Question 69 ONC05 - Master or Mate of LT 200 GRT

The Correct Answer is D ### Why option D ("July and August") is correct: The North Equatorial Countercurrent (NECC) flows eastward between the North Equatorial Current (NEC) and the South Equatorial Current (SEC) in the Pacific and Atlantic Oceans. Its strength is primarily driven by the seasonal migration of the Intertropical Convergence Zone (ITCZ) and the resulting wind patterns, specifically the seasonal weakening of the trade winds in the Northern Hemisphere and the presence of the monsoon trough. * **Seasonal Dynamics:** During the Northern Hemisphere summer (boreal summer), the ITCZ is located farthest north (typically between 5°N and 10°N, or even higher in the eastern Pacific). This northward shift causes a significant relaxation or reversal of the westward-blowing Northeast Trade Winds near the equator. * **Resulting Flow:** The reduced wind stress allows the NECC, which is maintained by the pressure gradient resulting from the piling up of water in the western ocean basin (due to the NEC and SEC), to flow strongly eastward. * **Peak Strength:** Consequently, the NECC typically reaches its maximum strength and volume transport in the months of **July and August**, corresponding to the period of maximum ITCZ northward migration and minimum wind stress in the equatorial zone. ### Why the other options are incorrect: * **A) October and November:** While the NECC is still relatively strong during this period (fall/early winter), the ITCZ is beginning its southward migration, and the Northeast Trade Winds are starting to re-establish and strengthen. Therefore, the NECC is usually past its peak annual strength, which occurs earlier in the summer. * **B) January and February:** These months fall during the boreal winter. The ITCZ is located farthest south (near or south of the equator). The Northeast Trade Winds are fully developed and at their maximum strength, pushing water strongly westward. This strong wind stress suppresses the NECC, making these months the period when the NECC is typically at its **weakest** or may even disappear entirely (especially in the Pacific). * **C) April and May:** These months are the transition period (spring) before the onset of the boreal summer. The ITCZ is moving northward, and the trade winds are beginning to weaken, leading to the gradual strengthening of the NECC. However, the current has not yet reached its peak strength, which is achieved later in the deep summer (July/August).