Insolation | ICSE Class 9 Geography Notes

This note covers insolation, terrestrial radiation, heating of the atmosphere, variations in solar energy, and the effects of latitude, altitude, distance from the sea, slope of land, winds and ocean currents on temperature.

What is insolation, and how is it different from temperature?

Definition: Insolation means incoming solar radiation, the energy received by the Earth from the Sun. The Earth's surface receives most of its energy in short wavelengths.

Radiation is the transfer of energy by electromagnetic waves. A wavelength is the distance between successive corresponding points on a wave. Short-wave solar radiation has shorter wavelengths than the long-wave radiation emitted by the heated Earth.

The Earth receives almost all of its energy from the Sun. This qualification matters: solar energy is overwhelmingly important, but saying that every form of energy on Earth comes from the Sun would make the claim too absolute.

What does temperature measure?

Temperature measures how hot or cold a substance or place is. Insolation describes incoming energy; temperature describes the thermal condition that results from the interaction of this energy with the Earth's surface and atmosphere, the envelope of gases surrounding the Earth.

The two terms therefore answer different questions. Insolation tells us about energy arriving from the Sun. Air temperature tells us how hot or cold the air is after processes of heating, cooling and heat transfer have acted upon it.

The amount of solar energy received differs between places and changes with time. The surface and atmosphere also transfer energy. Consequently, explaining a place's temperature requires more than identifying whether sunlight reaches it.

Which controls must be considered together?

The main temperature controls are latitude, the angular distance north or south of the Equator; altitude, height above sea level; distance from the sea; slope of land, its inclination; winds, air in horizontal motion; and ocean currents, flows of ocean water. The Equator is the imaginary circle dividing Earth into northern and southern halves.

Some controls affect the amount of solar energy received. Others affect how quickly a surface heats and cools, or bring warmer or colder air and water to a place. These different mechanisms explain why a single rule cannot describe every temperature difference.

How does terrestrial radiation heat the atmosphere?

Definition: Terrestrial radiation is the long-wave energy emitted by the Earth after its surface has been heated by incoming solar radiation.

The atmosphere is largely transparent to short-wave solar radiation. This means that much of it can pass through the air to the surface. It does not mean that the atmosphere allows every part of incoming radiation to pass through unchanged.

What is the sequence of heating?

Absorption means taking in radiant energy. Reflection redirects radiation back from a surface, while scattering redirects it in different directions. These processes help explain why the energy arriving at the ground differs from that reaching the top of the atmosphere.

1. Incoming solar radiation passes through the atmosphere, while some energy is reflected, scattered or absorbed.
2. The Earth's surface absorbs solar energy and becomes warmer.
3. The heated Earth emits energy in long-wave form as terrestrial radiation.
4. Atmospheric gases absorb long-wave radiation, heating the atmosphere from below; the atmosphere also radiates energy towards space.

Carbon dioxide and other greenhouse gases, gases that absorb outgoing long-wave radiation, are important in this indirect heating. The atmosphere is mainly heated by the Earth's long-wave radiation, rather than simply by the direct passage of sunlight through it.

What does heat balance mean?

Heat balance means a balance between incoming and outgoing energy for the Earth and atmosphere taken together. Energy received from the Sun is ultimately returned to space. This whole-system balance must be distinguished from differences in heating between individual places.

Receiving energy and losing energy are both part of the explanation. Terrestrial radiation is therefore essential to understanding cooling as well as atmospheric heating. It is emitted by the heated Earth, rather than being another name for sunlight reflected from the ground.

Why does latitude affect insolation and temperature?

Latitude influences the angle at which the Sun's rays meet the Earth's surface. At higher latitudes the rays make a smaller angle with the surface and are more slanting. Their energy is consequently spread over a larger area.

Why are vertical rays more concentrated?

Vertical rays strike a surface directly from above. Slanting rays meet it obliquely, at a smaller angle. For a comparable beam of sunlight, vertical rays cover a smaller area than slanting rays, so energy is more concentrated per unit area.

When the same energy spreads over more ground, each equal area receives less. The explanation concerns the distribution of energy across the surface. Merely saying that higher latitudes receive slanting rays leaves out the reason those rays produce less intense heating.

The rays also pass through a greater depth of atmosphere when they are slanting. More absorption and scattering occur along this longer atmospheric path. Less energy therefore reaches each unit of surface area.

