How thunderstorms, tornadoes and hurricanes form
Grade 9 Science Worksheet
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Card
a dry parcel cools 10 °C per km, a cloudy one 6 °C per km, and cloud base is 125 m per °C between air temperature and dew point. Surroundings at 3 km: 4 °C.
A parcel starts at 30 °C with a dew point of 22 °C. Bo lifts it to 3 km. How warm is it, and does it keep rising?
- 8 °C, which is 4 °C warmer than its surroundings, so it keeps rising
- 0 °C, which is 4 °C colder than its surroundings, so it sinks back
- 12 °C, which is 8 °C colder than its surroundings, so it sinks back
- 20 °C, which is 16 °C warmer than its surroundings, so it keeps rising
a dry parcel cools 10 °C per km. Surroundings at 1.5 km: 14 °C. Air at 28 °C is forced up a slope to 1.5 km. Jun compares it with the 14 °C surroundings. Does lift alone start a storm?
- Yes: air that cools while rising gets warmer than the air around it
- No: the parcel is 13 °C, 1 °C colder than its surroundings, so it needs more lift or heating
- Yes: the parcel is 13 °C, 1 °C warmer than its surroundings, so it keeps rising
- Yes: the parcel is 18 °C, 4 °C warmer than its surroundings, so it keeps rising
Card
The greatest updraft speed in a storm is about the square root of (2 × CAPE), in m/s, where CAPE is the energy available to rising air, in J/kg.
A day has CAPE of 1,800 J/kg. What greatest updraft speed does Luz calculate?
- About 42 m/s
- About 30 m/s
- About 60 m/s
- About 3,600 m/s
Winds above one spot, both from the southwest
8 m/s at the ground and 28 m/s at 6 km. Card: shear of about 20 m/s or more from the ground to 6 km favors supercells.
Milo finds the shear from the ground to 6 km. Does it favor a supercell?
- Yes: 28 − 8 = 20 m/s, which reaches the 20 m/s mark
- No: 8 m/s at the ground is too weak to count as shear
- No: both winds blow from the southwest, so there is no shear
- Yes: 28 + 8 = 36 m/s, which is above the 20 m/s mark
NOAA says supercell updrafts can top 160 km/h. What is that in m/s, by Pia's math?
- About 160 m/s
- About 44 m/s
- About 2.7 m/s
- About 576 m/s
Four ocean areas (example data)
Area Latitude Water at 50 m (°C) Wind shear (m/s) A 2° N 28.0 4 B 14° N 27.5 5 C 14° N 27.5 18 D 14° N 24.0 5 Ren needs warmth to 50 m (26.5 °C or more), low shear and a latitude over 5°. Which area can support a tropical cyclone?
- Area B, which passes all three tests
- Area C, which is warm and far enough from the equator
- Area A, which has the warmest water at 50 m
- Area D, which has low shear and is far from the equator
Two disturbances over warm water (example data)
Disturbance Latitude Water at 50 m (°C) Wind shear (m/s) P 3° N 29.5 4 Q 15° N 28.0 4 Tala compares the disturbances. Which one can spin up into a tropical cyclone, and why?
- Q: its lower water temperature leaves less heat to spin up the storm
- P: the equator spins fastest, so it starts rotation well
- Q: at 15° N the Coriolis effect is strong enough to help start rotation
- P: the warmest water, 29.5 °C at 50 m, wins over latitude
One hurricane's track (example data)
Hour Over Winds (mph) 0 warm water 110 6 warm water 115 12 coast 100 18 land 85 24 land 65 Zee reads the track. What best explains the fall in winds after hour 12?
- Land cuts off the heat and moisture that warm water supplied
- Land adds heat and moisture, which spreads the storm out
- Winds fall after 12 hours, whatever lies underneath
- Friction alone slowed the storm, which still had its heat and moisture
Saffir-Simpson Hurricane Wind Scale (NHC)
Category Sustained winds (mph) 1 74 to 95 2 96 to 110 3 111 to 129 4 130 to 156 5 157 or higher NHC reports sustained winds of 105 knots (1 knot = 1.15 mph). Which category does Esme name?
- Category 1, since 105 knots is about 91 mph
- Category 2, since 105 reads directly as 105 mph
- Category 3, since 105 knots is about 121 mph
- Category 4, since 105 knots is about 158 mph
A hurricane is about 300 miles wide with an eye about 30 miles wide. What share of its area does Kira say the eye covers?
- About 33%, since the eye is one third of 100 miles
- About 10%, the same as the ratio of the widths
- About 0.1%, one tenth of the ratio of the widths
- About 1%, since area goes with the square of the width