What is Weather?

What is Weather?

To put it mildly, weather is the state of the atmosphere at any given time and/or place.¹ Weather is all around us, there's no escaping it! Take a step outside and feel the fresh air. Look up at the sky, what do you see? Clouds?² A rainbow? Light pillars? Rain or snow?² What do you feel? Is it hot or cold?² Warm or cool?² Arid or humid?² Windy or calm?² All of these things are examples of weather, and although some weather is invisible to the naked eye, the forces of mother nature have the ability to reshape our lives and the landscape of Earth.¹ ²

Weather is a very underappreciated aspect of God's creation, as many take it for granted on a daily basis without even realizing it.¹ ³ Generally speaking, the only time people pay attention to the weather [forecast] is when there is a life-threatening situation underway that could impact their safety, such as incoming severe thunderstorms accompanied with damaging winds, hail, and even tornadoes, as well as hurricanes and blizzards that could be knocking on the doorstep.¹ ³

So, what causes the weather?

Almost all weather that occurs on Earth unfolds in the lower atmosphere, otherwise known as the troposphere.² ⁴ There are some weather phenomena that can occur in the stratosphere and mesosphere, e.g. nacreous clouds and polar mesospheric clouds, respectively, however, how and why these phenomena happen is a big area of research.²

Weather primarily depends upon three important things, including atmospheric pressure, temperature variations, and moisture differences between any two or more given locations.² These key differences are mainly a result of the fact that direct solar radiation from the sun is unevenly distributed to all latitudes of the globe.² Because of Earth's spherical shape, the equator receives the bulk of sunlight whereas the poles receive the least.²

As an outcome, the poles are much colder than the equator, which sets up a large temperature gradient (contrast) between the poles and tropics.² As such, large-scale atmospheric circulations such as the jet stream and the Hadley, Ferrel, and Polar Cells arise from the temperature contrast.² These large-scale atmospheric circulations are major players in not only the Earth-atmosphere energy balance, but also how the weather on smaller scales works.

On a much smaller scale, mid-latitude weather systems such as mid-latitude cyclones and thunderstorms are driven by irregularities in the jet stream, whereas tropical weather systems such as monsoons and tropical cyclones are driven by entirely different processes, which I will dive deep into further down the road.²

Given that Earth's surface is unevenly heated by solar radiation, pockets of air known as "parcels" are able to form over "heated spots" and rise high into the troposphere while cooler air from aloft sinks down to replace the warmer air.⁴ ⁵ ⁶ This rising warm air initially expands, which lowers the density and therefore the pressure.² 

Surface temperature differences can be caused by any number of reasons. Aside from Earth's spherical shape, it should also be taken into consideration that different surfaces heat faster than others; for instance soil or blacktop as compared to water.² ⁵ Furthermore, the weather itself may prevent surface heating, i.e. clouds, precipitation, and temperature inversions.² Vertical heat distribution by rising air is commonly referred to as "convection."⁶ 

As previously stated, the horizontal temperature differences between the poles and tropics is a function of solar radiation and Earth's spherical shape. This temperature contrast results in not only large atmospheric circulations, but also atmospheric pressure differences.⁴ ⁵ ⁶ Every area of low pressure is surrounded by an area of high pressure, in which winds develop in an attempt to balance the pressure differences.² ⁴ ⁵ ⁶ Wind flows from areas of high pressure to areas of low pressure just like heat flows from areas of warmer temperature to areas of cooler temperature.² ⁵ The Coriolis Effect allows the wind to be deflected (turned) towards low pressure systems.² 

High pressure systems or "anticyclones" spin clockwise in the Northern Hemisphere unlike low pressure systems or "cyclones," which spin counterclockwise. In the Southern Hemisphere, it's opposite, but it's easy to distinguish areas of high and low pressure by wind flow. Areas of high pressure are differentiated from areas of low pressure because winds in a high pressure system, regardless of the Hemisphere, diverge away from the center (as wind flows from high pressure to low pressure) while also sinking down towards the surface.⁴ Areas of low pressure are associated with an inflow of winds and convergence, which forces the air to rise, cool, and any water vapor within to cool and condense into clouds, which is why our storm systems are usually associated with low pressure areas.⁴



Weather vs. Climate

Such the case arises all too often where people confuse weather and climate. Surly there can't be that much of a difference, right? 

