GEOG1F91_Lab#2_Josh Sra_7570104

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1F91

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Apr 3, 2024

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GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 1 TEXT REFERENCE : Chapter 6 – Atmospheric Pressure, Wind and Global Circulation Chapter 7 – Atmospheric Moisture and Precipitation OBJECTIVES: This lab introduces atmospheric motion via convection cells in the atmosphere, and, coupled with adiabatic heating and cooling, describes how this circulation relates to meteorological phenomena such as cloud formation and precipitation. The instructor will first explain the processes of convection and motion, and adiabatic warming and cooling, as summarized in the rest of the introduction, and then you will study the process by means of experiments and demonstrations. The combined mechanisms of movement and heating and cooling lead directly into the evaporation and condensation process covered in the next lab. WHY IS THIS IMPORTANT? In the last lab, we saw that the effect of the energy striking the Earth’s surface is not uniform. Depending on the season or time of day (controlling the sun angle), or the nature of the surface (controlling the albedo, α, or the amount of longwave radiation being emitted, M out ), there can be quite different values of net radiation at the surface. As the atmosphere is heated from below by means of contact with the earth’s surface (via conduction), all of these factors play roles in determining air temperatures in different places. This differential heating is, in turn, responsible for the development of vertical (convective) and horizontal (advective) motions (i.e., wind ) in the atmosphere, resulting in convection cells ranging from thousands of metres (e.g., winds associated with urban heat islands - http://tinyurl.com/nshttoo ) to thousands of kilometres in size (e.g., the Hadley Cell - https://www.metoffice.gov.uk/learning/atmosphere/global-circulation-patterns ). PART ONE – CONVECTION AND MOTION The vertical movement of air may result from, for example, the overriding of warm air over a cold front, or the heating of the air near the Earth's surface by solar radiation (as seen in the previous lab) thus causing it to rise in a process referred to as convection . This experiment most closely resembles the latter example, and is representative of such natural phenomena as the Hadley Cell , thermal low pressure systems which can occur on hot summer days (often resulting in cloudiness and thunderstorms), land and sea breezes experienced along coasts and shorelines, or the urban heat island associated with cities. This portion of the lab illustrates this phenomenon, using water as a substitute for air. The experimental setup is as illustrated in Figure 2.1. As heat is applied to the one flask, “bubbles” or “parcels” of water in contact with the bottom of the flask become heated. These warmed parcels of water are less dense, and, hence, more buoyant than the surrounding water as a result of their higher temperature. Consequently, they begin to rise through the flask (as evident by the billowing plume of purple potassium permanganate used as a marker) and are replaced by cooler, denser

GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 2 water from other parts of the flask. In a short time, the entire heated flask is a relatively uniform purple due to this convective mixing. While it is evident that the heated water is less dense than cooler water, it must also be noted that warmer water occupies a larger volume than cooler water. This volumetric expansion is visible, and can be noted as a very slight rise in the water level in the heated flask and the top connecting tube. Note that, due strictly to the heating of the one flask, the water level in the heated flask is above that of the unheated flask.

GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 3 Due to this difference in water levels, there is a higher pressure at the top of the heated flask relative to the top of the unheated flask (Figure 2.2). This can also be viewed as a pressure differential, or a horizontal pressure gradient . The result is the spontaneous movement of water down this pressure gradient, from the top of the heated flask (high pressure) to the top of the unheated flask (low pressure), through the top connecting tube. The heated, purple water traces this movement. While attempting to equalize the pressures at the top of the two flasks, this process is transferring mass (i.e., water) from the heated flask to the unheated flask. As the heated flask is emptying, while the unheated flask is filling, there is an increase in pressure at the bottom of the unheated flask relative to the heated flask. (To think of this in another way, if the two flasks were originally balanced on a pan balance, this transfer of water from the heated to the unheated flask would have the effect of tipping the balance in favour of the unheated flask as it became heavier due to the transfer of water.) This establishes another horizontal pressure gradient , from the high pressure at the bottom of the unheated flask to the low pressure at the bottom of the heated flask. In order to balance this pressure differential, cool, unheated water flows across the bottom connecting tube towards the heated flask (Figure 2.3). As the cool water flows into the heated flask, it is heated and thus continues the convection cycle (Figure 2.4).

GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 4

GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 5 You are required to carefully observe and record this process as one flask of water is heated and the adjacent (and connected) flask is left unheated. As you will be working in groups, don’t forget to list the names of your lab partners in the appropriate space in the table. Use the supplied paper copy of the table during the lab to record your rough copy of the data. All of your data, observations and answers must be typed in a neat and organized fashion in the Word document supplied (available on Brightspace). PROCEDURE A. Check and record the initial temperatures of all four thermometers (they should all read approximately the same). S1 = top thermometer; S2 = bottom thermometer. Press the S1/S2 button to toggle back and forth. S1 or S2 will display in the top left corner of the digital readout. B. Observe the height of the water in the flask that will be heated. Once heating begins, it may be possible to see in increase in the water height, if you have a sharp eye and keen attention to detail . This is the result of the increase in water volume as the temperature rises and the density decreases. C. When you are ready to begin, have the Lab Instructor supply a quantity of potassium permanganate to the heated flask. Turn on the hot plate to begin heating the one flask. At this point, begin reading the temperatures of all four thermometers at one-minute intervals . To speed up the reading, have one person read the temperatures in each of the two flasks, while another person records the data. Note that condensation on the flasks may make reading difficult, so be prepared to wipe the flasks quite often. D. Record all visual observations , correlating them with the temperature readings by noting the time after the start of the experiment. E. Continue heating the flask until the purple colour is noted moving back towards the heated flask through the lower connecting tube, or at least until the purple colour has reached the level of the bottom tube in the unheated flask. This should correspond with the 15-minute mark. Question l. Observe and record the details & results of the experiment (i.e., both the temperatures & the visual observations) on the table provided. Save the information in this Word document, making sure to re-name the Word file so it is identified as yours. For example: e.g. GEOG1F91_Lab#2_Doe_John_99887766_Section13

GEOG 1F91 – Fall 2023 LAB 2 – Convection and Motion and Adiabatic Processes 6 This is necessary so we don’t receive large numbers of files with the same or similar names e.g. geog1F91assignment2 or 1F91Assignment2 or 1F91lab2 or table1. When you have completed the assignment, upload the Word file (including your data table) to Brightspace. (10 marks) EXPERIMENTAL DATA List your group’s members: TIME (Minutes) TEMPERATURE (°C) VISUAL OBSERVATIONS (at least 6-8 observations over the 15-minute experimental period) Heated Flask Unheated Flask Top Bottom Top Bottom 0 (initial) 21.3 24.5 23.4 21.3 Unheated is transparent and the regular colour of water, after the purple dye was added the water became purple at the bottom with diffusion taking place 1 21.4 24.5 23.4 21.3 Unheated is transparent water colour 2 21.4 24.5 23.4 21.4 3 21.5 24.5 23.4 21.4 Purple colour is spreading to the top of the flask 4 22.0 24.7 23.4 21.5 Unheated flask is transparent, heated flask is fully purple 5 22.3 25.5 23.4 21.5 6 22.8 26.4 23.4 21.6 7 23.3 27.0 23.5 21.7 Unheated is fully purple and unheated is defusing downwards water is slowly turning purple 8 23.8 28.0 23.8 21.9 9 24.8 29.0 24.7 22.1

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