Climate Features of Dakhla Oasis
95
Fig. 3 The relationship
between monthly averaged
humidity and monthly
maximum daily averaged
temperature (average from
2007 to 2016) in each month
in Dakhla Oasis
4.3 Wind Conditions
The wind conditions in Dakhla Oasis are controlled by the Harmattan wind, so the
wind direction is almost always due north except during the Khamsin wind. Although
the wind is nearly always northerly (Brookes 2001).
The wind speed is comparatively calm under the effect of high pressure: i.e.,
annual average was 1.9 m/s, and average maximum wind speed was 3.9 m/s in Dakhla
(from 2007 to 2016). However, on some days the maximum wind speed exceeds the
threshold wind speed for dust outbreak, as shown in Fig. 4 for 2016. If the threshold
wind speed for dust emission is 6.5 m/s (Tegen and Fung 1994), there is the potential
for dust emissions throughout the year, especially during the Khamsin period (from
DOY 61 to 121). In addition, a wind speed over 6.5 m/s usually causes degradation in
visibility. Strong winds may be caused by the development of a mixing layer specific
to the desert climate during the spring season in addition to during the Khamsin. For
comparison purposes, the wind conditions in Kharga Oasis are also shown in Fig. 4.