Solar radiation

The sun, our closest star, generates energy through thermonuclear reactions, emitting it into space. This energy comprises corpuscular (0.2%) and electromagnetic wave (99.8%) radiation, collectively known as solar radiation. Earth’s magnetic field shields it from corpuscular radiation, causing phenomena like auroras. Meteorologically crucial is the short-wavelength solar radiation (0.2 to 4 mm), divided into ultraviolet, visible (0.4 to 0.76 mm), and infrared (thermal) parts. This spectrum plays a vital role in understanding and studying meteorological processes.

The Atmosphere

The Earth’s atmosphere, crucial for life, shields against UV radiation, cosmic rays, and temperature extremes. 99% of its mass lies in the first 10 km, with a million times less mass than Earth’s solid part. The atmosphere is divided into the homosphere (up to 95 km) with constant gas ratios and the heterosphere above, where ratios vary.

Atmosphere composition

The Earth’s atmosphere primarily consists of nitrogen (78%), oxygen (21%), argon (1%), and trace gases, with water vapor at lower altitudes. Ozone, a vital component, constitutes less than 0.00001%, forming a thin layer at sea level. Aerosols, micro particles of natural and human-made origin, act as nuclei for cloud and precipitation formation. Natural aerosols include sea salt, pollen, and dust, while human-created ones consist of dust, soot, and various particles. In cities, the concentration of floating aerosol particles can be as high as 10^6 per cubic cm.

Distinct atmospheric layers

The Earth’s atmosphere consists of distinct layers based on temperature and characteristics. The troposphere, the lowest layer, extends 8-18 km in height and houses almost all water vapor, driving weather changes. Above it is the stratosphere, with the ozone-rich layer at 20-25 km, absorbing UV rays. The mesosphere follows, with a rapid temperature drop from 40 to 80 km, hosting unique night clouds. Lastly, the thermosphere spans 90-800 km, experiencing extreme temperature variations. These atmospheric layers collectively form 99.9% of the total mass, each playing a crucial role in Earth’s climate dynamics and phenomena.

layers of the atmosphere 1 e1706092984789


Heat, a form of energy, transfers between bodies due to temperature differences. Temperature, measured in Kelvin (K), reflects a substance’s energy state. In meteorology, solar radiation or ground heat flux unaffected air temperature at 2 meters height. It varies with time, weather, and geography, subject to sudden cold or hot air outbreaks, strong winds, and annual changes influenced by the Sun’s position, Earth’s distance, climate shifts, and location.

Ranges of Temperature

Air and surface temperatures vary regularly and irregularly. Periodic changes, linked to Earth’s radiation and insolation, depend on altitude, latitude, and surface factors. Irregular changes result from weather fluctuations. Statistical theory of secondary values aids in determining daily and annual averages. Large bodies of water with high specific heat undergo slow temperature changes influenced by salinity, leading to lower freezing points, like seawater freezing below 0°C.

Annual temperature range

  • Equatorial: Small range (1-5 °C), 2 highs and lows, medium 25-30 °C.
  • Monsoon: Larger range than equatorial type.
  • Oceanic: Delayed maximum (September), along western coasts in lower latitudes (15-40 °C) with cold sea currents.
  • Temperate: Pronounced extremes, 4 seasons, ranges above sea 10-15 °C, above land 20-40 °C.
  • Polar: Smallest middle, biggest range (especially above land), short summer (2 months), long winter (6 months), delayed extremes (2-3 months).

annual temperature range

Annual change of air temperature as influenced by the sea

If Earth were flat and atmospherically uniform, the temperature would rely solely on astronomical factors and latitude, termed solar-mathematical climate. Reality presents a physical climate influenced by land-sea distribution, orography, atmosphere diversity, clouds, and air currents. The northern hemisphere is 2 °C warmer, experiencing warmer summers and colder winters due to land-sea division. Earth’s average temperature is 14.3 °C, generally decreasing with latitude. The thermal equator, slightly north of the geographic equator, marks the warmest belt. Temperature typically declines with altitude in the lower atmosphere, averaging -0.65 °C / 100 m, higher in summer (-0.7 to -0.9 °C / 100 m) and lower in winter (-0.4 to -0.6 °C).

