Monday, November 14, 2016

Response from a Reader: Sailing into the Atlantic – Part II

Continuing from the previous post regarding a comment sent in by a reader asking for our response to his friend’s reaction to one of our articles about sailing off the Arabian coast and into the Indian Ocean, and asking for our response. Listing five factors in the previous post, we continue here with #5. 
5. “Nephi left right after harvest season…” 
    Response: As stated earlier, this covers a wide period of months, certainly from April through November, thus it can be said that the harvest time is basically during both monsoon seasons (see above #3 for a monthly period).
6. “They (winds) continue the whole season.” 
    Response: Without getting too exact and specific, the monsoon winds and the currents they drive, last for six months out of the year, then switch to an opposite flowing direction, thus for six months the currents and winds flow southwest off the Arabian coast (I am not including India in this example, since that is too far to the east of Arabia to have been a factor in Lehi’s voyage, though the entire areas is very similar), and for the next six months the currents and winds flow in the opposite direction.
In the midst of all this, is the little known Somali Current, which is heavily influenced by the monsoons and is the only major upwelling system that occurs on a western boundary of an ocean. The water that is upwelled by the current merges with another upwelling system, creating one of the most productive ecosystems in the ocean. This system, as is seen in the image above flows northeastward from March to May—in fact, during this season, shallow northward coastal current flows with 31- to 62-mile-width near the Somali coast, overlying a southward undercurrent. With alongshore winds, upwelling current flows to the coast. Near the equator, the East African Coast Current (EACC) flows northward across the equator.
    According to Friedrich A. Schott of the Institute of Oceanography at Kiel University, Germany, and Julian P. McCreary, of the International Pacific Research Center, University of Hawaii, the southern Somali Current flows northward as an extension of the East Africa Counter Current (EACC) from south to the 3-4°N ("The Monsoon Circulation of the Indian Ocean,” Progress in Oceanography. Vol 51, 2001, pp 1–123). Because of this, there is no way possible for Nephi’s wind-reliant sailing ship, “driven forth before the wind,” to have sailed south past Somalia and on toward Madagascar without being driven toward the east (not west along Africa).
    The southwestern summer monsoons occur from June through September, and generally begin around the beginning of June and fade away by the end of September. At this time, the Thar Desert (the world’s 17th largest desert and also known as the Great Indian Desert)—a large, arid region in the northwestern part of the Indian subcontinent that forms a natural boundary between India and Pakistan—and adjoining areas of the northern and central Indian subcontinent, heat up considerably during the hot summers. This causes a low pressure area over northern and central India, and the moisture-laden winds from the Indian Ocean rush in to fill this void. Rich in moisture, these winds are drawn towards the Himalayas, that act like a high wall, blocking the winds from passing into Central Asia, and forcing them to rise. As the clouds rise their temperature drops and precipitation occurs. Some areas of the subcontinent receive up to 390 inches of rain annually.
These moisture-laden winds on reaching the southernmost point of the Indian Peninsula, due to its topography, become divided into two parts: the Arabian Sea Branch and the Bay of Bengal Branch
Following the earlier discussion about the Bay of Bengal branch, we now turn to the Arabian Branch of the Southwest Monsoon first hits the Western Ghats of the coastal state of Kerala (making the first state in Indian to receive rain from the Southwest Monsoon). This branch of the monsoon moves northwards along the range of the Western Ghats with precipitation on coastal areas, west of the range. The eastern areas of the Western Ghats do not receive much rain from this monsoon as the wind does not cross this range. The Bay of Bengal Branch of Southwest Monsoon flows over the Bay of Bengal heading towards North-East India and Bengal. 
    The northeast winter monsoon blows from the north to the south and is referred to as the Retreating Monsoon, taking place mostly in December to March, when the surface high-pressure system is strongest. This winter monsoon results from the sun fast retreating south around September, and the northern land mass of the Indian subcontinent beginning to rapidly cool off. With this air pressure begins to build over northern India, the Indian Ocean and its surrounding atmosphere still holds its heat. This causes cold wind to sweep down from the Himalayas and the Indo-Gangetic Plain (Indus Ganga, North Indian River Plain), a 630-million-acre fertile plain encompassing most of the northern and eastern India, Pakistan and Bangladesh. While traveling towards the Indian Ocean, the dry cold wind picks up some moisture from the Bay of Bengal and pours it over peninsular India and parts of Sri Lanka. The jet stream in this region splits into the southern subtropical jet and the polar jet. The subtropical flow directs northeasterly winds to blow across southern Asia, creating dry air systems, which produce clear skies over India. Meanwhile, a low pressure system develops over Southeast Asia and Australisia and winds are directed to Australia known as a monsoon trough.
    While these winds may blow all year long, they do not blow in the same direction—about six months from southwest to northeast (summer monsoon), and the other six months from northeast to southwest (winter monsoon). 
7. “The ship following the winds would have taken them to [down the coast of] South Africa… 
The Somalia Current is impacted by the fast-moving current crossing the Sea of Arabia from east to west. Yellow Arrow is about where Lehi would have set sail out of the Khor Rori inlet of Salalah. The sailing of Nephi’s ship would have to coincide with the lessening of these currents, which would be in the Janaury to March time frame 

    Response: Obviously, the Somali Current is being forgotten here. This current is an ocean boundary current that runs along the coast of Somalia and Oman in the Western Indian Ocean and is analogous to the Gulf Stream in the Atlantic Ocean. To sail to the south from Arabia into the Indian Ocean, one must pass through or cross this Somalia Current. 
    This Somali surface current of the western Indian Ocean, caused during the northern summer months by the blowing of the southwest monsoon along the coast of East Africa, moves coastal waters northeastward along with it for almost 1,000 miles, with surface velocities reaching up to 9 miles per hour. At longitude 6°–10° N (off Somalia), the northeastward Somali flow turns eastward as the Monsoon Current. the monsoon’s reversal to the northeast in September, the current begins to weaken until, in the winter (about December to March), it disappears entirely, to be replaced by a slow southwestward drift.
(See the next post, “Response from a Reader: Sailing into the Atlantic – Part III,” for a continuation with item #8 and the continuation of this response)

No comments:

Post a Comment