Air in the atmosphere acts as a fluid. The sun's radiation strikes the ground, thus warming the rocks. As the rock's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. During convection, cooler water or air sinks, and warmer water or air rises. This movement causes currents. Ocean currents are like rivers of water moving through the sea. Some currents are caused by convection, while others, called surface currents, are driven by wind. Warm air is less dense than cool air, so it rises higher in the troposphere. This starts convection current. Convection mixes the air in the troposphere. Rising air is also a main cause of weather.

Convection currents are identified in Earth's mantle. Heated mantle material is shown rising from deep inside the mantle, while cooler mantle material sinks, creating a convection current. It is thought that this type of current is responsible for the movements of the plates of Earth's crust. The temperature structure of the stratosphere is one of warmer air over colder air. No, convection never occurs in the stratosphere because of this temperature structure. Convection currents generated within the asthenosphere push magma upward through volcanic vents and spreading centers to create new crust. Convection currents also stress the lithosphere above, and the cracking that often results manifests as earthquakes.Convection, a method of heat transfer, occurs in almost all Earth systems including the atmosphere, hydrosphere, and geosphere. Convection currents are heat-driven cycles that occur in the air, ocean, and mantle. They are caused by a difference in temperature, often due to a differing proximity to a heat source. The difference in temperature relates directly to the density of the material, causing this effect. Thermal energy also moves within the ocean and within the atmosphere through the process of convection. During convection, cooler water or air sinks, and warmer water or air rises. This movement causes currents. Ocean currents are like rivers of water moving through the sea. Air in the atmosphere acts as a fluid. The sun's radiation strikes the ground, thus warming the rocks. As the rock's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere.In the atmosphere, as air warms it rises, allowing cooler air to flow in underneath. Along with the turning of the Earth, this movement of air creates winds. Winds, in turn, create surface waves on the ocean. Convection also plays a role in the movement of deep ocean waters and contributes to oceanic currents. Ocean currents act much like a conveyor belt, transporting warm water and precipitation from the equator toward the poles and cold water from the poles back to the tropics. Thus, ocean currents regulate global climate, helping to counteract the uneven distribution of solar radiation reaching Earth's surface.

The lowest layer in the atmosphere/troposphere where convection starts per Rk Naresh' explantion above is the boundary layer (Atmospheric Planetary BL, aka Atmospheric PBL, or ABL).

Thanks Dr. G.Levy for participating in the discussion.

Atmospheric motions in the vertical direction. In meteorology, convection refers primarily to atmospheric motions in the vertical direction. As the earth is heated by the sun, different surfaces absorb different amounts of energy and convection may occur where the surface heats up very rapidly. Convection currents are heat-driven cycles that occur in the air, ocean, and mantle. They are caused by a difference in temperature, often due to a differing proximity to a heat source. The difference in temperature relates directly to the density of the material, causing this effect. The temperature structure of the stratosphere is one of warmer air over colder air. No, convection never occurs in the stratosphere because of this temperature structure. Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere. The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. All these elements contribute to mantle convection. Thermal energy also moves within the ocean and within the atmosphere through the process of convection. During convection, cooler water or air sinks, and warmer water or air rises. This movement causes currents. Ocean currents are like rivers of water moving through the sea. Air in the atmosphere acts as a fluid. The sun's radiation strikes the ground, thus warming the rocks. As the rock's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere.Some convection currents are relatively quick cycles, like those in the atmosphere, while others are very slow, like in the mantle. Governed by the principle that warm rises and cool sinks, convection currents cause plate tectonics, thunderstorms, desert and tropical regions, even the Earth's magnetic field. In the atmosphere, as air warms it rises, allowing cooler air to flow in underneath. Along with the turning of the Earth, this movement of air creates winds. Winds, in turn, create surface waves on the ocean. Convection also plays a role in the movement of deep ocean waters and contributes to oceanic currents.