8: Energy & Humidity
- Page ID
- 55049
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\dsum}{\displaystyle\sum\limits} \)
\( \newcommand{\dint}{\displaystyle\int\limits} \)
\( \newcommand{\dlim}{\displaystyle\lim\limits} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\(\newcommand{\longvect}{\overrightarrow}\)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\ket}[1]{\left| #1 \right>}\)
\(\newcommand{\bra}[1]{\left< #1 \right|}\)
\(\newcommand{\braket}[2]{\left< #1 \vphantom{#2} \right| \left. #2 \vphantom{#1} \right>}\)
\(\newcommand{\braopket}[3]{\left< #1 \vphantom{#2}\vphantom{#3} \right| #2 \vphantom{#1}\vphantom{#3} \left| #3 \vphantom{#1}\vphantom{#2} \right>}\)
\(\newcommand{\qmvec}[1]{\mathbf{\vec{#1}}}\)
\(\newcommand{\op}[1]{\hat{\mathbf{#1}}}\)
\(\newcommand{\expect}[1]{\langle #1 \rangle}\)
\(\newcommand{\dfn}[1]{\emph{\textbf{#1}}}\)
- 8.1: Energy Transfer
- This page explains kinetic energy in the context of thermal energy, linking it to the movement of molecules and temperature. It covers how temperature reflects average molecular kinetic energy and describes heat transfer methods: conduction (direct contact), convection (in fluids), radiation (without contact), and latent heat. Higher molecular speeds correspond to higher temperatures.
- 8.2: Latent Heat
- This page explains latent heat, the energy involved in phase changes of water, such as melting, evaporation, condensation, and freezing. It highlights that heat added to ice at 0°C causes melting without temperature change, and the importance of these processes in atmospheric science, particularly in weather phenomena like convection and thunderstorms. It also notes that different phase changes have varying latent heat requirements, with vaporization needing more energy than melting.
- 8.3: Saturation
- This page explains saturation in evaporation and condensation within a closed jar, emphasizing that it occurs when both rates are equal, influenced by temperature. It introduces vapor pressure, particularly saturation vapor pressure, and its relationship with temperature as per the Clausius-Clapeyron equation. Higher temperatures enable more water vapor, and boiling happens when saturation vapor pressure equals atmospheric pressure, exemplified by water boiling at 100 °C at sea level.
- 8.4: Humidity
- This page introduces several ways of describing the amount of water vapor in the atmosphere, including absolute humidity, specific humidity, mixing ratio, vapor pressure, and relative humidity. It emphasizes relative humidity and dew point and explains how temperature affects saturation and the amount of water vapor that can remain in the atmosphere. Examples illustrate why cold and warm air can both have 100% relative humidity while containing very different amounts of water vapor.
- 8.5: Why Do We Care So Much About Moisture?
- This page discusses the importance of moisture in the atmosphere, its effect on weather and stability, and the phases of water. It explains the lifting condensation level (LCL) for cloud formation and contrasts the moist adiabatic lapse rate with the dry rate, highlighting the role of latent heat. These concepts are vital for understanding atmospheric dynamics.
- 8.6: Atmospheric Stability and Lapse Rates
- This page explores atmospheric stability, emphasizing the roles of environmental lapse rates and moisture. It describes absolute instability, where higher environmental lapse rates enable warm, less dense air parcels to rise, and conditional instability, where buoyancy relies on saturation. Unsaturated parcels resist rising, while saturated ones can ascend.
Chapter 8: Energy & Humidity — Introduction
The atmosphere is constantly exchanging energy. Sunlight warms Earth’s surface, the surface transfers energy to the air above it, and moving air carries energy from one place to another. Water is an especially important part of these exchanges because it can exist in the atmosphere as a solid, liquid, or gas. As water changes from one phase to another, energy is absorbed or released, connecting the movement of water through the atmosphere directly to the movement of energy.
In this chapter, we will begin by examining the ways energy is transferred and the role of latent heat during changes of phase. We will then turn our attention to water vapor in the atmosphere. The amount of water vapor that can remain in the gas phase depends strongly on temperature, leading to the important concept of saturation. We will also examine several ways atmospheric moisture can be described, including relative humidity and dew point, and consider what these measurements tell us about the state of the atmosphere.
Finally, we will bring energy and moisture together to investigate atmospheric stability. Whether an air parcel rises, sinks, or remains at the same level depends on its temperature relative to the surrounding atmosphere, and condensation can change that behavior through the release of latent heat. These relationships between energy, moisture, and vertical motion provide the physical foundation for many of the weather processes we will encounter in the chapters ahead, including cloud formation, precipitation, thunderstorms, and larger weather systems.