Three Cities at 50°N: Planning for Winter Heat and Water

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Three Cities at 50°N: Planning for Winter Heat and Water

Use wind belts and ocean currents to explain why cities at one latitude differ.

Compare the three cities

Read the passage and Table 1, then answer questions 1–5.

The Future Cities Challenge

1Noor Castellanos's sixth-grade class is taking part in a Future Cities challenge. Each team advises a city planning office on how much energy homes will need for heating and how to plan the water supply. The cities are made up, but their data are based on real cities. All three lie at about 50° north latitude (50°N) on the same continent, so they receive about the same sunlight through the year. Westhaven is on the west coast, with the ocean to its west. Plainsview is in the middle of the continent, more than 1,500 km from any ocean. Eastport is on the east coast, with the ocean to its east.

2Planner Ingrid Mbeki gave the team a model of how air and ocean water circulate. Sunlight strikes Earth most directly near the equator, so the equator is heated more than the poles. This uneven heating sets air and ocean water moving, and the moving air and water carry heat from warm regions toward cold ones. Because Earth rotates, moving air is turned to the side instead of flowing straight north or south. As a result, the winds near the ground form wide belts around the planet. Between about 30° and 60° latitude, the winds usually blow from the west toward the east. They are called the westerlies.

3Winds also push on the ocean's surface and drive currents, and the coasts of the continents steer the currents into giant loops. Off Westhaven, the sea stays mild all winter, at about 8 °C. Off Eastport, a cold current flows south from the Arctic, and the sea is near 0 °C in winter. Ocean water warms and cools much more slowly than land does, so air that has just crossed an ocean tends to be mild in winter and cool in summer.

4In Westhaven, about 70% of the yearly precipitation falls from October to March, when more storms arrive on the westerlies. Home heating in Table 1 is the energy a typical house uses for heating in one year.

Table 1. Three Cities at About 50°N (long-term averages)
City	January avg. (°C)	July avg. (°C)	Precipitation (mm/yr)	Home heating (kWh/yr)
Westhaven (west coast)	4	18	1,500	9,000
Plainsview (inland)	−16	20	500	18,000
Eastport (east coast)	−5	16	1,400	15,000

1.

The yearly temperature range is the July average minus the January average.

The yearly range is °C in Westhaven and °C in Plainsview.

2.

A typical Plainsview home uses times as much heating energy each year as a typical Westhaven home.

3.

Which explanation of Westhaven's mild winters fits the passage and Table 1 best?

A. Warm air rising from the city's buildings keeps its winter air from cooling.B. Westerly winds carry air that has just crossed the mild ocean onto the city.C. Westhaven gets more direct winter sunlight than the other two cities.D. Westhaven lies closer to the equator than Plainsview and Eastport do.

4.

Eastport is also on a coast, yet its January average is 9 °C colder than Westhaven's. Which explanation fits the model best?

A. Its west winds arrive after crossing the cold continent, and its sea is cold.B. Eastport gets more precipitation than Westhaven, and the rain chills its air.C. The sea near Eastport cools down faster in winter than the land around it.D. Eastport is farther from the equator, so its winter sunlight is weaker.

5.

Why does Plainsview have the largest yearly temperature range of the three cities?

A. The westerlies bring ocean air to Plainsview before the coasts.B. Its low precipitation lets the cold winter air hold extra heat.C. It gets the most sunlight in July and the least sunlight in January.D. It is far from any ocean, and land heats up and cools down quickly.

Use the circulation model

Use paragraphs 2 and 3 and Table 1 to answer questions 6–9.

6.

Match each pattern to the cause the model gives for it.

7.

Which pair of data is the best evidence that an upwind ocean, not latitude, keeps Westhaven's winters mild?

A. The January averages of Westhaven and PlainsviewB. Westhaven's January average and its precipitationC. The July averages of Westhaven and EastportD. The precipitation of Plainsview and Eastport

8.

A fourth city, Sunmar, is on the west coast of the same continent at 15°N. There, the winds near the ground usually blow from the east (the trade winds). Compared with Westhaven, where does most of the air reaching Sunmar come from?

A. From over the ocean to its west, because trade winds blow from the westB. From over the ocean to its west, just like the air reaching WesthavenC. From over the land of the continent, so the ocean affects it lessD. From over the North Pole, carried south by the trade winds

9.

Use paragraph 4 and Table 1.

From April to September, Westhaven gets about mm of precipitation.

Advise the planners

Answer questions 10 and 11.

10.

Suppose the cold current off Eastport were replaced by mild water like the sea off Westhaven. Based on the model, how would Eastport's winters most likely change?

A. Rainier but just as cold as now, since sea temperature affects only how much precipitation fallsB. Somewhat milder, but likely still colder than Westhaven's, since its west winds still cross the cold continentC. Just as mild as Westhaven's, since the temperature of the nearby sea sets a city's whole climateD. Colder than now, since milder sea water would pull more heat out of the air over the city

11.

An Eastport council member says, "We are a coastal city at the same latitude as Westhaven, so we should plan for the same heating energy per home." Do you agree? Write a claim, give at least two pieces of evidence from Table 1 and the passage, and explain your reasoning using the westerlies and ocean currents.