An air mass is a vast body of air with relatively uniform temperature and moisture characteristics. Meteorologists classify these masses based on their source region: continental (over land) or maritime (over water), which dictates moisture content. Temperature is categorized by latitude as tropical, polar, or arctic. This system allows for the identification of distinct weather patterns. The Continental Tropical (cT) air mass is a specific classification that determines weather conditions over large areas.
Defining the Continental Tropical Air Mass
The designation Continental Tropical (cT) describes its two defining properties: extreme dryness and high temperature. The “continental” aspect indicates formation over a large landmass, which prevents the air from accumulating significant moisture. This results in very low humidity and dry conditions.
The “tropical” designation signifies development in low-latitude regions (typically 25 to 35 degrees latitude) where intense solar radiation makes the air extremely hot. The combination of heat and dryness creates a high degree of atmospheric stability. The lack of moisture means there is little energy for lifting and condensation, which actively suppresses cloud formation and precipitation. This stability maintains clear skies and prevents the development of significant weather systems like thunderstorms.
Geographical Source Regions
Continental Tropical air masses require specific geographical conditions, forming over large, flat, arid, or semi-arid land areas in subtropical zones. The air must remain stagnant over these regions for an extended period to acquire the high temperature and low moisture content of the underlying surface.
Globally, the most recognized source region is the vast Sahara Desert in North Africa, which exports this air mass across continents. Other deserts and arid basins at similar latitudes also serve as source regions, including the Arabian Peninsula and interior Australia.
In North America, a key source region is the desert Southwest of the United States and northern Mexico, particularly during the summer. Air masses originating here push northward, bringing intense heat and dryness into the central and western parts of the continent.
Weather Effects and Impact
When a cT air mass dominates a region, the primary effect is extreme heat, often resulting in heat waves and record-high temperatures. Temperatures can soar well above 30°C due to intense solar heating. The low moisture content ensures the atmosphere is exceptionally clear, leading to intense sunshine and excellent visibility.
The lack of moisture contributes to a large diurnal temperature range, meaning the difference between daytime highs and nighttime lows is significant. However, as the air moves, it can sometimes pick up fine dust or pollutants, leading to reduced visibility or a hazy appearance.
The prolonged presence of a cT air mass carries significant environmental and public health hazards. The suppression of precipitation leads directly to drought conditions, severely impacting agriculture and water supplies. The combination of extreme heat and dry vegetation increases the risk and spread of wildfires. The intense heat also poses a public health risk, contributing to heat-related illnesses and mortality.