Personal preparation for this post included searching for written quotations concerning weather. One eye-catcher affirmed my belief that light conversational banter about weather often exceeds actual understanding of the topic: “Don’t knock the weather; nine-tenths of the people couldn’t start a conversation if it didn’t change once in a while,” humorist Kin Hubbard (1868-1930) observed.
Weather was a staple of earth science courses in my classroom. My challenge was to shift the topic from mere observation to an exercise in comprehension. I hoped to instill a sense of wonder along with an understanding of weather’s dynamic processes. Weather supplies us with a great deal of knowledge about the physical events surrounding us. For instance, in order for precipitation to occur, liquid water must first evaporate into water vapor before it supplies rainfall at a distant location.
Students wondered, “What more is there to know?” When our science students first became aware of the phenomenon of water evaporating from liquid to gas, then back to liquid at a different location, that was only part of the story. I reminded them of a common swimming pool event: Climbing out of a swimming pool with wet skin into the warm sun can be a surprisingly chilly experience. The cold shivers belie the comfort of swimming in the heated pool water. Understanding the cooling phenomenon helped them grasp some hidden wonders of our earth’s weather machine.
The process of evaporating water consumes a tremendous amount of heat. When water evaporates from our moist skin, it uses up body heat. Then we feel cold. Heat from the evaporation process is removed with the water vapor. In this case, the body’s heat energy is necessary to break the hydrogen bonds holding the water molecules close together in the liquid state. When the water molecules break free from each other, the distance between them is increased by thousands of times. In my classroom I explained that to scatter any sort of matter, such as a pile of marbles, into a larger space, energy must be used up. In the swimming pool example heat energy is used up from our skin. Scientists call the heat energy needed for this process latent heat of vaporization.
As evaporation takes place from large water bodies and travels long distances, large quantities of heat travel along with it. Eventually warm moist air rises to cooler levels of the atmosphere. Cooling the air causes the warm, moist air to condense back into drops of water. Heat is given back into the air once more as water drops form. This heat is called latent heat of condensation, the opposite process of latent heat of vaporization. This causes the heated air to expand, become lighter again and rise to even cooler elevations. The condensation process repeats several times, giving heat back into the atmosphere each time. Ultimately the process is finished, but not before some seasonal thunderstorms bring lightning, thunder, wind, and heavy rain to the area. Living in the Midwest sometimes brings with it the “right of passage” of severe weather experiences.
Our weather systems are ultimately driven by heat energy from the sun falling unequally on some latitudes more directly than others. In turn, the earth’s heat balance is tuned by the wonderful processes of heat distribution we have described. Life-sustaining precipitation depends on the atmosphere’s ability to distribute water vapor and heat energy widely. We depend on “normal” rainfall for our geographic areas to supply moisture for normal regional crops. Many weather experts preach that there is hardly a normal or average for any given day. Normal
After reading the inspiring chapters of Job 36-38, one may experience a feeling of genuine humility in response to our life-sustaining planetary weather system. Some descriptions of weather events in Job are inspiring for their beauty. Others are genuinely frightening. The account of weather in Psalm 29 strikes terror as we are exhorted to “Ascribe to the Lord the glory due his name…” The author of Job 42 recounts the worshipful humility of Job after contemplating the wonder of God in nature, especially in weather events: “I know that you can do all things; no plan of yours can be thwarted. You asked, ‘Who is this that obscures my counsel without knowledge?’ Surely I spoke of things I did not understand, things too wonderful for me to know. You said, ‘Listen now, and I will speak; I will question you, and you shall answer me.’ My ears had heard of you but now my eyes have seen you. Therefore I despise myself and repent in dust and ashes.” (Job 42:2-6 NIV)