The Daily land temperature changes

Earth’s radiation and insolation influence daily land temperature changes. From sunrise to about 13 hours, temperatures rise due to lower radiation levels than insolation. Post 13 o’clock, radiation exceeds insolation, causing a temperature decline until the next sunrise. Minimum land temperatures occur pre-sunrise, while maximum temperatures peak around 13 o’clock. Daily amplitudes decrease with latitude and are lower in winter. Amplitudes increase with elevation. Annual land temperature changes depend on Earth’s radiation and insolation variations, with equatorial sites having the lowest amplitudes, increasing toward the Poles due to latitude changes.

Daily sea temperature changes

Daily sea temperature changes are modest, diminishing with depth and disappearing at 25 meters. Lakes exhibit an average daily amplitude of 2°C, while seas have around 0.04°C. Minimal Sea warmth is pre-sunrise, peaking between 15 and 16 o’clock, then gradually decreasing. Annual sea temperature changes increase with latitude, more pronounced than daily changes. Land and sea temperatures correlate, with maximum and minimum land temperatures preceding sea temperatures. Daily air temperature changes mirror land and sea patterns, showing minimums pre-sunrise and maximums around 14 o’clock. The Equator experiences the largest daily air temperature amplitudes, while the Poles have none.  

Daily air temperature changes

Air temperature changes above water differ from those over land due to water’s distinct physical characteristics. Over the ocean, minimum air temperature occurs between 1 and 3 o’clock after midnight, 2 hours before the surface minimum. Maximum air temperature over water peaks around 13-14 o’clock, considerably earlier than over the ocean surface. Annual air temperature changes increase with latitude. Equatorial water has a 1°C range, polar latitudes show 20°C, and moderate widths fall between 10 and 15°C.


The fundamental temperature gap is the difference between the boiling and freezing points of water at 101325 Pa. Celsius degrees result when this range is divided into hundred parts, while Kelvin is based on the thermodynamic temperature of the water’s triple point. Only a few countries use Fahrenheit degrees (°F), like the United States. On the Celsius scale, water freezes at 0°C and boils at 100°C, while on the Fahrenheit scale, freezing is at 32°F and boiling at 212°F. Thermometers and thermographs are devices used for temperature measurement.

Meteorological thermometers include dry-bulb and wet thermometers for air temperature and humidity measurement. The dry-bulb thermometer, filled with mercury, displays air temperature in Celsius. Extreme, minimum, and maximum thermometers use toluene or alcohol. The minimum thermometer’s wand, dipping with temperature decrease, displays the lowest temperature at the stick’s right end.

Meteorological thermometers include dry-bulb and wet thermometers for air temperature and humidity measurement. The dry-bulb thermometer, filled with mercury, displays air temperature in Celsius. Extreme, minimum, and maximum thermometers use toluene or alcohol. The minimum thermometer’s wand, dipping with temperature decrease, displays the lowest temperature at the stick’s right end.

temperature measurement


A thermograph monitors air temperature changes using a sensor, a bimetal ring or “Bourdon” tube filled with gas, recording results on a printer to produce a thermogram. To shield instruments from external influences, a thermometric house (shelter) is used, made of wood with white-painted shutter walls, positioned at about 2 m height on the observation deck, with the door facing north to avoid direct sunlight on the instruments when open.

temperature measurement 1


Air pressure is the force exerted by atmosphere molecules on a surface, measured in Pascals (Pa). The baric rate, or pressure change with height, is 1 hPa/8 m in the lower atmosphere. Atmospheric pressure is typically referenced to mean sea level (MSL). Isobars connect points with the same pressure, forming weather maps. Low-pressure centers (N, C, L, T) indicate cyclones, and high-pressure centers (V, A, H) represent anticyclones. Pronounced centers are primary, while fewer are side or secondary. Low-pressure areas are troughs, high-pressure areas are ridges, and the area between two centers is a saddle.

air pressure 1

Atmospheric pressure changes due to air heating and cooling above hot or cold surfaces. Heating reduces pressure, cooling increases it. These thermal changes result from the dynamic movement of air. Rising and dispersing air leads to falling pressure, while descending and accumulating air causes pressure to rise. Dynamic pressure changes occur throughout the day due to periodic and irregular factors. Periodic changes exhibit a double wave pattern, with the highest values 1 to 2 hours before noon or midnight. Daily amplitude is most pronounced in the tropics, decreasing with latitude, while irregular fluctuations range between 5 and 10 hPa.

