Monsoon

About: Monsoon is a research topic. Over the lifetime, 16087 publications have been published within this topic receiving 599888 citations.

Further case studies of tropical Atlantic surface atmospheric and oceanic patterns associated with sub-Saharan drought

Abstract: Sub-Saharan West Africa (10°–20°N) receives rainfall from westward-propagating disturbance lines that have their base within and receive most of their moisture from the low-level, wedge-shaped, southwest monsoonal flow off the tropical Atlantic. This paper builds on earlier research to further identify the tropical Atlantic surface atmospheric and oceanic patterns that accompany drought in sub-Saharan West Africa. Patterns for the four driest years since 1940 (1972, 1977, 1983, 1984) are compared with counterparts for the wettest of the last 20 years (1975) and 60-year (1911–70) average fields. The key results for the rainy season (July-September) of three of the four severe sub-Saharan drought years (1972, 1977, 1984) duplicate those obtained earlier. They include (i) a distinctive basinwide sea surface temperature (SST) anomaly pattern (positive departure to the south of ∼10°N; negative departures between 10°–25°N); (ii) a concomitant southward displacement (relative to the 1911–70 mean) of the...

Holocene aridification of India

Abstract: [1] Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ∼4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminiferGlobigerinoides ruberdetects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ∼4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India.

Holocene variability of the East Asian summer monsoon from Chinese cave records: a re-assessment

Abstract: Oxygen isotope records from stalagmites in caves in southern China, interpreted as proxy rainfall records reflecting the intensity of the East Asian summer monsoon, indicate gradual monsoon weakening for the last ~9000 years, as also documented for the Indian monsoon. Coupled with high-precision dating, the speleothem proxy records have been used to test monsoon links with orbital forcing, solar changes, iceberg discharges in the North Atlantic, ocean currents and atmospheric methane. However, these ‘benchmark’ cave records do not match other published, dated E Asian proxy rainfall record (specifically here, independently calibrated rainfall records from loess/palaeosol magnetic properties, and cave oxygen isotope intercomparisons), which show variable E Asian monsoon intensity through the entire Holocene. The strong correlation of the cave records with the extraregional Indian monsoon record yet their mismatch with these other dated Chinese rainfall records might be reconciled if the speleothem isotope variations reflect not changes in Holocene rainfall amount but in rainfall source. Declining Holocene influence of isotopically lighter, Indian monsoon-sourced moisture over China would have resulted in increasing proportions of isotopically heavier rainfall, sourced from the more oceanic E Asian monsoon. Individual speleothems may thus regionally record Holocene changes in Indian monsoon intensity and isotopic influence. Conversely, the other Chinese proxy records described here reflect changes in rainfall amount, and thus in E Asian summer monsoon intensity. For the Holocene, the E Asian and the Indian monsoon responses to orbital forcing are likely to have differed, specifically due to E Asian internal feedbacks and the seasonal contrasts between the two monsoon systems.

The Role of Vegetation in the Dynamics of West African Monsoons

Abstract: The focus of this paper is the role of meridional distribution of vegetation in the dynamics of monsoons and rainfall over West Africa. A moist zonally symmetric atmospheric model coupled with a simple land surface scheme is developed to investigate these processes. Four primary experiments have been carried out to examine the sensitivity of West African monsoons to perturbations in the meridional distribution of vegetation. In the control experiment, the authors assume a distribution of vegetation that resembles the natural vegetation cover in West Africa. Each perturbation experiment is identical to the control experiment except that a change in vegetation cover is imposed for a latitudinal belt that is 10° in width. The results of the numerical experiments demonstrate that West African monsoons and therefore rainfall distribution depend critically on the location of the vegetation perturbations. Changes in vegetation cover along the border between the Sahara desert and West Africa (desertifica...