No bottle of rum for these pirates: The unforeseen effect of ship attacks in the Indian Ocean

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Jack Sparrow, the central figure of the popular "Pirates of the Caribbean" movie tetrology, is an intriguing and charismatic character. Real-life pirates, however, are affecting scientists' work in identifying year-to-year and decades-long variations in the climate of the northwestern Indian Ocean.

Climate data from the region are important for accurately forecasting the strength and timing of the Indian summer monsoon—the seasonal winds that bring heavy summer rains to the Indian subcontinent and surrounding region. The monsoon rains are critical to food security, water supplies, forestry, fisheries, and water-based ecosystems. In fact, over a third of the world's population is affected by the monsoon season, and variations in it can literally result in feast or famine.

One of the main drivers of the Indian summer monsoon is the Somali low-level jet stream. This wind pattern flows from southwest-to-northeast, crossing the Arabian Sea toward the India coast between May and October. In the winter months, the flow reverses and heads south along the African coast. The natural variations in the monsoons are dependent on the strength, location and structure of the Somali jet. Thus, correctly measuring this wind current is critical to forecasting the variations in the monsoon.

Data used in studies of the Somali jet are collected by the few moored buoys in the Indian Ocean and, importantly, by merchant vessels carrying instruments that record wind and weather conditions. These ships have been under increasing attack by pirates operating in the Indian Ocean off the coast of Somalia, and in the Gulf of Aden, part of the important Suez Canal shipping route between the Mediterranean Sea and the Arabian Sea. Twenty-one thousand vessels cross this waterway annually.

Pirate attacks nearly doubled between 2008 and 2009, resulting in a change in vessel operation. Ships are warned to stay at least 600 nautical miles off the coast of Somalia, and those crossing the Gulf of Aden are advised to travel through a narrow corridor patrolled by naval forces. The decrease in traffic along "Pirate Alley," as the waters around the Somali coast have become known, and alteration of ship tracks have resulted in a hole in the marine weather-observing network of nearly 1 million square miles (2.5 million square km), including the core of the Somali jet. This, in turn, has led to inaccuracies in the wind field products from the vessel-based measurements, disrupting the continuity of several decades of important climate data.

In this era of high-tech pirate movies, certainly there are alternate means of measuring ocean level winds. Satellite-based wind data are now being collected using microwave energy to determine the shape of the ocean surface, which is largely a function of wind speed and direction. There is normally good agreement between the ship-based and satellite products, so why is the recent void in the long record of surface observations a concern? Reliable, consistent satellite observations of wind parameters are too brief to use for developing decades-long wind models. The satellite record of wind parameters began in 1991, and the most recent data stream from NASA's QuikSCAT satellite became unreliable in 2009, with no clear indication of when it will be replaced.

Volcanoes also play an important role in steering climate in the Asian monsoon region by affecting rainfall. Climate models suggest that after large, explosive eruptions, drier conditions might prevail, due to the cooling often observed from the release of solar-energy-blocking volcanic gases and particles. Lowered temperatures decrease the evaporation of water from the earth's surface, resulting in less rainfall. A 2010 study suggests however, that in the year of an eruption, significantly wetter conditions occur over mainland Southeast Asia, with drier conditions in central Asia. The study notes that current climate models may not yet include all of the important ocean-atmosphere dynamics that contribute to the effects of explosive volcanism on the climate of Asia.

Both pirates and volcanoes shape our understanding of how multiple forces act together to affect weather patterns. In the case of the monsoon, this information can help determine optimal times for planting crops, and is imperative for identifying how changes in water resources may affect human health, agriculture, forests and wildlife.


Volcano Activity Update

A lava lake has been present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow visible from the Jaggar Museum. The lake, which is deep within the vent cavity and visible by Webcam, dropped to a lower level last weekend during a period deflation, but has since risen back to a higher level as the volcano reinflated.

Effusion within eastern and western lava lakes in Pu‘u ‘Ō‘ō, on Kīlauea's east rift zone, also declined last week but has picked up again since. The resurgence in effusion led to overflows out of the crater and onto Pu‘u ‘Ō‘ō's east and west flanks. As this activity has developed, the lava lakes, impounded by levees made up of their own chilled lava, have begun to rise up out of the crater. As of Thursday, September 15, the eastern lava lake had stopped overflowing, while the western lava lake continued to repeatedly spawn flows that advanced down the western side of Pu‘u ‘Ō‘ō cone.

Two earthquakes beneath Hawai‘i Island were reported felt this past week. A magnitude-2.2 earthquake occurred at 9:36 p.m., HST, on Wednesday, September 14, 2011, and was located 6 km (4 mi) southwest of Laupāhoehoe at a depth of 13.4 km (8.3 mi). A magnitude-3.2 earthquake occurred at 5:06 a.m., HST, on Thursday, September 15, 2011, and was located 8 km (5 mi) northwest of Ka‘ena Point at a depth of 9.3 km (5.8 mi).