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 30km. In the diurnal variation shown in Fig. 3(b), the difference in temperature is 9K, 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.

HOUR

Fig. 3. Clear-sky case on 14 June, 2004. (a) Lidar data. From 6:00 to 15:00, the mixing layer develops and then it decays. (b) Variations of temperature, relative humidity, and water vapor pressure.

HOUR

Fig. 3. Clear-sky case on 14 June, 2004. (a) Lidar data. From 6:00 to 15:00, the mixing layer develops and then it decays. (b) Variations of temperature, relative humidity, and water vapor pressure.

6.1.2. Winter case

In winter, both temperature and relative humidity are low. As an example of clear sky, the case of 3 February, 2005 is shown in Fig. 4. Lidar data in Fig. 4(a) show nearly constant aerosol concentration up to 4 km, and the development of mixing layer is not seen. The variations of temperature and relative humidity are shown in Fig. 4(b). The changes in temperature and relative humidity are from 0°C-100C and from 55% to 20%, while the change in water vapor pressure is relatively small (from 3.5 to 2.3 hPa). The wind velocity becomes maximum in the daytime, and the direction is NNW with 10 m/s speed.

Fig. 4. Clear-sky case on 3 February, 2005. (a) Lidar data. No development of the mixing layer is observed. (b) The diurnal variation of temperature, relative humidity, and water vapor pressure.

6.2. Rainy weather case

During the precipitation, the cloud base almost touches the ground in both summer and winter. Nevertheless there is some seasonal difference in the observed lidar profiles.

6.2.1. Summer case

An example of 4 September, 2004 is shown in Fig. 5. The annually largest precipitation of 135.5 mm occurred on this day. Comparison of Figs. 5(a) and 5(b) indicates that the cloud indeed touches the ground during the precipitation period (2:00-3:00 and 19:00-24:00), when it is seen from the radar picture (not shown) that the cumulonimbus cloud covers Chiba prefecture moving from north-east to south-west. From 9:00 to 19:00, the cloud stays at a lower altitude (roughly 500 m), and the lidar signal that indicates the cloud base height fluctuates largely on a bad weather day. The weather map on this day shows that the stationary frontline stays off-shore of the Chiba prefecture.

6.2.2. Winter case

As an example of winter precipitation, Fig. 6 shows the data observed on 16 January, 2005. The total daily precipitation was 66.5 mm. The rain was almost over until 7:00. After that, the precipitation of roughly 1 to 2 mm lingered until the evening. The temperature was almost constant around 5° C-7° C.

Time (JST)

Fig. 5. Rainy weather case on 4 September, 2004. (a) Lidar data — The cloud base height touches the ground during the precipitation. (b) Diurnal variation of precipitation, temperature, relative humidity, water vapor pressure, and wind velocity.

Time (JST)

Fig. 5. Rainy weather case on 4 September, 2004. (a) Lidar data — The cloud base height touches the ground during the precipitation. (b) Diurnal variation of precipitation, temperature, relative humidity, water vapor pressure, and wind velocity.

Fig. 6. Rainy weather on 16 January, 2005. (a) Lidar data — The cloud base height becomes lower during the precipitation. (b) Precipitation, temperature, relative humidity, water vapor pressure, and wind velocity.

6.3. Sunshine and precipitation on the same day

The features during sunshine and precipitation periods are largely different, due mainly to the difference in relative humidity and temperature. The transition in a relatively short time period leads to a large-scale, vertical fluctuation.

6.3.1. Summer case

Under such a situation, the cloud base height rapidly moves up and down. Figure 7 shows the lidar data on 7 September, 2004. Rapid fluctuation of cloud occurs in an altitude range between 0.5 and 2.5 km. On that day, a

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time (JST)

Fig. 7. Lidar data on 7 September, 2004.

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 Time (JST)

Fig. 7. Lidar data on 7 September, 2004.

10 Feb., 2005

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