GG 140 - Lecture 16 - Frontal Cyclones

Mid-latitude frontal cyclones gain energy from temperature gradients rather than latent heat release as is the case with convective storms. They form in the belt of westerly winds and therefore generally move west to east in both the northern and southern hemispheres. A mid-latitude frontal cyclone develops from a kink in the polar front, and eventually warm and cold fronts develop around a low pressure center to form the storm. An example of this type of storm is a nor’easter, which commonly occurs in New England and is named for the northeasterly winds that precede the storm’s arrival.

GG 140 - Lecture 15 - Convective Storms

There are three main types of convective storms: airmass thunderstorms, severe thunderstorms and hurricanes. These storms are all driven by the release of latent heat into the atmosphere during condensation of water vapor. Severe thunderstorms include both squall line thunderstorms and tornados. They acquire energy from water vapor in the atmosphere over land and therefore typically require warm air temperatures and high humidity. Hurricanes gain energy from water vapor evaporated from the ocean surface. This requires warm ocean temperatures, and is the reason hurricanes weaken over land.

GG 140 - Lecture 14 - Coriolis Force and Storms

Large scale air motion in the atmosphere occurring sufficiently above the surface is in geostrophic balance. Areas of high and low pressure anomalies in the atmosphere are surrounded by rotating flow caused by the balance between the pressure gradient and Coriolis forces. The direction of rotation around these pressure anomalies reverses between the northern and southern hemispheres due to the reversal in sign of the Coriolis force across the equator.

GG 140 - Lecture 13 - Global Climate and the Coriolis Force

The circulation in the atmosphere is composed of three circulation cells in the northern and southern hemispheres. These cells are caused by the rotation of the Earth which creates the Coriolis force. The Coriolis force deflects northern hemisphere motion to the right and southern hemisphere motion to the left. The majority of large-scale motion in the atmosphere is in geostrophic balance, meaning the Coriolis force acting on the motion is balanced by a pressure gradient force.

GG 140 - Lecture 12 - Circulation of the Atmosphere (Exam I review)

There is a latitudinal gradient of heat on the Earth caused by the tilt of the Earth’s axis with respect to the sun. This tilt produces seasonal fluctuations in heat input from the sun, as well as an excess of heat received on average annually near the equator. Heat is transferred poleward by both the ocean and atmosphere in an attempt to balance the Earth’s energy budget. The circulation of the Earth also causes a separation of the atmospheric circulation into three main circulation cells, each transporting heat towards the poles.

GG 140 - Lecture 11 - Clouds and Precipitation (Cloud Chamber Experiment)

Scattered visible light and microwave radar can used used to detect clouds and precipitation. Cloud formation in rising air can be simulated in the classroom by suddenly dropping the pressure in a glass chamber. The small cloud droplets formed in this way fall too slowly to ever reach the earth. There are two main mechanisms by which precipitation is generated from clouds. Collision coalescence occurs mainly over tropical oceans whereas the ice phase mechanism is more common and also more relevant to the practice of cloud seeding.

GG 140 - Lecture 10 - Water in the Atmosphere II

Air is able to hold a limited amount of water vapor, and that amount depends on the temperature of the air. When this saturation vapor pressure is exceeded, liquid water begins to condense and clouds form. There are several different types of clouds, some which rain and others which do not, and each with characteristics specific to it. Vortices are a particular type of cloud phenomenon in which there is a low pressure anomaly in the center of the cloud with rotating air around it, forming funnel clouds as seen in tornados.

GG 140 - Lecture 9 - Water in the Atmosphere I

The lapse rate describes the rate at which air cools with altitude. Atmospheric stability depends on the lapse rate. When an air parcel is lifted or lowered, it can continue to rise or descend based on the temperature of the surrounding air at the new altitude, which indicates an unstable atmosphere. Inversions can occur in the atmosphere, meaning the air near the ground will be cooler than air aloft. This type of temperature profile can cause air to be trapped near the Earth’s surface in a boundary layer, which can also lead to pollutants being trapped near the ground.

GG 140 - Lecture 8 - Horizontal Transport

This lecture describes how pollutants mix in the atmosphere. Three cases are considered: confined mixing, unconfined mixing, and unconfined mixing with wind. In a confined volume, the concentration of pollutant in the air depends on the volume and the mass of the air present in the volume. Unconfined mixing is also known as diffusion, in which the pollutant disperses through the air from the source over time. When wind is considered, the pollutant disperses from the source in the direction of the wind. The change in temperature with height in the atmosphere is also discussed.

GG 140 - Lecture 7 - Hydrostatic Balance

The hydrostatic law describes the weight of a fluid overlying a given area, or the pressure at a particular point. It can be used to calculate the approximate atmospheric mass over a particular area, or to calculate the change in pressure over a given change in altitude. A calculation of the pressure difference from the ground to the twelfth floor of Klein Biology Tower is found to agree well with measurements taken at both locations. The hydrostatic law also applies to pressure changes with depth in the ocean.

Subscribe to Open Yale Courses RSS