Kerbal Weather Project
A state-of-the-art numerical weather model (MPAS) was run for five years to simulate the weather on Kerbin. The output from this multi-year simulation was retrieved for the location of each launch site shown below.
Caption: Location of Kerbin launch sites from the base game (black circles): Kerbal Space Center (KSC), Desert launch site (DLS), and Woomerang launch site (WLS). Terrain height is shaded. Black contours show the coastlines of Kerbin's continents. Additional launch sites from Kerbin Side Remastered (red triangles) are included in the mod but left out of the following discussion for brevity.
The wind rose charts below show the distribution of wind speed and wind direction at select launch sites on Kerbin. The circular shape of the wind rose highlights the direction from which the wind blows. The length of each "spoke" around the circle shows how often the wind blew from that direction. The colors on each spoke provide details on the wind speed from each direction. The direction of the longest spoke shows the most frequent wind direction.
The wind roses above display the distribution of surface wind speed and direction for select launch sites on Kerbin. Radial numbers show the proportion of the distribution for a given wind direction. Stacked bars are extended in the direction from which the wind is blowing. Colors on the bars indicate the distribution of wind speed as a function of wind direction. At the KSC the wind most frequently blows onshore from the northeast (around 26% of the time). Winds out of the northeast, at the KSC, vary in speed from around 5 to 25 knots. At the Desert launch site winds blow out of the southeast while at the Woomerang launch site surface winds are predominantly westerly (i.e. from the west). The highest surface wind speeds are observed at the Woomerang launch site which is well above sea level, in the mid-latitudes. Surface wind speeds at the Woomerang launch site reach up to 55 knots and average around 20 knots.
The wind speed and direction at 10 km above sea level (ASL), at select launch sites, is shown above. Radial numbers highlight the frequency distribution for a given wind direction. Stacked bars are extended in the direction from which the wind is blowing. Colors on the bars indicate the distribution of wind speed as a function of wind direction. 10-km above the KSC winds are southeasterly and typically quite weak (0 - 20 knots). In contrast, winds above the Desert launch site and Woomerang launch site are almost exclusively westerly. Above the Woomerang launch site wind speeds, at 10-km ASL, often exceed 100 knots. This is due to the presence of the jet-stream which is typically observed in the mid-latitudes between 8-12 km ASL. The large range of wind speeds observed above the Woomerang can be explained by the wavy nature of the jet-stream which only occasionally meanders above the launch site.
Hourly wind profiles are provided below for select launch sites. These charts, which are used in spaceflight meteorology, show wind barbs that depict the wind speed (shaded) and wind direction as a function of time and height above each launch site. Note that wind barbs show the strength of the horizontal wind only. If the tail of the wind barb (the end with stems or flags) is pointing upward this indicates a northerly wind (i.e. wind from the north). Vertical profiles through the full depth of the atmosphere are shown on the left side of each chart. On the right, a more detailed view of winds by time/height are shown for the lowest ten kilometers of the atmosphere (i.e. troposphere). Times are shown in Kerbin Time (UT). For reference, sunrise and sunset at the KSC occur just after 01 UT and 04 UT, respectively.
Above, hourly wind profiles are provided for the KSC on the 180th day of the MPAS simulation. On this particular day, winds in the lowest part of the atmosphere shifted from northeasterly to northerly between 0 and 6-km, ASL. Above 6-km winds are more variable. Overall, winds in the troposphere are weak, ranging from 5-10 knots near the surface to 20-knots at 5-km ASL. In the stratosphere, between 25 and 45-km ASL, easterly winds are predominant reaching speeds of up to 40 knots. Near the top of the atmosphere, winds were light and variable. At the KSC, there was little change in the wind direction or strength on this day, which is typical in the tropics. In the tropics, a relatively uniform temperature distribution (i.e. lack of fronts) results in little horizontal variability in wind speed or strength.
The chart above displays the hourly wind profile for the Desert launch site (DLS) on the 180th day of the MPAS simulation. At the DLS, winds turned clockwise with height as northerly surface winds gradually gave way to southeasterly winds at 4-km ASL. Wind speeds also increased with height above the DLS, reaching 55-knots at 7-km ASL. This significant change of horizontal wind direction/speed with height is called vertical wind shear. On this day, the vertical wind shear above the DLS was strongest between 4-6 km ASL, where wind speeds increased from 15 to 50 knots and the wind direction shifted from south-easterly to southerly. At the boundary of the troposphere and stratosphere wind abruptly shift from esterly to easterly. Stratospheric and mesospheric winds above the KSC and DLS are similar as both launch sites are located in the tropics near the equator.
Wind direction and speed is shown by time and height at the Woomerang launch site (WLS) for the 180th day of the MPAS simulation. In contrast to the KSC and DLS wind profiles, the wind direction throughout the depth of the atmosphere is fairly consistent. Strong vertical wind shear is observed in the troposphere, where winds vary from 20-knots at the surface to 170 knots at 10 km ASL. The layer of strong 120+ knot winds between 8-14 km ASL is associated with the jet stream, which on this day, is present above the WLS. Being in the mid-latitudes, the WLS is subject to much larger variations in temperature and wind speed/direction than the DLS and KSC. Between 00 UT and 05 UT, near-surface winds shifted from southwesterly to westerly. This westward shift in wind direction propagated upward as time progressed. At 10-km ASL wind speeds increased with time, from 140 knots at 00 UT to 170 knots at 05 UT. The presence of a strong jet above the WLS and the gradual shift of near-surface winds from southwesterly to westerly marks the advance of an incoming cold front. Although not shown in this figure, the following day, near-surface winds at the WLS shifted from westerly to northwesterly.