Ch 3 Quiz: Temperature — Variations, Inversions & Profiles

The diurnal temperature variation is driven by the daily cycle of incoming solar radiation (heating during daytime) vs outgoing terrestrial longwave radiation (cooling, especially at night). Maximum temperature typically occurs 1-2 hours after solar noon.

Surface temperature maximum typically occurs 1–2 hours after solar noon because the ground continues to absorb more solar energy than it radiates until the balance tips. This lag reflects the thermal inertia of the surface.

A temperature inversion is an increase in temperature with altitude, the reverse of the normal lapse rate. Inversions strongly suppress convection and vertical mixing, can trap pollutants, and create low-level shear.

Radiation inversion forms when clear skies allow rapid longwave cooling of the surface. The cold surface cools the air near it by conduction, creating a temperature inversion in the lowest few hundred feet. Most common in calm, clear nights.

Subsidence inversion forms in anticyclones (high pressure systems) where air sinks (subsides) from upper levels. Descending air warms by compression but loses this warmth at the base. Creates a stable, persistent inversion capping the boundary layer.

The surface temperature minimum occurs just before sunrise because the Earth continues to lose heat by radiation throughout the night. Cooling begins at sunset and continues until incoming solar radiation exceeds outgoing radiation.

A frontal inversion forms at a warm front where warm air rises up and over a wedge of colder air. The boundary between the warm air aloft and cold air below creates a temperature inversion. Associated with ceilings and icing.

The Föhn effect: moist air rises windward (SALR cooling), loses moisture as precipitation. Now drier air descends leeward at the faster DALR. Net result: air arrives warmer and drier than it started. Temperature gain can be 10–20°C.

Inversions trap pollutants and moisture below them, reducing visibility. They cap convection, but wind shear at the inversion top can create low-level turbulence. Warm frontal inversions also indicate icing risk.

In the lower stratosphere (ISA, 11–20km), temperature is constant at -56.5°C — the isothermal layer. Above ~20km, temperature begins to increase due to ozone absorbing UV radiation.

Continental interiors in summer experience the greatest diurnal temperature range. Low humidity (little latent heat), clear skies, and minimal maritime influence allow intense daytime heating and rapid night-time cooling.

A thermal is a localised column of buoyant (warm) air that rises from the surface when solar heating creates a patch of warmer air than surroundings. Thermals are exploited by gliders and cause convective turbulence for commercial aircraft.

Warm SSTs transfer heat (sensible) and moisture (latent) to the overlying atmosphere. This destabilises the marine boundary layer, promotes convection, and can lead to intense weather systems (e.g., tropical cyclones require SST >26°C).

Low-level inversions create wind shear — the wind speed and direction change at the inversion boundary. On final approach, crossing the inversion boundary can cause a sudden change in headwind/tailwind component, creating dangerous airspeed excursions.

Advection fog forms when warm, moist air is horizontally transported (advected) over a cool surface (cold sea, snow-covered land) and cooled to its dew point. Common in coastal areas and over cold ocean currents.

Freezing rain occurs when rain falls from a warm layer aloft (above freezing), passes through a shallow cold layer at the surface, and freezes on contact with below-freezing surfaces. Creates dangerous ice accretion.

Tropical regions have small diurnal temperature ranges (typically 5–10°C) due to: high humidity/cloud cover (limiting radiative heating/cooling), maritime influence, and consistent solar radiation angles year-round.

A thermograph (temperature-altitude sounding from radiosonde) plots the actual temperature profile. Meteorologists use it to: assess stability (thunderstorm potential), find freezing level, identify inversions, and forecast icing.

At higher latitudes, the sun is at a lower angle, spreading solar radiation over a larger surface area. Also, polar regions have longer periods of darkness. This reduces absorbed solar energy per unit area, causing colder temperatures.

Clouds act as a ‘blanket’ — they reduce both the maximum (by reflecting/absorbing solar radiation) and minimum (by emitting longwave radiation back to the surface) temperatures. This reduces the diurnal temperature range.

Radiosondes are balloon-borne instruments that measure temperature, humidity, and pressure (from which wind data can be derived). Released twice daily (0000 and 1200 UTC typically), they provide vertical atmospheric profiles for weather analysis and models.

The 0°C isotherm (freezing level) marks where liquid water starts to freeze. Above it, supercooled water droplets can exist causing structural icing. The precipitation type (rain/snow/sleet/freezing rain) depends on temperature profile relative to 0°C.

Temperature inversions cap convection and trap moisture below them. This promotes the development of stratus and stratocumulus clouds at the inversion base. Cumulonimbus cannot break through a strong inversion.

Desert surfaces have low albedo (dark soil absorbs solar radiation), extremely low humidity (no evaporative cooling), sparse vegetation, and high solar insolation. This drives surface temperatures above 50°C in summer months.

