Meteorology/Climate

Weather and Climate:Climate describes a location’s composite or average temperature over a time period of 30 years. The climate of a location is determined by the state of and interactions between different components of Earth’s climate system. There are 4 parts to the climate system: the atmosphere, hydrosphere, lithosphere, and biosphere. The atmosphere is the collection of all gases in the area, the hydrosphere is the collection of all water in the area, the lithosphere is the collection of all land or natural solids in the area (rocks), and the biosphere is the collection of all living organisms in the area. Quantitative Description: The climate of a location can be described as: average daily temperature, average monthly temperature (AMT), yearly average temperature, daily temperature range, and yearly temperature range. Climate Change: There are various causes to the issue of global warming such as the Greenhouse Effect. The greenhouse effect is a theory that explains one of the major causes of global warming. When the sun normally shines light upon Earth and heats the Earth’s surface, and because of this, Earth has to regulate its temperature so it releases that energy back into the atmosphere and later into space. But because of various greenhouse gases such as carbon dioxide, water vapor, methane, nitrous oxide, and chlorofluorocarbon, that energy gets trapped in the atmosphere. This then causes a buildup of heat in the atmosphere and in turn it makes the Earth hotter. Since the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat-trapping capability of the Earth and its atmosphere. Sulfate aerosols cool the atmosphere by reflecting light back into space; however, sulfates are short-lived in the atmosphere and vary regionally. Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. Plant respiration and the decomposition of organic matter release more than 10 times the CO2 released by human activities; but these releases have generally been in balance during the centuries leading up to the industrial revolution with carbon dioxide absorbed by terrestrial vegetation and the oceans. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of U.S. carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions. In 1997, the United States emitted about one-fifth of total global greenhouse gas emissions. Effects of Climate Change: Surface temperature has increased dramatically since the 19th century, about 0.5 to 1F*. The 20th century’s 10 warmest years all occurred in the last 15 years of the century. 1998 being the warmest. The snow cover in the Northern Hemisphere has melted off and the floating chunks of ice in the Arctic Ocean have increased. The sea level has increased about 4 to 8 inches over the past century. Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall has increased throughout much of the United States. Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change. Scientists expect that the average global surface temperature could rise about 1 to 4.5 degrees fahrenheit in the next 50 years, and 2.2 to 10 degrees in the next century, with significant regional variation. Evaporation will increase as the climate warms, which will increase average global precipitation. Soil moisture is likely to decline in many regions, and intense rainstorms are likely to become more frequent. Sea level is likely to rise 2 feet along most of the U.S. coast. Evolution: The modern atmosphere is sometimes referred to as Earth’s “third atmosphere”, in order to distinguish the current chemical composition from previous compositions. The original atmosphere (about 4.6 billion years ago) was primarily helium and hydrogen. Heat from the still-molten crust, the sun, and a probably enhanced solar wind, dissipated this atmosphere. About 4.4, billions of years ago, the surface had cooled enough to form a crust. It was heavily populated with volcanoes, which released steam, carbon dioxide, and ammonia. This led to the early “second atmosphere”, which was primarily carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. This second atmosphere had approximately 100 times as much gas as the current atmosphere, but as it cooled water vapor precipitation out to form oceans, and much of the carbon dioxide was dissolved in the seas and precipitated out as carbonates. The later “second atmosphere” contained larger nitrogen and carbon dioxide. It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide and methane, kept the Earth from freezing. The oxygen-nitrogen atmosphere that we have now is the “third atmosphere”. The oxygen in the third atmosphere resulted from photosynthesis, starting with anaerobic bacteria approximately 3.5 billions years ago. Between 200 and 250 million years ago, up to 35% of the atmosphere was oxygen )as found in bubbles of the ancient atmosphere preserved in amber), but this percentage has dropped to what it is today. Greenhouse gases: The gases are called greenhouse gases for their direct role in it. Greenhouse gases occur naturally; however, their increasing atmospheric concentrations due to human activity is the primary cause of human induced climate change. The relative “strength” of a greenhouse gas is often described using a quantity known as global warming potential (GWP), which compares the absorption of longwave radiation by a gas to that of an equivalent amount of carbon radiation and how long the gas remains in the atmosphere (its “lifetime”). By definition, the global warming potential of carbon dioxide over any time frame must be equal to 1.When the concentrations of these gases in the atmosphere are accounted for, and they are ranked by their contribution to the greenhouse effect, the most important greenhouse gases are: Water vapor, which contributes 36 - 70%, carbon dioxide, which contributes 9 - 26%. Methane, which contributes 4-9%, ozone, which contributes 3-7% nitrous oxide, which