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Reading Meteorological Data

Reading Meteorological Data. ATS 315. Stuff You’ll Need. strings typecasting. Strings. Strings are sets of characters. Maybe a word, for example. char station[5];. Strings. The “type” for strings is “char”. char station[5];. Strings.

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Reading Meteorological Data

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  1. Reading Meteorological Data ATS 315

  2. Stuff You’ll Need • strings • typecasting

  3. Strings • Strings are sets of characters. Maybe a word, for example. • char station[5];

  4. Strings • The “type” for strings is “char”. • char station[5];

  5. Strings • In square brackets, you need to specify how long the string is capable of being. • Usually overestimate, just to be sure. • char station[5];

  6. What We Use Strings For • The variables that contain information such as the names of the observing stations will be strings.

  7. Strings Are Tricky • Seems like this should work to assign a string…but “=“ doesn’t work for strings. main () { char station[5]; station = “KOMA”; }

  8. Strings Are Tricky • Rather, use the strcpy function (“string copy”). main () { char station[5]; strcpy(station,“KOMA”); }

  9. Strings Are Tricky • Use the %s format specifier to print strings… main () { char station[5]; strcpy(station,“KOMA”); printf (“%s\n”,station); }

  10. Strings Are Tricky • …or to scanf or fscanf a string. main () { char station[5]; scanf (“%s”,&station); }

  11. Typecasting • How you convert between two variable types. • Normally used to convert int to float. main () { float Temp; int iTemp; iTemp = 47; Temp = (float) iTemp; }

  12. Typecasting • Notice the types of Temp and iTemp. main () { float Temp; int iTemp; iTemp = 47; Temp = (float) iTemp; }

  13. Typecasting • The integer “47” becomes the float “47.0000000” with this “typecast”. main () { float Temp; int iTemp; iTemp = 47; Temp = (float) iTemp; }

  14. Typecasting • The new “type” is in parentheses, just before what is to be converted. main () { float Temp; int iTemp; iTemp = 47; Temp = (float) iTemp; }

  15. What We Use Typecasting For • The temperature codes in METAR are in tenths of a degree Fahrenheit. • 224 needs to be converted to 22.4 • temp = ((float) tempcode) / 10.0;

  16. Where are the observation files? • The most recent surface observations are kept in a file called /var/data/ldm/convert/current_sao.wxp fin = fopen (“/var/data/ldm/convert/current_sao.wxp”,”r”);

  17. What do *_sao.wxp files look like? WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  18. What do *_sao.wxp files look like? • The first line will always read WXPSFC. • SkipToEndOfLine(fin); WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  19. SkipToEndOfLine(fin); void SkipToEndOfLine (FILE *f) { fscanf (f,"%*[^\n]\n"); } main () { FILE *fin; fin = fopen (“/var/data/ldm/convert/current_sao.wxp”,”r”); SkipToEndOfLine(fin); fclose(fin); }

  20. What do *_sao.wxp files look like? • The second line will always be the time the observations were taken. • This mixture of numbers and letters is a string. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  21. What do *_sao.wxp files look like? • char timecode[15]; • fscanf (fin, “%[^\n]s\n”, &timecode); WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  22. What do *_sao.wxp files look like? • Each line after that is one decoded METAR from one station. • There are 1000s of observations. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  23. What do *_sao.wxp files look like? • Each observation consists of a series of values, separated by spaces. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  24. What do *_sao.wxp files look like? • The first value is a string—the station identifier. • Usually declared to be at least 5 characters long. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  25. What do *_sao.wxp files look like? • Second value: integer that codes up the temperature in tenths of a degree FAHRENHEIT. • Needs to be typecast to a float, then divided by 10. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  26. What do *_sao.wxp files look like? • Third value: integer that codes up the dewpoint in tenths of a degree FAHRENHEIT. • Needs to be typecast to a float, then divided by 10. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  27. What do *_sao.wxp files look like? • Fourth value: integer that codes up the wind direction and speed. • Use the function provided in the handout to decode. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  28. What do *_sao.wxp files look like? • Fifth value: integer that codes up the altimeter setting. • Read it in, but we aren’t going to use it for anything in this class. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  29. What do *_sao.wxp files look like? • Sixth value: integer that codes up the mean sea level pressure. • Decode it like you would in a station model. • If the code is -99, make your variable pres something negative. WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

  30. What do *_sao.wxp files look like? • The rest of the line contains visibilities, comments, etc… stuff that we aren’t going to work with in this course. • SkipToEndOfLine(fin); WXPSFC 0900Z 12 FEB 04 K17Y 86 50 3204 31 -99 10.0 -99C - @0848 #AO2 $ KEDE 428 356 0000 22 -99 10.0 -99M - @0845 #AO2 $ MPTO 752 716 0000 980 -99 -99 20F - @0900 $ MMMD 734 734 0000 992 133 7.0 -99C - @0846 #50000 977 $ MMUN 752 716 1406 996 155 7.0 20F,250S - @0845 #57006 8/508 956 $ KMRN 374 338 0000 17 -99 5.0 13B,24O !RA @0847 #AO2 P0003 $

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