Lab 1 - Weather Instruments and Measurements & Surface Weather Observations PDF

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Weather Instruments and Measurements & Surface Weather Observations...

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Lab 1: Weather Instruments and Measurements & Surface Weather Observations

1Lab

MET 205 Lab Manual

1

Weather Instruments and Measurements

DUE: 9 SEPTEMBER 2020, 12:00 NOON MOUNTAIN TIME Objectives:    

Become familiar with weather instruments used to measure pressure, temperature, precipitation, and wind speed. Record observations of temperature, dew point temperature, relative humidity, pressure, and wind speed Apply the ideal gas law to demonstrate the relationships between pressure, temperature, and density Learn how to convert between quantitative units of measurement, particularly English and Metric units

Introduction: In this lab, you will receive an introduction to the main atmospheric variables and how various weather instruments are used to routinely measure and report ever-changing weather conditions. Specifically, you will use and read a barometer, thermometer, rain gauge, hygrometer, and anemometer. Your instructor will review the purpose and operation of each instrument, and then you will be given an opportunity to make a current weather observation and compare it with official reports. You will become familiar with the importance of reporting and converting atmospheric units of measurement. You will also participate in a class exercise to discover how pressure, density, and temperature are related via the Ideal Gas Law, and then assess how these variables change with height.

Background: The atmosphere is a compressible fluid, composed of air molecules that are pulled to Earth’s surface by gravity. As a result, the molecules that make up the atmosphere are most compressed close to Earth’s surface, and atmospheric density decreases most rapidly with height there. While there is no clear “top” to the atmosphere, it thins out around 100 kilometers (km), so we can essentially consider this to be the atmosphere’s upper lid. The atmosphere can be broken up into various layers, based on how temperature changes with height. These layers are described in Chapter 1. You will be looking at these layers at the end of lab. However, if you hope to describe the state of the atmosphere at any given time and location using atmospheric variables, then you must be able to express those variables with appropriate quantitative units of value. To avoid misunderstanding, scientists around the world have agreed to adhere to an internationally recognized standard of metric units called the MKS (or SI) System. MKS stands for the basic units of length (meters), mass (kilograms), and time (seconds) in the metric system. MKS units are simple to use because length and mass units are based on powers of 10. Hence, we can

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

convert to other metric units by multiplying or dividing by powers of 10 and assigning the prefixes shown in Table 1 to either the meter or the gram.

The metric prefixes are easy to remember if you recognize that a millennium is 1000 years, a century is 100 years, and a decade is 10 years. Compare to the English system where there are, for example, 12 inches per foot, 3 feet per yard, and 5280 feet per mile. These conversions are less intuitive. Nonetheless, conversion factors are needed to change units from MKS to English units, or vice versa. Suppose we want to convert 10 miles to an equivalent distance in kilometers. There are 0.62 miles in every kilometer. To make the conversion, we simply write down the original value and multiply it by the conversion factor in a fractional format, where the final unit sought is written in the numerator. Thus,

The result tells us that 10 miles is the same distance as 16.1 km. Therefore, miles are longer than kilometers since fewer miles are needed to cover the distance. Consider another common but more complex example, where it is more important to keep track of the unit variables. Suppose we want to convert 1 mile per hour to meters per second. We need to know that there are 60 sec/min, 60 min/hr, 5280 ft/mi, and 3.28 ft/m. The conversion is written as follows:

We’ve applied 4 conversion factors in succession to change from English to MKS units, written in such a way that the units conveniently cancel out to leave us with meters per second. This example shows that the same speed reported in m/s is just under half that reported in mi/hr. It is easy to make most unit conversions using your computer, calculator, or cell phone. However, without practicing the conversions, we cannot learn to interpret the physical meaning of a given quantity based on only its units. Knowledge of the metric system is essential for all scientific applications (example: the Mars Climate Orbiter crashed while entering orbit in 1999 because the rocket scientists failed to make a simple unit conversion in their distance algorithm). Temperature is also recorded using different scales, and hence, reported with different units. We use the Fahrenheit temperature scale in the United States, but degrees Celsius are reported everywhere else. Scientists generally use the Kelvin temperature scale because, in theory, all molecular motion ceases at a temperature of zero Kelvin (K). The conversions between these three temperature scales are written as follows:

