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2. An interpolation between the non-removed values. Either linear- or nearest neighbour interpolation 5 may be used. 3. Every data point in the gap is set to the cloud base value. 1600 Zero filter 23/07/2010 22:00 Linear interpolation 1600 1600 Cloud base filter 1400 1400 1400 1200 1200 1200 1000 1000 1000 Height [m] 800 Height [m] 800 Height [m] 800 600 600 600 400 400 400 200 200 200 0 0 100 200 Backscatter [1/(10 8 *srad*m)] 0 0 100 200 Backscatter [1/(10 8 *srad*m)] 0 0 100 200 Backscatter [1/(10 8 *srad*m)] Figure 14: A cloud topped ABL showing the three different cloud filtering methods. These three filtering methods can be seen in Figure 14. If there is fog an extrapolation is made from the first above ground ’non-removed ’ β value. As mentioned in section 2.7, it is a matter of definition where to identify the BLH in a CTBL. But with these three different filtering methods it is possible to detect the BLH matching the chosen definition of the CTBL. The cloud definition value β(z) = 1000 is chosen relatively high to ensure the presence of a cloud. A lower value of cloud definition β(z) = 800 has been tested, with no noticeable differences from the higher value. 4.6 Minimum turbulence kinetic energy The wind lidar provides measures of wind velocity fluctuations. These are given as the standard deviations of the mean wind velocity components σ u , σ v and σ w and may be used to calculate the TKE of the wind field with equation 3. The TKE approaches zero at the top of the ABL as the wind velocity fluctuations are small in the laminar flow above the ABL. The BLH may therefore be estimated as the height where the TKE drops below a critical value (Vickers and Mahrt, 2004). Figure 15 shows the vertical profiles of σ u , σ v and σ w and the associated vertical profile of the TKE. The height of the wind lidar measurements is limited by the height of the aerosol content in the atmosphere, leading to height limited vertical profiles of σ u , σ v and σ w . Therefore the minimum value of the TKE is used as a BLH estimate in this study, instead of defining a critical value. If there are more than one equal minimum values the lowest one is used as a BLH estimate. 5 The nearest neighbour method takes the value of the nearest point only, yielding a piecewise interpolation. DTU Wind Energy Master Thesis M-0039 27
24/04/2010 06:20 1000 σ w 1000 ē 900 σ u 900 σ v 800 800 700 700 Height [m] 600 500 Height 600 500 400 400 300 300 200 200 100 0 0.2 0.4 0.6 0.8 Std [m/s] 100 0.1 0.2 0.3 0.4 0.5 0.6 TKE [m 2 /s 2 ] Figure 15: Left: The vertical profiles of the wind velocity fluctuations. Right: The vertical profile of the calculated TKE. Data is from the wind lidar on April 24 2010. 28 DTU Wind Energy Master Thesis M-0039
Page 1 and 2: DTU Wind Energy Master Thesis M-003
Page 3 and 4: Contents 1 Introduction 5 1.1 Thesi
Page 5 and 6: 1.1 Thesis contents The content of
Page 7 and 8: and Batchvarova, 1994; Stull, 1988)
Page 9 and 10: ∂ē ∂t = g w ′ θ v ′ − u
Page 11 and 12: 2.7 Boundary-layer clouds The prese
Page 13 and 14: the square root of the variance. Ro
Page 15 and 16: 3 Site and measurements In this sec
Page 17 and 18: occasionally use the term “radial
Page 19 and 20: Ultrasonic Wind Sensor uSonic-3 Sci
Page 21 and 22: 4 Boundary-layer height detection T
Page 23 and 24: 90/(10 8 m srad), respectively). Fo
Page 25: 1400 β profile 16/04/2010 11:40 14
Page 29 and 30: Decoupled Clouds Clouds that are no
Page 31 and 32: 1600 Zero filter 23/07/2010 22:00 N
Page 33 and 34: 5.2 Continuous and average data The
Page 35 and 36: of the error bars during the day. T
Page 37 and 38: also be explained by the shape of t
Page 39 and 40: increases from 19:00-20:00. A resid
Page 41 and 42: 1400 1200 BLH estimations 01/05/201
Page 43 and 44: 5.4 Cold front passage On April 8 2
Page 45 and 46: Wind vectors at 10m height. Metmast
Page 47 and 48: 0.3 The inverse Obukhov length 1/L
Page 49 and 50: Wind vectors at 10m height. Metmast
Page 51 and 52: 0.1 The inverse Obukhov length 1/L
Page 53 and 54: 1400 BLH from minimum TKE 16 June 2
Page 55 and 56: 70 60 Threshold night day Easterly
Page 57 and 58: Threshold Westerly winds Ideal prof
Page 59 and 60: 140 120 Threshold night day Easterl
Page 61 and 62: Threshold Easterly winds Ideal prof
Page 63 and 64: 400 300 Threshold night day Easterl
Page 65 and 66: 5.9 Intra-annual variation The BLH
Page 67 and 68: wind lidar (Sathe et al., 2011). Ho
Page 69 and 70: distributions. It is clear that the
Page 71 and 72: A Appendix Abbreviations ABL Atmosp
Page 73 and 74: References Batchvarova, E., X. Cai,
Page 75: Sinclair, V. A., S. Niemelä, and M

Boundary-layer height detection with a ceilometer at a coastal ... - Orbit

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