5  REM ****              PROGRAM SKEWT              ****
10 REM ****         THIS PROGRAM CONSTRUCTS         ****
15 REM ****         A SKEW T  LOG P DIAGRAM         ****
20 REM ****        AND MOVES AIR VERTICALLY.        ****
30 DECLARE SUB PLOT (T1, P1, T2, P2, CLR, RD, FF)
40 REM **** PHYSICAL CONSTANTS ****
50 PBOT = 1.05 * 10 ^ 5: PTOP = 1.5 * 10 ^ 4: DP = -500
60 RD = 287: RV = 461.7: EPS = .622: CP = 1004: KPA = 2 / 7
70 L0 = 2.5 * 10 ^ 6: DLDT = -2338: ES0 = 610.8: CPV = 1848
80 TK0 = 273.15: P0 = 10 ^ 5: NPL = (PTOP - P0) / DP + 1
90 SCREEN 12: PRCLR = 14
100 GOSUB 2500
110 IF NCH = 2 THEN 2000 ELSE CLS
120 REM **** GRAPH COORDINATES ****
130 TMIN = 233: TMAX = 313: YF = 12
140 YMIN = -RD * LOG(PBOT): YMAX = -RD * LOG(PTOP):
150 XMINF = YMIN / YF: XMAXF = YMAX / YF
160 XMIN = TMIN + XMINF: XMAX = XMIN + TMAX - TMIN
170 WINDOW (XMIN, YMIN)-(XMAX, YMAX)
180 PCLR = 4: TCLR = 2: THCLR = 9: WCLR = 13: TWCLR = 15: SCLR = 11
190 REM **** ISOTHERMS ****
200 FOR T = TMIN TO TMAX STEP 10
210 X1 = XMIN + T - TMIN: Y1 = YMIN
220 IF T > XMAX - YTOP / YF THEN X2 = XMAX ELSE X2 = T + YTOP / YF
230 IF T > XMAX - YTOP / YF THEN Y2 = (XMAX - T) * YF ELSE Y2 = YMAX
240 LINE (X1, Y1)-(X2, Y2), TCLR
250 NEXT T
260 FOR T = TMIN - 30 TO TMIN - 10 STEP 10
270 X1 = XMIN: Y1 = YF * (XMIN - T)
280 X2 = T + YMAX / YF: Y2 = YMAX
290 LINE (X1, Y1)-(X2, Y2), TCLR
295 NEXT T
300 REM **** ISOBARS ****
310 FOR I = 2 TO 10
320 P = I * 10 ^ 4
330 Y = -RD * LOG(P)
340 X1 = XMIN
350 LINE (X1, Y)-(XMAX, Y), PCLR
360 NEXT I
400 REM **** DRY ADIABATS ****
410 FOR THTA = 233 TO 383 STEP 10
420 P1 = P0
430 T1 = THTA * (P1 / P0) ^ KPA
500 FOR K = 1 TO NPL
510 P2 = P1 + DP
520 T2 = THTA * (P2 / P0) ^ KPA
530 CALL PLOT(T1, P1, T2, P2, THCLR, RD, YF)
570 P1 = P2: T1 = T2: REM X1 = X2: REM Y1 = Y2
580 NEXT K
590 NEXT THTA
600 REM **** CONSTANT MIXING RATIO LINES USING Td ****
610 FOR I = 1 TO 11
620 P1 = P0
630 WS = (10 ^ -3) / 32 * 2 ^ I
640 ES1 = P0 * WS / (EPS + WS)
650 REM ****FIND TD USING SUCCESSIVE APPROXIMATIONS ****
660 LM = L0 + DLDT * (-35 + 5 * I)
700 FOR J = 1 TO 4
710 TD1 = (1 / TK0 - RV / LM * LOG(ES1 / ES0)) ^ (-1)
720 LM = L0 + DLDT * (TD1 - TK0) / 2
730 NEXT J
740 L = L0 + (TD1 - TK0) * DLDT
800 FOR K = 1 TO NPL
810 L = L0 + (TD1 - TK0) * DLDT
820 TD2 = TD1 + DP * RV * TD1 ^ 2 / (P1 * L)
830 P2 = P1 + DP
840 CALL PLOT(TD1, P1, TD2, P2, WCLR, RD, YF)
