Between 1995 and 2005, the North Atlantic averaged 4.1 major hurricane

 ‎ ‎ ‎ ‎ ­Between 1995 and 2005, the North Atlantic averaged 4.1 major hurricanes (category 3 or stronger) yearly. From 1971 through 1994, however, only 1.5 such hurricanes had swept through each year. According to an analysis by K. Halimeda Kilbourne, this spike in major-hurricane activity reflects a return to normal frequency after a lull in the 1970s and 1980s, rather than the development of a new pattern. Two factors thought to strongly influence hurricane development are wind shear an atmospheric phenomenon in which adjacent layers of air move at different speeds or in different directions-and sea-surface temperature. Strong wind shear tends to rip apart tropical storms before they strengthen into hurricanes, while higher sea-surface temperatures can provide more energy to a forming hurricane.

 ‎ ‎ ‎ ‎ ­Kilbourne and her colleagues noted that observed variations in wind shear and sea-surface temperature correlate not only with variations in hurricane activity but also with corresponding variations in two biological phenomena. The luminescence of coral growth rings under ultraviolet light reveals periods in which more organic matter was washed from land by heavy storm rains, which are less likely in conditions that favor higher wind shear. And populations of the microorganism G. bulloides in the upper layers of the tropical ocean are more abundant when there is persistent upwelling of relatively cool, nutrient-rich waters. This upwelling occurs as a result of strong trade winds, which also correlate with relatively high wind shear. When these microorganisms die, they become deposited in seafloor sediments, which thus record changes in their abundance.

 ‎ ‎ ‎ ‎ ­The researchers examined these biological phenomena in samples from North Atlantic areas in which hurricanes form. Based on these observations, they concluded that overall, between 1730 and 2005, the North Atlantic experienced an annual average of 3.25 category-3-or-stronger hurricanes. However, at least six lengthy intervals since 1730 showed increased hurricane activity.

 ‎ ‎ ‎ ‎ ­Other analyses of long-term natural records bolster these results. Coastal geologist Jeffrey Donnelly studied lake and lagoon sediments to compare the timing of hurricanes during the past 5,000 years with that of El Niños-weather phenomena that increase North Atlantic wind shear-and found that periods with strong, frequent El Niños experienced a lower-than-average number of hurricanes.

1. According to the passage, which of the following statements about hurricane frequency in the North Atlantic is true?

A. Hurricane frequency before the mid-twentieth century cannot be reliably estimated without accurate records of when El Niños occurred.

B. Major-hurricane frequency has remained at above-average levels during some protracted periods in the past few centuries.

C. Periods during which North Atlantic hurricane frequency is low are characterized by high sea-surface temperatures.

D. An increase in hurricane frequency can sometimes contribute to an increase in wind-shear strength.

E. From 1971 through 1994 in the North Atlantic, hurricane intensity was lower, but hurricane frequency was greater, than the historical average


2. Which of the following most accurately describes the way in which the second paragraph functions in the context of the passage?

A. It summarizes, and discusses some further possible consequences of, the conclusions reached in the study described in the passage.

B. It introduces some crucial elements of the study described in the passage and summarizes the goals of that study.

C. It provides background information essential for understanding why the study described in the passage was needed.

D. It describes some long-established methodologies in order to emphasize, by contrast, the innovative nature of the study described in the passage.

E. It explains the relevance of certain types of observations that formed the basis of the methodology used in the study described in the passage.


3. The passage indicates that which of the following is true of Kilbourne's research?

A. Based on indirect evidence, it drew conclusions that Donnelly's research corroborated through direct observations of weather phenomena.

B. It was based on observations of marine biological records whose relevance to weather phenomena was first established by Donnelly's research.

C. It used the same methods that Donnelly's research used in investigating weather phenomena but arrived at conclusions that were inconsistent with Donnelly's.

D. Its conclusions were about weather phenomena that overlapped with, and time periods that were a subset of, those investigated by Donnelly's research.

E. The questions that it was designed to answer were raised by, but not answered by, the research that Donnelly had previously conducted


4. Based on the passage, it can be most reasonably inferred that at the time Kilbourne undertook the study described in the passage, at least some hurricane researchers were

A. skeptical toward proposed explanations regarding the mechanisms by which wind shear influences North Atlantic tropical storm development

B. unable to form useful working hypotheses regarding recent sea-surface temperature ranges in the North Atlantic

C. sympathetic to the idea that the frequency of major North Atlantic hurricanes from 1995 to 2005 represented a significant departure from historical norms

D. receptive to the notion that reliable records of El Ninos are a sufficient basis for accurate predictions of annual numbers of North Atlantic major hurricanes

E. dismissive of attempts to correlate seafloor sediment composition with wind shear in areas of the North Atlantic in which hurricanes form