Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing

Linden, Steven van der; Baas, Peter; Hooft, Antoon van; Hooijdonk, Ivo G. S. van; Bosveld, Fred C.; Wiel, B.J.H. van de

doi:10.1175/jamc-d-17-0011.1

Cited by 24 publications

(25 citation statements)

References 51 publications

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“…The first regime is characterized by relatively strong winds and a weak inversion in the order of 5 K. In the second regime, the winds are weak but the temperature difference over the lowest 10 m may be as large as 25 K. The transition between these two states is abrupt and occurs at a 10-m wind speed of 5-7 m/s. These findings corroborate the conceptual model that was proposed by van de Wiel et al (2017). The relation between the inversion strength and the wind speed was previously studied by Hudson and Brandt (2005).…”

supporting

confidence: 91%

“…Wind speeds lower than ∼ 4 m/s are associated with very strong 10-m inversions of 20-25 K. In contrast, wind speeds higher than ∼7 m/s correspond to relatively weak inversions of order 5 K. As emphasized by the time series of the individual events, the transition between the two regimes is highly nonlinear in the chosen phase space. In fact, the relation between the inversion strength and the wind speed reflects the shape of an inverted "S," as was anticipated by van de Wiel et al (2017).…”

Section: Resultsmentioning

confidence: 53%

“…The results presented here show that in conditions typical for the Antarctic Plateau, the conceptual framework of van de Wiel et al (2017) needs refinement. They stated that at a particular reference level a single "threshold" wind speed exists below which the boundary layer collapses as a whole.…”

Section: Discussionmentioning

confidence: 90%

“…For example, the present results indicate that at Dome C the regime transition at 10-m height is related to the depth of the turbulent layer being thinner or thicker than 10 m. Thus, the 10-m wind speed is an internal parameter (say "consequence") of the system rather than a proper proxy of the external (mechanical) forcing as it is modified by turbulent stress divergence: as shown in Figure 8 the stress divergence at this level effectively counteracts the tendency in the geostrophic wind. This explains why van der Linden et al (2017) and Baas et al (2018) found much smoother regime transitions when taking the geostrophic wind speed rather than an observed boundary layer wind speed as the independent parameter.…”

Section: Discussionmentioning

confidence: 97%

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Transitions in the wintertime near‐surface temperature inversion at Dome C, Antarctica

Baas

Wiel

Meijgaard

et al. 2019

Quart J Royal Meteoro Soc

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In this work we study the dynamics of the surface‐based temperature inversion over the Antarctic Plateau during the polar winter. Using 6 years of observations from the French–Italian Antarctic station Concordia at Dome C, we investigate sudden regime transitions in the strength of the near‐surface temperature inversion. Here we define “near‐surface” as being within the domain of the 45‐m measuring tower. In particular, we consider the strongly nonlinear relation between the 10‐m inversion strength ( T 10m – T s ) and the 10‐m wind speed. To this end, all individual events for which the 10‐m inversion strength increases or decreases continuously by more than 15 K in time are considered. Composite time series and vertical profiles of wind and temperature reveal specific characteristics of the transition from weak to very strong inversions and vice versa. In contrast to midlatitudes, the largest variations in temperature are not found at the surface but at a height of 10 m. A similar analysis was performed on results from an atmospheric single‐column model (SCM). Overall, the SCM results reproduce the observed characteristics of the transitions in the near‐surface inversion remarkably well. Using model output, the underlying mechanisms of the regime transitions are identified. The nonlinear relation between inversion strength and wind speed at a given level is explained by variations in the geostrophic wind speed, changes in the depth of the turbulent layer and the vertical divergence of turbulent fluxes. Moreover, the transitions between different boundary layer regimes cannot be explained without considering the contribution of subsidence heating.

