News from Rolex Award Winners

Measurements of the atmosphere and sunlight in South-Central Texas began on 04 Feb 1990 from a field outside my rural office. The data include the total ozone column, total water vapor, optical depth (haze) and direct UV-B. In 1994 various full-sky measurements of sunlight, including UV-B, and photographs of the solar aureole (the glow around the sun caused by aerosols in the sky) were added. 

Fig. 1. Solar UV-B at or near solar noon at South-Central Texas from 1994-2011 on (a) days without clouds at sun and (b) clear days only.

Figure 1 includes two charts that show the UV-B measured at or near solar noon on days when clouds were present but did not block the sun (higher UV-B) and clear days with very few or no clouds (reduced UV-B). (Not included are days when I was away.)

The chart that shows all days (Fig. 1.a.)  indicates much higher UV-B caused by scattering from clouds. For details of this phenomenon, see Mims and Frederick, 1994. Note that this chart shows a significant reduction in cloudiness beginning in 2002.

The chart that shows UV-B on clear days (Fig. 2.b) has much less noise. The gradual reduction of UV-B over the years is primarily due to the gradual recovery of the ozone layer after the significant reduction in ozone that occurred after the volcanic eruption of Mount Pinatubo in June 1991. Noise in the clear sky data is caused by ozone fluctuations and seasonal dust and smoke events.

The UV-B radiometer that collected the data described here was made possible by funds from a 1993 Rolex Award.  

Reference.
F. M. Mims III, and John E. Frederick, Cumulus Clouds and UV-B, Nature 371, 291, 1994.

The International Space Station (ISS) is by far the largest artificial satellite. It’s also among the brightest objects in the night sky.

If you haven’t yet seen it passing overhead, it’s well worth the effort required, especially when its accompanied by one of the Space Shuttles.

My best ISS sighting occurred the evening of May 8 during a lonely stay at Hawaii’s Mauna Loa Observatory. The ISS was brighter than Venus.

The nearby ISS photo I made that night (Canon EOS 40D, 50 mm fixed-focus lens, 32 sec at f/4.6) doesn’t begin to do justice to the actual experience of watching the giant space station glide by overhead. Now that NASA has added new solar panels to the Space Station, which is almost the size of a football field, the ISS is often among the brightest objects in the sky. Seeing it is an unforgettable experience.

You can find out when and where to watch for the ISS at http://www.spaceweather.com. Click on “Satellite Flybys” in the right margin and then select your country or enter your postal zip code (US and Canada). Click “Go,” and a page will appear listing the brightest satellites visible over the next 10 days for your site.

The ISS is not visible every night, but it’s worth the wait. And it’s worth getting up early when it flies over before sunrise.

 Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org
twitter.com/fmims
www.youtube.com/fmims

The chart shows the ozone layer measured from my site in South-Central Texas, USA, since 4 February 1990.  The measurements were made by a series of NASA satellites and my instruments, including TOPS-1, the Microtops sponsored by the 1993 Rolex Award and the commercial Microtops II. The black line is the 90-day running mean of my data. (The running mean does not begin in 1990 due to the transition from the original, homemade TOPS-1 instrument to more advanced versions of TOPS.)

Note the annual variation in the data, with the peak occurring during the spring ozone maximum. Of interest is the decline in ozone following the volcanic eruption of Mount Pinatubo in June 1991. This decline was accompanied by an increase in solar ultraviolet-B. Also of interest is the unusually low ozone that occurred during the spring of 2008.

My ozone measurement program and related research benefitted greatly from a 1993 Rolex Award, which provided the funds that resulted in the development of Microtops and various other instruments that I use to monitor the atmosphere. This time series, which will be 20 years in February 2010, would not have continued beyond the first several years had funds provided by the Rolex Award not been available.

I will post more about the ozone layer and solar ultraviolet in the future.

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org
twitter.com/fmims

SOHO image of the quiet sun on 23 August 2009.

The ongoing interval between solar cycles 23 and 24 could provide an important opportunity to compare various natural observations with those made during recent solar cycle peaks when the sun was much more active than earlier in the 20th century and before. For current images of the solar disk, see: http://sohowww.nascom.nasa.gov/

Of interest is that Arctic temperature this summer rose above freezing later than in 50 years of measurements. See http://ocean.dmi.dk/arctic/meant80n.uk.php for a chart that is updated every day.

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org
twitter.com/fmims

Global aerosol optical depth (AOD) forecast by Naval Research Laboratory (USA) for 4 August 2009.

Considerable Saharan dust has reached Texas during much of July and the first few days of August, where the dust on windows is probably from Africa. While we receive Saharan dust most summers, the present outbreak is among the biggest and longest lasting Saharan dust events I’ve measured since 1990 using various sun photometers. My main aerosol measurements since 1994-5 have been made with various Microtops and Microtops II sun photometers developed with the help of a Rolex Award.

This major dust event provides a unique opportunity for students and others looking for a research project.

The Navy Research Lab NAAPS aerosols model dust and smoke forecasts are well worth checking: http://www.nrlmry.navy.mil/aerosol/ Scroll down to the second box and select your choice(s). The NAAPS model shows Saharan dust occasionally reaching up into Europe. It also shows considerable smoke from sub-Sahara Africa over the Atlantic.

For ground aerosol measurements in major Texas cities, see http://www.tceq.state.tx.us/cgi-bin/compliance/monops/particulates.pl

Back trajectories across Texas are here: http://www.tceq.state.tx.us/compliance/monitoring/air/monops/airtraj.html

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org
twitter.com/fmims