Chapter 15: Atmosphere and Climate of Théxar
"The sky of Théxar is frozen flame. Gold of day, purple of twilight, red coal of sunset — colors in which we recognize the breath of the planet itself." — From the treatise "Heavens of Khar'Vex", Era of Prosperity
Related sections: → see [Ch.03, "Planet Théxar"], → see [Ch.14, "Oceans of Théxar"], → see [Ch.12, "Geological Evolution"] Key principle: Théxar's atmosphere is the result of a complex balance between near-Earth orbital irradiation, elevated CO₂ (0.8%), and active tectonics. The golden-bronze sky, slow circulation, and powerful dust storms are its hallmark.
Introduction
Théxar's atmosphere is one of the key features making the planet habitable. Its composition, density, and dynamics are the result of a complex balance between geological processes, biological activity, and astrophysical factors.
Elevated CO₂ content, the presence of biogenic hydrogen sulfide (H₂S), the characteristic golden-bronze color of the sky, and a thinner ozone layer — each of these factors has played its role in the evolution of local life and the formation of civilization.
Théxar's atmosphere represents a "pristine" example of an equilibrium greenhouse state.
15.1 Atmospheric Composition
KEY FACT
The main distinction of Théxar's atmosphere is its CO₂ content of 0.8%. This is not the result of a catastrophe, but an equilibrium greenhouse effect: CO₂ compensates for the low insolation of the star Khar'Vex.
15.1.1 Chemical Composition of Dry Air
TABLE 15.1: Listed atmospheric constituents at the surface
Gas Formula Share (Théxar) Role Nitrogen N₂ 71.8% Buffer gas Oxygen O₂ 22.6% Respiration, photosynthesis Argon Ar 2.9% Decay product of ⁴⁰K Carbon dioxide CO₂ 0.8% Greenhouse gas Water vapor (separate, variable wet-air fraction) H₂O 0.5–2.0% Greenhouse gas Neon Ne 0.05% Inert Methane CH₄ 0.0003% Biogenic Hydrogen sulfide H₂S 0.0008% Biogenic; atmospheric sulfur chemistry Carbon monoxide CO 0.00005% Volcanic
The elevated argon content (2.9%) is a result of more intensive radiogenic decay of ⁴⁰K in Théxar's mantle. This indirectly confirms the planet's age and geological activity.
H₂S at 0.0008% is supplied by volcanism and microbial metabolism. It participates in atmospheric sulfur chemistry and can serve as an electron donor in some ecosystems. Visible sky colour depends on the stellar spectrum, molecular scattering and aerosols.
15.1.2 Vertical Structure
TABLE 15.2: Atmospheric layers
Layer Height (mo) T at boundary T gradient Feature Troposphere 0–2.2 19.0°X −32.0 K/mo Clouds, weather, turbulence Stratosphere 2.2–9.1 16.8°X Isothermal Ozone layer (thinner by 30%) Mesosphere 9.1–17.3 −6.6°X −14.8 K/mo Airglow, meteors Thermosphere 17.3–71.1 208.2–588.9°X +49.2 K/mo Ionosphere, aurorae Exosphere >71.1 — — Sparse hydrogen
15.1.3 Ozone Layer
Théxar's ozone layer contains ~30% less O₃ per unit volume. Main reasons:
- Lower O₂ content in the stratosphere (thin stratosphere)
- Presence of H₂S, which reacts with ozone: H₂S + O₃ → SO₂ + H₂O
- Elevated UV flux (due to proximity to the star)
Consequence: elevated UV-B flux at the surface has exerted significant evolutionary pressure on local life — Théxar's organisms possess high radiation resistance.
15.2 Sky Color
The color of Théxar's sky is one of the most striking visual features. It is determined by three factors:
15.2.1 Physics of Scattering
- Scattering by air molecules and suspended aerosols
- H₂S alters the scattering of shortwave radiation through the formation of sulfuric acid aerosols in the stratosphere
- The orange dwarf Khar’Vex supplies the illuminating spectrum; atmospheric scattering also shapes the observed colour.
COMPARISON: Sky color
Condition Théxar Physics Noon Golden-bronze Aerosol and molecular scattering + stellar spectrum Sunset Deep red Long optical path through air and aerosols Twilight Purple Scattering and atmospheric airglow Horizon Bright orange Suspended dust and aerosols
15.2.2 Color Perception
The Xha'ri are tetrachromats with sensitivity in the 320–780 nm range. → see [Ch.05, "Anatomy"] Thanks to this, they distinguish up to 7 color bands in the sky (from ultraviolet halo to deep-red glimmer), giving them an advantage in navigation at twilight.
15.3 Radiation Balance and Greenhouse Effect
15.3.1 Energy Budget
TABLE 15.3: Radiation balance of Théxar
Parameter Théxar Unit Star luminosity 0.41 Lk Distance from star 0.63 AU Orbital flux ≈1.026 S⊕ Albedo (average) 0.31 — Atmospheric absorption 24 % Greenhouse amplification +16.9 °X Average surface T 51.6 °X
At a stellar luminosity of 0.41 L☉ and a distance of 0.63209 AU, the flux at Théxar’s orbit is about 1.026 times Earth’s solar constant. Surface temperature also depends on reflection, atmosphere, clouds and ocean heat transport.