Urban heat island results from: reduced green space (less evaporative cooling), concrete/asphalt surfaces with low albedo absorbing more heat, waste heat from buildings and vehicles, and altered airflow patterns.

Temperature advection = transport of thermal energy by horizontal wind. Warm advection (winds from warm areas) brings warmer air; cold advection (winds from cold areas) brings colder air. Critical for frontal forecasting.

The Thar Desert experiences the most rapid radiative cooling on clear nights due to: no cloud cover (clear desert skies), low humidity (minimal greenhouse effect), minimal vegetation, and sandy soil with low heat capacity.

The frost point is the temperature to which air must be cooled for ice crystals to form directly (sublimation from vapour to ice). It is slightly lower than the dew point for the same moisture content.

In the upper stratosphere (above ~20km), ozone (O₃) absorbs UV radiation from the sun, causing the temperature to increase with altitude, reaching ~0°C at the stratopause (~50km). This is the ‘warm stratosphere.’

ISA temperature at 2,000ft = 15°C – (1.98°C × 2) = 15 – 3.96 ≈ 11°C. Wait: 1.98 × 2 = 3.96, so ISA = 15 – 3.96 = 11.04°C ≈ 11°C. Let me recalculate: 1.98 × 2 = 3.96, 15 – 3.96 = 11.04°C. Closest is 11°C. With more precision: exactly 15 – (6.5×0.6096) = 15 – 3.962 ≈ 11.04°C.

Satellite-based infrared radiometers (e.g., AVHRR on NOAA satellites) and microwave sounders measure emitted/transmitted radiation at different wavelengths to infer temperature profiles remotely without physical sensors in the atmosphere.

Using the Magnus formula approximation: RH=30%, T=45°C. Dew point ≈ T – (100-RH)/5 ≈ 45 – 14 = 31°C. More precisely around 24–28°C. The spread T-Td ≈ 20°C is indicative of dry conditions preventing fog/low cloud.

Katabatic (cold air drainage) flow occurs when air near mountain slopes cools radiatively at night, becomes denser than the surrounding air, and flows downslope under gravity. Can create valley fog and frost.

The Peltier effect is a thermoelectric phenomenon where a temperature difference is created by applying voltage across a junction of dissimilar materials. Used in precise temperature control and measurement devices.

The meridional temperature gradient results from differential insolation: equatorial regions receive more solar radiation per unit area (higher sun angle, less atmospheric path length) than polar regions, maintaining a persistent temperature difference.

Cold fronts associated with Western Disturbances in northern India (November–March) produce rapid uplift of moisture-laden air. The resulting mixed-phase clouds at cold temperatures create ideal conditions for severe aircraft icing.

Most severe icing occurs between 0°C and -20°C where supercooled liquid water droplets are most abundant. Below -20°C, water tends to freeze in clouds (ice crystals don’t accrete as readily). Below -40°C, spontaneous glaciation makes icing rare.

Water has a much higher specific heat capacity than land, absorbing and releasing heat more slowly. Also, evaporation consumes large amounts of energy. Maritime locations thus experience much smaller diurnal and seasonal temperature ranges.

The nocturnal jet (low-level jet) forms after sunset when boundary layer turbulence decreases, ‘decoupling’ the surface from the atmosphere aloft. Without surface friction, winds can accelerate to 30–50kt in a narrow layer near the top of the nocturnal inversion.

The Environmental Lapse Rate (ELR) describes the actual decrease of temperature with altitude in the troposphere. The ISA ELR is 1.98°C/1000ft or 6.5°C/1000m. Any layer where this is reversed is an inversion.

Wind mixes air vertically and horizontally, distributing heat more evenly. Strong winds prevent the formation of radiation inversions and reduce the diurnal temperature range. Still nights show the greatest diurnal range.

The heat index combines dry bulb temperature with relative humidity to estimate how hot it ‘feels.’ High humidity reduces the body’s ability to cool by perspiration, making temperatures feel higher than they are. Critical for human heat stress assessment.

In a Skew-T Log-P diagram, temperature lines are skewed to the right with altitude. A temperature trace that curves to the right (increasing temperature with height relative to the skewed base) indicates a temperature inversion.

IMD provides upper wind and temperature forecasts for Indian airspace as part of its meteorological watch responsibilities. These are derived from NWP models (Unified Model, GFS) and provided as charts and digital data for flight planning.

Ground frost can form even when the screen air temperature (measured at 1.25m) is slightly above 0°C, because the actual surface temperature can be several degrees colder due to intense radiative cooling, particularly on calm, clear nights.

A Skew-T Log-P diagram has the vertical axis as the logarithm of pressure (so equal height spacing approximates geometric height) and the horizontal axis as temperature (skewed to allow temperature-pressure lines to be nearly vertical). Used for atmospheric sounding analysis.

