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Monsoon Part Ⅰ What is a monsoon What makes a monsoon What is a monsoon • A term from early Arabs called the "Mausin," or "the season of winds." • The seasonally shifting winds in the Indian Ocean and surrounding regions, including the Arabian Sea and the Bay of Bengal. monsoon—A monsoon results from the circulation induced by temperature contrasts between a warm (cold) continent and a cold (warm) ocean. Ramage (1971) based on wind directions • It is now more applied to tropical and subtropical seasonal reversals in both winds and associated precipitation. • People are more concerned about the precipitation for two reasons: a:natural disasters, like flooding and drought ; b: latent heat in the global diabatic heating. The hydrologic cycle and latent heat release latent heat absorb latent heat ice Condensation release latent heat This heat anomalies produce circulation anomalies vapor evaporation Absorb latent heat Liquid Monsoonal or non-monsoonal? Total summer precipitation Annual range of rain Ratio of summer rain to yearly rain TAO. 1987 Members in the Asian-Australian summer monsoon system B: trade wind C: crossequatorial flow D: SW monsoon L EASM L L c H A India monsoon, East Asian monsoon, Meiyu front H Austrilian high A Mean onset date of the summer monsoon Monsoon is a mixed blessing Life-giving rain & Wild storms It annually shapes the lives of both the people and the wildlife of the monsoon regions. In late spring, the grassy plains and forested hillsides of southwestern India are among the hottest places on the earth. "The air is on fire and the leaves are perfectly still as if holding their breath." "there is a curious sense of anticipation.“ ——— Shantipriya Animals and human alike await the monsoon Monsoon onset Monsoon Race Clouds : Ci, Sc, Ns, Cu As clear blue sky just gives its way to white clouds, the dark clouds that carry rains are coming. Before monsoon hits the Arabian coast, the fishing boats are pulled on the coast, packed, and tightly tied with the ropes for the support. Monsoon break Crocodiles spawn Weaver birds build their nests during monsoon break. Monsoon withdrawal Farmers plant rice paddies after monsoon rains. Wild storms: People rest on the pavement of a flooded street in Bombay. Monsoon rains have killed 41 people across India over the past two days. (Yahoo News. Wed,Jul 5,2006) Monsoon peak India's financial capital Bombay came to a virtual standstill Tuesday in the torrential rainfall, killing 7 people. (Yahoo News. Jul.4,2006) Yangtzs valley in China East Asian monsoon area Meiyu front Monsoon rains come too late this year (2006). Monthly rainfall anomaly:-80% Mei-yu front does not come to the middle-lower reaches of Yangtzs River this year. Monthly precipitation anomaly in Jun.2006 Flooding 1998 Global population distribution 1.03b in India 1.37b in China The most densely populated areas are in monsoon regions. Regional summer monsoon domains North African monsoon from Reddiman 2001 From Simona 2004 From Berbery et al. 2005, From Ramage 1971 Global summer monsoon rainy season Summer rain Winter rain Global summer monsoon rainy season Summary • Monsoon means seasonal reversals both in winds and precipitation • Monsoon’s onset, peak and withdrawal • Monsoon rainy season has inter-annual variations (floods, droughts) What makes a monsoon • How is the atmosphere heated at the earth’s surface? • Energies driving the atmosphere to move are primarily come from the sun. Nearly half of the total sun’s energy is concentrated within the visible light wavelength Solar radiation Solar radiation absorbed by atmosphere Visible solar radiation is not absorbed by air About 51% of solar radiation is absorbed by surface How is the atmosphere heated Energy gained by atmosphere: +160 Energy lost by atmosphere: -160 +19 +7 +23 +111 51% of the solar radiation is absorbed by the earth Ocean currents move heat downward into deep water Temperature at 1000hPa summer (JJA) winter (DJF) Land-sea distribution makes the imbalance of the heat Just as sea breeze Warmer air High pressure Low pressure Warmer air The earth’s rotation around the sun produces the heat imbalance between the two hemispheres . Seasonal variations of solar radiation • The pattern of Absorbed Solar Radiation has a strong zonal component that is dominated by orbital effects. Tibetan Plateau, the third pole of the earth. It is a heat source at its surface. Average elevation is 4500m.Total area is about 2,400,000km2 Rainfall center Latent heat is most intense over Tibet Interaction between the two hemispheres ISM H EASM H Three factors contribute to monsoon Tibetan Plateau 60 50 40 Interactions between the two hemispheres 30 East Asian monsoon regions 20 North American monsoon regions 10 North African monsoon regions 0 -10 South American monsoon regions -20 Australian monsoon regions South African monsoon regions -30 -40 -50 -60 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 Summer Monsoon Domain 60 80 100 120 140 160 180 Seasonal overturning in winds Summary • The first driving force is solar radiation • The second driving force is land-sea distribution • The three is the huge topography.