Observations of the Daytime Internal Boundary Layer In Onshore Flow
3.2 Intercomparison of the Internal Boundary Layer Heights.
There are many other IBL studies that have been conducted along the coastal area. Interestingly some of these studies have been carried out at different fetches (X). It is the intention of this section to compare the Z
IBL that was obtained in this study to those found in the literature. Three different studies (Ogawa & Ohara, (1985), Smedman & Hogstrom, (1983) and Druilhet et. al., (1982)).who their studies at different places and at a different fetches will be used as a guide to observed the Z
IBL growth with fetch distance.
Table 3 highlight the Z
IBL obtained from this study (30th. June 1994, as a function of stability) and studies that have being conducted by the people mentioned above.
Table 3
The Tabulation of the ZIBL against fetch (X)
| X (m) | ZIBL (m) |
| 30 | 8a |
| 90 | 11a |
| 160 | 24a |
850
(Our study) | 74d |
| 1000 | 79c |
| 1500 | 76b |
| 2000 | 105c |
| 3000 | 123c |
| 4000 | 138c |
| 5000 | 151c |
| 6000 | 162c |
Note:
a = from Ogawa and Ohara, (1985)
b = from Smedman and Hogstrom, (1983)
c = From Druilhet et. al., (1982)
d = Obtained ZIBL from stability function (30th. June 1994)
From table 3 it can be observed that the Z
IBL obtained as a function of stability on the 30th. June 1994 is significantly correlated to the ZIBL growth with fetch conducted from the other studies . The Z
IBL growth presented statistically by Hsu (1988) when he formularised the boundary layer height from the three different studies mentioned above as
ZIBL = (1.91 ± 2 x 0.38) X1/2
The Z
IBL obtained as a function of stability on the 30th. of June was in the increasing slope of the Internal Boundary Layer height with fetch (lies in the range between 30m to 6000m downwind distance).
4. Discussion
Two methods had been used to obtained the thickness of the adjusted Surface Boundary Layer (SBL) and the Internal Boundary Layer (Z
IBL); the first from the best fit straight line drawn on the wind speed and potential temperature profile and the SBL and Z
IBL was obtained from which the two straight lines intersect and abstrupt and; the second was determined as a function of stability (Richardson number). The layer of separation between the bottom and the top layer can be seen when there is an abstrupt change on the profile behavior. The top of the Z
IBL was determined when fresh incoming onshore flow on top of the land surface atmospheric layer. The corresponding potential temperature behavior at the top of Z
IBL, which displayed an inversion characteristic gave evidence of this fresh onshore wind.
Data on 30/6 were examined in order to investigate the Z
IBL growth. This was done by using both methods. The result explained showed the existence of the Internal Boundary Layer height on 30/6/94 during the summer of 1994. Comparatively the Z
IBL that was obtained lay within the increase slope of the Internal Boundary Layer height proposed by Hsu (1988).
References
- Druilhet, A., Herrada, A., Pages, J. P., and Saissac, J., (1982). Etude experimentale de la couche limite interne associee a la brize de mer. Boundary Layer Meteor., 22, 511-524.
- Hsu, S. A. (1988). Coastal Meteorology. 260pp. ISBN 0-12-357955-4. Academic Press Inc. London.
- Ogawa, Y. and Ohara, T., (1984). The Turbulent Structure of the Internal Boundary Layer near the coast, Boundary Layer Meteorol. 31, 369-384.
- Smedman, A. S. and Hogstrom, U., (1983). Turbulent Characteristic of a shallow Convective Internal Boundary Layer. Boundary Layer Meteorology, 25, 271-287.