In winter, cold, dry continental air (from central Asia/Himalayas) combined with clear skies, low humidity, and snow-covered/dry surfaces allows intense radiative cooling. Areas like north India see fog and near-0°C temperatures in January-February.

Virtual temperature (Tv) is the temperature at which dry air would have the same density as moist air at the same pressure. Since moist air is less dense, Tv > T. Used in calculations of density, convective available potential energy (CAPE), and thermodynamics.

During the Indian monsoon, the freezing level over the plains is typically 14,000–16,000ft (~4,300–4,900m) in deep moist airmasses. Over the foothills and Himalayas, the spatial variation is significant.

A maximum thermometer (traditionally containing mercury, now often electronic) records the highest temperature reached during a measurement period. Six’s thermometer records both maximum and minimum temperatures using an index float.

Water has the highest specific heat capacity (~4,180 J/kg·K), followed by moist soil/vegetation, with dry sand having significantly lower heat capacity. This difference drives the land-sea breeze and explains why coastal climates are moderate.

Cumulus clouds develop when thermals rise from surface heating. Maximum surface heating occurs in the afternoon (1400–1700 local), when thermals are strongest, surface temperature is maximum, and CAPE is highest.

In an absolutely stable environment, ELR < SALR (< ~6°C/1000m or ~1.5°C/1000ft). In conditionally unstable air, SALR < ELR < DALR. The atmosphere is absolutely stable when ELR is less than the SALR.

Adiabatic wet bulb temperature (Tʷ) is the temperature reached by an air parcel when brought to saturation by evaporating water into it adiabatically. It is the temperature of the wet bulb thermometer in a psychrometer, related to but slightly different from the isobaric wet bulb.

The Himalayas act as a thermal and dynamic barrier: in winter, they block the intrusion of cold continental air from Central Asia, keeping the Indo-Gangetic plains warmer than they would otherwise be. In summer, they help trap monsoon heat and moisture.

Thermal wind = the vector difference between geostrophic winds at two levels. It is directly related to horizontal temperature gradients (temperature advection). In the Northern Hemisphere, cold air is to the LEFT of the thermal wind vector.

Radiation error occurs when direct solar radiation heats the thermometer (or its housing) above the true air temperature. Modern observations use ventilated radiation shields (Stevenson screens) to minimise this error.

In the mesosphere (50–85km), there is insufficient ozone to absorb UV radiation (most is absorbed in stratosphere). CO₂ and other molecules radiate thermally to space causing net cooling. Temperature decreases from ~0°C at the stratopause to ~-90°C at the mesopause.

TAS = IAS × √(ρ₀/ρ). In ISA-15, air is denser (ρ > ISA ρ). The ratio ρ₀/ρ is smaller, so TAS is lower than ISA TAS for the same IAS. Counter-intuitively: colder air means slightly lower TAS (not higher) at the same IAS.

A low inversion traps smoke, haze, dust, and moisture in a shallow layer, reducing horizontal visibility to below approach minimums. In Indian cities like Delhi in winter, inversions at 200–300ft can bring visibility to near zero (dense fog/smog).

Comparing the ELR with DALR and SALR determines atmospheric stability: whether a displaced air parcel returns (stable), continues to move (unstable), or neither (neutral). This determines whether thunderstorms, fog, or fair weather prevails.

IMD’s Upper Wind and Temperature Charts (also called SWH — Significant Weather High-level charts) provide forecasts of temperature and wind at standard pressure levels (FL180, FL240, FL300, FL390) for the Mumbai and Chennai FIRs.

The rough rule: cloud base (ft) ÷ 400 ≈ T – Td spread (°C). Equivalently, T-Td spread increases by ~2.5°C per 1,000ft of cloud base height. If T-Td = 10°C, expected cloud base ≈ 4,000ft.

An isothermal layer is one where temperature remains constant with altitude (zero lapse rate). The most significant isothermal layer in the standard atmosphere is the lower stratosphere (-56.5°C from 11–20km). Also found in temperature inversions that are exactly isothermal.

Rule: Cloud base (ft) = (T – Td) × 400 = (30 – 18) × 400 = 12 × 400 = 4,800ft above the surface. This is the Lifting Condensation Level (LCL) — the height at which a surface parcel reaches saturation.

The Environmental Lapse Rate is measured by radiosondes — weather balloons carrying temperature, humidity, and pressure sensors that transmit data as they ascend. Typically launched at 0000 and 1200 UTC. Upper-air data supplements satellite soundings.

For supersonic aircraft (Concorde, military), aerodynamic heating (ram rise in temperature) adds to ambient temperature. The colder lower stratosphere moderates the total heat load. Temperature recovery (TAT = SAT + ram rise) is critical for structural limits.