While the two terms are very similar in context, they can not be used interchangeably, because there are two fundamental differences between "weather" and "climate." Firstly, weather is all about daily fluctuations and extremes, while climate is more about averages.² ⁷ ⁹ ¹⁰ ¹¹ Moreover, the primary difference between weather and climate is that weather is a measure of the weather over a short period of time; generally seconds, minutes, hours, days, weeks, or months.² ⁷ ⁹ ¹⁰ ¹¹ Climate conversely, is the average weather pattern observed over a lengthy period of time.² ⁷ ⁹ ¹⁰ ¹¹ From a daily high or low temperature to the amount of rain or snow one location receives on any given day, these are examples of weather.² ⁷ ¹¹ Long-term temperature or precipitation trends are examples of climate.² ⁷

Climatic averages come in a variety of forms; they can be daily averages, weekly averages, monthly, seasonal, or annual averages. For instance, when all weather data from one particular location is summed up over a fixed number of years, and then divided by the number of years, the end result is the "average" or "climatic normal."⁸ While averages can be determined with any number of years, the standard from NOAA is the arithmetic average of 30 years.⁸ The most recent set of averages are from the 30-year period of 1981 to 2010.⁸ In 2021, a new set of averages will be calculated for the period 1991 through 2020.⁸

You will often see your local television broadcast meteorologist mention these "climatic normals" when they are explaining how temperatures or precipitation stack up compared to the 30-year average while presenting the weather forecast.⁸

What's quite ironic is that "normal" weather rarely happens.⁷ ⁸ This is because thermometers don't measure "average temperature," they measure the maximum and minimum temperature for every day. Averages are calculated either by hand or computer. Thus the saying "climate is what you expect, weather is what you get" is true.⁸ It can also be thought of as if the climate is the atmosphere's "personality," while the weather is the atmosphere's "mood."⁷

Around the world are numerous different climates and even subclimates.⁴ ⁹ For instance, Antarctica's climate is far different than that of Europe's. These different climates exist because of once again, Earth's spherical shape.⁷ Polar climates of higher latitude vary far differently than climates in mid-latitudes and the tropics.⁷ ⁹ ¹¹ However, latitude doesn't guarantee that places at the same latitude will have the same climate.⁷ ⁹ ¹¹ Factors such as elevation and whether or not a location is by a sea can influence a location's climate potentially far greater than the latitude at which it resides!⁷ ⁹ ¹¹

Meteorological Madness! 🠈 Previous       Next 🠊 The Atmosphere

REFERENCES

[1] 

[2] "Weather." Wikipedia, the free encyclopedia. May 25, 2019. Accessed June 7, 2019. https://en.wikipedia.org/wiki/Weather.

[3] "How weather works." Met Office: weather and climate change. Accessed June 7, 2019. https://www.metoffice.gov.uk/weather/learn-about/weather/how-weather-works.

[4] "Weather: The Basics." UCAR Center For Science Education. Accessed June 7, 2019. https://scied.ucar.edu/shortcontent/weather.

[5] "What Drives Weather." North Carolina Climate Office | Climate Education Modules. Accessed June 7, 2019. https://climate.ncsu.edu/edu/Drivers.

[6] Spencer, Roy. "What causes weather?" WeatherStreet - Weather Questions and Answers. January 8, 2011. Accessed June 7, 2019. http://weatherstreet.com/weatherquestions/What_causes_weather.htm.

[7] "Climate and Weather." North Carolina Climate Office | Climate Education Modules. Accessed June 7, 2019. https://climate.ncsu.edu/edu/Climate.

[8] "Climate vs. Weather." National Weather Service - JetStream. Accessed June 7, 2019. https://www.weather.gov/jetstream/climate_v_wx.

[9] Combs, Felicia. "Wednesday's Weather Word: Climate." West Palm Beach News and Headlines | WPTV-TV | WPTV.com. April 5, 2017. Accessed June 7, 2019. https://www.wptv.com/weather/weather-blogs/wednesdays-weather-word-climate/.

[10] Skilling, Tom. "How is meteorology different from climatology?" WGN-TV | Chicago's Very Own source for breaking news, weather, spots and entertainment. October 24, 2018. Accessed June 7, 2019. https://wgntv.com/2018/10/24/how-is-meteorology-different-from-climatology/.

[11] "What's the Difference Between Weather and Climate?" NOAA SciJinks - All About Weather. Accessed June 7, 2019. https://scijinks.gov/weather-v-climate/.