.54 cm).
Overall, 1999 was a slightly wetter year than 1998. In 1998, totals of 17.28 and 12.88 cm of precipitation were recorded at the Near Field and Cactus Flats sites, respectively, between 1 December 1997 and 30 November 1998. Over the same time period in 1999, 22.88 cm of precipitation was recorded at Near Field and 19.66 cm was recorded at the Cactus Flats site. In addition to being wetter, mean annual temperatures were approximately two degrees lower in 1999 than in 1998. Although February, March and April were warmer in 1999, this was offset by approximately 0.3 degrees cooler temperatures in May, June and July of 1999. Given the differences in precipitation and temperature it is not surprising that total solar radiation was also lower in 1999, with Cactus Flats receiving 6449 MJ m-2 in 1999 compared with 7984 MJ m-2 in 1998, and the Near Field site receiving 6575 MJ m-2 in 1999 compared to 7222 MJ m-2 in 1998. In contrast, annual mean wind patterns (velocity and direction) were very similar between years, although some differences appeared in seasonal wind patterns.
Tables presenting meteorological data summarized herein are available on the CEMRC web site at http://www.cemrc.org