Air pressure measurement

Air pressure measures the weight of the air column compared to a liquid, usually mercury. Torricelli’s mercury column method (1643) was the first. Barometers, aneroids, and barographs measure it, with the latter recording continuous changes. Corrections for temperature and mean sea level are necessary. Mercury barometers have a glass tube filled with mercury, and thermometers measure barometer temperature. Aneroids measure pressure-induced distortions in metal bodies. Barographs continuously measure changes, creating barograms for meteorological mapping. Altimeters are aneroids with altitude scales.

Air humidity

Air humidity, the water vapor in the air, increases with warmer temperatures. Concentrated mainly in the lower atmosphere, it diminishes with altitude. Evaporation intensity varies, being stronger on freshwater surfaces compared to salty ones. Three air humidity types include continental, with low summer and high winter humidity; monsoon, featuring low winter and high summer humidity linked to rainfall; and mountain, similar to monsoon but with heightened humidity related to increased convection.

air humidity


Air humidity is measured using hygrographs, psychrometers, and hygrometers. Hygrographs continuously record humidity values, displaying changes on a bar powered by a clock mechanism. The resulting time record is called a hygrogram. Psychrometers, comprising wet and dry thermometers, measure humidity based on temperature differences caused by water evaporation from a moistened cloth wrapped around the wet thermometer’s mercury tank. More significant temperature differences indicate lower air humidity.

air humidity measurement


Wind involves horizontal and vertical air movements. In maritime measurements, airspeed is in nautical miles (1 kt = 1 Nm/h, 1 Nm = 1852m). The Beaufort scale gauges wind strength. The wind direction is named for the side from which it blows. The wind rose illustrates wind direction and corresponding speeds. Global winds like trade winds, seasonal monsoons, and local winds occur due to uneven surface warming. Swirl or rotating winds include tornadoes and strong winds. Wind direction is influenced by baric gradient, with Coriolis’ force, centrifugal force, and friction affecting wind speed. Daily wind changes depend on solar position, causing variations in speed and direction. Marine winds are weaker during the day and stronger at night, while continental winds peak at noon and decrease in the evening.

wind in general



Permanent winds

Permanent winds, like Trade Winds and Easterlies, maintain consistent directions throughout the year. Trade Winds flow east-to-west in the equatorial region (30°N to 30°S latitudes), historically benefiting European-American voyages. Easterlies, prevailing winds from the east, include equatorial trade winds and polar winds. Westerlies, permanent west-to-east winds, occur in middle latitudes (30 to 60 degrees), known as anti-trades, steering extratropical cyclones towards the poles

Seasonal winds

Seasonal winds, exemplified by monsoons, result from predictable changes in large-scale weather patterns. Monsoons are low-latitude winds that shift direction between winter and summer. In winter, they bring dry air from the land, while in summer, they carry warm, moist air from water to land, causing substantial changes in precipitation and temperature.

Local winds

Local winds are predictable air circulations occurring in specific areas during particular periods. Examples include land breezes, flowing from land to sea at night, and sea breezes, from sea to land due to differing heat capacities of water and land. Anabatic winds occur on mountain slopes, driven by warmer temperatures. Katabatic winds, on the other hand, are downslope currents from colder mountain surfaces. Foehn winds are dry, warm, downslope winds in the lee of a mountain range.