1. Latitude affects the angle made by incoming sunlight with the surface.
2. At higher latitudes the rays are more slanting.
3. The solar energy spreads over a larger area and travels through more atmosphere.
4. The energy received per unit area decreases, helping to explain lower temperatures towards higher latitudes.

What do the surface-energy figures show?

The tropics are the low-latitude region around the Equator. The poles are the northern and southern ends of the Earth's axis, the imaginary line about which it turns. This turning is called rotation.

Surface insolation varies from about 320 watts per square metre in the tropics to about 70 watts per square metre at the poles. A watt measures energy transferred per second; watts per square metre express this rate for each square metre of surface.

The approximate figures illustrate the broad contrast, rather than fixed readings for every place or every day.

Latitude is a major control, but it operates alongside cloud cover, altitude and the movement of air and water. A broad poleward decrease in temperature does not require every place on one latitude to have an identical temperature.

Why does the amount of insolation vary with time and atmospheric conditions?

Insolation varies during a day, through a season and over a year. Its controls include the Earth's rotation, the angle of the Sun's rays, the length of the day, atmospheric transparency and the configuration of the land in terms of its aspect, meaning the direction a slope faces.

Rotation is the Earth's turning on its axis, the imaginary line through its poles. Day length is the duration of daylight. Atmospheric transparency describes how readily radiation passes through the atmosphere. Aspect is the direction a slope faces.

How do duration and angle work together?

The angle of the rays affects the concentration of energy on the ground. Day length affects the time available to receive sunlight. Both must be considered when explaining seasonal differences in incoming energy.

The Earth's tilted axis influences the insolation received at different latitudes. In winter, the middle and higher latitudes receive less radiation than in summer. Middle latitudes are the regions between the low-latitude tropics and the high-latitude polar areas.

Atmospheric transparency and land configuration also influence insolation, but have less influence than the other controls in this list. They should be included without treating all the factors as equally important.

Why is the Equator not the surface-insolation maximum?

Maximum surface insolation occurs over subtropical deserts, where cloudiness is least. Subtropical regions lie just beyond the tropics. The Equator receives comparatively less insolation than the tropics, so a simple latitude rule needs qualification by atmospheric conditions.

Generally, at the same latitude, insolation is greater over continents than over oceans. The word generally preserves the broad nature of this comparison. It is not a rule that every land location receives more than every ocean location at that latitude.

Very small suspended particles scatter visible light, producing the blue colour of the sky and the red colour of the rising and setting Sun. These colours are evidence that sunlight interacts with the atmosphere on its way to the Earth's surface.

Note: Distinguish a control on incoming solar energy from a control on the resulting air temperature. The angle and duration of sunlight affect insolation; sea influence and moving air also help explain temperature.

How does altitude affect air temperature?

Altitude describes a place's height above sea level. Temperature generally decreases as altitude increases. The atmosphere receives heat indirectly from terrestrial radiation below, so places near sea level record higher temperatures than places at higher elevations.

What is the normal lapse rate?

The normal lapse rate is the rate at which temperature decreases with increasing height. Its value is 6.5°C per 1,000 m. Here °C means degrees Celsius, a temperature unit, and m means metres, a unit of length.

This relationship links a vertical height difference to a temperature decrease. For a lapse-rate calculation, both the temperature at the starting level and the difference in height must be known. The stated rate is then applied to that height difference.

In the following rule, = means equals, × means multiply and ÷ means divide.

Temperature decrease = height increase in metres × 6.5 ÷ 1,000. The result is in degrees Celsius. Subtract this decrease from the lower-level temperature to estimate the higher-level temperature, assuming the normal lapse rate applies.

This calculation rule expresses the supplied rate rather than a guarantee about a particular day's weather. An actual temperature cannot be inferred from altitude alone without a starting temperature and an appropriate assumption about the rate of change.

Why must the word “generally” be retained?

Temperature inversion is a reversal of the normal decrease: temperature increases with height through an affected layer. Thus, “temperature generally decreases with height” is more accurate than “temperature always decreases with height”.

A long winter night with clear skies and still air provides ideal conditions for inversion. The surface loses the heat acquired during the day by radiation, and by early morning it can be cooler than the air above it.

In hills and mountains, cold, dense air can also move downhill and collect in valley bottoms, with warmer air above. This is air drainage. It shows why local conditions can modify the normal relationship between temperature and elevation.