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

K = ºC + 273

ºC = ( ºF - 32 ) / 1.8

MET 205 Lab Manual

ºF = ( 1.8 × ºC ) + 32

It is useful to remember that -40 °C = -40 °F, 0 °C = 32 °F (water freezes), 10 °C = 50 °F, and 100 °C = 212 °F (water boils). Another issue faced by meteorologists is the need for a 'synchronous time'. To get a good picture of the state of the atmosphere at a given time, meteorologists around the world must all take their observations at about the same time. It would be confusing to construct a global weather map if observations were recorded at the same local time, such as dawn. To get around this problem, meteorologists have adopted a time standard known as the Universal Time Coordinate (UTC) or Greenwich Mean Time (GMT) or 'Zulu' Time (Z). All three terms essentially mean the same thing and can be used interchangeably, but UTC has been adopted as the standard for meteorology. UTC is a time coordinate based on a 24-hour clock (0000 is midnight, 1200 is noon, 2300 is 11:00 PM), which coincides with the local time in Greenwich, England. Refer to the page linked on Canvas for a guide on converting between UTC and local time. Note that Mountain Standard Time (MST) is seven hours behind UTC, while Mountain Daylight Time (MDT) is 6 hours behind UTC. In meteorology, as in all physical sciences, no variable can be measured perfectly. We will not worry about significant digits in this class. However, the rule of thumb will be that most calculations should merely retain one digit after the decimal (tenths digit), and never more than 3 digits (thousandths digit). For example, if you calculate the barometric pressure to be 853.666667 mb, simply express your final answer as 853.7 mb (rounded).

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Name Jake Woodrum Date/Time September 8th 2020 Part 1: Weather Instruments and Observations Weather Instruments Match the following weather instruments with the atmospheric variable that they measure and an example of appropriate reported units for that variable. To do this, match the appropriate number (variable) and letter (units) to each instrument (column 1) Barometer

__5____ ___c___ 1. Rainfall Rate

A. Meters per second (m s-1)

Thermometer

___4___ ___D___2. Humidity

B. Degrees Fahrenheit (oF)

Rain Gauge

____1__ ___E___ 3. Wind Direction

C. Millibars (mb)

Hygrometer

___2___ ___F___ 4. Temperature

D. Degrees (o)

Anemometer

___6___ ___A___ 5. Pressure

E. Millimeters per hour (mm h-1)

Wind Vane

___3___ ____B__ 6. Wind Speed

F. Percent (%)

Weather Observations

1. Look up the current conditions at the UNC campus weather station (See Lab – General Resources on Canvas: Ross Hall Rooftop Weather). Please provide a screenshot depending on when you obtain this information. a. What is the current reported temperature (oF), relative humidity (%), and wind speed (mph)? Reported Temp – 32.9 Degrees Fahrenheit Relative Humidity – 92% (current) Wind Speed – 9MPH(current)

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

b. Convert the reported wind speed from miles per hour (mph) to knots (kt): 9 MPH is 7.82079 in Knots

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

2. SHOWING ALL WORK (see unit conversion examples in the Introduction), perform the following calculations and LABEL your answers with APPROPRIATE UNITS: b. Convert your recorded outside temperature from Fahrenheit to Celsius: (32.9-32)/1.8 = .5 Degrees Celsius

c. Convert your answer in part (a) to Kelvin, K: .5+273 = 273.5 K

d. Convert your recorded outside barometric pressure value from millibars to Pascals: (There was no “current” recorded pressure so with a low of 29.82” and a high of 30.15” I feel 29.5 is a good current guess as it is fairly between the two) 29.5*100 = 2,950 Pascal

e. Convert your outside wind speed value from knots to kilometers per hour: 7.82*1.852 = 14.48 KPH

f. Convert your answer from (e) to meters per second:

