# AT 351 Introduction to Weather and Climate - Lab

ATS 351 Introduction to Weather and Climate Lab Spring 2010 Weather vs. Climate Weather tells you what to wear each day, but the climate helps you figure out what should be in your closet Units, Conversions, and Equations Peta Tera Giga Mega Kilo Hecto Deca

No Prefix Deci Centi Milli Micro Nano Pico Femto P T G M k h da d

c m n p f 1,000,000,000,000,000 1,000,000,000,000 1,000,000,000 1,000,000 1,000 100 10 1 0.1 0.01

0.001 0.000001 0.000000001 0.000000000001 0.000000000000001 1015 1012 109 106 103 102 101 100 10-1 10-2 10-3

10-6 10-9 10-12 10-15 Units, Conversions, and Equations Physical Quantity Length Mass Time Temperature Amount of substance Electric current Quantity Name Force Pressure Energy

Power Name of SI Unit Meter Kilogram Seconds Kelvin Mole Ampere Derived Unit Newton (N) Pascal (Pa) Joule (J) Watt (W) Symbol

m kg s K mol A MKS kg m s-2 (Nm-2) = kg m-1 s-2 (Nm) = kg m2 s-2 (Js-1) = kg m2 s-3 Units, Conversions, and Equations Meteorology often uses non standard units for both temperature and pressure. Conversions for temperature: (9/5 x C) + 32 = F

(F - 32) x 5/9 = C K = C + 273.15 Conversions for pressure: 100 Pa = 1 hPa = 1 millibar (mb) = .75 mm Hg 1 standard atm = 1013.25 mb = 1013.25 hPa = 760 mm Hg Local Time All the US time zones are earlier than UTC (Coordinated Universal Time), since we are west of England Our 4 main time zones (Eastern, Central, Mountain, and Pacific) are 5, 6, 7, and 8 hours behind UTC UTC does not observe daylight savings time Currently, Fort Collins is in MST (UTC minus 7 hours)

During the summer, we are in MDT (UTC minus 6 hours) Time Zone Map Atmospheric Structure and Composition & Energy 8 Chemical (Gas) Composition 9 Chemical (Gas) Composition

Each constituent has a Source: Production Sink : Destruction (e.g. Plant photosynthesis, decay See Ahrens) 10 Gas Characteristics Expand or compress due to pressure, containers, etc Easily mixed Individual molecules far apart Individual molecules have distinct mass Most common measurements: temperature, pressure, and volume

11 Atmospheric Pressure pressure = force/area Measure of the weight of air above you Force = push or pull, especially on other air molecules Compressible

More air (mass) above means more compression Air closer to the surface more dense, because compressed by the weight of the air above it Pressure decreases with height exponentially 12 13 Hydrostatic Balance

We tend to make the assumption that the atmosphere is in Hydrostatic Balance. Hydrostatic Balance is when the net upward force on a slab of air equals the net downward force. dP g dz 14 Temperature and Density

Temp is the measure of Warmer air is less dense

the kinetic energy of molecules (speed) KE = mv2 Consider the ideal gas law: P=RT If we consider constant pressure, then: P/R = T Or: Constant = T We can see then, if the temperature increases, density must decrease It follows: Colder air is more dense 15 16

Atmospheric Temperature Complicated vertical profile Can depend on atmospheric composition current conditions lapse rate: the rate at which the air temperature decreases with height 17

Layers of the Atmosphere 18 Layers of the Atmosphere Defined by changes in temperature with height Troposphere Stratosphere

Ozone absorbs solar radiation, warming results Mesosphere Sun warms surface, surface radiates No ozone, molecules lose more energy than they absorb Thermosphere

O2 absorbs solar radiation 19 Energy Conduction: Energy transfer by molecular collisions Convection: energy transfer by the motion of matter from one location to another

Ex: The sun warms the ground, and this heats a thin layer of air above the surface In general, air is a poor conductor Ex: parcel of air rising Important in our atmosphere Radiation: transfer of energy not requiring contact between bodies or a fluid between them Ex: the sun warms the surface of the earth

20 Surface Analysis Variables of interest Temperature Pressure Dew point Cloud Cover Wind direction and speed Weather occurring 21 Wind

Wind direction is named for where the wind is coming from. Expressed in either cardinal directions (N, S, E, W, NW, SE, etc.) or degrees from north 0 90 180 0 90 270

270 180 Mathematical Meteorological 22 Station Plot Wind speed, direction, and peak gust Temperature (oF)

G23 Station Pressure 72 Visibility (miles) 998 9 Current Weather Dewpoint (oF)

-16 45 Sky Cover FNL .09 Station ID 3 hour pressure change

3 hour precipitation 23 Station Plot G2 3 72 9 Station Pressure 998 -16 45

FNL .09 Sea-level pressure is plotted in tenths of millibars (mb), with the leading 10 or 9 omitted. For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values: 410: 1041.0 mb 103: 1010.3 mb 987: 998.7 mb 872: 987.2 mb 24 Deciphering Station Plot

25 Deciphering Station Plot 26 Station Plots Wind Barbs 1 kt = 0.514 ms-1 = 1.15 mph 27 Surface Analysis One of the earliest maps produced from measurements Each point contains data taken from

specific surface station Designed to relay maximum data 28 Example Station Data 29

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