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supporting

confidence: 91%

Section: Resultsmentioning

confidence: 53%

Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 97%

See 2 more Smart Citations

Transitions in the wintertime near‐surface temperature inversion at Dome C, Antarctica

Baas

Wiel

Meijgaard

et al. 2019

Quart J Royal Meteoro Soc

Self Cite

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“…van der Linden et al . () refined this approach and proposed using bin averages of the ambient geostrophic wind determined by horizontal pressure gradients. For their observations, ensemble averages of the net radiation, friction velocity and turbulent heat flux organized surprisingly well when binned using the geostrophic wind speed.…”

Section: Introductionmentioning

confidence: 99%

Classifying the nocturnal atmospheric boundary layer into temperature and flow regimes

Pfister

Lapo

Sayde

et al. 2019

Quart J Royal Meteoro Soc

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We propose a classification scheme for nocturnal atmospheric boundary layers and apply it to investigate the spatio‐temporal structure of air temperature and wind speed in a shallow valley during the Shallow Cold Pool Experiment. This field campaign was the first to collect spatially continuous temperature and wind information at high resolution (1 s, 0.25 m) using the distributed temperature sensing technique across a 220 m long transect at three heights (0.5, 1.0, 2.0 m). The night‐time classification scheme was motivated by a surface energy balance and used a combination of static stability, wind regime and longwave radiative forcing as quantities to determine physically meaningful boundary‐layer regimes. Out of all potential combinations of these three quantities, 14 night‐time classes contained observations, of which we selected three for detailed analysis and comparison. The three classes represent a transition from mechanical to radiative forcing. The first night class represents conditions with strong dynamic forcing caused by locally induced lee turbulence dominating near‐surface temperatures across the shallow valley. The second night class was a concurrence of enhanced dynamic mixing due to significant winds at the valley shoulders and cold‐air pooling at the bottom of the shallow valley as a result of strong radiative cooling. The third night class was characteristic of weak winds eliminating the impact of mechanical mixing but emphasizing the formation and pooling of cold air at the valley bottom. The proposed night‐time classification scheme was found to sort the experimental data into physically meaningful regimes of surface flow and transport. It is suitable to stratify short‐ and long‐term experimental data for ensemble averaging and to identify case studies.

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Modeling the Dynamics of the Atmospheric Boundary Layer Over the Antarctic Plateau With a General Circulation Model

Vignon

Hourdin

Genthon

et al. 2018

J Adv Model Earth Syst

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Observations evidence extremely stable boundary layers (SBL) over the Antarctic Plateau and sharp regime transitions between weakly and very stable conditions. Representing such features is a challenge for climate models. This study assesses the modeling of the dynamics of the boundary layer over the Antarctic Plateau in the LMDZ general circulation model. It uses 1 year simulations with a stretched‐grid over Dome C. The model is nudged with reanalyses outside of the Dome C region such as simulations can be directly compared to in situ observations. We underline the critical role of the downward longwave radiation for modeling the surface temperature. LMDZ reasonably represents the near‐surface seasonal profiles of wind and temperature but strong temperature inversions are degraded by enhanced turbulent mixing formulations. Unlike ERA‐Interim reanalyses, LMDZ reproduces two SBL regimes and the regime transition, with a sudden increase in the near‐surface inversion with decreasing wind speed. The sharpness of the transition depends on the stability function used for calculating the surface drag coefficient. Moreover, using a refined vertical grid leads to a better reversed “S‐shaped” relationship between the inversion and the wind. Sudden warming events associated to synoptic advections of warm and moist air are also well reproduced. Near‐surface supersaturation with respect to ice is not allowed in LMDZ but the impact on the SBL structure is moderate. Finally, climate simulations with the free model show that the recommended configuration leads to stronger inversions and winds over the ice‐sheet. However, the near‐surface wind remains underestimated over the slopes of East‐Antarctica.

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Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing

Cited by 24 publications

References 51 publications

Transitions in the wintertime near‐surface temperature inversion at Dome C, Antarctica

Transitions in the wintertime near‐surface temperature inversion at Dome C, Antarctica

Classifying the nocturnal atmospheric boundary layer into temperature and flow regimes

Modeling the Dynamics of the Atmospheric Boundary Layer Over the Antarctic Plateau With a General Circulation Model

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