Lecture 1: The basics

The ideal gas laws describe the relationship between pressure, volume, and temperature of an ideal gas. They are significant in meteorology as they help explain how changes in temperature and pressure affect atmospheric conditions and weather patterns.

The key descriptors of weather include:

1. Temperature: Measures the warmth or coldness of the atmosphere.
2. Pressure: Refers to the weight of the air above a given point, influencing weather patterns.
3. Humidity: Indicates the amount of moisture in the air, affecting precipitation and comfort levels.

Yes, some spontaneous processes can be fast, like the free expansion of a gas into a vacuum, while others can be very slow, such as the conversion of diamond to graphite.

During equinoxes, the distribution of sunlight is uniform across the Earth:

• Hours of Sunlight: All latitudes receive 12 hours of sunlight.
• Equinox Dates: Occur twice a year, marking the transition between seasons (spring and fall).
• Implication: This uniformity indicates that day and night are approximately equal in length globally, regardless of latitude.

1. Longer day time: Days are longer in summer, allowing more time for sunlight to reach the surface.

2. Larger sun angle: The sun is higher in the sky, which means sunlight is more direct and concentrated.

3. Thinner atmosphere: The atmosphere is less dense, allowing more sunlight to reach the surface without scattering or absorption.

During the June solstice, the northern hemisphere is tilted towards the Sun, resulting in the longest number of daylight hours of the year.

The nearer you are to the North Pole, the longer the daylight hours you experience. Inside the Arctic Circle, there can be 24 hours of daylight.

During the June solstice, daylight hours range from 24 hours at the North Pole to 9 hours near the Tropic of Capricorn.

During the winter solstice, the Northern Hemisphere is tilted away from the Sun, resulting in the lowest number of daylight hours. The closer one is to the North Pole, the shorter the daylight hours, with regions inside the Arctic Circle experiencing 24 hours of night.

The tilt of the Earth causes variations in daylight hours:

1. June Solstice: North Pole receives 24 hours of daylight.
2. December Solstice: North Pole experiences 24 hours of darkness.
3. Spring/Autumnal Equinox: Daylight hours are equal at all latitudes, with 12 hours of daylight.

A larger sun angle at noon results in more solar energy per unit area, making the region hotter. Conversely, a lower sun angle spreads solar energy over a larger area, leading to cooler temperatures. This relationship can be expressed as E ~ sin²θ, where θ is the sun angle.

The sun angle varies on different days of the year, affecting the amount of solar energy received in a region. This variation is crucial for understanding seasonal temperature changes and climate patterns.

Earth-Sun relationships influence weather and climate through:

• Solar Radiation: The amount of sunlight received affects temperature and weather patterns.
• Seasons: The tilt of the Earth's axis leads to seasonal variations in climate.
• Day Length: Changes in day length throughout the year impact temperature and weather conditions.

Climate is the long term average of weather data, typically measured over scales of months to millions of years.

There is no such thing as global weather change; the correct term is global climate change, which refers to long-term changes in climate patterns rather than short-term weather fluctuations.

Meteorology is the scientific study of the phenomena of the Earth's atmosphere, including elements such as rain, cloud, surface temperature, and air pressure.

Most meteorological phenomena occur in the troposphere, which is the lowest 10 km of the atmosphere from the Earth's surface.

The Ideal Gas Law relates the temperature (T), volume (V), and pressure (P) of a gas, expressed in the equation PV = nRT.

The gas constant (R) in the Ideal Gas Law is 8.314 Jmol⁻¹K⁻¹.

In winter, lower temperatures lead to higher air density, which results in higher air pressure. Conversely, warmer temperatures result in lower air density and lower air pressure.

Energy is defined as the ability to do work, such as pushing, pulling, or lifting. The unit of energy is Joules (J), where 1 J = 1 N x 1 m.

The scientific definition of work involves the ability to move an object against a force, while everyday usage may refer to any effort or task. For example, lifting a ping pong ball is considered work, but pushing against a wall without moving it is not.

Kinetic energy (KE) measures the energy of objects in motion and is calculated using the formula:

KE = ½ mv²
where m is the mass and v is the speed of the object.

Potential energy (PE) measures the energy stored in an object that could be released to do work but is not currently doing so. Unlike kinetic energy, which is associated with motion, potential energy is related to the position or state of an object.

Chemical energy is the energy stored in the chemical bonds between atoms. It is released or absorbed during a chemical reaction.

