*5.1. Meteorological Conditions in Different Operating Environment*

Targeting a vertiport network operation 99% of the operating hours per year in the metropolitan area of Munich, future UAM vehicles have to withstand headwind of 20 m/s (39 kts) after the average hourly windspeed, measured at 66 weather stations in the area of interest between 2016–2018, was evaluated [102]. In order to compensate local bad weather conditions an blackouts in the charging infrastructure, a diversion reserve of 10 km (32,808 ft) is demanded.

Moving UAM operations to the U.S. and considering METAR data of 28 metropolitan areas, ref. [100] derived a headwind requirement of 10 kts (5.14 m/s) if at least 50% of the operational window should be covered. This requirement is followed due to the assumption that not all flights are fully facing headwind conditions and necessary reserves will account for uncertainties and additional deviation. Furthermore, if the eVTOL aircraft can withstand wind of 20 kts (10.3 m/s) and 35 kts (18 m/s) of gusts, the operation can be conducted in any of the 28 metropolitan areas a minimum of 95% of the time meeting wind constraints and 95% of the time in all but two cities meeting gust constraints.

The meteorological repercussion on UAM operations in various U.S. cities was further analyzed by [190], who determined the average number of weather-impacted hours for each area of interest. Considering an annual operation with a daily operational window of 7 a.m. to 6 p.m., seven years of METAR surface data (2010–2017) were examined together with supplemental data of pilot reports. In order to elaborate potentially impacted hours, a set of "impact scores" is elaborated rating the captured METAR observation from 1 (minimum impact) to 10 (significantly impactful). This includes among others temperature, rain, ceiling, visibility, wind, hazel and snow grains, but also appearances of dust storms, tornadoes and volcanic ash. An hourly average impact score of three was defined as a threshold between minimal and significant potential impact. Throughout the areas of interest, ref. [190] concluded that an average of 6.1 h per day during the winter, 7.3 h per day in the spring, 2.9 h per day in summer and 2.2 h per day in fall could be potentially affected by considerable impactful weather conditions.

All three examples show that different operating environments call for changing operating hours and vehicle requirements. [191] highlights regional and local variation of weather amongst others caused by geographic influences like latitude defining solar radiation and temperature, major water bodies being the source of moisture, mountains affecting range of altitude and air density and landcover gradients providing differential heating. Other influences are described as diurnal and seasonal cycles, weather systems (wind, clouds, precipitation) and the cityscape causing local scale wind and turbulence. Additional weather challenges need to be considered such as winds at and above ground level (turbulent eddies, extreme and rapid changes in wind speed and direction, microburst translation), ceilings and visibility (sub-grid micro climates) and temperature (heat island effect, effects on density altitudes) [192].
