SEESat Data Analysis GE 115 Section 10, November 2003

In lieu of the actual data that would have been collected from the GE115 balloon launch, each team should examine the data recorded from the National Weather Service balloon launches on or around the 20th of November 2003. I’d suggest data from 12 Z (zulu: or 5 am MST) 20 Nov, 0 Z (5 pm MST) 21 Nov, and 12 Z (5 pm MST) 21 Nov. Note: there is 7 hours difference between Z time and MST.

The following NOAA site catalogs the radiosonde data from all weather stations. The web address is: http://raob.fsl.noaa.gov/. From this site, input date for data recall, hours of data (leave on the All Times for only a day or two of data), wind speed units, and station (select State). From the next window, select SD from the state list and YES for the view/select stations. Leave the other options as is. From the next screen, select Rapid City and get the data. Save the data as a TXT file from Explorer and open in Excel, which should be able to manipulate the data into the appropriate columns of data (see attached FSL Output Format description). Note: missing data is given as 99999 so your team may wish to go through the data set and remove these values.

Hopefully, if we get the balloon launch off yet this term, we will be able to use this data to compare to our collected data.

Background:

The sounding is launched from the NWS office up on the Star Village hill. The first line of data (begins with a line type of 9) is the actual pressure, temperature, dewpoint, etc, at the ground up there and the elevation is in meters above sea level. Note units are in tenths where indicated. I would suggest converting the data from the ‘tenths’ format to include the tenths after a decimal point, for ease of understanding and using.

The next 1 or two lines will be extrapolated heights above sea level (elevations will be below 1037 m). These lines are extrapolated to show what the elevations would be to have recorded pressures of 1000 and 925 mb. The NWS uses these extrapolations to create a map depicting conditions across the country near sea level with station elevations factored out. Meteorologists extrapolate like this because they want to isolate pressure variations between stations due to elevation differences (quite large) from pressure variations due to weather systems (much smaller). Where the surface is low, we have storms. Where the surface is high, we have generally fair weather. Of course, temperature, dewpt., winds, etc., are not available where this pressure level is below the surface!1 Note: standard pressure at sea level is 1013.25 mb.

Although the balloon reports conditions every few seconds, to compress data meteorologists do not transmit reports from these levels as long as there is a linear trend in all parameters except winds from the last reported level. When there is a change in trend, a report is made at that level. These levels where the trend of at least one parameter changes are called significant levels (linetype 5).

Certain levels are reported whether there is a change in trend at them or not because weather charts of conditions at these levels are routinely prepared. These are called mandatory levels (linetype 4), and they include 1000, 925, 850, 700, 500, 300, 200, 150, 100, 50, 30, 20, 10 mb. Conditions at the tropopause (the 250 mb level) also are always reported. Of course if the balloon bursts before it reaches the upper levels, no report is made from them. No reports are made on descent.

Wind only, at some levels, is reported whether there is a change in trend or not because wind maps are routinely prepared at these levels for aviation interests (5000 ft, 10000 ft,….), or because there is a significant change in wind direction or speed at that level.

Troposphere (closest to earth) is typically considered well mixed. The boundary level is called tropopause, and is around 10 km. Above this is the stratosphere, where the air begins to be heated by ozone absorbing UV radiation. The peak temperature occurs near 50 km, where there is a balance of ozone concentration and UV absorption.

At the Rapid City NWS, balloons are launched approximately 45 minutes before the “recorded” time. This is so that all of the data has been received at the “recorded” time. This is done at all balloon launching sites so that there is a single “snap shot” of the weather in the entire USA two times a day.

Data Analysis Suggestions:

- Examine effect of elevation on atmospheric pressure.

- A rule of thumb1, for a well-mixed atmosphere, is that the air temperature cools 1°C for every 100 m elevation gained. How does the data agree with this R.O.T.?

- Other ideas for analysis are left up to the team to consider and do.

1 Private communication with Dr. Andrew Detweiler, IAS/Atmospheric Sciences Department, SDSM&T, Rapid City, SD, 24 November 2003.