15.3.2 Long-Term Stability
On Théxar, the key role in CO₂ regulation is played by:
- Volcanic degassing — CO₂ input from the mantle (active tectonics)
- Biological fixation — photosynthesis and chemosynthesis binding carbon
- Oceanic pump — dissolution of CO₂ in the cold waters of Gharra
The balance of these processes maintains CO₂ concentration at 0.8% with fluctuations of ±0.05% over the last 500 million cycles.
15.4 Atmospheric Circulation
15.4.1 Global Circulation
Théxar has a 6-cell model of atmospheric circulation, but with important differences:
TABLE 15.4: Circulation cells
Cell Latitudes Direction Weather character Kharak (equatorial) 0°–28° Ascending Abundant precipitation, jungles Tor (temperate) 28°–55° Descending Dry zones, deserts Thel (polar) 55°–90° Weak Cold dry air
Due to slower rotation (27.3 h), the cells are wider and weaker:
- Cell width: 10–15% greater
- Wind speeds: 20–30% lower (average global speed ~2.4 mo/h)
- Trade winds: less pronounced but more stable
- Monsoons: practically absent due to weakened seasonal circulation
15.4.2 Jet Streams
Théxar's planetary jet streams:
| Stream | Latitude | Average speed | Height | Seasonality |
|---|---|---|---|---|
| Northern polar | 55°N | 24.4 mo/h | 1.6–2.0 mo | Stronger in winter |
| Northern subtropical | 28°N | 16.3 mo/h | 2.0–2.4 mo | Stable |
| Southern subtropical | 28°S | 15.2 mo/h | 2.0–2.4 mo | Stable |
| Southern polar | 55°S | 28.5 mo/h | 1.6–2.0 mo | Stronger in winter |
15.4.3 Seasonal Variations
Théxar's axial tilt is 14.2°. This leads to:
- Less pronounced seasons — summer-winter difference in temperate latitudes is ~8.2°X
- Weak seasonal wind shifts — monsoon circulation is practically absent
- At temperate latitudes, daylight lengthens in summer and shortens in winter.
15.5 Weather Phenomena
15.5.1 Rain and Precipitation
Average annual precipitation on Théxar is ~880 mm/year. Distribution:
| Precipitation type | Share | Feature |
|---|---|---|
| Rain | 74% | Slightly acidic (pH 5.2–5.8) due to CO₂ |
| Snow | 18% | At latitudes >45° and highlands |
| Sulfuric acid (H₂SO₄) | 6% | Near volcanic zones |
| Coal dust (dry) | 2% | In Kharak's deserts |
The slightly acidic nature of rain (pH 5.2–5.8) is due to the dissolution of CO₂ forming carbonic acid. This phenomenon is a planetary norm, not a result of pollution.
15.5.2 Tropical Cyclones
Frequency: 20–35 cyclones per year, but intensity is lower due to longer days weakening the Coriolis effect.
| Category | Wind speed | Frequency | Damage |
|---|---|---|---|
| Kh-1 (weak) | 12.8–24.0 mo/h | 12–15/year | Minimal |
| Kh-2 (moderate) | 24.2–36.0 mo/h | 6–8/year | Moderate |
| Kh-3 (strong) | 36.2–42.3 mo/h | 2–4/year | Significant |
| Kh-4 (very strong) | 42.5–51.0 mo/h | 0–1/year | Severe |
| Kh-5 (devastating) | >51.2 mo/h | 1 in 10–20 years | Catastrophic |
Cyclone season follows local seasonal conditions; Gharra-Ven and Thel-Mor are names from a regional calendar.
15.5.3 Dust Storms
Dust storms are the most serious local weather threat on Théxar. They are significantly stronger due to:
- Lower air humidity in desert regions
- Active volcanic activity supplying fine ash
- Wider circulation cells creating sustained winds
The most powerful storms can:
- Transport up to 800 million tons of dust
- Color the sky a deep orange-red for 2–3 weeks
- Block up to 60% of starlight over an area of 0.2–0.3 million mo²
- Carry dust across the ocean from Kharak to Rhuval (distance >609.8 mo)
KEY FACT
Théxar's dust storms are the main factor in erosion and mineral transport. Approximately 1.5 billion ru of dust is transported between continents annually.
15.5.4 Electrical Phenomena
| Phenomenon | Frequency | Feature |
|---|---|---|
| Lightning | ~1.2 billion/year | High discharge energy |
| Corona discharge | Common | Glow on high peaks (corona effect) |
| Aurorae | Moderate | Observed down to latitude 35° |
| Volcanic lightning | Frequent | Accompanies ash emissions |
Aurorae on Théxar are observed at lower latitudes (down to 35°) due to the characteristics of the magnetosphere.