14.48/3.6 = 4.02 MPS

3. Answer the following about time coordinates: a. Write down the local date and time that you recorded your weather observations today: Greeley Colorado – UNCO Weather Station – September 8th, 2020 - 9:00 AM

b. Is today’s date representative of Mountain Daylight Time (MDT) or Mountain Standard Time (MST)? Todays date and time is representative of Mountain Daylight Time (MDT) c. Given your answer to (b), convert the local date and time of your observations to UTC. Write out any calculations necessary to get your answer: September 8th, 2020 - 3:00PM (+6hours from MDT)

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Surface Weather Observations Objectives:   

Interpret symbols on weather maps from surface station plots Draw isopleths and centers of both high and low pressure on real surface maps Relate surface map features to various weather conditions.

Introduction: In this lab, you will gain experience in reading and interpreting surface weather maps. You will be provided with some idealized examples to learn how to identify various weather information reported at specific locations, and then you will practice drawing isolines of various weather parameters, including temperature. Finally, you will make use of your new skills and perform some basic analysis on real surface weather maps.

Background: Extensive networks of instruments record weather data around the globe. In particular, the Automated Surface Observing System (ASOS) comprises thousands of weather instrument stations that collect weather observations at the surface every hour. The spatial pattern of various weather variables at a particular time is portrayed visually on a surface weather map. This display provides ease of interpretation for meteorologists. The skill of interpreting and understanding surface weather maps can also be used to recognize subtle details in regional weather conditions that are specific to particular interests (e.g., travel, outdoor activities, trained severe weather spotting). However, surface maps can present a confusing picture to anyone without knowledge of the conventions used for such a display. ASOS data are plotted on surface weather maps using standardized conventions. This convention is known as a surface station model. Each station model will have the following atmospheric variables presented (Table 5-1): Table 5-1: List of primary surface station model weather variables and basic interpretation of plot convention Variable Units Interpretation o Temperature F Value rounded to whole degrees o Dew-point F Value rounded to whole degrees Sea Level Pressure

mb

Includes tenths digit but drops decimal point; must add 9 or 10 at beginning to interpret value Significant Weather symbol See Figure 5-1 for list of weather symbols Wind Speed knots Wind barbs plotted on flag staff Wind Direction degrees Flag staff indicates direction wind is blowing from Cloud Cover symbol Fill in station circle with appropriate shading, based on fractional cloud coverage Figure 5-1 below illustrates the conventions of the surface station model, used to plot surface observations at the location where those observations were recorded:

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Image Source: NOAA (Public Domain)

Figure 5-1: Surface Station model example with visual key of symbols for significant weather, cloud cover, wind speed, and wind direction. Note DRIZZLE follows the same format as rain and snow, but with a comma symbol: , , = light drizzle, etc. Surface maps of station model plots provide an essential depiction of weather but can suffer from clutter. Weather maps are most useful when their information is analyzed in some fashion. One way to simplify the map is to draw isopleths, or lines connecting locations that have the same value of an atmospheric variable. Such lines may be referred to as contours, and the process of drawing an isopleth is often called contouring. Several kinds of isopleths may be used. The following are examples of the most common isopleths: ISOBAR ISOTHERM ISODROSOTHERM ISOTACH

isopleth of equal pressure isopleth of equal temperature isopleth of equal dew-point isopleth of equal wind speed

Today’s meteorologists often use computer programs to draw isopleths. In this lab, you will be drawing some of your own isobars and isotherms, in order to better understand the information they provide. Isotherms (and isodrosotherms, FYI) are drawn in 5oF intervals, including the 0oF contour, whether that specific value can be contoured on the map or not (e.g., 50, 55, 60, 65, 70). Isobars are drawn in 4-mb intervals, including the 1000-mb isobar, whether that particular value can be identified on the map or not (e.g., 992, 996, 1000, 1004, 1008, 1012). Once isobars are

