A spectral analysis of upper-air winds measured by LAPS wind profiler in Shou County,
Anhui province
Ding Yihui, Wang Zunya, Kang Tianyi, Li Huiyun, Su Lirong

Abstract
The present paper studied the power spectra of upper-air winds over Shou County, Anhui
province, using the daily upper-air winds of 110 days from 1 April to 19 July, 2004 measured byLASP wind profiler. Figure 1 shows the vertical distributions of the wind. And figure 2 denotes
the change of the wind with the time. It can be seen that the wind has evident oscillations. We
have found the following multi-scale oscillations at different levels through the wavelet analysis.
At 300-meter level (Figure 3), three obvious periods can be detected in U-wind. As ahigh-frequency oscillation, the 4~8-day oscillation is obvious during the 110 days. The other twooscillations are low-frequency ones, whose periods are quasi-14-day and quasi-40-day,respectively. Both the two oscillations are strongest from May to June, during the rainy season.
They passed the 90 % confidence level. As to the V-wind and W-wind, there are two obviousperiods, namely, 4~8-day and quasi-12-day. Same as U-wind, the high-frequency oscillation ismore significant. The quasi-12-day oscillation is statistically significant in mid-May in V-wind,
but in mid-June in W-wind.
At 600-meter level (Figure not shown), there is the similar situation in U-wind as on
300-meter level. However, the two low-frequency oscillations are relatively weaker. V-wind andW-wind both have the 4~8-day oscillation and the quasi-12-day oscillations and the latter in
V-wind is stronger than that on 300-meter level.
At 900-meter level (Figure not shown), the quasi-40-day oscillation is not obvious in U-windand it almost can’t pass the 90 % confidence test. The quasi-12-day oscillation in U-wind is alsoweak. The 4~8-day and the quasi-12-day periods remain significant in V-wind. And, the situationin W-wind is same as that on 300 and 600-meter levels.
The situation on 1500-meter level (Figure 4) is almost same as that on 900-meter level, only
the low-frequency oscillations are relatively weaker and the high-frequency oscillation isrelatively stronger.
At 3000-meter level (Figure 5), there are two obvious periods in U-wind, the 4~8-dayoscillation and the quasi-12-day oscillation. The quasi-12-day oscillation is statistically significant
in early-June. The periods in V-wind and in W-wind are same as that on 1500-meter level.
In total, U-wind have such three obvious periods as the 4~8-day, the quasi-12-day and thequasi-40-day. The high-frequency oscillation is significant during the 110 days and thelow-frequency oscillations are statistically significant from May to June. At the low level, thequasi-40-day oscillation is stronger than at the high level. V-wind and W-wind have two
significant oscillations, the 4~8-day oscillation and the quasi-12-day oscillation, mainly inhigh-frequency domain. Though there is the quasi-40-day oscillation, it didn’t pass the 90 %confidence level. The 4~8-day oscillation is also obvious through the 110 days. The quasi-12-day
oscillation in V-wind passed the 90 % confidence level in late May, but that in W-wind did in
mid-June. The periods in V-wind and W-wind change little with the height. Overall, thehigh-frequency modes dominate in all levels understudied, whereas the low-frequency modes aremainly found in low levels. It is not clear yet if the PRL have an more active low-frequency
oscillation. This problem remains to be further clarified.

a .U-windb. V-windc. W-wind
Fig 1 The distribution of the winds in Z-T plane, the positive values are shadeda. U-wind (real line) and V-wind (dashed line)c. W-windFig 2 The time series of the winds at 300-meter levela. U-windb. V-windc. W-wind
Fig 3 Wavelet analysis of the winds. In the top panel, positive values are shaded. In the bottom
panel, the dashed lines denote boundary effects and shaded areas denote values exceeding the 90%
confidence level.

a. U-winda. U-windb. V-windb. V-windc. W-windc. W-wind

Fig 4 Same as Fig 3, just for 1500-meter levelFig 5 Same as Fig 3, just for 3000-meter level