Exam 1 (Chaps. 1-6 of the notes)

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1 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 1 Exam 1 (Chaps. 1-6 of the notes) ATS 541 students: Answer all questions ATS 441 students: You may delete problem 3 or problem 5 1. [10 pts] a) Check the following quantities that are conserved when unsaturated air experiences an adiabatic expansion (e.g., by vertical lifting with no mixing)? dewpoint temperature (T d ) enthalpy (h) entropy (s) equivalent potential temperature (θ e ) mixing ratio (r v ) potential temperature (θ) relative humidity (f) water vapor pressure (e) wet-bulb potential temperature (θ w ) wet-bulb temperature (T w ) a) Check the following quantities that are conserved when saturated air is lifted adiabatically (no mixing, and all condensed water stays with the parcel)? dewpoint temperature (T d ) enthalpy (h) entropy (s) equivalent potential temperature (θ e ) mixing ratio (r v ) potential temperature (θ) relative humidity (f) water vapor pressure (e) wet-bulb potential temperature (adiabatic, θ w ) wet-bulb temperature (T w )

2 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 2 2. [30 pts] Consider a parcel with the following thermodynamic values: p = 900 hpa T = 25 C r v = 10 g kg -1 Using the skew-t diagram on the following pages, find the following parameters graphically. Also write the equation that would be used to determine the most precise values. a) saturation point T and p values (T sp and p sp ; give equation for T sp only) b) saturation mixing ratio c) potential temperature d) equivalent potential temperature f) wet-bulb potential temperature g) dew-point temperature h) relative humidity i) vapor pressure j) the temperature of a parcel that ascends adiabatically to 600 mb k) the adiabatic mixing ratio of the parcel at 600 mb Show all work on the skew-t diagrams on the next two pages.

3 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 3

4 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 4

5 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 5 3. [15 pts] What is the volume, in m 3, of 5 kg of dry air at 300 mb and -40 C?

6 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 6 4. [10 pts] A parcel of moist air has a total pressure of 975 hpa and a temperature of 15 C. If the mixing ratio is 1.8 g kg -1, what are the water vapor pressure and the virtual temperature?

7 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 7 5. [15 pts] An isolated rain drop that is evaporating into air with a temperature of 18 C has a water surface temperature of 12 C. a) Find (using a skew-t) the mixing ratio of the air. b) Indicate what equation you would use to solve this problem precisely.

8 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 8 6. [20 pts] a) Convert the First Law of Thermodynamics from the T, α form (dq = c v dt + pdα) to the T, p form. Show all steps. b) Derive potential temperature (θ) from this form (dq = c p dt - αdp) of the First Law c) Explain why a correction factor in the exponent is used when water vapor is present.

9 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 9 Equations and constants pα = (R*/M)T = RT p = ρ m R d T v. e = ρ v R v T dq = c v dt + pdα. dq = c p dt - αdp. dq = Tds = du + pdα. Tα η-1 = const (T c vα R d = const) Tp -κ = const (T c pp -R d = const κ = R d /c p and η = c p /c v. pα η = const (p c vα c p = const) c pm = c pd ( r v ) R m = R d ( r v ). θe Lvlr vs = θexp cptsp θ e 2675r = θ exp Tsp vs ds dq T rev θ = p0 T p R c d p ( r )) v f u Ts g = u - Ts + pα dp/dt = Δs/Δα = -ΔH fusion /(TΔα) dlne s /dt = L vl /(R v T 2 ) e s (T) = Ae -B/T A = 2.53x10 8 kpa, B = 5.42x10 3 K r v = m v /m d = εe / [p-(1-e)e] εe/p q v = εe / [p-(1-e)e] ε = f = r v / r vs (T,p) = r vs (T d,p)/r vs (T,p) e/e s (T) T v T(1+0.61r v ) T d = T d (r vs,p) = B Aε ln rp v = f(r v,p) T iw = T - (L lv /c p )[(ε/p)ae -B/T w - rv ], T ie = T + L lv r v /c p. T sp 2840 = lnT ln e χ = ρ m [r vs (T sp,p sp ) - r vs (T sat,p) θe=const ]

10 10/12/06 ATS Atmospheric Thermodynamics and Cloud Physics 10 θ = T e K 1000 p (1 0.28r ) v exp r Tsp v ( r ) v c v = 717 J K -1 kg -1 c p = J K -1 kg -1 c wv = 1463 J K -1 kg -1 c wp = 1952 J K -1 kg -1 R d = 287 J kg -1 K -1 R v = J kg -1 K -1 L vl = 2.50 x 10 6 J kg -1 (0 o C) latent heat of condensation (function of T) L vl = 2.25 x 10 6 J kg -1 (100 o C) L il = 3.34 x 10 5 J kg -1 latent heat of melting L vi = 2.83 x 10 6 J kg -1 (0 o C) latent heat of deposition L vl = ( at c ) x 10 6 J kg -1, where a = C -1 and T c is the dry bulb temperature in C. Table 5.1. Saturation vapor pressures over water and ice, and latent heats of condensation and deposition. T ( C) e s (Pa) e i (Pa) L vl (J kg -1 ) x 10 6 L vi (J kg -1 ) x

Chapter 5. On-line resource

Chapter 5. On-line resource Chapter 5 The water-air heterogeneous system On-line resource on-line analytical system that portrays the thermodynamic properties of water vapor and many other gases http://webbook.nist.gov/chemistry/fluid/