EOSC 114 - Storms + Waves units

types of lightning: cloud to ground

• negative (-) charge most common, can also be positive (+)

• leaders moves too fast ot be seen by eye or cameras

• to make a spark in air, you need approximately 3 billion volts / km

• more powerful, esp +

types of lightning: cloud to cloud

• doesnt touch the ground

• jumps from cloud to cloud

types of lightning: intra-cloud

• occurs within a single cloud, doesnt touch ground

• might not see visible bolt, sometimes looks like a flash within a cloud

lightning safety

• 30/30 rule: if 30 sec or less btwn when u see light flash + hear thunder, move indoors

• if stuck outdoorsL avoid: small stuctures, metallic objects nearby, trees, water, open fields

thunderstorm clouds

thunderstorm evolution of cells

• made of large cells evolving abt 15-45 min

• most ts has 2+ cells, each in diff evo stage (called multicell ts)

• sometimes v large rotating single cell ts forms (called supercell ts)

supercell types

• low precipitation

  • can produce lots of hail

• classical

  • rainy downdraft, rain-free updraft

• high precipitation

  • rainy updraft

thunderstorm life cycle

1. cumulus stage (updraft, no rain, no anvill)

2. mature stage (up & down drafts, heavy rain, crisp anvill)

storm hazards

• rain downpours

• downbursts & gust fronts (of air)

• haboobs (sand storms)

squall lines

line of thunderstorms

• tornado outbreaks often associated with this

• often forms along cold fronts

mammatus clouds

cloud striations

virga clouds

• related to downbursts

storm can create dense air where rain falls; due to evaporative cooling of ‘virga’: precipitation that evaporates before it reaches the ground

haboobs and arc clouds

• related to downbursts & gust fronts

• haboobs - if dry ground

• arc clouds - if moist air

downbursts & gust fronts

downbursts - falling air from storm

• Downdraft speeds of 20 to 90 km/h.

• Horizontal wind speeds near ground of up to 250 km/h.

• Microbursts are small diameter (≈ 1 km) downbursts.

gust fronts - leading edge of cool air

• can form shelf cloud

• marks sudden wind shift

• moves ahead of storm

humidity - saturation - latent head

humidity - moisture in air, converts to latent heat

latent heat - energy produced when water vapour condenses to liquid

saturation - when air becomes saturated it has 100% moisture + cannot hold more, trigger point where energy gets released

advection + adiabatic cooling

advection - movement of air by wind

• Can continuously feed a storm system = longer lasting storm

adiabatic cooling - as air rises, pressure drops → air expands → cools

• Cooling leads to condensation

• heat cannot leave the system

best thunderstorm viewing

• off to the side of the storm path

• preferred side is to the southeast of the storm (at X)

• look at the storm toward northwest

• resulting supercell storm looks like the sketch at upper left

fujita scale

meausres tornadoes based on amt of damage to buildings

EF0 = v weak, might break few windows

EF5 = extreme, destroy entire buildings like GONE

tornado evolution

from supercell (rotating thunderstorm)

• 3 stages

  • developing (dust whirl, funel cloud, not connected to ground yet)

  • mature (fully formed, at strongest)

  • dissipating (rope)

tornado outbreaks

6 tornadoes in 1 day and 1 region

or many tornadoes in a week

mesocyclones

inside a supercell storm

rotating updraft

forces in atmosphere

buoyancy force - vertical (causes updrafts & downdrafts)

pressure-gradient force (PGF) (horizonal or vertical, depending on PGF)

acceleration

changes of velocity (v) during time interval (∆𝑡𝑡 ), where velocity has both speed and direction.

measured as velocity (m/s) change per time (s) = acceleration units of (m/s2)

hail

tiny crystals of ice swept into thunderstorms updraft (usually supercell)

collide w supercooled water - liquid w temp below freeezing

water freezes, ice grows

wave properties

crest = highest point

trough = lowest point

wave height = vertical disatance from crest to trough

amplitude (a) = H/2 (half of the height) above or below sea level

steepness = H/L (height divided by wavelength)

wave anatomy: motion

period (T) = time (in sec) btwn successive cycles (or time it takes 2 crests to past a fixed point)

frequency (f) = # of cycles per 1 second (in hertz; 1 Hz = 1 cycle per second); f = 1/T

celerity, c = L/T, wavelength per time perod (eg meters per second) often js called speed

rogue waves

created by constructive interference btwn 2 smaller waves

what is a seiche?

standing waves oscillating in a closed or semi-enclosed body of water (lakes, bays etc) - great lakes esp

has long wvlengths & periods

• period of a seiche is

what direction do tornadoes move

SW to NE (in N. America)

continuity

• Air molecules tend to spread themselves smoothly and evenly

• They don't leave any gaps (i.e., they don't leave a vacuum)

• They don't get bunched together