Cooperative Institute for Research in Environmental Sciences

Research Applications
NBL Stability/Structure/Evolution

The high-resolution profiles provided by the TLS are highly suitable for studies of the evolution of the NBL by repeatedly profiling the atmosphere throughout the night. The system has been used in support of a dispersion and urban boundary layer study around the Pentagon (Pentagon Shield Experiment) and for field experiments focused on the study of the nocturnal boundary layer.

During the Cooperative Atmosphere-Surface Exchange Study 1999 campaign (CASES-99), the CIRES TLS was used to profile the NBL and part of the residual layers at approximately 15 minutes intervals. The NBL structure was shown to exhibit an abrupt change with the breakdown of a well defined low-level jet accompanied by the appearance of a surprisingly steep temperature gradient. The steepest portion consisted of a 1 K temperature increase within as a little as 5 cm corresponding to a temperature gradient in excess of 20 K m^-1.

Click on image for larger version.

Click on image for larger version.

The left panel shows the appearance of the sharp temperature interface that accompanies the collapse of the Low Level Jet. The straight line to the right-hand side of each plot depicts the 9.8 K km^-1 dry adiabatic lapse rate. The right panel shows the drop in altitude of the interface as seen by four vertically spaced turbulence packages.

The figure below shows how a succession of profiles collected at 15 minute intervals provides an excellent description of the evolution of the NBL temperature, velocity, and turbulence profiles.

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The TLS is also capable of deriving stability profiles such as Brunt Vaisala frequency N and Richardson number Ri which can be compared with the concurrent measurements of turbulence.

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For further details see the related publication:

Balsley BB, Frehlich RG, Jensen ML, et al.: "Extreme gradients in the nocturnal boundary layer: Structure, evolution, and potential causes". JOURNAL OF THE ATMOSPHERIC SCIENCES 60 (20): 2496-2508 OCT 2003.

Balsley BB, Fritts D, Frehlich RG, et al.: "Up-gully flow in the great plains region: A mechanism for perturbing the nighttime lower atmosphere?". GEOPHYSICAL RESEARCH LETTERS 29 (19): Art. No. 1931 OCT 1 2002.