Kerbal Weather Project
Soundings
The figures below show simplified Skew-T plots. This type of plot is created using data from weather balloons (radiosondes) and is commonly used by meteorologists to examine the state of the atmosphere. On the x-axis lines of constant temperature (isotherms) are “skewed” (i.e. at an angle). Lines of constant pressure (isobars) are plotted on the y-axis along with height ASL (see right y-axis). Colored lines show the profiles of temperature and dew point above the KSC on the 337th day of the year, at 01 UT. At the KSC, sunset occurs just after 01 UT. The blue dashed line indicates the freezing line (0°C isotherm). On the right, wind barbs show the direction and speed of the wind as a function of pressure/height. In the DLS and WLS soundings, the height of the terrain is notably higher than in the game. This is due to the coarse resolution of terrain in the MPAS model.
Caption: MPAS sounding showing profiles of temperature and dew point temperature at the KSC just before sunset at 01 UT on the 337th day of the year.
Kerbal Space Center (KSC)
Throughout the depth of the troposphere temperature decreases with height above the KSC. At 75 hPa (18 km) temperature begins increasing with height. In meteorology, this is referred to as a temperature inversion. The temperature inversion above 75 hPa is due to the presence of ozone. The 75 hPa pressure level thus marks the beginning of the stratosphere where the presence of ozone causes an increase in temperature with height.
Between 275 and 200 hPa (10-12 km ASL) the temperature and dew point are nearly equivalent. This moist layer, where the relative humidity is near or at 100% is likely due to the presence of high-level cirrus clouds above the KSC. Below this layer the spread between the temperature and dew point profiles indicates that the air is relatively drier, suggesting that mid-level clouds are sparse or not present at this time. Just above the surface, between 850-900 hPa, the gap between the dew point and temperature profiles narrows considerably, hinting at the presence of low-level cumulus clouds.
The wind barbs on the right shows a shift in the wind from northeasterly below 3-km to northwesterly above 3-km. These low-level northeasterly winds are trade winds, commonly observed in the tropics. The height at which the wind direction changes marks the height of the atmospheric boundary layer, the bottom layer of the troposphere affected by friction with the planet’s surface.
Desert Launch Site (DLS)
Just above the surface, there is a weak temperature inversion. 05 UT is just before sunrise at the DLS. Low-level temperature inversions often form overnight as the surface cools faster than the air above it. Due to the short day/night length on Kerbin, when nocturnal inversions occur they are typically weak and short-lived.
Surface temperatures are generally colder at the DLS than at the KSC since it is located nearly 1-km ASL. The spread between the temperature and dew point profiles indicates a drier atmosphere with little to no cloud cover.
This makes sense given that the DLS is located in a relatively arid region. The tropopause, defined as the boundary between the troposphere and stratosphere, is located around 100 hPa (~15 km ASL). At the tropopause the temperature profile is isothermal, that is the temperature remains constant with height.
Wind barbs on the right show southeasterly winds within the boundary layer (below 700 hPa). Above 8-km ASL the winds are westerly. In the upper troposphere, westerly winds strengthen with height, reaching speeds of 100 knots at approximately 20 km ASL.
Caption: MPAS sounding showing profiles of temperature and dew point temperature at the DLS just before sunrise at 05 UT on the 387th day of the year.
Woomerang Launch Site (WLS)
Caption: MPAS sounding showing profiles of temperature and dew point temperature at the WLS at 05 UT on the 145th (left) and 146th (right) day of the year.
Unlike the KSC and DLS, the WLS is located in the mid-latitudes at (45°N, 136°E). Geographically, the WLS is situated in the foothills of a mountain range, located on the northern edge of a peninsula (see map below). In MPAS, the elevation of the WLS is notably higher than it is in the game. This is due to the proximity of the WLS to high terrain and the limited resolution of the MPAS model. As a result, temperatures at the WLS are typically well below freezing.
WLS Sounding (left): 01 UT, Day of Year: 145
On this particular day surface temperatures at the WLS were near -19°C (-2°F). The divergence of the dew point and temperature profiles, below 500 hPa, reveals a relatively dry atmosphere below 5-km ASL. Near the surface, a low-level temperature inversion is present. The source of this temperature inversion is revealed in the wind profile, which shows low-level winds turning from southeasterly to southwesterly. When the wind direction turns clockwise with height this is referred to as veering. In meteorology, a veering wind is associated with rising motion and the transport of warm air into the region (i.e., warm air advection). In this sounding, warm air advection is responsible for the temperature inversion above the surface. As a layer of warm air flows from the south, over the WLS, the temperature profile extends rightward creating a noselike bulge. Since this warm advection occurs aloft (2-4 km ASL), temperatures at the surface remain cold, and an inversion forms.
Above 500 hPa the temperature and dew point profiles are closer together implying higher humidity aloft and the potential for a deep cloud layer. Wind speed increases with height above 700 hPa, exceeding 100 knots around the tropopause level. In this sounding, the tropopause is located at around 175 hPa (12 km ASL).
WLS Sounding (right): 01 UT, Day of Year: 146
This second sounding (right) from the WLS was retrieved one day after the previous sounding (left). Since the previous day, near-surface temperatures increased by over 10°C. A veering wind is still present at low-levels as southerly winds continue to advect relatively warm air into the region. Aloft, maximum wind speeds now reach 150 knots, just below the tropopause, between 10-12 km ASL. The increase in wind speeds aloft suggests the presence of a strong jet stream over the WLS.
In contrast to the previous sounding, the gap in the dew point and temperature profiles no longer exists above 500 hPa. In fact, the atmosphere is now at or near 100% relative humidity all the way down to 700 hPa. This remarkable change in temperature and humidity, below 500 hPa, is largely a consequence of warm air advection and precipitation. As warm moist air moved into the region the temperature and dew point profiles shifted rightward. The advection of this warm air promoted rising motion and the development of clouds aloft. Over the course of a day, cloud formation above 500 hPa produced wintry precipitation (i.e., snow). As snow fell through the dry layer below it had a cooling effect on the surrounding air. This cooling effect reduced the ambient temperature bringing it closer to the dew point temperature. In combination with moisture advection, this process allowed the 500-700 hPa layer to reach saturation, wherein the temperature and dew point profiles overlap.
Between the surface and 700 hPa, the dew point and temperature profiles diverge indicating that the relative humidity is below 100%. Nevertheless, since this layer is thin and the air temperature is well below freezing, snow is likely falling at the surface. Given the strong speed shear (20 to 150 knots) and deep cloud layer (3-12 km ASL), this day would probably not be a great day for a rocket launch at the WLS!
The map below is provided for reference. The soundings discussed above were retrieved at the base game launch sites marked in black
