Go or No-Go? Air Masses at the Launch Site

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Go or No-Go? Air Masses at the Launch Site

Use a launch team's weather records to explain how moving air masses change the weather.

A month of launch-site weather

Read the passage and Table 1. Then answer questions 1–4.

The Weather Briefing

1Hana Oduya, a sixth grader, won a student pass to watch a mission briefing at the Cape Halcyon Launch Center on the southeastern coast of the United States. The center, the people and the numbers here are made up, but they are based on how real launch teams use weather data. A cargo rocket was set to carry food and supplies to a space station, and the weather officer, Dagny Ferraro, had to say whether the weather was "go" or "no-go."

2Ms. Ferraro explained the two launch rules that this briefing would use. First, there can be no thunderstorms or tall storm clouds within 20 km of the launch pad, because lightning can strike a rocket as it climbs. Second, wind gusts at the pad must be less than 35 km/h.

3To show what kind of weather to expect, she shared last May's records for the launch site. Each day, her team noted which air mass was over the site. Warm, humid air often flows in from the ocean to the southeast. Cooler, drier air sometimes moves in from the land to the northwest, behind a front. On a few days, a front passed the site and one air mass replaced another. When a front arrives, the advancing air can force the air ahead of it to rise.

4She also explained what the dew point means: it is the temperature to which air must cool before its water vapor starts to condense. A higher dew point means the air holds more water vapor. On sunny days, the ground heats the air above it, and that warm air rises and cools as it goes up.

5The launch was first planned for Tuesday. Hana copied the team's noon readings for the countdown week and the readings from two other stations at noon on Tuesday.

Table 1. Last May at the Launch Site (31 days)
Air over the site	Days	Dew point (°C, avg.)	Days with storms	Storms after noon
Warm, humid ocean air	20	22	15	14
Cool, dry air from land	8	9	1	1
Front passing	3	17	3	1

1.

On what percent of the days with warm, humid ocean air did a thunderstorm form? %

2.

Use paragraph 4 and Table 1. Why were storms so much more common on days with warm, humid ocean air than on days with cool, dry air from land?

A. The dry air came with stronger sunshine, and sunshine breaks storm clouds apart as they form.B. The humid air held more vapor, so rising warm air formed more storm clouds as it cooled.C. The dry air was heavier, so it pressed down on the clouds and squeezed the water out before noon.D. The humid air was warmer, so it sat closer to the Sun and heated faster after noon.

3.

All 3 days when a front passed had storms, and on 2 of them the storms came before noon. Which explanation fits the passage best?

A. The front kept the ground from heating, so the air could not rise on those days.B. The arriving air pushed the humid air upward, so storms could form at any hour.C. The front's dry air held more water vapor, so storms formed sooner in the day.D. The front brought ocean air over the land, so its dew point rose above 22 °C.

4.

On days with warm, humid ocean air, what percent of the days had a thunderstorm that began before noon? %

Countdown week

Use paragraphs 2 and 5 and Tables 2 and 3 to answer questions 5–9.

Table 2. Noon Readings at the Launch Pad
Day	Wind from	Temp (°C)	Dew point (°C)	Gusts (km/h)	Weather
Monday	Southeast	30	23	20	Storms after 2 p.m.
Tuesday	Southwest	31	23	25	Storms by 1 p.m.
Wednesday	Northwest	24	11	50	Clear and windy
Thursday	North	25	9	15	Clear, light wind

Table 3. Three Stations at Noon on Tuesday
Station	Where	Wind from	Temp (°C)	Dew point (°C)
Inland airport	300 km northwest	Northwest	23	9
Launch pad	0 km	Southwest	31	23
Ocean buoy	150 km southeast	Southeast	28	24

5.

From Tuesday noon to Wednesday noon, the dew point at the launch pad fell by °C.

6.

Use Tables 2 and 3. Where did the air over the launch pad on Wednesday and Thursday most likely come from?

A. From over the land to the northwest, where the airport already had dry airB. From over the ocean to the southeast, where the buoy read a 24 °C dew pointC. From right above the pad, where Tuesday's storms dried out the airD. From the tops of Tuesday's storm clouds, which sank and spread over the pad

7.

Use paragraph 2 and Table 2. On which day did the weather meet both launch rules?

A. ThursdayB. MondayC. TuesdayD. Wednesday

8.

Wednesday was clear, yet the launch was still no-go. Which statement explains why, and what changed to make Thursday better?

A. The air was too cold at 24 °C, and the rules call for warmer air at launch.B. Storms were still within 20 km, and Thursday's wind blew them out to sea.C. The dew point on Wednesday was too low, and Thursday's air was more humid.D. Gusts of 50 km/h broke the wind rule, and Thursday's gusts were far lower.

9.

Circle each change from Tuesday noon to Wednesday noon at the launch pad that is evidence a different air mass had arrived.

Planning a backup date

Use Table 1 and what you learned from the countdown to answer questions 10–12.

10.

A later mission is set for a Sunday in May. The forecast says southeast winds will bring warm, humid ocean air over the site that day, with a noon dew point near 22 °C. The rocket can launch from 8 to 10 a.m. or from 3 to 5 p.m. Based on Table 1, which window is the better choice?

A. Either one, because storms in humid air form at random times of dayB. 3 to 5 p.m., because the humid air will have dried out by the afternoonC. 8 to 10 a.m., because in humid air most storms began after noonD. 3 to 5 p.m., because the morning air will be too cool for the rocket

11.

Suppose instead the forecast says a front will reach the site on Sunday morning, with cool, dry air from the northwest arriving behind it by Monday. Which plan fits the data best?

A. Wait for Monday, as long as the gusts behind the front stay below 35 km/h.B. Launch Sunday morning, since storms with a front tend to wait until afternoon.C. Wait for humid ocean air to return, since it had the fewest storm days in May.D. Launch Sunday afternoon, since the front will have cooled the ground by then.

12.

A news reporter writes, "The launch slipped from Tuesday to Thursday because the weather at the Cape changes at random." Do you agree? Write a claim, give at least two pieces of evidence from Tables 2 and 3, and explain how moving air masses changed the weather at the launch pad.