contributes 2-4%. Aerosols and Particulates: An aerosol is a suspension of a solid or liquid particle within a gas. Important aerosols in the atmosphere include sulfate and black carbon aerosols. Particulates are solid particles suspended in the air. Ejections of particles from volcanic eruptions can have a significant effect on short-term climate. While technically different, the terms “aerosol” and “particulate” are frequently used interchangeably. Sulfate aerosols consist of solid or liquid particles containing the sulfate ion. They occur naturally as a result of ocean sea spray; however, most sulfate aerosols result from human burning of sulfate-containing fossil fuels. These aerosols are very reflective, and as a result can directly impact climate by reflecting incoming solar radiation. Sulfate aerosols can also indirectly affect climate by acting as cloud condensation nuclei, resulting in more clouds or clouds or clouds with different properties. Both the direct and indirect effects of sulfate aerosols have a cooling effect on atmospheric temperature. The aerosols also have short atmospheric lifetimes (on the order of days), and as a result their effects on climate are the most near the locations where emissions of sulfurous compounds occur. Large volcanic eruptions eject particles and gases such as water, carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrofluoric acid. Sulfur dioxide may react with hydroxide and water to form sulfate aerosols. The force of an explosive eruption can push these aerosols into the stratosphere, where they are not removed by precipitation via wet deposition. As a result, these sulfate aerosols can last in the stratosphere for 2-3 years and have a more widespread global effect in the short-term climate. For example,  the eruption of Mount Tambora in 1815 is believed to have contributed significantly to abnormally cold temperatures in Europe the following year, often called the year without a summer. Black carbon aerosols are soot with very high amounts of carbon. Like tropospheric sulfate aerosols, black carbon aerosols have short lifespans and as a result their effects are generally limited to the geographic region where they are produced. In contract to sulfate aerosols, black carbon aerosols absorb incoming solar radiation very effectively, producing a warming effect.  Earth’s Radiative Energy Balance: Sunlight is the source of energy for the Earth’s oceans, atmosphere, land, and biosphere in meteorology, sunlight is often referred to as “insolation”, an abbreviation for incoming solar radiation. A portion of the insolation that reaches Earth is absorbed, raising its temperature. The Earth, as a result of its temperature, radiates infrared radiation into the atmosphere and space. Insolation, mostly shorter wavelength visible radiation, is also called “short-wave radiation”, while terrestrial radiation emitted by Earth, mostly longer wavelength infrared radiation, is called “long-wave radiation”.  A balance between the amount of energy received as incoming shortwave radiation and the amount of energy released through outgoing longwave radiation is key for stable temperature in Earth’s climate system; imbalances result in changes in climate. Albedo is the ratio of the amount of radiation reflected by a surface to the amount of radiation that initially reached that surface. Surfaces may have an albedo between 0 and 1, with less reflective features such as forests having an albedo closer to zero and more reflective features such as glaciers having an albedo closer to one. The overall average albedo of Earth is about 0.3, meaning that about 30% of insolation is reflection back to space rather than absorbed. Particularly on local scales, albedo may be altered by land use changes, such as deforestation, agricultural expansion, and urbanization. An urban heat island is a phenomenon in which temperatures in urbanized areas are significantly higher than pre-urbanization or surrounding rural areas in part due to a decrease in the local albedo. Emissivity is a quantity that describes how effectively something can emit radiation due to its temperature. It is inversely related to albedo. For example, something that is pure white would have an albedo of 1, but an emissivity of 0. Something that is pure black would have an albedo of 0, and an emissivity of 1. Similar to albedo, emissivity can range between 0 and 1, with zero representing a theoretical material that emits no radiation and one representing a material that is a “perfect emitter.” In models of Earth’s radiative energy balance, the emissivity of zero represents no greenhouse effect, while an atmospheric emissivity of 1 represents a perfect greenhouse effect. Climate Variability and Classification: The climate at a location is usually characterized by two factors: the temperature and the amount of precipitation. Both the overall magnitude and seasonal variation of these two are significant. These factors affect the types of vegetation that can survive at a location. Temperature controls: Latitude - main factor, higher the latitude, the lower the average yearly temperature and larger the yearly temperature range. Altitude - average rate of decrease 6.5 C per kilometer. Land/sea boundary - areas in close proximity to a large body of water will tend to have a smaller range of temperatures (less extreme temperatures) than areas at similar latitudes and elevation that are far from large bodies of water (known as continentality). Prevailing winds - moderates temperatures; effect doesn’t extend past the first high mountain range. Warm or cold ocean currents can affect the temperature of an area. Rainfall controls: Latitude - wet belt or dry belt. Mountains - windward sides are rainy, leeward sides have dry, descending winds called chinooks and foehns (known as the rain shadow effect). Distance from the sea - drier near the interior of the continent (not a guarantee). Climate Classification: Koppen Classification, Group A: Tropical/megathermal climates - Tropical rainforest climate (Af), Tropical monsoon climate (Am), Tropical wet and dry or savanna climate (Aw). Group B: Dry (arid and semiarid)(climate's precipitation is less than potential evapotranspiration) - Subtropical desert (Bwh), Subtropical steppe (Bsh), Mid-Latitude desert (Bwk), Mid-Latitude Steppe (Bsk). Group C: Temperate/mesothermal climates- mediterranean climates (Csa, Csb), Humid subtropical climates (Cfa, Cwa), Maritime Temperate climates or Oceanic climates (Cfb,  Cwb,  Cfc), temperate climate with dry winters (Cwb), Maritime Subarctic climates or Subpolar Oceanic climates (Cfc), Group D: Continental/microthermal climate - Hot Summer continental climates (Dfa, Dwa, Dsa,), Warm Summer continental or Hemiboreal climates (Dfb, Dwb, Dsb), Continental Subarctic or Boreal (taiga) climates (Dfc, Dwc, Dsc). Group E: Polar climate (ET), Ice cap climate (EF). Group H: Highland climates, in which altitude plays a role in determining climate classification.   Koppen vs Thornthwaite: The Koppen classification depends on average monthly values of temperature and precipitation. Koppen’s rival system was modified/developed by an American climatologist and geographer C. W. Thornthwaite. Thornthwaite’s classification system utilizes the monitoring of the soil water budget using evapotranspiration. Semi-Permanent Highs and Lows:  Semi-permanent highs and lows are pressure systems that last over a certain location throughout the year. They affect the climate by steering weather systems and hurricanes. Aleutian Low: The Aleutian low is located west of ALaska in the Bering Sea, near the ALeutian islands. The Aleutian low is most intense during the winter and awakens drastically in the summer. It intensifies cyclones and steers them into the Pacific Northwest. Icelandic Low: The Icelandic low is located near Iceland and Greenland. It is similar to the Aleutian law. It is strongest in the winter and weak in the summer. It also intensifies cyclones. Bermuda High: The Bermuda high is located in the Atlantic Ocean  in the northern hemisphere around 30N. It is close to the east coast in the summer and drifts further east in the winter. It directs moit air onto the east coast during the summer. It also has a major impact on the path of hurricanes in the Atlantic and where it will make landfall. It allows the gulf stream to dip in winter and helps drive the Gulf Stream. Europeans often refer to the Bermuda High as the Azores High. Siberian High: The Siberian high is located over Russia in Siberia. It forms during the winter and is the strongest semi-permanent high in the northern hemisphere. It consists of very cold air. North Pacific High: The North Pacific High is located in the northeast Pacific, northeast of Hawaii but west of California. It is usually strongest in the summer and shifts towards the equator in the winter. The North Pacific High is responsible for dry summer in California and year round trade winds in Hawaii. South Pacific High: The South Pacific high is located in the south Pacific ocean off the coast of South America. It causes the west coast of South America to be very dry. Thermal Low: A thermal low is not one specific pressure system, but is a type of semi-permanent pressure system. They usually occur over deserts where there is intense daytime heating, which causes the heated air to rise, creating low. They occur during the summer. They have little to no precipitation and weak cyclonic circulation.  El Nino and La Nina: El Nino and La Nina are officially defined as sustained sea surface temperature anomalies of magnitude greater than 0.5 C across the central tropical Pacific Ocean. When the condition is met for a period of less than five months, it is classified as El Nino or La Nina conditions; if the anomaly persists for five months or longer, it is classified as an El Nino or La Nina episode. Historically, it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years. El Nino: The first signs of an El Nino are a rise in air pressure over the Indian Ocean, Indonesia, and Australia, then a fall in air pressure over Tahiti and the rest of the central and eastern Pacific.  Trade winds in the south Pacific weaken or head east, and then warm air rises near Peru, causing rain in the northern Peruvian deserts. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current, also known as the Peru Current, which supports great populations of food fish. In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Niño conditions last for many months, more extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious. During non-El Niño conditions, the Walker circulation is seen at the surface as easterly trade winds, which move water and air warmed by the sun towards the west. This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. The western side of the equatorial Pacific is characterized by warm, wet low-pressure weather as the collected moisture is dumped in the form of typhoons and thunderstorms. The ocean is some 60 cm higher in the western Pacific as the result of this motion. Also refer to Walker Circulation model and how it relates to ENSO. La Nina: In the Pacific, La Nina is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, compared to El Nino, which is characterized by unusually warm ocean temperatures in the same area. Atlantic tropical cyclone activity is generally enhanced during La Nina. The La Nina condition often follows the El Nino, especially when the higher is stronger.  Thermohaline Circulation: The term thermohaline circulation (THC) refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from “thermo-”, referring to temperature , and “-haline”, referring to salt content. These factors together determine the density of seawater. