Question

CCS/ERTH 303: Weather & Climate Name: Dew (F) 46 5.7 Section 1: Expressing Humidity Complete the table below using the provided data collected at the NWS Station in Missoula, MT,on Ist September 2015. Use this table to select the correct answers in the next 5 questions. ** Ser your pressure to 1000 mb for all calculations on the websites, and round answers to nearest degree "F and the MR's to the nearest 0.1g/kg as you carry them alone. ** a Calculate the WBD. b. Find the DPT and RH from this website: http://www.weather.gov/epz/wxcale wetbulb c. Find the saturation and mixing ratios from this website: http://www.weather.gov/ep/wxcalc_mixineratio Dry Wet Wet Sat. Relative Obs. Date/Time Bulb Temp Bulb Point Mixing Bulb Temp Humidity Mixing Depression Ration (°F) Temp Ratio COF) (F) (g/kg) (g/kg) 9/1/2015 0:00 42 74 77 9/1/2015 4:00 9/1/2015 8:00 9/1/2015 12:00 9/1/2015 16:00 26 30 15 24.1 9/1/2015 20:00 9/2/2015 0:00 - 40 59 9.0 5.3 Section 2: The Mountain While there are a number of mechanisms that can cause a parcel to rise in the atmosphere, orographic lifting is a relevant example in Missoula. In the figure below, imagine that an air parcel is moving from the left to the right and is forced up and over the mountain. Initially it will cool at the Dry Adiabatic Lapse Rate (DALR; 10°C/1000m); if it reaches the lifting condensation level (LCL) it will begin cloud formation and cool at the Moist Adiabatic Lapse Rate (MALR; 5°C/1000m). The dew-point temperature will cool at the Dew Point Lapse Rate (DPLR; 2°C/1000m), because of decreasing pressure, until reaching the LCL after which it cools at the MALR. Once the air is over the mountain and nothing is forcing it to remain elevated, it will begin to sink down towards the surface, warming at the DALR. The dew point temperature will also warm, but at the DPLR Windward Side Leeward Side та T To 2500 m - 2000 m 2000 m 1500 m 1000 m 1000 m - 500 m 12°C Sea level 20°C

Answer 1

Section 1: Expressing Humidity

a. Calculate WBD (Wet Bulb Depression)

WBD = Dry bulb temperature - Wet bulb temperature

b. Find the DPT and RH from the website

c. Find the saturation and the mixing ratios from the website

All the calculations are performed and the complete table is given below -

Date/Time	Dry Bulb Temp(oF)	Wet Bulb Temp(oF)	Wet Bulb Depression(oF)	Dew Point Temp(oF)	Relative Humidity(%)	Sat. Mixing Ratio(g/kg)	Obs.Mixing Ratio(g/kg)
9/1/2015 0:00	50	46	4	42	74	7.7	5.7
9/1/2015 4:00	45	43	2	41	85	6.4	5.5
9/1/2015 8:00	56	49	7	42	60	9.7	5.7
9/1/2015 12:00	75	57	18	42	31	19.0	5.7
9/1/2015 16:00	82	56	26	30	15	24.1	3.5
9/1/2015 20:00	64	50	14	36	35	13.0	4.5
9/2/2015 0:00	54	47	7	40	59	9.0	5.3

Section 2: The mountain

Given T = 20 oC , Td = 12 oC at sea level

For T

DALR = 10 oC/1000m i.e. 5 oC/500m and MALR = 5oC/1000 i.e. 2.5 oC/500m

Note that MALR will come into play only after Liquid Condensation Level(LCL) is reached, which is, when the air gets saturated.

For Td

DPLR = 2oC/1000m i.e. 1 oC/500m and MALR = 5oC/1000m i.e. 2.5oC/500m

MALR will come into play after LCL is reached

Windward Leeward side T Ta 2500m 2.5 2.5 °C soc 200pm 7.5°C 3.5°C 200pm .se 15oom 75c 7.500 (Soom 18 17:5c 5.5°C (odom 6 1000m soom. soom ise/lic sea level 120e lic T Tod

Calculations for Windward side

Till 1000m, T cools with DALR and Td with DPLR

*Note that LCL is reached(air reaches saturation temperature) at 1000m. After that both T and Td cool with MALR

Altitude	T	Td
0m i.e. sea level	20oC	12oC
500m	15oC	11 oC
1000m	10oC	10oC
1500m	7.5oC	7.5oC
2000m	5oC	5oC
2500m	2.5oC	2.5oC

Calculations for leeward side

On the leeward side T warms with DALR and Td warms with DPLR

Altitude	T	Td
2000m	7.5oC	3.5oC
1000m	17.5 oC	5.5 oC