Note: Latitude and altitude are different controls. Latitude concerns position north or south of the Equator; altitude concerns height above sea level. Identify which difference is relevant before explaining a temperature contrast.

Why does distance from the sea affect temperature?

Land and sea respond differently to heating and cooling. Land heats up and cools down quickly, whereas the sea heats up slowly and loses heat slowly. Temperature therefore varies less over the sea than over land.

What is the moderating influence of the sea?

Places near the sea come under the moderating influence of land and sea breezes. A breeze is a wind; a sea breeze blows from sea to land, while a land breeze blows from land to sea.

These movements connect coastal air with the neighbouring sea. Because the sea's temperature changes more slowly, its influence moderates coastal temperatures. Distance from the sea therefore helps explain why temperature changes can be more pronounced in continental interiors.

Continentality means the influence of a large land mass and reduced sea moderation on climate. Climate describes the characteristic weather conditions of a place over a long period; weather describes atmospheric conditions at a particular time.

How should a coastal and inland comparison be explained?

Start with the difference in how land and sea heat and cool. Then explain the coastal influence of breezes and the weaker sea influence inland. This builds a causal explanation rather than simply naming distance from the sea.

Do not describe the sea's effect as continuous cooling. Its important role is moderation, because it gains and loses heat slowly. The mechanism concerns a reduction in temperature variation, rather than a claim that the coast must be colder in every comparison.

A coastal location can still be affected by latitude, elevation, winds and ocean currents. Distance from the sea is therefore one part of a full explanation. Compare those other controls before attributing every difference between two places to coastal or inland position.

How do slope and aspect influence temperature?

The slope of land is its inclination relative to a level surface. Its aspect, or facing direction, affects its exposure to sunlight. Two slopes at the same latitude and similar altitude can consequently receive different amounts of solar energy.

Why does the direction a slope faces matter?

A slope facing the Sun receives rays more directly than a slope facing away. With other conditions comparable, the sun-facing slope receives more concentrated energy and tends to be warmer. A slope receiving less direct sunlight tends to remain cooler.

This is a local application of the ray-angle principle. The distinction is between the orientation of the land surface and the direction of incoming sunlight. It is not simply a rule that every steep slope is warmer than every gentle slope.

In the Northern Hemisphere, the half of Earth north of the Equator, south-facing slopes generally receive more solar heating than north-facing slopes. In the Southern Hemisphere, the half south of the Equator, the general contrast is reversed.

These are general aspect relationships, particularly useful outside the tropics. Actual exposure also depends on the Sun's seasonal position and local shading. Identify the hemisphere and exposure before deciding which slope should be warmer.

How is aspect different from altitude?

Altitude compares height above sea level; aspect compares the direction faced by a slope. Higher places generally have lower temperatures, while a sun-facing slope may receive more solar heating than an otherwise comparable slope facing away.

A clear explanation therefore keeps the controls separate: height affects the normal vertical temperature pattern, and orientation affects local solar exposure. Both can operate within the same mountain area, alongside wind and the movement of cold air down slopes.

Draw a hill in cross-section with parallel rays approaching from one side. Label the slope facing the rays and the slope facing away. Show that their exposure to the incoming rays differs.

How do winds transfer heat and change temperature?

Wind is air in horizontal motion. Moving air carries the thermal characteristics of the region from which it comes. A place influenced by warm air experiences higher temperature, while one influenced by cold air experiences lower temperature.

What is an air mass?

An air mass is a large body of air with little horizontal variation in temperature and moisture. Air remaining over an extensive, fairly uniform surface for a sufficiently long time acquires characteristics of that surface.

When such air moves into another area, it affects the receiving area's temperature. The direction and source of the air therefore matter. Simply stating that a place is windy does not establish whether the wind makes it warmer or colder.

How do advection, convection and conduction differ?

Advection transfers heat through the horizontal movement of air. It connects the wind factor directly to temperature: air movement redistributes energy between places. Local summer winds called the loo in northern India illustrate the advection process.

Convection is vertical heat transfer through moving air. Air in contact with the heated ground rises and transfers heat upwards. Its direction of movement distinguishes it from horizontal advection.

Conduction transfers heat between bodies in contact. Energy moves from the warmer body to the cooler body until their temperatures are equal or their contact is broken. It is important in heating the lower atmospheric layers.