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion,  it is used to refer to the meridional overturning circulation (often abbreviated as MOC). Oceanic Circulation Path: Wind Driven surface currents (such as the Gulf Stream) head polewards from the equatorial Atlantic Ocean, cooling all of the while and eventually sinking at high latitudes (forming North Atlantic Deep water). The formation and movement of the deep water masses at North Atlantic Ocean creates sinking water masses that fills the ocean basins and flows very slowly into the deep abyssal plains of the Atlantic. This high latitude cooling and the low latitude heating drives the movement of the deep water in a polar southward flow. The deep water flows through the Antarctic Ocean Basin around South Africa where it is split into two routes: one into the Indian Ocean and one past Australia into the Pacific. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. At the Indian Ocean, some of the cold and salty water from the Atlantic – drawn by the flow of warmer and fresher upper ocean water from the tropical Pacific causes a vertical exchange of dense, sinking water with a lighter water above. The out-flowing undersea of cold and salty water makes the sea level of the Atlantic slightly lower than the Pacific and salinity or salinity of water at the Atlantic higher than the pacific. These characteristics of the Pacific generate a large but slow flow of warmer and fresher upper ocean water from the tropical Pacific – causes a vertical exchange of dense, sinking water with lighter water above. The out flowing undersea of cold and salty water makes the sea level of the atlantic slightly lower than the pacific and salinity or salinity of water at the Atlantic higher than the Pacific. These characteristics of the Pacific generate a large but slow flow of warmer and fresher upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelago to replace the cold and salty Antarctic Bottom Water. This is also known as Haline forcing (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific also flows up through the South Atlantic to Greenland, where it cools off and undergoes evaporative cooling and sinks to the ocean floor, providing a continuous thermohaline circulation. It is known as overturning. Hence, a recent and popular name for the thermohaline circulation, emphasizing the vertical nature and pole-to-pole character of this kind of ocean circulation, is the meridional overturning circulation. Impact on Earth’s Climate: As such, the state of the circulation has  a large impact on the climate of the Earth. Because of this massive circulation, extensive mixing takes place between the ocean basins, reducing differences between them and making the Earth’s ocean a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. If this system were to shut down, this changed flow would alter the climates of the entire Earth, and there would be no more circulation of salt or water. This would change the ocean habitats as well, and would affect marine life. Representative Concentration Pathways (RCP): Four greenhouse gas concentration (not emission) trajectory adopted by the IPCC (Intergovernmental Panel on Climate Change) for its 5th assessment report.The four RCPs, RCP2.6, RCP4.5, RCP6, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively). Daisyworld Model: The Daisyworld Model is a hypothetical idea in which a planet is covered in black and white daisies. The daisies have different albedos, so the growth of both daisies affect the planet’s temperature and overall population. The Daisyworld Model is a demonstration of the Gaia Theory. Milankovitch Cycles: Obliquity: The angle of the Earth’s axial tilt (obliquity) varies with respect to the plane of Earth’s orbit. These slow 2.4 degree obliquity variations are roughly periodic, taking approximately 41,000 years to shift between a tilt of 22.1 degrees and 24.5 degrees and back again. When the obliquity increases, the amplitude of the seasonal cycle in insolation (INcoming SOLar radiATION) increases, with summers in both hemispheres receiving more radiative flux from the Sun, and the winters less radiative flux. As a result, it is assumed that the winters become colder and summers warmer. But these changes of opposite sign in the summer and winter are not of the same magnitude. The annual mean insolation increases in high latitudes with increasing obliquity, while lower latitudes experience a reduction in insolation. Cooler summers are suspected of encouraging the start of an ice age by melting less of the previous winter’s ice and snow. So it can be argued that lower obliquity favors ice ages both because of the mean insolation reduction in high latitudes as well as the additional reduction in summer insolation. We are presently in a period of decreasing obliquity. Eccentricity: The Earth’s orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth’s orbit varies from being nearly circular (low eccentricity of 0.005) to being mildly elliptical (high eccentricity of 0.058) and has a mean eccentricity of 0.028 (or 0.017 which is current value). The major component of these variations occurs over a period of 413,000 years (eccentricity version of plus minus 0.012). A number of other terms vary between 95,000 and 136,000 years, and loosely combine into a 100,000 year cycle. The present eccentricity of 0.,017. Precession: Precession is the change in the direction of the Earth’s axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal focus exerted by the sun and the moon on the solid Earth, associated with the fact that the Earth is not a perfect sphere but has an equatorial bulge. The sun and the moon contribute roughly equally to this effect. In addition, the orbital ellipse itself processes in space (anomalistic precession), primarily as a result of interactions with Jupiter and Saturn. This orbital precession is in the opposite sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 25, 77.5 to 21,636 years.