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

displayed, locations of relative high pressure are often denoted with a BLUE, capital ‘H’ symbol. Locations of relative low pressure are often denoted with a RED, capital ‘L’ symbol. Some surface maps might only contain station model plots, displayed at various locations across the country. Other surface maps might only display various isopleths, such as isotherms and isobars, with regions of high and low pressure labeled with appropriate symbols. Other maps may contain a combination of station model plots with isopleths overlaid. Figure 5-2 below displays a surface map of the contiguous U.S. from February 28th, 2015 at 22 UTC. The map shows various station model plots around the country, with overlaid isobars of sea level pressure. Regions of high and low pressure are labeled with appropriate symbols.

Figure 5-1: Analyzed surface map from 28 February 2015 at 22 UTC

Enough background information! It’s time to start becoming familiar with surface weather data and perform some simple analyses. Good luck!

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

Date/Time September 8th, 2020 @9:00 AM

Name Jake Woodrum

Part 1: Station Model Interpretation 1. Decode the requested information from each of the following surface station models. And don’t forget to include proper units:

Temperature

62 oF

Temperature

37 oF

Dew-point Temperature 43 oF

Dew-point Temperature 16 oF

Sea Level Pressure

125 MB

Sea Level Pressure

948 MB

Cloud Cover

none

Cloud Cover

Half

Wind Speed

5 Knots

Wind Speed

Calm

Wind Direction

Calm

Temperature

78 oF

Wind Direction

Temperature

South

59 oF

Dew-point Temperature 57oF

Dew-point Temperature 70 oF

Sea Level Pressure

948MB

Sea Level Pressure

017 MB

Cloud Cover

Full Coverage

Cloud Cover

¾ Coverage

Wind Speed

15 Knots

Wind Speed

15 Knots

Wind Direction

North

Wind Direction

South-West

Lab 1: Weather Instruments and Measurements & Surface Weather Observations

MET 205 Lab Manual

2. Look at the station models provided (Stations 1 and 2 below), and answer the following:

Station 1

Station 2

a. What is the significant weather being reported at station 1? Very Cloudy with High winds of 20 Knots and a light drizzle b. What is the significant weather being reported at station 2? Very Cloudy, below freezing, with HEAVY rain c. Estimate the relative humidity of the air at the surface at station 2? Im not to sure how close the correlation of light, moderate, and heavy rain compares to humidity, however, I believe that the more humidity in the air, the more intense rain we will get! So maybe 80%humidity at station 2. HINT: No need to perform a calculation in (c). Just compare the reported temperature and dew-point values.

Part 2: Contouring Isopleths One must follow some basic rules in order to contour correctly. They are:  

 

Before drawing any lines, scan the data to locate the areas of minimum and maximum values; this will help to get an overall view of the data distribution. Choose an intermediate valued isopleth to draw first so that the high data values fall on one side of it, and the low data values fall on the other. This practice divides the map into two smaller pieces that can be further divided by additional isopleths. All isopleths should have at least one data point on each side. Do not draw isopleths into or through regions were no data is available (i.e., don’t analyze “off the map”). Isopleths should never branch, merge, or intersect; instead, sometimes it is necessary to draw two consecutive isopleths of the same

Lab 1: Weather Instruments and Measurements & Surface Weather Observations



MET 205 Lab Manual

Isopleths should appear smooth and continuous. Where interpolation is necessary, the spacing should reflect a steady transition between available values (i.e., linear interpolation).

1. Consider the map of idealized station models, below. The 60oF isotherm has already been drawn. Notice that the isotherm is smooth and represents perceived curvature in the field. The isotherm is drawn directly through station centers that are reporting that exact value. The ends of the isotherm are both labeled with the appropriate value of temper...