Wind measurement

Weathercocks or vanes indicate wind direction with a rod and arrow moved by wind. Anemometers, electric or mechanical, portable or permanent, measure wind speed. Prandtl or Pitot tubes determine wind speed by static and dynamic pressure differences. Anemographs continuously record wind speed and direction. Beaufort charts estimate wind strength by effects on the observer’s horizon, categorizing into 12 degrees (13-17 for special cases). A larger scale used in Taiwan and China isn’t globally recommended.

wind measurement


A cloud is a visible cluster of droplets or frozen crystals in the atmosphere, formed from water vapor, ice cores, and a conducive process. They are categorized by formation, height, form, and special types

High-level clouds and examples

 High-level clouds, like Cirrus clouds, form above 6,000 meters and consist mainly of ice crystals due to low temperatures

Cirrus clouds are fluffy, icy, with a silky white glow, and their appearance can vary. They are indicative of changing weather, with fast-moving cirrus signaling bad conditions. While they don’t cause precipitation, their presence forecasts forthcoming weather changes, making them valuable for predicting wind patterns and general weather conditions.

high level clouds cirrus

Cirrostratus (Cs) – located 1 km below cirrus clouds, form a thin, icy veil covering the sky. They exhibit optical phenomena such as halos, arches, and rings, often creating fake suns. Cirrostratus clouds are indicators of impending bad weather.

high level clouds cirrostratus

 Cirrocumulus (Cc) – Noctilucent clouds, associated with cirrus and cirrostratus, are considered a result of their degeneration. Small icy clouds resembling “sheep” consist of tiny white spots, creating a lace-like appearance. Arranged in groups or stripes, they have holes revealing the blue sky, resembling a net. Noctilucent clouds do not cause precipitation.

high level clouds cirrocumulus

Mid-Level Clouds and examples

Mid-Level clouds are “alto” clouds. Clouds with the prefix “alto” are middle-level clouds with bases between 2000 and 7000 m (6500 to 23,000 ft.).

Altocumulus (Ac) – Altocumulus clouds form from the degeneration of cirrus and cirrostratus clouds. Comprising small, icy “sheep-like” clouds, they look lacy across the sky. Arranged in groups or stripes with occasional holes, they don’t lead to precipitation.

mid level clouds altocumulus

Altostratus (As) – Altocumulus clouds are mid-level clouds between 2,000 and 6,000 meters. They form white or gray patches or layers, often resembling a field of cotton balls. These clouds do not typically bring heavy precipitation but may signal changes in the weather.

mid level clouds altostratus

Low-Level Clouds and examples

Low-level clouds generally consist of water droplets. However, they can also contain ice particles and snow at very cold temperatures.

Nimbostratus (Ns) – Nimbostratus clouds are dense, gray layers covering the Sun, leading to a gray sky and causing rainfall, usually rain or snow.

low level clouds nimbostratus

Stratocumulus – (Sc) – Stratocumulus clouds are gray and white lumpy-layered clouds that appear in cylindrical or irregular shapes. They form a dense, uneven gray mass but do not cause precipitation.

low level clouds stratocumulus

Stratus (St) – Noctilucent clouds, or night-shining clouds, often appear during the cold season, resembling a thin gray curtain several hundred meters above the ground. Composed of tiny water droplets and more significant drops, they cause only light rain (drizzle) and are also called high fog. When these clouds touch the ground, they are referred to as fog.

Vertical Clouds and examples

Clouds with vertical development start in the low section of the atmosphere and travel up through the higher section.

Cumulus (Cu) – Cumulus clouds are elevated, chunky clouds formed by water droplets, resembling giant cauliflower with illuminated, glittering white parts and shadowed dark horizontal bases. They rise high and are not formed or sustained over the sea, serving as orientation when approaching the coast from the open sea.

vertical clouds cumulus

Cumulonimbus clouds (Cb) – are thick, heavy water clouds lifted by upward solid air currents. Their upper part freezes, resembling a flattened crest, causing storms, snow, rain, thunderstorms, and lightning.

vertical clouds cumulonimbus

Special Types of Clouds and Their Examples

Luminous night clouds in the mesosphere (75-90 km) resemble cirrus and cirrostratus clouds, illuminated by the Sun below the horizon. Composed of volcanic ash, ice crystals, and meteoritic dust, they’re visible mainly in northern regions.

