Kerbal Weather Project
A state-of-the-art numerical weather model (MPAS) was run for five years to simulate the weather on Kerbin. An hourly climatology of Kerbin was developed by averaging the results of this five-year-long simulation by the hour.
Upper-Air Analyses
Weather patterns aloft drive changes in weather at the surface. For this reason, meteorologists often examine upper air charts to predict the development and movement of surface weather features such as cold fronts and low-pressure systems. Below you'll find a collection of upper-air charts that depict the climatology of Kerbin. In all of these charts, grey lines depict landmasses while gridded white lines show parallels of latitude and meridians of longitude.
This figure displays the average (climatological) height of the 500 hPa pressure surface. The height of the pressure surface above sea level is shaded and contour labeled every 60 meters. On Kerbin (and on Earth), sea level pressure is around 1000 hPa. The height of the 500 hPa pressure surface divides the atmosphere in half vertically, half the mass of air being above and half below that height. Darker colors indicate lower heights while lighter colors indicate higher heights. The 500 hPa heights displayed above are a function of the average temperature between the surface and 500 hPa. Where the air is colder (e.g. over the poles) the density of the air is higher and thus more compact (taking up less volume). Wind barbs indicating the velocity (i.e., speed and direction) of the 500 hPa wind are drawn in black. In meteorology, the 500 hPa level is often referred to as the steering level as weather beneath this level travels with the winds at 500 hPa.
Above, the climatological wind speed (shaded) at 250 hPa. The 250 hPa pressure surface is commonly used in meteorology to evaluate the speed of the jet stream (narrow bands of fast-moving air in the upper atmosphere). Darker colors show regions where the wind speed is higher, while lighter areas show regions of lower wind speed. The height of the 250 hPa pressure surface is contoured in black. Heights are displayed in meters above sea level. Wind barbs indicating the velocity (i.e., speed and direction) of the wind are drawn in black. Strong winds aloft are associated with strong temperature gradients near the surface (i.e., large changes in temperature over short distances). Thus, the mid-latitude jet stream is often located above regions where surface fronts are common.
In Kerbin’s northern hemisphere, the annual average location of the mid-latitude jet stream is around 30-50 N. Within the jet stream, a local maximum in wind speed is called a jet streak. In the northern hemisphere, jet streaks are observed downstream (east) of high terrain. The most prominent jet streak is observed around 30 N just west of the prime meridian. Winds are enhanced in this region due to the large temperature gradient between the (warm) ocean water and the (cold) high terrain. In the southern hemisphere, a weak jet streak is observed just east of the southern islands. In this region, the presence of sea ice around the southern ice cap amplifies the temperature gradient increasing the jet speed around (-40°S, 100°W).
Note that the black contours, depicting the height of the 250 hPa pressure surface, are spaced more tightly together where the jet streaks are, this is because wind speeds are stronger where the slope of the 250 hPa pressure surface is larger. Furthermore, the wind barbs generally parallel height contours, except near the poles where the map is distorted.
The figure above displays the climatological air temperature (shaded) at 850 hPa. The height of the 850 hPa pressure surface, above sea level, is contoured in black. Wind barbs indicating the velocity (i.e. speed and direction) of the wind are drawn in black. In meteorology, the 850 hPa level is typically just above the boundary layer, the layer of the troposphere directly influenced by friction with the Earth’s surface. At this level, the diurnal cycle of temperature (i.e., the change in temperature between day and night) is often negligible. In mountainous regions of Kerbin, 850 hPa may be at or below the surface. Over the KSC continent, 850 hPa temperatures dip below 250K (-23°C) as far south as 30°N. In contrast, 850 hPa temperatures over the ocean to the east of the KSC continent are quite warm, averaging around 280K (7°C) at 30°N. This enormous (30 K) temperature differential is responsible for the strong jet observed in the previous figure. In contrast, over the tropics, there is no significant meridional (longitudinal) variations in 850 hPa temperature. The warmest 850 hPa temperatures are observed over the continent east of the KSC.
The climatological relative humidity (shaded) at 700 hPa is displayed above. Darker colors show regions where the humidity is higher, while lighter show areas of low humidity. The height of the 700 hPa pressure surface is contoured in black. Heights are labeled in meters above sea level. Wind barbs indicating the velocity (i.e., speed and direction) of the wind are drawn in black. In meteorology, the 700 hPa level may be considered the top of the lower troposphere. Relative humidity at this level is used to evaluate the availability of low-level moisture for precipitation. In the tropics, low-level (trade) winds converge, producing rising motion and precipitation just south of the equator, west of the prime meridian. Over the large (central) continent, east of the prime meridian, much of the land is well above sea level (> 1km ) and populated with little vegetation (e.g. badlands). Winds aloft, at 700 hPa, are easterly (out of the east). Easterly winds over the continent and westerly winds over the ocean converge along the coastline around (-10° to 0°W).
L
H
H
Zooming in on this region in the tropics, it becomes apparent that there is also a gradient in 700 hPa heights between the continents and ocean. Over the KSC continent, 700 hPa heights are relatively high (3100 m). Over the ocean to the east 700 hPa fall and reach a local minimum (3010 m). Further east, 700 hPa heights over the continent rise again. This High-Low-High pattern is characteristic of a type of atmospheric wave called a Kelvin wave. These waves influence patterns of rainfall in the tropics (Frierson, 2007) and can aid, or suppress, the development of tropical cyclones (Schreck, 2015). On Kerbin, precipitation is enhanced west of the wave minima (L) over the ocean east of the KSC. One could imagine how this might complicate launches from the KSC.
References:
Frierson, D. M. W., 2007: Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model. J. Atmos. Sci., 64, 2076–2090, https://doi.org/10.1175/JAS3945.1.
Schreck, C. J., III, 2015: Kelvin waves and tropical cyclogenesis: A global survey. Monthly Weather Review, 143, http://dx.doi.org/10.1175/MWR-D-15-0111.1