Geoscience Reference
In-Depth Information
relative humidity exhibits some correlation (but not very significant) with
precipitation and with temperature. Wind speed does not change so much
annually, and the average speed is about 5 m/s. The average temperature
in April and November is about 15
◦
C: as mentioned later, the lidar data
show different behaviors above and below 15
◦
C, though the temperature
difference (maximum temperature - minimum temperature) in a day stays
between 15
◦
and 25
◦
throughout the year.
6. Classification Based on Meteorological Conditions
Although the diurnal behavior of relative humidity generally shows anti-
correlation with diurnal temperature variation, the monthly average relative
humidity exhibits positive correlation with the monthly average tempera-
ture (Fig. 2(b)). The inspection of lidar data indicates that the average
temperature of 15
◦
provides an important benchmark, in accordance
with the classification of summer and winter in Japan. Therefore, in the
following discussion, we treat summer and winter cases to highlight the
characteristics. The following six cases will be treated below: (i) clear
sky, (ii) rainy weather, (iii) sunshine and precipitation on the same day,
(iv) cloud-top boundary layer, (v) frontal passage, and (vi) sudden change of
cloud height. The last two cases correspond to variable weather conditions.
6.1
. Clear sky case
On a clear day, PAL data gives information on distributions of aerosol
particles. As the light-scattering of particles is strongly affected by relative
humidity, lidar signal behavior strongly differs in summer and winter.
6.1.1
. Summer case
Clear conditions continued from 14th to 16th in June, 2004. One-day PAL
THI data on June 14, 2004 are shown in Fig. 3(a). From 6:00 JST, the
boundary layer starts ascending and reaches 3 km at 15:00 JST, then, it
descends down to 1 km in the evening. The visibility on this day was very
good, ranging from 20 to 30 km. In the diurnal variation shown in Fig. 3(b),
the difference in temperature is 9 K, but according to this variation, the
relative humidity changes from 80% to 40%, with the small change of water
vapor pressure from 19 to 13 hPa. The time of maximum temperature agrees
well with the time of the highest mixing layer height.