Winds explain why local temperature is not determined entirely by local sunlight. Air can bring heat from elsewhere or replace warmer air with colder air. The temperature effect should always be linked to the character of the incoming air.

How do ocean currents influence coastal temperature?

Ocean currents are flows of ocean water. Warm and cold currents influence the temperature of coastal places. Coasts influenced by warm currents record higher temperatures than coasts influenced by cold currents, with other controls considered in the comparison.

The sea's general moderating influence and the effect of a particular current are related but distinct. The first follows from the slow heating and cooling of water. The second concerns whether the water flowing near the coast is relatively warm or cold.

Case study: Why is the North Atlantic warmer in January?

The Gulf Stream and the North Atlantic Drift are warm ocean currents. They make the northern Atlantic Ocean warmer. This influence appears in the January temperature pattern, where lines of equal temperature bend northwards over the ocean.

These lines are called isotherms. Each connects places with equal temperature. Their bends show departures from the broad latitude-related pattern. A northward bend over the North Atlantic indicates that a given temperature extends farther towards higher northern latitudes over the ocean.

Over land in Europe, temperature decreases sharply and the isotherms bend southwards. The contrast shows that latitude does not act alone: land and sea distribution and ocean currents help shape the temperature pattern.

How can the mechanism be expressed clearly?

1. Identify whether the coastal place is influenced by a warm or cold current.
2. Relate the current to the temperature of the nearby ocean water.
3. Explain the resulting warmer or colder influence on the coastal area.
4. Use the temperature pattern as evidence while also considering latitude, land distribution and winds.

The North Atlantic example supplies both a named cause and an observable pattern. The warm currents explain the warmer ocean; the northward bending January isotherms show how this influence modifies the expected relationship between latitude and temperature.

A complete comparison should specify the thermal character of the current. Naming “ocean currents” without saying warm or cold leaves the direction of the temperature effect unexplained.

How can temperature maps bring the controls together?

Temperature maps use isotherms to connect places with equal temperature. They help reveal broad latitudinal patterns and departures caused by land, sea and ocean currents. Read the month as well as the temperature labels before interpreting a map.

What changes between January and July?

Isotherms are generally parallel to latitude lines, showing the strong influence of latitude. Departures from this pattern are more pronounced in January than July, especially in the Northern Hemisphere, where the land surface area is much larger than in the Southern Hemisphere.

The world map carries temperature-labelled isotherms. Lines bend northwards over the North Atlantic and southwards into the northern continents. Across the southern oceans, the lines follow a more nearly east-west course.

See Fig. 8.4(a) in your NCERT textbook

The world map shows isotherms across continents and oceans, including a closed warm area over southern Asia. Lines across the Southern Hemisphere are comparatively regular, illustrating the contrast between large northern land masses and southern oceans.

See Fig. 8.4(b) in your NCERT textbook

In the Southern Hemisphere, isotherms are more or less parallel to latitudes and temperature changes more gradually than in the Northern Hemisphere. This wording describes the broad ocean-dominated pattern without claiming that every line is perfectly straight.

Case study: What does the Eurasian interior show?

Eurasia is the combined land mass of Europe and Asia. Its north-eastern interior has a January-to-July temperature range of more than 60°C because of continentality. Here, range means the difference between the temperatures of the two months being compared.

January mean monthly temperature, meaning the average temperature for that month, ranges from −18°C to −48°C in the Eurasian continental interior. The minus sign indicates temperatures below zero on the Celsius scale. These figures demonstrate the severity of inland winter cooling.

In latitude labels, ° means degrees of angular distance. Temperature degrees measure something different. Keeping these meanings separate prevents confusion between the position of a place and its temperature when reading maps.

The two case studies complement each other: the North Atlantic shows warm-current influence, while the Eurasian interior shows continentality. Together they explain why actual temperature patterns depart from a simple set of uniform latitude belts.

