The dewpoint is always lower or equal to the air temperature, hence why dew or fog often occurs during the early morning hours, when the air temperatures are typically lowest and the dewpoint highest. How could the humidity be so low, when it feels so high? The answer: dewpoint!!ĭewpoint is the temperature at which water vapor in the air condenses into liquid water, such as in the form of dew, fog, or possibly rain. You may have checked on the humidity, only to find it was at a meager 50%. Remain constant for a dry adiabatic ascent (See above discussion).Hot and sticky weather is always a staple of the summer months. Rate over 500 meters, the air parcel cools by 5 Celsius degrees,ĭewpoint = 5° C For this simple model, the dewpoint is assumed to Lift of the air is needed to saturate the air.Īir temperature = 5° C See above discussion using the dry adiabatic lapse Since the parcel only needs to cool by 5Ĭelsius degrees (= 10☌ - 5☌) to become saturated, only a 500 meter Lapse rate of 10 Celsius degrees per 1000 meters and that the surfaceĭewpoint remains constant. Assume that the air parcel cools at a dry adiabatic Just becomes saturated is 500 meters (1/2 km). The height of the cloud base, where the lifted air What is the air temperature at this level? A.3. Physical phase changes and that the dewpoint remained constant). Mountain range would the air have to be lifted in order for it toīecome saturated? (Assume no change in moisture content of the air, no How far up the west (windward) slope of the This air parcel is forced to ascend the Coastal Surface, has an initial air temperature of 10☌ and a dewpoint
(Clearly show your work for partial credit!) An air parcel is part of a Pacific maritime air mass moving ADIABATIC PROCESSES - THE MOUNTAIN BARRIER PART A. NOTE: Suggestion that b is more humidīecause of a higher relative humidity is incorrect!Ģ.
Recall that theĭewpoint is the best indicator of actual water vapor content of theĪir. Lower, but the dewpoint is essentially the same. Higher (80% as compared with 50% in a), the air temperature is Meant to illustrate that while the relative humidity in b is Since the dewpoint in each case is approximately 56☏ equivalently,īoth have a vapor pressure of approximately 15.3 mb. (Use this latter value for the nextīoth cases, a and b, have essentially the same water vapor Pressure of 15.2 mb - or 55.8☏ (using a simple interpolation), whichĬan be rounded up to 56☏. Now enter the table to find the dewpoint corresponding to this vapor Vapor pressure, by rearranging the equation from above to yield:Į = e s x RH/100% or e = 18.96 mb x = 15.17 mb. The relative humidity is known (80%), you can solve for the actual Pressure e s = 18.96 mb can determined from the Table. In this case from the air temperature = 62☏, the saturation vapor To become equal to the actual vapor pressure, e). Would reduce the value of the saturation vapor pressure, e s , Using the dewpoint temperature of 56☏, the tabularĮntry would indicate an actual vapor pressure of e = 15.30 mb (sinceĬooling the air from 76☏ to 56☏ to get saturation and dew to form Saturation vapor pressure e s at that temperature to be 30.64 Since the air temperature is 76☏, you can determine that the would have moreĪcceptable) The relative humidity is determined from RH = e/e s If air temperature were 62☏ and the relative humidityĬ. If the air temperature were 76☏ and the dewpoint wereī. Homework page) to calculate the following:Ī. Use the table for saturation vapor pressure (see bottom of 1 st Thus, you need to make this Wet-bulb depressionġ5° C - 12° C = 3° C 70% 9.6° C (10☌ is acceptable) Tables contain the Wet-bulb depression, defined as the arithmeticĭifference between the dry bulb (or air) temperature and the wet-bulb Note that the vertical columns in the Psychrometric This question involves reading (hopefully, correctly) the Psychrometric Temperature is 15˚C and the wet bulb temperature is 12☌. To determine the dewpoint and relative humidity when the air Use Tables 6.5 and 6.6 of your textbook ( The Psychrometric Tables), Answer Key to Hmk #3 Summer 2004 ATM OCN (Meteorology) 100 Answers for Homework 3 Summer 2004