Received: from general.amug.org (amug.org) by Lowell.Edu (4.1/Lowell-Complex) id AA15791 for delivery to bas; Tue, 26 Dec 95 23:22:40 MST Received: from [204.62.193.147] (d27-ts0.amug.org [204.62.193.147]) by general.amug.org (8.7.1/8.6.9) with SMTP id XAA07488; Tue, 26 Dec 1995 23:22:27 -0700 (MST) Message-Id: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Tue, 26 Dec 1995 23:25:45 -0600 To: bas@lowell.edu From: bsanden@amug.org (Bernie Sanden) Status: R Brian - Hope your holidays are going well. Now you can see what I've been doing, at least with some of my time... I combined the short article you wrote with my personal account. I don't know if you feel the result "flows", but I thought both were appropriate as part of the article. You may feel otherwise. Also, there are various other issues to address (like your official title at Lowell), my grammar, syntax, direction, examples, etc. Please feel free to critique aggressively as you see fit. I am not a writer by trade, it won't bruise my ego, and it can probably only help. If necessary, use this only as an outline to start fresh. [NOTE: The only issue I deal with daily is the amount of free time available (very little). I did this with the couple days off I had over Christmas. Once the new year begins, I will find it hard again to spend a lot of time fine-tuning the article]. Enough for the apologies / disclaimer. I did not include a lot of the "stuff" I've done with the data (including, for instance, a visual graph which depicts degrees of cloudiness by shades of gray) because, even though it tells a story, it may be too narrow-interest and require too much explanation. Be aware, however, that this article references a table and two graphs (which I did not include for now, partly because we still have to GET the remaining data from 1995). Finally, I did not intend to make it sound as if the worldwide cloudiness sections of the article were my own composition. However, the article is in 'first person' and it seems (to me) to flow smoothly as written. There may be a better way to relay the information in third person or otherwise without diluting the "personality" of the article. That way, we can ensure that the readers realize your heavy contribution to the actual article itself (beyond just contributing the database). I do not expect this to be the final draft. Hope it is a decent start, though. ***BY THE WAY...I DO NOT HAVE DAILY CLOUDINESS DATA FOR MARCH, APRIL, AND MAY 1995 (AND OF COURSE I NEED DECEMBER AS SOON AS IT IS READY)*** Sixteen Years of Lowell Observatory Cloudiness Data by Bernie Sanden and Brian Skiff When I first heard of it a few years ago, I was astonished. Brian Skiff, a Staff Astronomer at Lowell Observatory in Flagstaff Arizona [help Brian!], had been noting nighttime cloudiness since 1978, and had daily data on hand since 1979. As an Arizona amateur astronomer, I immediately saw the usefulness of this remarkable record for my own purposes. After graciously allowing me access to the data, I transferred it onto a computer spreadsheet (much of it from calendars!) for the purpose of better grasping the 5000+ lines of information. Brian had done the customary analysis with the data. Table 1 displays the total number of "photometric" nights (completely cloud-free from dawn to dusk) for each year along with the total number of clear hours, which includes time from partly clear nights. In addition, the best month(s) for each year is noted along with the number of clear nights in that month(s). On average, each year offers about 100 clear nights in Flagstaff, but the annual variation is wide. The total number of clear hours is more consistent, averaging about 1100 per year. These numbers seem low compared to those the Chamber of Commerce would advertise. For amateur and professional astronomers alike, standards must be set a lot stricter as to the definition of a clear sky. Most deep-sky observers would agree that the thin, scattered cirrus so common throughout the Southwest can play havoc with a night of observing. Brian instantly puts a night such as this into the "spectroscopic" category, adding zero hours to the tally of clear ones. Observatory reports often give the number of "useful" nights, ranging up to 300 per year or more. Unless the site is northern Chile, these are not all clear nights. All the developed sites in the desert Southwest -- from McDonald in the east to Sacramento Peak in southern New Mexico across Arizona to southern California and up to Lick Observatory toward San Francisco -- all experience roughly one clear night in three over the long term. Mauna Kea in Hawaii, San Pedro Martir in Baja California, and the Canary Islands have similar amounts of photometric weather. All other sites in the northern hemisphere from which any significant science is produced (e.g. Dominion in British Columbia, Calar Alto in Spain) have worse weather. It may be that some places in central Asia (Tadjikistan, Kazakhstan) have more clear nights, but at present the logistical problems of operating an observatory there are overwhelming. In the southern hemisphere, things are generally better. Surprisingly, the best sites in Australia are not good photometric sites -- dark, yes, but not clear much. Next best are various places in southern Africa, especially the South African Astronomical Observatory's Sutherland Station, which evidently gets 40 - 50% of nights photometric. The driest place on Earth outside certain valleys in the Antarctic is the Atacama Desert in northern Chile. The site now being developed by the European Southern Observatory (ESO) on Cerro Paranal had on average about 85% photometric nights throughout the 1980s when site-testing was done for comparison with already developed sites farther south (specifically La Silla, the current ESO site). This is a place where no clouds appear for several months consecutively. Of course the landscape makes the Sonoran Desert appear lush by comparison. The well-known Chilean sites (the U.S. facility at Cerro Tololo, La Silla, and the Carnegie Institution's Las Campanas) average about 60 - 75% photometric, but there is a winter "cloudy" spell when only 40% of the nights are clear, i.e. like the "best" month in Arizona. The comparisons were enlightening, but there was more that the Lowell database could reveal. Figure 1 shows the percent of clear nights by month, averaged from 1980 - 1995. May and June exhibit the highest overall percentages, but October is a surprisingly close third. The July and August numbers portray the effects of the "monsoon" season, when moisture from the gulf invades Arizona. It is no wonder that observatories such as Kitt Peak close down for maintenance activity during the height of this season. Plotting the number of clear nights for each month through the years illustrates the risk associated with generalizing seasonal predictions. Figure 2 displays the sum of clear nights for the past sixteen Junes. The outlier of the group represents the cloudy June of 1988, when only 1 photometric night was recorded at Lowell. It was particularly memorable for a group of visiting Australian amateurs who made their Arizona travel arrangements that year based upon recommendations to visit during the "dependable" June Arizona skies. By far, the most fun I've had with the database involves disproving the standard amateur whines concerning full-moon clearings and weekend cloudiness. My analyses show no more likelihood for clouds at and around new moon than full, or on weekends than during the week. Of course, this is based upon data from Flagstaff and no doubt is not representative of your favorite observing site! My intention when I received the database was to ascertain general trends, hopefully to aid in predictability. I was again reminded, this time with an arsenal of data, that the weather in Arizona is never a sure thing. But although the unreliability of the weather and percentage of clear nights here in Arizona is far behind Chile, the average amateur is not likely to do better in terms of clear skies by moving any place where they would be likely to find a job. (end of article) - _________________________________________________________