THERMODYNAMIC DIAGRAMS

1. THERMODYNAMIC DIAGRAMS

2. AEROLOGICAL DIAGRAMS DIAGRAMS USED FOR THE STUDY OF THERMODYNAMIC PROCESSES OF THE ATMOSPHERE SUCH AS DRY ADIABATIC, ISOBARIC, PSUDOADIABATIC ETC, ARE OFTEN REFERRED TO AS AEROLOGICAL DIAGRAMS. THESE DIAGRAMS ARE DEVISED TO INDICATE, IN PICTORIAL MANNER, THE DISTRIBUTION OF TEMPERATURE AND MOISTURE ABOVE A STATION.

5. COORDINATES TEMPERATURES AND HUMIDITIES ARE USUALLY DETERMINED AT FIXED PRESSURES. SINCE IT IS KNOWN THAT THE LOGARITHM OF PRESSURE IS CLOSELY RELATED TO THE ALTITUDE, ‘TEMPERATURE’ AND ‘LOGARITHM OF PRESSURE’ ARE GENERALLY USED AS COORDINATES OF THERMODYNAMIC DIAGRAMS.

6. DESIRABLE PROPERTIES OF THERMODYNAMICS • THERE ARE FOUR DESIRABLE PROPERTIES WHICH PRACTICAL THERMODYNAMIC DIAGRAMS SHOULD POSSES: • THE AREA ENCLOSED BY THE LINES REPRESENTING ANY CYCLIC PROCESS SHOULD BE PROPORTIONAL TO THE CHANGE IN ENERGY OR THE WORK DONE DURING THE PROCESS. • AS MANY AS POSSIBLE OF THE LINES, REPRESENTING BASIC PROCESSESES, SHOULD BE STRAIGHT. • THE ANGLE BETWEEN THE ISOTHERMS (LINES OF EQUAL TEMPERATURE) AND THE DRY ADIABATS (LINES OF EQUAL POTENTIAL TEMPERATURE) SHOULD BE AS LARGE AS POSSIBLE. • IN THE LOWER ATMOSPHERE, THE DRY ADIABATS (INDICATING DRY ADIABATIC PROCESS) SHOULD MAKE AN APPRECIABLE ANGLE WITH THE SATURATION ADIABATS (INDICATING PSEUDO-ADIABATIC PROCESS).

7. DESIRABLE PROPERTIES OF THERMODYNAMICS…….CONTD FOR A FINITE PROCESS WITH INITIAL AND FINAL STATES DESIGNATED BY THE NUMBER 1 AND 2, THE WORK DONE PER UNIT MASS IS GIVEN BY THE INTEGRAL THIS SUGGESTS THAT SPECIFIC VOLUME (α) AND PRESSURE (p) CUOLD BE USED AS COORDINATES TO SATISFY THE FIRST CRITERION. IN PRACTICE, HOWEVER, THE ANGLE BETWEEN THE ISOTHERMS AND THE DRY ADIABATS IS QUITE SMALL. HENCE, AN (α-p) DIAGRAM DOES NOT SATISFY THE THIRD CRITERION.

8. THE TEPHIGRAM

9. ISOHYGRICS SATURATED ADIABATS ISOTHERMS DRY ADIABATS ISOBARS INDIA METEOROLOGICAL DEPARTMENT FREE AIR TEMP(T) Stn : DELHI Date : 17 APR 01 Ht in GPM : 220M TOA : 1200 UTC (amsl) Surface Pressure : 977 hPa P O T E N T I A L T E M P E R A T U R E S C A L E O F E N T R O P Y DEW POINT TEMP (Td)

10. USES OF T- GRAM • DETERMINING MET PARAMETERS • STUDYING THE FORCES WHICH COME INTO PLAY WHEN ATMOSPHERE IS SUBJECTED TO VETICAL MOTIONS • DETERMINING THE STABILITY OF THE ATMOSPHERE • PREDICTION OF CONVECTIVE PHENOMENON

11. FEW IMPORTANT DEFINITIONS • ADIABATIC PROCESSES. AN ADIABATIC PROCESS IS DEFINED AS ONE IN WHICH A SAMPLE OF GAS NEITHER GAINS HEAT FROM NOR LOSSES HEAT TO ITS SURROUNDINGS. NO TRANSFER OF HEAT TAKES PLACE I.E., NO HEAT IS ADDED OR TAKEN AWAY FROM A SAMPLE OF GAS. • POTENTIAL TEMPERATURE. DEFINED AS THE TEMPERATURE THAT A SAMPLE OF GAS WOULD HAVE IF IT WERE BROUGHT ADIABATICALLY FROM AN INITIAL STATE P AND T TO A PRESSURE OF 1000 HPA. • MIXING RATIO (r). IS THE RATIO OF THE MASS OF WATER VAPOUR (mv) TO THE MASS OF DRY AIR (md) IN A GIVEN SAMPLE OF MOIST AIR IS THE MIXING RATIO. • SATURATION MIXING RATIO (rs). IS THE MIXING RATIO OF THE SAMPLE OF AIR WHEN IT IS COMPLETELY SATURATED.

