Week 4 - Orographic Lift and Lapse Rate Lab Instructions Please carefully read and complete this lab prior to attempting Week 4 Quiz. Calculations and questions answered in this lab will be needed to answer questions #19-30 on Week 4 Quiz. You will also be required to upload this document for Question #31. Introduction Orographic lift refers to the forced lifting of air as it travels over high elevation. As elevation forces an air parcel to ascend, the air temperature cools at the dry adiabatic lapse rate (10oC every 1000 meters) and the dew-point temperature cools at 2oC every 1000 meters. Once the air temperature cools to the dew-point temperature the air parcel becomes saturated. The temperature and dewpoint temperature of a rising saturated air parcel cools at the moist adiabatic lapse rate (5 oC every 1000 meters). Once the air parcel reaches its peak and begins to descend the air temperature warms at the dry adiabatic lapse rate (10oC every 1000 meters) and the dew-point temperature warms at 2oC every 1000 meters. See the image below as an example of orographic lift. Note in this example the moist adiabatic lapse rate is 6oC every 1000 meters. This process forms clouds and precipitation along the windward slopes. In the western United States, the west side of the Cascades and Sierra Nevada Mountain ranges can receive excessive rainfall and snowfall as air is forced to rise significantly to travel over the mountains. Along the leeward slopes conditions can be much warmer and drier. Objectives The goals of this lab include: • understanding orographic lift and weather associated with the windward and leeward slopes of mountains. • understanding the role of dry and moist adiabatic lapse rates in cloud formation • understanding the dew-point temperature lapse rate. Assignment Answer the following questions, in the spaces provided. These responses will be needed to answer questions #19-30 on Week 4 Quiz. Then upload this document for Question #31. Please make sure to include units in your responses. Below is a diagram of air approaching a mountain as it travels from west to east. Once reaching the mountain it is forced up from sea level (Location A) over the mountain before reaching the mountain’s peak at Location D. Afterwards, it sinks back to sea level (Location G). Determine the air and dew-point temperatures of the air as it ascends and descends. 1. Calculate dew-point temperature at Location A using the following formula: 100−𝑅𝐻 𝑇𝑑 = 𝑇 − ( 5 ) where Td is dew-point temperature, T is air temperature, and RH is relative humidity. Please show work and include units. 2. Determine the temperature and dew-point temperature for all locations from the orographic lift diagram. Remember the following lapse rates when completing the table below: a. Dry adiabatic lapse rate is 10oC every 1000 meters b. Moist adiabatic lapse rate is 5oC every 1000 meters. c. Dew-point temperature lapse rate 2oC every 1000 meters. Location Temperature A 30OC B C D E F G 3. At what elevation does the cloud base form? 4. At what location(s) is the relative humidity 100%? 5. What locations are along the windward slope of the mountain? 6. What locations are along the leeward slope of the mountain? Dew-Point Temperature
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