15.6 Climate Zones
TABLE 15.5: Climate zones of Théxar
Zone Latitudes Avg T Precipitation Characteristic biome Equatorial 0°–8° 60.3–62.5°X 348.8–581.4 pa Rainforests Subequatorial 8°–20° 57.0–60.3°X 174.4–348.8 pa Savannas, woodlands Tropical 20°–30° 54.8–58.1°X 23.3–69.8 pa Deserts, steppes Subtropical 30°–45° 51.6–55.9°X 46.5–139.5 pa Forests, maquis Temperate 45°–60° 47.3–52.6°X 69.8–139.5 pa Deciduous forests Subpolar 60°–75° 42.4–47.3°X 34.9–69.8 pa Taiga, tundra Polar 75°–90° 31.5–42.4°X 11.6–34.9 pa Glaciers, deserts
Axial tilt affects seasonality; climate-zone boundaries also depend on circulation, terrain and the ocean.
15.6.1 Climate Records
| Parameter | Value | Location |
|---|---|---|
| Maximum T | 75.5°X | Shan Desert, Kharak |
| Minimum T | 19.0°X | Northern polar ice sheet |
| Max precipitation | 837.2 pa/year | Southern slopes of Khar-Tor |
| Min precipitation | 2.1 pa/year | Inner Shan Desert |
| Max wind speed | 87.8 mo/h | Cyclone in Irkhen Sea (+3,890) |
| Sunniest region | 3,800 h/year | Serrin Plateau |
15.7 Long-Term Climate Cycles
Théxar's climate experiences periodic fluctuations caused by astronomical and geological factors.
15.7.1 Orbital Cycles
Théxar's orbital cycles include:
| Cycle | Period (years) | T amplitude | Cause |
|---|---|---|---|
| Eccentricity | ~95,000 | ±0.7°X | Orbital change |
| Axial tilt | ~41,000 | ±0.4°X | Axial nutation |
| Precession | ~38,600 | ±0.3°X | Equinox drift |
KEY FACT
Théxar's axial precession has a period of ~38,600 years, due to the planet's smaller mass with a comparable moment of inertia, making the axis more sensitive to tidal influences from the satellites Serrin and Thel.
15.7.2 Volcanic Winters
Major eruptions (VEI-7+) can temporarily alter the planet's climate:
| Event | Time | VEI | T drop | Duration |
|---|---|---|---|---|
| Tor-7 eruption | ~12,000 ya | 7.2 | −1.7°X | 4 yr |
| Raal supervolcano | ~48,000 ya | 8.1 | −3.2°X | 8 yr |
| Irkhen chain | ~3,890 Y.E. | 6.8 | −0.8°X | 2 yr |
Over the last 100,000 years, 5–7 major events were recorded; their magnitude and duration varied, as the table examples show.
15.7.3 Current State
The modern climate of Théxar is in an interglacial phase that began ~12,000 years ago. The current average temperature (51.6°X) is close to the interglacial maximum. Polar caps occupy their minimum area in the last 100,000 years — 0.3 million mo².
The warming of the last 500 years is linked not to anthropogenic activity (the Xha'Ruun civilization's industry runs on fusion and renewable sources), but to a natural recovery from a mini-ice age phase.
Chapter Summary
Key takeaways:
- Théxar's atmosphere contains 0.8% CO₂ — the result of an equilibrium greenhouse effect.
- The orange dwarf Khar’Vex supplies the illuminating spectrum; atmospheric scattering also shapes the observed colour.
- The ozone layer is 30% thinner, leading to increased radiation resistance in local life.
- Atmospheric circulation is 6-cell, weakened by slow rotation (27.3 h).
- Dust storms transport ~1.5 billion ru of dust per year between continents.
- The climate is stable due to an equilibrium carbon cycle maintained by tectonics and the biosphere.
- Axial precession is short (~38,600 years) due to tidal influence of the satellites.
- Slightly acidic rain (pH 5.2–5.8) is the planetary norm.
- Atmospheric composition: N₂ 71.8%, O₂ 22.6%, Ar 2.9%, CO₂ 0.8%
- Pressure: 1.00 tyazh
- Average T: 51.6°X, range: 19.0–75.5°X
- Axial tilt: 14.2°
- Sky color: golden-bronze (noon), red (sunset), purple (twilight)
- Ozone layer: 30% thinner
- Dust storms: annual transport ~1.5 billion ru
- Axial precession: ~38,600 years
- Cyclones: up to Kh-5, 20–35 per year
Connections to other chapters:
- → see [Ch.02, "Star System"] — Khar'Vex spectrum and radiation flux
- → see [Ch.03, "Planet Théxar"] — general planet profile
- → see [Ch.12, "Geological Evolution"] — volcanism as source of CO₂ and H₂S
- → see [Ch.14, "Oceans of Théxar"] — atmosphere-ocean interaction
- → see [Ch.13, "Continents"] — regional climate features
- → see [APP:physical-ref] — physical parameters of the planet