12. FEW IMPORTANT DEFINITIONS • RELATIVE HUMIDITY. IT IS THE RATIO OF THE AMOUNT OF WATER VAPOUR ACTUALLY PRESENT IN AIR TO THE AMOUNT OF WATER VAPOUR NECESSARY TO MAKE IT SATURATE AT THAT TEMPERATURE AND PRESSURE AND IS EXPRESSED IN PERCENTAGE. • DEW POINT TEMPERATURE (Td). IT IS THAT TEMPERATURE TO WHICH MOIST AIR MUST BE COOLED DURING A PROCESS IN WHICH P AND r REMAIN CONSTANT IN ORDER THAT THE AIR BECOMES JUST SATURATED WITH RESPECT TO WATER. IF AIR IS COOLED BELOW THE DEW POINT TEMPERATURE CONDENSATION TAKES PLACE AND DEW FORMS.

13. FEW IMPORTANT DEFINITIONS • DRY ADIABATIC LAPSE RATE. IT IS THE RATE AT WHICH THE PARCEL OF UNSATURATED AIRMASS COOLS OR WARMS UP WHEN PARCEL IS LIFTED UP OR BROUGHT DOWN ADIABATICALLY. • THE LIFTING CONDENSATION LEVEL (LCL). IT IS THE LEVEL TO WHICH A PARCEL OF AIR HAS TO BE LIFTED ADIABATICALLY TO MAKE IT SATURATED. AT THE LCL, THE MIXING RATIO BECOMES EQUAL TO THE SATURATION-MIXING RATIO. • CONVECTIVE CONDENSATION LEVEL (CCL). IT IS THE LEVEL TO WHICH A PARCEL OF AIR IF HEATED SUFFICIENTLY FROM BELOW WILL RISE ADIABATICALLY UNTIL IT IS JUST SATURATED. • CONVECTIVE TEMPERATURE. IT IS THE SURFACE TEMPERATURE THAT MUST BE ATTAINED TO START THE FORMATION OF CONVECTIVE CLOUDS BY SOLAR HEATING OF THE SURFACE AIR.

14. FEW IMPORTANT DEFINITIONS • LEVEL OF FREE CONVECTION (LFC). IT IS THE LEVEL TO WHICH A PARCEL OF AIR, LIFTED DRY-ADIABATICALLY UNTIL SATURATED AND SATURATED ADIABATICALLY THEREAFTER UNTIL IT BECOMES WARMER (LESS DENSE) THAN THE SURROUNDING AIR. THE PARCEL WILL THEN CONTINUE TO RISE FREELY ABOVE THIS LEVEL UNTIL BECOMES COLDER (MORE DENSE) THAN THE SURROUNDING AIR.  • EQUILIBRIUM LEVEL (EL). IT IS THE LEVEL WHERE THE BUOYANTLY RISING PARCEL OF AIR ATTAINS THE TEMPERATURE OF THE ENVIRONMENT.

15. Saturated Mixing Ratio rs = 7 g/kg Mixing Ratio r = 5.5 g/kg RH (700hPa) = (r/rs) x 100 = (5.5/7)x`100 =78.57%

16. Te=330oA SALR NORMAND POINT 700 hPa WB Temp (700hPa)=2.5oC DALR 700 hPa  = 305oA w = 290oA ISOHYGRIC 700 hPa

17. + ive Area = CAPE Mintra Level=285hPa LCL=910hPa CCL=830hPa LFC=640hPa EL=250hPa DML = 630 hPa CT=24oC - ive Area = CINE

18. ISOHYGRIC DALR SI=T500-TP500 = -14 –(-13)= -01

19. Tp800 hPa=07.5oC Tw800 hPa= 07oC PII=Tw800 hPa-Tp800 hPa= - 0.5oC

20. TOTAL TOTAL INDEX (TTI) I- VERTICAL TOTAL INDEX (VTI) : T 850 hPa – T 500 hPa II- CROSS TOTAL INDEX (CTI) : Td 850 hPa – T 500 hPa TTI = VTI + CTI GEORGES INSTABILITY INDEX K = (850 hPa TEMP - 500 hPa TEMP) - I + (850 hPa DEW POINT) - II - (700 hPa DEW POINT DEPRESSION) -III I - REPRESENTS LAPSE RATE AND IS CALLED LAPSE RATE PARAMETER II - REPRESENTS LOW MOIST EMPERATURE III - REPRESENTS THE VERTICAL EXTENT OF MOIST LAYER

21. MCL = 860 hPa MIXING CONDENSATION LEVEL

22. CONCLUSION • THE STANDARD ELEMENTS OBSERVED FROM RADIO-SONDE ASCENTS ARE PRESSURE, TEMPERATURE AND HUMIDITY. THESE ELEMENTS CAN BE VERY SIMPLY REPRESENTED ON A TEPHIGRAM. • TWO CURVES ARE USUALLY PLOTTED AND DRAWN ON THE TEPHIGRAM FOR EACH SOUNDINGS. • ONE REPRESENTS THE FREE-AIR TEMPERATURE (T) AND THE OTHER THE DEW-POINT TEMPERATURE (Td). • FROM A PLOTTED TEPHIGRAM CERTAIN METEOROLOGICAL QUANTITIES, SUCH AS THE HUMIDITY PARAMETERS LIKE MIXING RATIO, VAPOUR PRESSURE, RELATIVE HUMIDITY ETC., AND THERMODYNAMIC PARAMETERS LIKE POTENTIAL TEMPERATURE, EQUIVALENT TEMPERATURES ETC. MAY BE EVALUATED. • BY COMPUTING THE VARIOUS INDICES IT ALSO HELPS IN DETERMINING THE STABILITY OF THE ATMOSPHERE. PREDICTION OF CONVECTIVE PHENOMENON.