Glossary

• Insolation — Incoming solar radiation received by the Earth, mainly in short wavelengths.
• Terrestrial radiation — Long-wave energy emitted by the Earth after solar radiation has heated its surface.
• Temperature — A measure in degrees of how hot or cold a substance or place is.
• Latitude — The angular distance of a place north or south of the Equator.
• Altitude — The height of a place above sea level, used when comparing vertical temperature differences.
• Normal lapse rate — The normal decrease of temperature with height, at 6.5°C per 1,000 metres.
• Aspect — The direction a slope faces, affecting its exposure to incoming solar radiation.
• Continentality — The influence of a large land mass and reduced sea moderation on climate.
• Air mass — A large body of air with little horizontal variation in temperature and moisture.
• Conduction — Transfer of heat through contact from a warmer body to a cooler body.
• Convection — Vertical heat transfer through moving air as heated air rises from near the surface.
• Advection — Transfer of heat through the horizontal movement of air from one region to another.
• Isotherm — A line on a map joining places that have the same temperature.
• Temperature inversion — A reversal of the normal vertical pattern, with temperature increasing rather than decreasing with height.

Common errors and misconceptions

• Misconception: Insolation and temperature mean the same thing. Correct: Insolation is incoming solar energy, whereas temperature measures how hot or cold a substance or place is.
• Misconception: Terrestrial radiation is sunlight reflected from the ground. Correct: It is long-wave energy emitted by the Earth after the surface has been heated.
• Misconception: Slanting rays heat more strongly because they cover more ground. Correct: Spreading energy over a larger area reduces the energy received per unit area.
• Misconception: The atmosphere absorbs no incoming solar radiation. Correct: It is largely transparent to short waves, but some incoming energy is absorbed, scattered or reflected.
• Misconception: Air temperature always decreases with increasing height. Correct: It generally decreases; a temperature inversion reverses this pattern through the affected layer.
• Misconception: The sea's influence simply makes coastal places colder. Correct: Slow heating and cooling moderate temperature variation; currents and winds also influence coastal temperature.
• Misconception: All places on the same latitude have identical temperatures. Correct: Altitude, sea influence, slope, winds and ocean currents also affect temperature.
• Misconception: A sun-facing slope is warmer because it must be lower. Correct: Aspect concerns exposure to sunlight, while altitude concerns height; these are separate controls.

Exam-style questions with model answers

Q1. Define insolation and terrestrial radiation, distinguishing the source of each. [2 marks]

1. Insolation is incoming solar radiation received by the Earth from the Sun, mainly in short wavelengths.
2. Terrestrial radiation is long-wave energy emitted by the Earth after its surface has been heated by solar radiation.

Q2. Explain three reasons why higher latitudes receive less intense solar heating than lower latitudes. [3 marks]

1. At higher latitudes, the Sun's rays meet the surface at a smaller angle, so they are more slanting than at lower latitudes.
2. Slanting rays spread their energy across a larger surface area, reducing the solar energy received by each unit of area.
3. They also pass through a greater depth of atmosphere, where more absorption and scattering reduce the energy reaching the surface.

Q3. A standard atmosphere has a sea-level temperature of 15.2°C. Calculate its temperature at 1,000 m above sea level using a normal lapse rate of 6.5°C per 1,000 m. State why this assumption matters when applying the calculation to actual weather. [3 marks]

1. The height above sea level is 1,000 m, so the stated rate gives a temperature decrease of 6.5°C from the sea-level value.
2. Subtracting the decrease from the sea-level temperature gives 15.2°C − 6.5°C = 8.7°C at 1,000 m above sea level. Here − means subtract.
3. This result assumes the normal lapse rate applies throughout the height difference. Temperature generally decreases with height, but an inversion can reverse the usual pattern.

Q4. Explain how distance from the sea affects temperature, using four connected points about land, water and coastal influence. [4 marks]

1. Land heats up quickly when it receives energy, allowing its temperature to change more rapidly than that of the sea.
2. Land also loses heat quickly, whereas the sea both gains and loses heat slowly, so temperature varies less over water.
3. Coastal places experience the moderating influence of land and sea breezes, linking their air temperature to the neighbouring sea.
4. Continental interiors have less sea moderation and can show stronger temperature contrasts, although latitude, altitude and other controls must also be considered.

Q5. Explain how each of these six factors affects temperature: latitude, altitude, distance from the sea, slope aspect, winds and ocean currents. [6 marks]

1. Latitude affects the angle of the Sun's rays. More slanting rays at higher latitudes spread energy over a larger area and pass through more atmosphere.
2. Altitude affects the vertical temperature pattern. Temperature generally decreases with height because the atmosphere is indirectly heated from below by the Earth.
3. Distance from the sea affects moderation. The sea heats and cools slowly, while land changes temperature quickly, making inland contrasts more pronounced.
4. Slope aspect affects exposure to sunlight. With other conditions comparable, slopes facing the Sun receive more direct radiation and tend to be warmer.
5. Winds bring air from other regions. Warm air raises the receiving area's temperature, while cold air produces a colder influence.
6. Ocean currents modify coastal temperature. Warm currents produce a warmer influence than cold currents, helping explain differences between coastal areas.