 Nacreous clouds, rare in winter over Alaska and Northern Europe, consist of cold droplets and spherical ice particles. Traces of condensation form behind aircraft in cold atmospheres.

special types of clouds

 Fire clouds, or flammagenitus/ pyrocumulus, are dense cumuliform clouds result from fires or volcanic eruptions, potentially producing dry lightning.


Precipitation refers to water particles in liquid or solid form falling from clouds to the Earth’s surface or accumulating on objects and soil from the air. Virga, fog, sea smoke, snow blizzards, and strong winds, collectively known as hydrometeors, are associated phenomena. Processes leading to precipitation include pre-distillation, attraction of oppositely charged particles, coagulation, and more. Precipitation primarily falls from mixed clouds, resulting in ice particles like snowflakes, sleet, and granular snow. Hail forms through a combination of processes. Dew and frost are ground-level precipitation forms. Drizzle, moderate, and shower precipitation are categorized based on size and intensity. 

Types Precipitation

Precipitation types depend on the phase and character of falling water. Convective precipitation, more intense but shorter, and orographic precipitation, forced by mountains, contrast with stratiform precipitation, caused by air mass movements. Precipitation can be liquid (rain, drizzle) or solid (snow, hail), with freezing variations.  

The World distribution of precipitation

The Earth’s annual precipitation averages around 100 cm, varying across regions. Equatorial and Southeast Asian monsoon zones receive the highest levels, while middle latitudes experience moderate precipitation. Subtropical deserts and polar regions have minimal rainfall. Rainfall correlates with rising air, causing heavy precipitation in rising zones and dry conditions in descending zones. Trade winds contribute to rain on the east coast in the subtropics, while the west coast tends to be dry. In high latitudes, the west coasts are wetter.

Measurement of precipitation

measurement of precipitation

Precipitation is quantified by the volume of water sediment falling on Earth’s surface. Intensity, measured in millimeters, represents the water volume on a square meter. Instruments like pluviometers and ombrographs are used for measurement. Pluviometers capture total precipitation over a period, while ombrographs continuously record precipitation and intensity, generating ombrograms. Hellman’s pluviometer, frequently used, has a 200 cm² opening on a one-meter pillar, often placed in low-wind areas. Totalizers handle large precipitation volumes in inaccessible locations. Additional instruments like pluviographs and weighing precipitation gauges contribute to accurate measurements.


analyses of weather data

Forecasting weather relies on continuous ocean, land, and atmosphere observations. The World Meteorological Organization establishes a global observing system using satellites, radars, sonars, and surface measurements. Private citizens contribute valuable data, especially regarding precipitation, through social media. Scientists use mathematical methods to integrate measurements into snapshots of the land and atmospheric state, forming the basis for weather forecasts on various scales. This data supports environmental applications and scientific research on the climate system. Technology and data integration advances contribute to more accurate and comprehensive weather predictions.

Forecast Techniques

Meteorologists use diverse forecasting methods. Climatology analyzes long-term averages for specific locations and days. The analog method identifies past days with similar weather patterns. Persistence and trends rely on historical climate transitions. Numerical weather prediction uses supercomputers and models to consider various atmospheric conditions. Each method contributes to comprehensive weather forecasting with unique strengths and limitations.

Analysis of weather maps

A synoptic analysis integrates current and past weather data on a broader geographic scale to predict future weather developments. This process involves using synoptic maps, which are specialized weather maps displaying the network of synoptic stations, meridians, and parallels within a specific geographic area. Each synoptic station is represented by a cellular circle on the map, surrounded by symbols and numbers reflecting meteorological elements obtained through simultaneous measurements.

Weather maps, crucial for maritime purposes, come in smaller formats for port and ship use. These maps incorporate meteorological data and provide additional information on storm movements, thrombi, tornadoes, tropical cyclones, etc. The data from surface synoptic observations is essential for ground maps, while height maps include aerologic observations from various sources like pilot balloons, radio probes, satellites, aircraft, and rockets.

Synoptic maps are further categorized into ground and height maps, each serving distinct purposes. Decoding meteorological reports into understandable symbols relies on international keys, ensuring uniformity across languages and sailing regions. Numeric codes corresponding to specific meteorological elements enable the creation of a comprehensible synoptic map. Onboard, synoptic keys like FM 21 D SHIP and FM 11 D SYNOP aid in decrypting map drawing reports, facilitating effective maritime communication.

