Weather or Not | Hitting homers a breeze

Citizens Bank Park, a launching pad for long balls, gets an assist from the wind.

Posted: August 27, 2007

When Jim Thome first walked onto the field at Citizens Bank Park, he had a sensation akin to that of a very hungry man entering a bakery and picking up the scent of a buttercream layer cake.

Something was in the air, and he knew he was going to like it.

Thome, who hit 47 home runs in 2003, the Phillies' last year at the Vet, still remembers that first batting practice, on April 3, 2004, as the ball club prepared to open its brand-new stadium with an exhibition game.

"The ball carried really well," Thome recalled on a June visit with his current team, the Chicago White Sox.

Really well.

It wasn't long after opening day that fans started calling the park "cozy," a "bandbox" and a "joke." The phenomenon was the buzz of the dugout, too.

Dave Montgomery, the Phillies' president, insists that the club did not intend to make the park a crowd-pleasing, homer-friendly arcade. The outfield dimensions are similar to those of Veterans Stadium - and, statistically, the Vet favored neither hitters nor pitchers.

So what is it?

The team has gradually come to the conclusion Thome says he sensed that very first day: Something is in the air. Specifically, wind. While players such as Braves star John Smoltz and former Phillies closer Billy Wagner have expressed skepticism, several experts say the atmospheric argument makes sense.

Statistics alone give a strong hint: As a hitters' park overall, the new stadium is in the middle of the pack. Yet it often has been the most homer-friendly park in the majors, even besting Denver's renowned Coors Field, according to stats from ESPN.com.

Some things have been tweaked over the last three years.

Before the 2006 season, the Phillies moved the left-field fence back five feet. And thanks to the intrepid work of Inquirer sportswriters, the team corrected the 369-foot marker on the left-center field fence, moving it to where the distance from home actually is 369 feet, not 3581/2. (The fence itself is straight, whereas the Vet's was bowed, another difference.)

Meanwhile, the balls are still flying out.

Here's why: In contrast to hulking Veterans Stadium, winds pour through Citizens Bank Park like water through a flow-through tea bag. Balls that get airborne are lifted up, up and away.

The most obvious suspects are the prevailing southwest and south winds of summer, which blow straight out to center and right-center fields. Those winds increase with height. Other factors might also be at work.

What is clear is that the atmospheric environment in the new park is utterly different from that of its predecessor, even though it is across the street from the old park.

Montgomery believes that the structural mass of Veterans Stadium - totally enclosed save for the exit-ramp openings - had a blocking effect on the movement of air. Jim Eberwine, a meteorologist at the National Weather Service in Mount Holly, says Montgomery is on sound scientific footing. A massive building would affect air currents the way an island distorts approaching waves.

The sports complex is in an urban prairie, with few wind-blocking structures nearby. But the Vet's impressive mass - an estimated 7,600 tons of steel and 625,000 concrete blocks, for starters - could have stopped winds almost anywhere.

Eberwine is a sports fan, and he used to frequent the Vet. On his first visit to the new park, he noticed that the breezes were fresher and stronger.

"You can see the difference in what the winds are doing," he said. "Those flags are waving. The Vet was like the catacombs."

The meteorologist said the Vet's solid walls had another effect: Occasionally they forced winds upward, where they would swirl as eddies, and at times even descend as downdrafts into the stadium.

Montgomery is convinced that such a downdraft in 1972 caused Kite Man to crash into the stands as he attempted to deliver the first ball on opening day.

Larry Shenk, the Phillies public relations man throughout the Vet era, remembered that when the flags atop the stadium were blowing southwest, toward center, the wind inside the park was actually blowing northeast, toward home plate. In the new park, a wind blowing toward center outside the park blows toward center inside, too.

An important difference between the two stadiums is how Citizens Bank Park uses prevailing winds to benefit hitters.

Well after the park was designed, the Phillies retained a Canadian engineering firm to study air-flow patterns at the site. Using Weather Service data, RWDI Inc. determined that the prevailing winds on summer nights were from the south, averaging about 12 m.p.h.

The old and new stadiums' dimensions may be similar but their alignments are not. So even if the Vet's structure had been identical to the new park's, the winds would have played differently. At the Vet, due north more or less followed the third-base line. At Citizens Bank, the home-center field line was pivoted so that a south-to-north wind would shoot almost straight to center.

Some other differences hover in the realm of the theoretical:

Official weather data. RWDI used data from the official measuring station at Philadelphia International Airport. Although the stadium is not far away, Eberwine points out that the stadium's location near the confluence of the Delaware River and the Schuylkill could be significant. The winds there might be a tad stronger and more volatile than at the airport. It also might be a little more humid, and water vapor makes air ever-so-slightly lighter - adding a tiny bit of lift.

Heat island. Eberwine also hypothesizes a "heat island" effect that could be exerting a subtle force on the baseballs. At the Vet, the fans were farther from the field - 60 feet from home plate to the stands, compared with 49.5 feet at the new ballpark. And the Vet's food concessions were recessed into invisibility; the new park's concessions are plainly visible and well-lighted at night.

Warm air rises because it is less dense than cool air. The proximity of the crowd and the heat generated by the lighted food stands could combine to give a tiny lift to batted balls.

"It's a mini-city in there," Eberwine said.

The big gap. Citizen Bank's wide-open center field might also make a difference. "This could precipitate a wind flow toward the open end," said Charles R. Smith, a mechanical engineering professor at Lehigh University.

These factors were beyond the scope of the RWDI study. With the park still under construction, the engineers used computer models to simulate how the winds alone - unaffected by architecture - would aid or exert a "drag force" on the ball. It did not compare the projected flight paths with those of the Vet.

The study did have one encouraging note for pitchers. When the wind is from the north, it can cut the projected flight path of a ball by 50 feet or more compared to no wind. Unfortunately for the pitchers, north winds are infrequent in summer.

And north winds have their quirks. The computer models found that when winds are blowing briskly from the north, an unexplained uplift undercuts the dampening effect on balls hit to left field.

In fact, on June 13 - the day Thome reflected on that batting practice at the new park three years earlier - a stiff wind was blowing straight in from center. Aaron Rowand, who the Phillies acquired from the White Sox for Thome, hit a drive to left field . . .

. . . and beyond, in a game-sealing grand slam.


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Contact Anthony R. Wood at 610-313-8210 or at twood@phillynews.com.

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