870 TD1 = TD2: P1 = P2: REM X1 = X2: REM Y1 = Y2:
880 NEXT K
890 NEXT I
900 REM **** MOIST ADIABATS USING Tw ****
910 FOR I = 1 TO 12
920 P1 = P0
930 TW1 = 233 + 10 * I
1000 FOR K = 1 TO NPL
1020 LM = L0 + (TW1 - TK0) * DLDT / 2
1030 L = L0 + (TW1 - TK0) * DLDT
1040 ES = ES0 * EXP(LM / RV * (1 / TK0 - 1 / TW1))
1050 W = EPS * ES / (P1 - ES)
1060 F1 = 1 + W + (L + .61 * RD * TW1) * P1 * W / (RD * TW1 * (1 + .61 * W) * (P1 - ES))
1070 F2 = CP + CPV * W + .61 * RD * W + (L + .61 * RD * TW1) * P1 * W * L / (RV * TW1 ^ 2 * (P1 - ES))
1080 DTW = DP * F1 / F2 * RD * TW1 * (1 + .61 * W) / P1
1090 TW2 = TW1 + DTW
1100 P2 = P1 + DP
1110 CALL PLOT(TW1, P1, TW2, P2, TWCLR, RD, YF)
1170 P1 = P2: TW1 = TW2: REM X1 = X2: REM Y1 = Y2
1180 NEXT K
1190 NEXT I
1200 REM **** LABELS FOR LINES ****
1205 COLOR PCLR
1210 LOCATE 1, 1: PRINT PTOP / 100;
1222 LOCATE 11, 1: PRINT "300";
1232 LOCATE 19, 2: PRINT "500";
1237 LOCATE 24, 2: PRINT "700";
1240 LOCATE 30, 1: PRINT "1000";
1245 LINE (XMIN, YMIN)-(XMAX, YMIN), PCLR
1246 LINE (XMIN, YMAX)-(XMAX, YMAX), PCLR
1248 COLOR TCLR
1252 LOCATE 23, 11: PRINT "-40";
1254 LOCATE 8, 14: PRINT "-60";
1262 LOCATE 23, 52: PRINT "0";
1272 LOCATE 23, 31: PRINT "-20";
1274 LOCATE 23, 72: PRINT "20";
1300 COLOR WCLR
1310 LOCATE 27, 3: PRINT ".125";
1312 LOCATE 27, 11: PRINT ".25";
1314 LOCATE 27, 18: PRINT ".5";
1316 LOCATE 27, 27: PRINT "1";
1318 LOCATE 27, 35: PRINT "2":
1320 LOCATE 27, 44: PRINT "4";
1322 LOCATE 27, 54: PRINT "8";
1324 LOCATE 27, 64: PRINT "16";
1326 LOCATE 27, 75: PRINT "32";
1350 COLOR THCLR
1360 LOCATE 17, 3: PRINT "273";
1362 LOCATE 17, 19: PRINT "293";
1364 LOCATE 17, 34: PRINT "313";
1366 LOCATE 17, 50: PRINT "333";
1368 LOCATE 17, 66: PRINT "353";
1400 COLOR TWCLR
1410 REM LOCATE 17, 64: PRINT "16";
1412 REM LOCATE 17, 75: PRINT "32";
1414 LOCATE 13, 3: PRINT "286";
1416 LOCATE 13, 17: PRINT "307";
1418 LOCATE 13, 38: PRINT "341";
1420 LOCATE 13, 59: PRINT "392";
1500 IF NCH = 3 THEN 2000
1510 WHILE INKEY$ = "": WEND
1520 END
2000 REM **** MOVE PARCEL VERTICALLY ****
2010 P1 = PPAR1: T1 = TPAR: TD1 = TDPAR
2020 DP = (PPAR2 - PPAR1) / 200
2030 THTA = T1 * (P0 / P1) ^ KPA
2100 FOR K = 1 TO 200
2110 IF T1 < TD1 THEN 2200
2120 REM **** DRY ADIABATIC MOTION ****
2130 L = L0 + (TD1 - TK0) * DLDT
2140 TD2 = TD1 + DP * RV * TD1 ^ 2 / (P1 * L)
2150 P2 = P1 + DP
