Storms 2: Supercells, Rain and Air Upbursts

Satellite imaging

Satellite

Visible Imaging: show clouds during day time only

IR (infrared) images show clouds during both day and night

What does radar imaging show?

Precipitation inside the storm

in updraft, downdraft, stem of mushroom cloud

dbZ

a disaster intensity scale for radar echo strength

• indicator of Rainfall Rate

• dbz (radar echo intensity (in decibles)

• Scale: 0.1-2 light, above 90 (extreme)!

Mesocyclone

A rotating thunderstorm ( includes supercells)

more info about squall lines

Many thunderstorms in a linear/quasi linear line

• forms a cold-front! (front of thunderstorm direction is cold!)

• Can cause gust front or gustnados

3 types of supercells and what they do

1) low precipitation- LP supercell, produces lots of hail

2) classic supercell- rainy downdraft, rain-free updraft

3) high precipitation- HP supercell, updraft mostly surrounded by rain

What does a rainfall rate of 90-100 and a Radar Echo intensity of over 50dbZ mean?

extreme rain fall (downpours can cause flash floods!!)

Downburst

What: cold dense air sinking that come down from thunderstorm

Why: thunderstorm can create dense air where rain falls; due to evaporative cooling

Risks: often invisible but a hazard to aircrafts

Gust front

what: leading edge of cold horizontal straight line winds

why: downburst air hit ground & spreads outward in straight lines

visible: haboob (if dry ground); arc cloud (if moist air); gustnado

risk: can blow down large trees and destroy weak structures, hazard to aircraft take off and landing

safety: avoid weak buildings and trees

What is a haboob?

A sand storm caused by gust front

Mixing ratio

The amount of water vapour divided by amount of all other gases

ex. 2 parts water vapor with 5 parts all other gases 2/5=0.4

Saturation

When Mixing ratio—> equillibrium:

condensation rate = evaporation rate

What is saturation value important for?

is important in controlling atmospheric humidity

• warmer air can hold more water vapour at equilibrium than cold air!

• air that contains max water vapour = saturated (cloudy//foggy). air with less is unsaturated!

What is the relationship between Saturation mixing ratio and temperature?

Its exponential. As temperature goes up, so does the mixing ratio (so it gets more saturated)

Advection

movement of air by the wind. water vapor can be advected into a thunderstorm by the wind

How do storms strengthen (heat wise)?

when latent heat—> sensible heat

When does condensation occur?

When the saturation humidity value becomes smaller than actual humidity value

condensation does what 3 things?

1) releases latent heat back into sensible heat—> makes storms warmer

2) reduces the humidity down to equilibrium (saturation) value

3) produces or increases liquid cloud drops—> become rain drops

What the difference between a mesocylones and supercell?

They are both rotating thunderstorms

however:

Mesocyclone are ANY rotating thunderstorms

Super cells are very large and single-cells (and cause the most violent weather!)

Explain a LP supercell

It can produce lots of hail

Explain a classic supercell

rainy downdraft & rain-free updraft

Explain a HP supercell

supercell updraft mostly surrounded by rain

Explain a Hybrid or “mix-mode storm”

They are in between or contain 2 more types of HP, Classic, or LP supercells

What is a key safety measure to remember during flash floods if you are in a car?

Do not attempt enter flood water (or drive through it) if you dont know the height of the water before you. Even if it looks shallow.

What are 2 big hazards for aircraft?

Downbursts and Gustfronts

Haboobs (dry ground) , arc clouds (moist air) , gustnados are all examples of?

Gust fronts

What is the composition of Air

0-4% water vapor

78% nitrogen

21% oxygen

the rest trace gases

Humidity formal definition

the amount of water vapor in the air

Mixing Ratio Question: if you mix 2 parts water vapor with 5 parts other gases, what is the mixing ratio?

r=2/5= 0.4

Mixing Ratio Question 2: if you mix 78 parts (nitrogen) + 21 parts (oxygen) + 1 part (water), what is the mixing ration?

r= 1/ (78+21)= 1/99 = 0.011

SATURATION VALUE

Maximum humidity that air can hold

If air is cloudy or foggy, what does it mean?

The air is saturated / high saturation value

When a thermal of unsaturated air rises adiabatically, what happens?

the thermal cools roughly 10º celcius/ km rise

• cooler air hold less water as water vapour

• so some vapour must condense into liquid droplets

• condensation releases latent heat

What type of energy does conensation release?

Latent heat!

Adbiatic Cooling

Changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or decents in the atmosphere

with no exchange of heat with the surronding air