Effects of airborne particles on optical equipment

Abstract

Observatories are affected by dust particles in the air and those that settle on the mirror surfaces. Here we analyze seven years of weather and dust particle data from the Apache Point Observatory (APO) in Sunspot, New Mexico, to find correlations between dust and other weather factors, and also find correlations between the APO data and the Magdalena Ridge Observatory(MRO) weather data. Exposure of optics to strong dust events should be avoided, so we considered different possible observatory closure criteria based on these data.

Looking for Correlations between Dust Events and Weather at Observatories in New Mexico

“…APO is northeast of the White Sands National Monument, while MRO is located east and northeast of two large deserts extending into Arizona and Mexico, the Sonoran and Chihuahuan. The weather data from APO has been shown to be almost identical to the data from MRO, except that some of the events are slightly staggered temporally because of the difference in longitude and latitude of the observatories (Gorgievska & Steinebach 2004). The prevailing wind direction at MRO is out of the southwest to west (Klinglesmith et al 2004).…”

“…Our analysis included different combinations of weather phenomena, such as temperature and barometric pressure, dew point and wind speed, etc. We chose to examine combinations of weather phenomena because previous studies at this and other observatories (Gorgievska & Steinebach 2004;Giordano & Sarazin 1994;Porceddu et al 2002) found no single correlatable weather phenomenon useful for predicting dust events. Hence, we examined the data looking for a set of two or more levels or changes in levels in meteorological measurable quantities which precede most dust events.…”

“…It is mounted in a weather-tight enclosure about 50 feet above the ground on the APO weather tower, which places the instrument in free air flow, away from the effects of most human activities at the site (Varsik et al 1997). It operates by drawing air through a tube into the counter, where photodiodes measure the light transmitted by an infrared laser and scattered by the dust particles (Gorgievska & Steinebach 2004). The air pump draws 0.1 cubic feet of air per minute through the counter which is operated for 1 minute every 15 minutes throughout the day.…”

“…However, mountain environments are known for complex weather associated with the motion of winds along the slopes and over the mountain, and for phenomena such as mountain waves (see Salby 1996). While no correlation has been found with the wind speed or direction at the time of the dust events at APO (Gorgievska & Steinebach 2004), winds are not monitored at APO along the slopes of the mountain itself to determine larger scale trends around the mountain. Also, APO, as with most observatories, has no provision for measuring the chemical content of the dust arriving during the dust events.…”

“…We undertook a study of archival weather data from the Apache Point Observatory (APO) to look for possible correlations between documented dust events and other possible weather precursors. We chose APO because it has a vast amount of archival weather data available online, and because in previous research by Gorgievska & Steinebach (2004) it was concluded that the weather at APO is very similar to that at MRO due to the observatories' proximity to each other. This paper covers the analysis of 223 dust events during 17 months from the APO site where we looked for a phenomenon, or group of phenomena, preceding a dust event within about 1 day.…”