Monsoons PDF

Monsoons Monsoons refer to the seasonal reversal of atmospheric pressure and winds and their accompanying rainfall. CAUSES Differential heating & cooling of land and adjacent sea areas = changes in atmospheric pressure & winds ITCZ moves northwards in th...

Monsoons Monsoons refer to the seasonal reversal of atmospheric pressure and winds and their accompanying rainfall. CAUSES Differential heating & cooling of land and adjacent sea areas = changes in atmospheric pressure & winds ITCZ moves northwards in the northern hemisphere and southwards in the southern hemisphere (in summer) causing trade winds to converge = convectional rain Himalayan mountain range influences movement of the ITCZ and triggers high rainfall on the Indian side during July. Wet monsoon +s Wet monsoon -s Dry monsoon -s Irrigation = Flooding Drought conditions crop yields Destruction of Water shortages for Water for crops agriculture industrial use Loss of Reduced crop yields Water for habitats Water scarcity for domestic use Fatalities and industrial & domestic use Drinking injuries Increased risk of wildfires water Destruction of Negative impact on Cleans up infrastructure ecosystems and habitats environment Economic Economic stress on farming Cools down impact communities environment Spread of Increased air pollution due diseases to lack of rain to cleanse the air Dry Monsoons (Winter) Dry monsoons occur Cold plateau, higher pressure during winter Land experiences cold temperatures and has an intense high-pressure. Ocean is warmer and has a low-pressure. Air moves from a high- pressure on land to a low- Warm sea, lower pressure on the ocean. pressure Results in intense rainfall over the ocean And drought and arid/dry conditions over land Wet Monsoons (Summer) Hot plateau, lower pressure Wet monsoons occur during summer. Land experiences warm temperatures and has an intense low-pressure. Ocean is cooler and has a high-pressure. Colder sea, Air moves from a high- higher pressure pressure on the ocean to a low-pressure on land. Results in intense temperatures and rainfall over the land. This rain is mostly relief rain and often results in flooding Föhn Winds A föhn wind is a dry, hot wind that descends on the windward side of a mountain that originates in a mountainous area or in an area where there are significant changes in altitude. PROCESS Air rises up the windward side of a mountain and it cools at the dry adiabatic laps rate. The air becomes saturated and continues to rise up the slope, but now cools at the wet adiabatic lapse rate. This cooling causes condensation to occur and clouds, rain or snow to form on the windward slope. Air descends on the leeward side and heats up at the dray adiabatic lapse rate. The wind at the foot of the slope is hot and dry. Examples Föhn winds can cause droughts, dry out forest areas and increase the risk of wildfires, and cause snow to melt which may result in avalanches and flooding. WINDS LOCATION BERG WIND Coastal areas of southern Africa CHINOOK Rocky mountains in the USA ZONDA Andes mountains in Argentina SANTA ANA Southern California, USA Lapse Rate A measure of how much a pocket or air changes (in °C) with a change in height (per 100m) DRY ADIABATIC WET ADIABATIC LAPSE RATE LAPSE RATE (DALR) (WALR) If air is unsaturated If air is saturated (very little (very moist) then it moisture) and dry will heat/cool fairly then it will slowly heat/cool faster that Measure: 0,5°C if there was water change per 100m on vapour present the windward side Measure: 1°C 0,5°C/100m change per 100m on the leeward side 1°C/100m