2160 T2 = THTA * (P2 / P0) ^ KPA
2170 IF NCH <> 2 THEN CALL PLOT(T1, P1, T2, P2, PRCLR, RD, YF)
2175 IF NCH <> 2 THEN CALL PLOT(TD1, P1, TD2, P2, PRCLR, RD, YF)
2180 P1 = P2: T1 = T2: TD1 = TD2
2185 IF T2 < TD2 THEN PCL = P2: TCL = T2
2190 GOTO 2300
2200 REM **** MOIST ADIABATIC ASCENT ****
2210 LM = L0 + (T1 - TK0) * DLDT / 2
2220 L = L0 + (T1 - TK0) * DLDT
2230 ES = ES0 * EXP(LM / RV * (1 / TK0 - 1 / T1))
2240 W = EPS * ES / (P1 - ES)
2250 F1 = 1 + W + (L + .61 * RD * T1) * P1 * W / (RD * T1 * (1 + .61 * W) * (P1 - ES))
2260 F2 = CP + CPV * W + .61 * RD * W + (L + .61 * RD * T1) * P1 * W * L / (RV * T1 ^ 2 * (P1 - ES))
2270 DT = DP * F1 / F2 * RD * T1 * (1 + .61 * W) / P1
2280 T2 = T1 + DT: P2 = P1 + DP
2290 IF NCH <> 2 THEN CALL PLOT(T1, P1, T2, P2, PRCLR, RD, YF)
2300 T1 = T2: P1 = P2
2310 NEXT K
2330 IF NCH <> 2 THEN 2460
2400 REM **** PRINTING PARCEL TEMPERATURES ****
2410 COLOR PRCLR
2420 IF PCL = 0 THEN 2450
2430 LOCATE 26, 26: PRINT "CONDENSATION LEVEL = "; PCL / 100
2440 LOCATE 27, 22: PRINT "AT CONDENSATION LEVEL, T = "; TCL - TK0
2450 LOCATE 28, 22: PRINT "FINAL PARCEL TEMPERATURE = "; T2 - TK0
2460 WHILE INKEY$ = "": WEND
2480 END
2500 REM **** SUBROUTINE FOR DESCRIBING THE PROGRAM ****
2510 LINE (0, 0)-(640, 10), 2, BF
2520 LINE (0, 0)-(10, 480), 2, BF
2530 LINE (0, 470)-(640, 480), 2, BF
2540 LINE (630, 0)-(640, 480), 2, BF
2550 LOCATE 5, 28: PRINT "THE SKEWT - LOG P CHART"
2555 COLOR 12
2560 LOCATE 12, 5: PRINT "TYPE 1     TO SEE THE SKEW T CHART ONLY"
2570 LOCATE 13, 5: PRINT "TYPE 2     FOR PARCEL CHANGES ONLY "
2580 LOCATE 14, 5: PRINT "TYPE 3     TO SEE BOTH CHART AND PARCEL"
2585 COLOR 14
2590 LOCATE 13, 55: INPUT " YOUR CHOICE = ", NCH
2600 IF NCH = 1 THEN 2790
2610 COLOR 11
2620 LOCATE 19, 27: PRINT "ENTER AIR PARCEL PROPERTIES"
2630 LOCATE 21, 5: INPUT "ENTER STARTING P(MB)  = ", PPAR1
2640 PPAR1 = PPAR1 * 100
2650 LOCATE 22, 5: INPUT "ENTER ENDING P(MB)    = ", PPAR2
2660 PPAR2 = PPAR2 * 100
2670 LOCATE 23, 5: INPUT "ENTER T(øC)  = ", TPAR
2680 TPAR = TPAR + TK0
2690 LOCATE 24, 5: INPUT "ENTER Td(øC) = ", TDPAR
2700 TDPAR = TDPAR + TK0
2790 RETURN

3000 SUB PLOT (T1, P1, T2, P2, CLR, RD, YF)
3010 Y1 = -RD * LOG(P1): Y2 = -RD * LOG(P2)
3020 X1 = T1 + Y1 / YF: X2 = T2 + Y2 / YF
3030 LINE (X1, Y1)-(X2, Y2), CLR
3040 IF CLR = 14 THEN 3050 ELSE 3070
3050 FOR JJ = 1 TO 150
3060 NEXT JJ
3070 END SUB