International Analysis Code (IAC Fleet) for marine radio weather

To closely monitor the weather, sailors rely on the synoptic report from a specific area, generated using the International Analysis Code (IAC). The IAC encrypts synoptic reports detailing coordinates of key points like fronts and isobars. Unlike the cellular model, this already-processed weather map provides a comprehensive synoptic situation. The analysis involves diagnosing baric systems’ impact, movement, expression, frontal influence, air mass characteristics, precipitation type and intensity, overall maritime weather, and navigation adjustments to ensure ship safety.

Air masses

air masses

An air mass is a vast body of air with nearly uniform temperature and humidity across different altitudes, covering an area from 500 to 5000 km and influencing several million square kilometers. It forms when the atmosphere interacts with a large, uniform land or sea surface for an extended period, adopting the surface’s temperature and moisture characteristics. A warm air mass has higher temperatures in lower layers, while a cold air mass, originating from polar zones or cold continents, exhibits stable balance, low humidity, and very low temperatures.

Atmospheric fronts

A frontal zone, a transition between air masses, spans up to 1000 km in length and 100 km in width, extending through the atmosphere. Frontolysis widens, while frontogenesis narrows the frontal belt. Fronts projected onto Earth’s surface include Arctic, polar, and tropical. Temperature-based categories are cold, warm, and occluded fronts. Warm fronts occur when warm air lifts cold air, creating a stable layered overcast. Cold fronts, displacing warm air, can be slow or fast-moving, causing thunderstorms. Occluded fronts combine warm and cold front features in cyclones’ final stages. Stormy stripes ahead of cold fronts experience intense instability and storms. Convergence zones indicate airlift, influencing cloud types based on humidity and lifting force. Warm and cold occlusions depend on the temperature relationship between catching-up cold air and preceding cold air.

Cyclone and anticyclone

cyclone and anticyclone

A cyclone is a low-pressure area, forming a counterclockwise whirlpool in the northern hemisphere and clockwise in the southern hemisphere, traveling west to east. It ranges from a few hundred to a few thousand kilometers. An anticyclone, a high-pressure area, has opposite air movement: clockwise in the northern hemisphere and counterclockwise in the southern. It exhibits clear and warm conditions in summer and variable conditions in winter. Subtropical anticyclones, like the Azores anticyclone, are nearly stationary and influence trade winds. Cold anticyclones form in cold air layers and may include stationary, mid-cyclone, final, and blocking anticyclones with varied characteristics, locations, and durations. Blocking anticyclones obstruct cyclones in moderate and higher latitudes, lasting up to a month.



Storms are complex meteorological phenomena characterized by a combination of atmospheric conditions, including lightning storms, strong winds, ascending and descending air currents, precipitation, hail, low visibility, electric discharges, turbulence, icing, sudden temperature and air pressure changes, and other associated effects. Convective clouds, such as Cumulus (Cu) and Cumulonimbus (Cb), play an integral role in storm formation, developing with the lifting of unstable air, particularly in warmer and more humid conditions.

The development of convective clouds, reaching from Cumulus to Cumulonimbus, is most significant over land in the late afternoon. At the same time, instability above the sea is more common at night due to the cooling of the lower and middle tropospheric layers. Cumulonimbus clouds, the culmination of this process, result in substantial rainfall, ice, and snow, potentially penetrating the highest layers of the troposphere and even breaching the stratosphere.

Lightning, a diverse electrical spark, occurs within specific temperature ranges and altitudes, generating millions of volts and thousands of amperes of electricity in a short duration. Thunder, a sound phenomenon accompanying lightning, stems from the rapid expansion and contraction of air caused by intense warming. Tornadoes, characterized by strong wind whirlpools, typically occur over land with varying dimensions, wind speeds, and durations, ranging from minutes to hours. Understanding these interconnected elements of storms is crucial for comprehending their dynamics and providing valuable insights into meteorological events and their potential impacts.



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