Electric energy is the energy stored in the configuration of electric charges. It can be found in systems like batteries or capacitors.

Magnetic energy is the energy stored in magnetic materials or in systems of moving charges (electric currents). It is associated with the magnetic fields generated by these charges.

Elastic potential energy is the energy stored in a stretched spring or string. It is released when the object returns to its original shape.

Thermal energy is commonly referred to as heat or heat energy. It is the energy that comes from the temperature of matter, reflecting the kinetic energy of the particles in a substance.

Heat is a form of energy that is associated with the random kinetic energy of atoms and molecules.

The higher the temperature, the more kinetic energy atoms and molecules carry on average.

The kinetic theory of gas states that all atoms and molecules in nature are in constant random motion.

Temperature is a measure of the average kinetic energy of the materials, which is consistent with its daily usage.

Higher temperature gas contains more energy, meaning that particles in 30°C air move faster than those in 25°C air.

By definition, it makes no sense to talk about the temperature of a vacuum because a vacuum lacks matter and therefore cannot have kinetic energy or temperature.

Two objects are defined to be at the same temperature if no heat flows spontaneously from one to the other.

In this context, 'spontaneous' refers to a natural tendency for a change to occur without needing to be driven by doing work of any kind.

The three common scales of temperature measurement are Fahrenheit, Celsius, and Kelvin.

In the Celsius scale, 0°C refers to the freezing point of water, and 100°C refers to the boiling point of water at one atmospheric pressure.

The conversion formula from Celsius to Fahrenheit is:

F = (9/5) * C + 32

• 20°C is equivalent to 68°F
• 30°C is equivalent to 86°F

The Kelvin (K) scale is the absolute temperature scale defined by absolute zero (0 K) and the triple point of water (273.16 K).

The conversion from Celsius to Kelvin is given by the formula:

K = °C + 273.15

Absolute zero is the coldest attainable temperature, defined as 0 K, where it is impossible to extract any heat energy from the molecules. Nothing can be colder than 0 K.

The three ways of heat transfer are conduction, convection, and radiation.

Convection is the process of heat transfer through the bulk motion of fluid (gas or liquid), where warmer, less dense fluid rises and cooler, denser fluid sinks, creating a continuous cycle.

In a boiling pot of water, hot water rises due to its lower density, while cooler water sinks, creating a cyclic motion that facilitates heat transfer throughout the liquid.

In a room with a flame at the bottom, hot air particles (red) rise while cooler air particles (blue) sink, establishing convection currents that distribute heat throughout the space.

Radiation is the transfer of heat via electromagnetic waves. It does not require an intermittent medium and can occur in a vacuum.

Energy from the Sun drives all meteorological phenomena on Earth through the process of radiation.

Heat always flows from hot to cold places, regardless of the method of transfer.

Yes, all three methods of heat transfer can take place simultaneously in a given scenario.

Air pressure is the weight of the air above a surface at a specific location. It is measured in terms of force per unit area.

Air particles move around and bounce off the walls of their container, exerting force on it. This movement and collision of particles create pressure on the surrounding environment.

The SI unit of pressure is Pascal (Pa), defined as 1 Pa = 1 N/m².

1 bar = 1000 millibar = 100,000 Pa.

1 atm = 1.01325 bar = 1013.25 millibars.

Air pressure acts from all directions, and typically, the pressure inside the body is equal to the outside pressure, making it unnoticeable. However, differences in pressure can be felt in situations like moving lifts or during ascent/descents in planes.

A mercury barometer operates on the principle that air pressure exerts force on the surface of mercury in a dish, causing the mercury to rise in a vacuum tube. The height of the mercury column is directly proportional to the air pressure.

The higher the altitude, the lower the air pressure due to the decreasing weight of the air above that location.

Isobars are lines on a weather chart that connect locations of the same air pressure. They are typically labeled with values in millibars and indicate regions of high and low pressure, marked by 'H' for high pressure and 'L' for low pressure.

Moist air exerts greater pressure than dry air when compared at the same temperature and same volume.

The additional pressure exerted by moist air is called vapor pressure at that temperature.

Air pressure readings must be adjusted based on altitude to compare them accurately. For example, in San Francisco at sea level, the pressure reading is 1008 mb with no correction, while in Denver at 1600 m, the pressure reading is 840 mb with a correction of 172 mb, resulting in a corrected value of 1012 mb.

The saturation vapor pressure is the vapor pressure when the air is fully saturated with water vapor. It increases with increasing temperature, meaning warmer air can hold more moisture before reaching saturation.

