Regime Transitions in Near-Surface Temperature Inversions: A Conceptual Model

Abstract

A conceptual model is used in combination with observational analysis to understand regime transitions of near-surface temperature inversions at night as well as in Arctic conditions. The model combines a surface energy budget with a bulk parameterization for turbulent heat transport. Energy fluxes or feedbacks due to soil and radiative heat transfer are accounted for by a ''lumped parameter closure,'' which represents the ''coupling strength'' of the system.Observations from Cabauw, Netherlands, and Dome C, Antarctica, are analyzed. As expected, inversions are weak for strong winds, whereas large inversions are found under weak-wind conditions. However, a sharp transition is found between those regimes, as it occurs within a narrow wind range. This results in a typical S-shaped dependency. The conceptual model explains why this characteristic must be a robust feature. Differences between the Cabauw and Dome C cases are explained from differences in coupling strength (being weaker in the Antarctic). For comparison, a realistic column model is run. As findings are similar to the simple model and the observational analysis, it suggests generality of the results.Theoretical analysis reveals that, in the transition zone near the critical wind speed, the response time of the system to perturbations becomes large. As resilience to perturbations becomes weaker, it may explain why, within this wind regime, an increase of scatter is found. Finally, the so-called heat flux duality paradox is analyzed. It is explained why numerical simulations with prescribed surface fluxes show a dynamical response different from more realistic surface-coupled systems.

The nocturnal boundary layer transition from weakly to very stable. Part I: Observations

“…Van de Wiel et al . () compared the mean wind speed to thermal stratification at both SBL regimes, finding that the stratification increases over a narrow range of wind speeds, and that in the very stable regime thermal stratification stays at a maximum as the mean wind speed decreases. A similar behavior is found in the present case, and this comparison further evidences the contrasting connection between the mechanical and thermal structures in both regimes (Figure ).…”

“…At each level, there is a range of mean wind speeds for which the SBL may be in either regime, in agreement with the findings from Van de Wiel et al . (). The classical dependence found at upper levels with a slight increase in V TKE as V increases in the very stable regime (Sun et al ., ; Acevedo et al ., ) likely arises, therefore, from clumping data from both regimes in the same mean wind speed bins.…”

“…The MSHF framework has been further elaborated by Van de Wiel et al . (), who combined effects of different processes that affect the surface radiative budget into a lump parameter. They showed that the wind speed at which the regime transition occurs depends universally on such a parameter.…”

“…(; ; ), Van de Wiel et al . (; ; ) and Van Hooijdonk et al . () provide explanations on the physical controls of the mean wind speed for the SBL regime, there are still many doubts regarding the triggering of the transition and how the vertical structure of the SBL changes from one to the other regime.…”

The nocturnal boundary layer transition from weakly to very stable. Part II: Numerical simulation with a second‐order model

“…This reasoning has been expanded by Van de Wiel et al . (), who attributed the control of the regime transition to the “coupling strength” between the surface and the atmosphere. It is affected by the surface energy budget, being therefore dependent on the quantities that control this budget, such as cloudiness and the surface thermal properties.…”