Q6. A January map shows isotherms bending northwards over the North Atlantic and southwards over Europe. The Gulf Stream and North Atlantic Drift are warm currents in the ocean. Explain this pattern in four points, beginning with the meaning of isotherms. [4 marks]

1. Isotherms are lines connecting places with equal temperature, so their bends show where a particular temperature occurs beyond a simple latitude pattern.
2. The Gulf Stream and North Atlantic Drift carry warm water and make the northern Atlantic Ocean warmer.
3. This ocean warmth allows the same temperature to occur farther north, explaining the northward bend of isotherms over the North Atlantic.
4. Temperature decreases sharply over the European land surface in January, producing the contrasting southward bend over the continent.

Q7. Explain atmospheric heating in five points, covering short-wave passage, surface absorption, terrestrial radiation, greenhouse-gas absorption and outgoing energy. [5 marks]

1. The atmosphere is largely transparent to incoming short-wave solar radiation, allowing much of this energy to travel towards the Earth's surface.
2. The surface absorbs solar energy and becomes warmer. Some incoming energy has already been reflected, scattered or absorbed during its passage.
3. The warmed Earth becomes a radiating body and emits long-wave energy. This emission from the heated surface is called terrestrial radiation.
4. Carbon dioxide and other greenhouse gases absorb long-wave radiation, so the atmosphere is indirectly heated from below by the Earth's surface.
5. The atmosphere also radiates energy towards space. Returning energy to space is part of the balance between incoming and outgoing energy.

Q8. The January-to-July temperature range exceeds 60°C in north-eastern Eurasia, while the least range is 3°C in the belt between 20° south and 15° north. State what the range compares, identify the larger contrast, and explain the Eurasian result through continentality. [3 marks]

1. Here, temperature range compares the temperatures of January and July by taking the difference between the two monthly values.
2. North-eastern Eurasia has the larger contrast: its range exceeds 60°C, compared with the stated minimum range of 3°C in the low-latitude belt.
3. Continentality explains the large Eurasian range. The extensive land mass heats and cools quickly and its interior has less of the sea's moderating influence.

Key takeaways

• Insolation is incoming solar energy; terrestrial radiation is long-wave energy emitted by the heated Earth.
• The atmosphere is largely transparent to short-wave radiation and is mainly heated indirectly from below.
• Slanting rays spread energy over larger areas and pass through more atmosphere, reducing surface energy per unit area.
• Temperature generally decreases with altitude at the normal lapse rate, but temperature inversions reverse the usual pattern.
• The sea heats and cools slowly, moderating coastal temperature variation compared with continental interiors.
• Slope aspect affects solar exposure; distinguish this local control from the effect of height above sea level.
• Winds redistribute heat through moving air, while warm and cold ocean currents influence coastal temperature.
• Isotherms reveal latitude's broad influence and departures caused by land, sea and ocean currents.

Test yourself

What does the word insolation mean?

It means incoming solar radiation, the energy received by the Earth from the Sun.

Why is terrestrial radiation different from reflected sunlight?

Terrestrial radiation is long-wave energy emitted by the heated Earth, whereas reflection redirects incoming radiation.

Give two reasons why slanting rays produce less intense surface heating.

They spread energy over a larger area and pass through a greater depth of atmosphere.

What is the normal lapse rate, and what is its main qualification?

It is a temperature decrease of 6.5°C per 1,000 metres of height. Temperature generally decreases with height, but inversions can reverse the pattern.

What is the difference between altitude and aspect?

Altitude is height above sea level; aspect is the direction a slope faces and affects its solar exposure.

Why does the sea moderate temperature?

The sea heats and cools slowly, and land and sea breezes bring its moderating influence to coastal places.

How does advection differ from convection?

Advection transfers heat through horizontal air movement, while convection transfers it through vertical air movement.

What do isotherms connect, and why do they bend northwards over the North Atlantic in January?

They connect places of equal temperature. The Gulf Stream and North Atlantic Drift warm the ocean, extending equal temperatures farther north.