When the air is saturated, the rates of condensation and evaporation are equal, resulting in a stable state where the amount of water vapor remains constant.

Saturation vapor pressure increases with increasing temperature.

Saturation vapor pressure increases with increasing temperature. This means that warmer air can hold more water vapor, leading to higher humidity levels.

Absolute humidity for the air parcel decreases as its altitude increases.

Mixing ratio is not affected by changes in pressure and temperature.

Relative humidity indicates how near the air is to saturation rather than the actual quantity of water vapour in the air.

Relative humidity changes when water vapour content changes in the atmosphere and when air temperature changes, as the amount of saturation moisture increases with temperature.

Relative humidity depends on temperature; as the temperature decreases, the same mass of water vapor results in an increase in relative humidity. For example, at 20°C with 7 grams of water vapor, the relative humidity is 50%, but at 10°C, it reaches 100% with the same amount of vapor.

When relative humidity reaches 100%, condensation occurs. This indicates that the air is saturated with water vapor, and any further cooling or addition of moisture will lead to the formation of liquid water.

The saturation mixing ratio changes with temperature, affecting relative humidity. For instance, at 20°C, the saturation mixing ratio is 14 grams, while at 10°C, it drops to 7 grams. Relative humidity is calculated as the ratio of actual water vapor content to the saturation mixing ratio at a given temperature.

When air is cooled from 20°C to 10°C with a constant water vapor content of 7 grams, the relative humidity increases from 50% at 20°C to 100% at 10°C, as the saturation mixing ratio decreases.

At 0°C, with a water vapor content of 3.5 grams, the relative humidity reaches 100% because the saturation mixing ratio at this temperature is also 3.5 grams, indicating the air is fully saturated.

Relative humidity measures how close the air is to being saturated, while dew point measures the actual moisture content of a parcel of air.

A high dew point indicates moist air, while a low dew point indicates dry air.

The dew-point temperature is always less than or equal to the air temperature.

As long as the air temperature is higher, the dew-point temperature does not change with the air temperature.

The principle motion is Rotation, where the Earth spins on its axis in about 24 hours.

1. Rotation: The Earth spins on its axis.

2. Revolution: The Earth moves around the Sun in an elliptical orbit in about 365.25 days.

The tilt of the Earth's rotation axis is the primary reason for the changing seasons, as it causes the Sun's daily path across the sky to vary throughout the year.

During the summer solstice, which occurs on June 21/22, the Sun is directly above the northernmost point of the Earth.

The winter solstice, occurring on December 21/22, is significant because the Sun is directly above the southernmost point of the Earth.

The sun angle is largest on the summer solstice (approximately 73.5 degrees) and smallest on the winter solstice (approximately 26.5 degrees).

During the summer solstice at 40° latitude, the sun reaches a high angle of 73 1/2°, resulting in the longest day of the year, occurring around June 21-22.

At the equinoxes (March 21-22 and September 22-23) at 40° latitude, the sun is positioned at an angle of 50°, resulting in equal day and night durations.

During the winter solstice at 40° latitude, the sun is at a low angle of 26 1/2°, leading to the shortest day of the year, which occurs around December 21-22.

At very high latitudes, the sun does not set during summer, resulting in 24 hours of daylight.

Earth travels in an elliptical orbit around the Sun with a small ellipticity, having a major to minor axis ratio of 2%.

The difference in the power delivered by the Sun to Earth varies by approximately 10%, which is much less than the actual difference observed in power received.

No, Earth's elliptical orbit is NOT the major factor that leads to the seasons.

Earth's orbit around the Sun is depicted as an ellipse.

Earth reaches its closest point to the Sun, called perihelion, on January 3.

When Earth is closest to the Sun in December, it is summer for the southern hemisphere and winter for the northern hemisphere.

Key dates include:

1. June solstice: June 21 or 22
2. Aphelion: July 4
3. September equinox: September 22 or 23
4. December solstice: December 21 or 22
5. Perihelion: January 3
6. March equinox: March 20 or 21

The land has to absorb solar energy for some time before it can give us hotter days, which is why the hottest day often occurs in July.

The actual temperature is influenced by a combination of factors including the location of the Sun, the Earth's surface materials, and the atmosphere.

Weather refers to the short-term atmospheric conditions in a specific area, including temperature, humidity, precipitation, and wind. Climate, on the other hand, is the long-term average of weather patterns in a particular region over extended periods, typically 30 years or more.

