Climate| 10 Minutes Rapid Revision | Class 9 SST

Climate and Weather: Understanding Key Concepts

Introduction to Climate and Weather

• The chapter focuses on the concepts of climate and weather, highlighting their significance in Class 9 Geography.

• It discusses various climatic controls that influence weather patterns, particularly in India, including seasonal changes like the cold and hot weather seasons.

Definitions and Differences

• Weather refers to daily atmospheric conditions such as wind, rain, or sunshine; it is variable and not fixed.

• Climate is defined as the long-term average of weather conditions over time, encompassing factors like temperature and rainfall.

India's Unique Climate

• India experiences a monsoon-type climate characterized by seasonal wind reversals leading to significant rainfall.

• Temperature variations across regions are notable; for instance, Rajasthan can reach up to 50°C while Jammu & Kashmir may only be around 20°C during summers.

Factors Influencing Climate Variability

• Precipitation also varies significantly across India; northeastern states receive up to 400 cm of rainfall while areas like Ladakh see only about 10 cm.

• These climatic variations impact cultural practices, clothing styles, and dietary habits across different regions.

Key Climatic Controls

Latitude's Role

• Latitude affects solar insulation received at different locations; lower latitudes receive more sunlight compared to higher latitudes near the poles.

Altitude Effects

• As altitude increases, temperature decreases due to lower atmospheric density at higher elevations. This results in distinct climates in hilly areas compared to plains.

Pressure Systems and Winds

• Atmospheric pressure systems depend on latitude and altitude; they dictate wind directions which subsequently affect temperature and precipitation patterns.

Distance from Sea (Continentality)

• Areas close to oceans experience moderated temperatures due to sea breezes. For example, Delhi has extreme temperatures while Mumbai remains more temperate due to its coastal location.

Ocean Currents Influence

• Warm ocean currents lead to increased evaporation resulting in rainfall whereas cold currents often correlate with arid conditions leading to deserts nearby.

Factors Affecting India's Climate

Latitude Impact on India’s Climate

• The Tropic of Cancer divides India into tropical and subtropical climates influencing overall weather patterns throughout the country.

Altitude's Protective Role

• The Himalayan mountains prevent harsh winter winds from Central Asia from entering India, contributing to milder winters within the country.

Climate Influences on India

Factors Affecting India's Climate

• The third factor influencing India's climate, compared to Central Asia, is pressure and winds. Surface winds like southwestern and northeastern winds bring and carry rain in the region. Additionally, upper air circulatory winds such as jet streams also impact India's climate.

• Cyclonic disturbances from the Western Mediterranean Sea affect India, demonstrating how pressures and winds influence the country's climate. This results in multiple seasons across India, primarily characterized by a monsoon type climate but with varying weather conditions.

Seasonal Breakdown of Indian Weather

Cold Weather Season (Winter)

• The cold weather season, or winter, lasts from mid-November to February, with December and January being the coldest months. Temperature drops significantly from south to north; however, regions like the Peninsular Plateau do not experience a well-defined cold season due to maritime influences.

• In northern areas like the Himalayas, snowfall occurs with temperatures dropping below zero degrees Celsius. Northeastern winds flow from land towards sea as dry winds without precipitation; however, Tamil Nadu receives some rainfall due to moisture-laden winds from the Bay of Bengal.

Hot Weather Season (Summer)

• The hot weather season or summer spans March to May when temperature gradually increases due to shifting pressure belts northward with the sun's movement. Northern India experiences extreme heat during this period as maritime moderation is absent.

• Strong gusty hot dry winds known as "loo" can be fatal if one is directly exposed for too long; intense weather can lead to storms that cause minor rains referred to as pre-monsoon showers in West Bengal known as "Kal Baishakhi." These showers help ripen mango crops before monsoon onset.

Advancing Monsoon Season

• The advancing monsoon season begins in early June when low-pressure systems attract southwest trade winds carrying moisture over oceans into mainland India within a month leading to widespread rainfall across the country termed rainy season or southwest monsoon.

• Upon inflow of these southwest monsoon winds, there’s a dramatic change in weather patterns: heavy rainfall occurs particularly in western ghats while intensity decreases moving eastward across central India into northeastern states where maximum rainfall is recorded.

Retreating Monsoon Season

• The retreating monsoon occurs around October-November when low-pressure systems transition back into high-pressure conditions marking a shift from hot rainy seasons back into dry winter seasons; humidity levels rise post-rainfall leading to phenomena like October heat and potential tropical cyclones developing over Bay of Bengal causing destruction along eastern coasts.

Rainfall Distribution Across Seasons

• Rainfall distribution varies significantly across regions: northeastern states receive up to 400 centimeters while arid regions like Ladakh may only see about 10 centimeters annually; moderate rainfall is observed in northern plains and Deccan plateau areas indicating diverse climatic impacts throughout India based on geographical features such as mountains and plateaus affecting local climates despite overarching seasonal trends influenced by monsoons acting as unifying factors for festivals and agricultural cycles across different regions of India.