How thunderstorms, tornadoes and hurricanes form

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   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: the parcel is 13 °C, 1 °C warmer than its surroundings, so it keeps rising
   • Yes: air that cools while rising gets warmer than the air around it
   • Yes: the parcel is 18 °C, 4 °C warmer than its surroundings, so it keeps rising
   • No: the parcel is 13 °C, 1 °C colder than its surroundings, so it needs more lift or heating

2. Read this first

   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.

3. 2.

   A day has CAPE of 1,800 J/kg. What greatest updraft speed does Luz calculate?

   • About 42 m/s
   • About 60 m/s
   • About 30 m/s
   • About 3,600 m/s

4. 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.

5. 3.

   Milo finds the shear from the ground to 6 km. Does it favor a supercell?

   • No: both winds blow from the southwest, so there is no shear
   • Yes: 28 − 8 = 20 m/s, which reaches the 20 m/s mark
   • Yes: 28 + 8 = 36 m/s, which is above the 20 m/s mark
   • No: 8 m/s at the ground is too weak to count as shear
6. 4.

   Noah orders the steps that give a supercell its rotating updraft. Which order is correct?

   • Shear tilts the updraft upright, then rain rolls it into a horizontal tube
   • Shear rolls air into a horizontal tube, then the updraft tilts it upright
   • Earth's spin rolls air into a horizontal tube, then the updraft tilts it upright
   • The updraft rolls air into a horizontal tube, then shear tilts it upright
7. 5.

   NOAA says supercell updrafts can top 160 km/h. What is that in m/s, by Pia's math?

   • About 576 m/s
   • About 2.7 m/s
   • About 44 m/s
   • About 160 m/s

8. 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

9. 6.

   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 A, which has the warmest water at 50 m
   • Area C, which is warm and far enough from the equator
   • Area B, which passes all three tests
   • Area D, which has low shear and is far from the equator

10. 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

11. 7.

    Tala compares the disturbances. Which one can spin up into a tropical cyclone, and why?

    • Q: at 15° N the Coriolis effect is strong enough to help start rotation
    • Q: its lower water temperature leaves less heat to spin up the storm
    • P: the equator spins fastest, so it starts rotation well
    • P: the warmest water, 29.5 °C at 50 m, wins over latitude

12. 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

13. 8.

    Zee reads the track. What best explains the fall in winds after hour 12?

    • Land adds heat and moisture, which spreads the storm out
    • Land cuts off the heat and moisture that warm water supplied
    • Winds fall after 12 hours, whatever lies underneath
    • Friction alone slowed the storm, which still had its heat and moisture

14. Winds of one storm (example data)

    Hour	Sustained winds (mph)
    0	75
    12	95
    24	115

15. 9.

    Rapid intensification means a gain of 35 mph or more in 24 hours. Did Ari's storm do it, and which categories did it span?

    • No: winds above 74 mph are steady, so a gain of 40 mph does not count
    • Yes: it gained 40 mph in 24 hours, going from Category 2 to Category 4
    • No: it gained just 20 mph in the first 12 hours, under 35 mph
    • Yes: it gained 40 mph in 24 hours, going from Category 1 to Category 3
16. 10.

    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 10%, the same as the ratio of the widths
    • About 0.1%, one tenth of the ratio of the widths
    • About 33%, since the eye is one third of 100 miles
    • About 1%, since area goes with the square of the width