Weather refers to the continuously changing phenomena in the atmosphere, typically observed over time scales of hours or days, and represents the state of the atmosphere at a specific time and place.

Gravitational Potential Energy (GPE) is the potential energy held by an object due to its height above the ground. It is calculated using the formula:

GPE = mgh
where m is the mass, g is the acceleration due to gravity, and h is the height above the ground.

You only need to know 2 of the 3 parameters (temperature, volume, and pressure) to determine the remaining one in the Ideal Gas Law.

Kinetic energy (KE) measures the energy of objects in motion and is calculated using the formula:

[ KE = \frac{1}{2} mv^2 ]

where m is the mass and v is the speed.

Climate helps to describe the environment of a place or region by providing insights into its average weather patterns over time.

The average pressure at sea level is about 101,325 N/m², which is also called 1 atm.

Potential energy (PE) measures the energy stored in an object that could be released to do work but is not currently doing so. Unlike kinetic energy, which is associated with motion, potential energy is related to an object's position or state.

Example:

• Gravitational Potential Energy (GPE) is calculated as:

[ GPE = mgh ]

where m is the mass, g is the acceleration due to gravity, and h is the height above the ground.

Heat will be transferred from high temperature to low temperature.

At one atmosphere (1 atm) of pressure, the height of the mercury column is 76 cm, which is often referred to as 76 cm Hg.

To reverse the natural flow of heat, we have to do work. For example, supplying electrical energy to a refrigerator allows heat to be moved from the cooler inside to the warmer outside.

In conduction, thermal energy is transferred through a chain of collisions of atoms or molecules in contact. Particles at higher temperature have higher kinetic energy and transfer energy to nearby cooler particles through collisions.

During solstices, the number of sun-lit hours varies significantly with latitude:

• June Solstice (Northern Hemisphere Summer):

  • Arctic Circle (66 ½° N): 24 hours of sunlight
  • Tropic of Cancer (23 ½° N): 13 ½ hours of sunlight
  • Equator (0°): 12 hours of sunlight
  • Tropic of Capricorn (23 ½° S): 10 ½ hours of sunlight
  • Antarctic Circle (66 ½° S): 0 hours of sunlight

• December Solstice (Northern Hemisphere Winter):

  • Arctic Circle (66 ½° N): 0 hours of sunlight
  • Tropic of Cancer (23 ½° N): 10 ½ hours of sunlight
  • Equator (0°): 12 hours of sunlight
  • Tropic of Capricorn (23 ½° S): 13 ½ hours of sunlight
  • Antarctic Circle (66 ½° S): 24 hours of sunlight

Relative humidity is the ratio of the current amount of water vapor in the air to the maximum amount of water vapor the air can hold at a given temperature, expressed as a percentage. It is calculated using the formula:

Relative Humidity (%) = (Actual Water Vapor Content / Saturation Mixing Ratio) × 100

For example:

• If the air can hold 20g of water and there is only 5g, then relative humidity is 25%.
• If there is 10g of water vapor, then relative humidity is 50%.
• If there is 20g of water vapor, then relative humidity is 100%.

Low air pressure is typically associated with cyclones, including hurricanes and typhoons. These weather systems form and intensify in areas of low pressure, leading to strong winds and heavy rainfall. The lower the pressure, the stronger the cyclone can become, as seen in events like Hurricane Katrina and Typhoon Tip.

During ascent, the middle ear pressure is higher than the outside pressure, causing the eardrum to bulge outward. Conversely, during descent, the middle ear pressure is lower than the outside pressure, leading to the eardrum bulging inward. Equalization occurs when the eustachian tube opens, balancing the pressures.

When dry air is in contact with water, more evaporation than condensation takes place.

Changes in pressure and temperature affect the volume of air, which in turn influences absolute humidity, even if the amount of water vapor remains constant, as described by the Ideal Gas Law.

During the vernal equinox (March 21/22) and autumnal equinox (September 22/23), there are exactly 12 hours of daytime and 12 hours of night.

The angle is 23.5°.

In winter, the combination of shorter daytime and lower sun angle leads to reduced solar energy reaching the Earth's surface, contributing to colder temperatures.

During the summer solstice in the northern hemisphere, the sun rises highest in the sky at noon, resulting in a larger sun angle compared to other times of the year.

On the day of winter solstice, light must travel through a thicker atmosphere to reach the ground in the northern hemisphere. This increased thickness leads to greater scattering of light, resulting in less solar energy reaching the surface.