Positive surface temperature feedback in the stable nocturnal boundary layer

Walters, Justin T.; McNider, Richard T.; Shi, Xingzhong; Norris, William B.; Christy, John R.

doi:10.1029/2007gl029505

Cited by 52 publications

(96 citation statements)

References 24 publications

(40 reference statements)

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“…To further complicate matters for T Min , McNider et al (1995), Van de Wiel et al (2002), and Walters et al (2007) demonstrate that the NBL in which T Min is measured acts as a delicate, nonlinear dynamical system. In some parameter spaces this system responds with large changes in T Min for only slight changes in parameters, such as roughness, wind speed, or radiative forcing.…”

Section: ) General Discussionmentioning

confidence: 99%

Surface Temperature Variations in East Africa and Possible Causes

2009

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Surface temperatures have been observed in East Africa for more than 100 yr, but heretofore have not been subject to a rigorous climate analysis. To pursue this goal monthly averages of maximum (T Max ), minimum (T Min ), and mean (T Mean ) temperatures were obtained for Kenya and Tanzania from several sources. After the data were organized into time series for specific sites (60 in Kenya and 58 in Tanzania), the series were adjusted for break points and merged into individual gridcell squares of 1.258, 2.58, and 5.08.Results for the most data-rich 58 cell, which includes Nairobi, Mount Kilimanjaro, and Mount Kenya, indicate that since 1905, and even recently, the trend of T Max is not significantly different from zero. However, T Min results suggest an accelerating temperature rise.Uncertainty estimates indicate that the trend of the difference time series (T Max 2 T Min ) is significantly less than zero for 1946-2004, the period with the highest density of observations. This trend difference continues in the most recent period , in contrast with findings in recent periods for global datasets, which generally have sparse coverage of East Africa.The differences between T Max and T Min trends, especially recently, may reflect a response to complex changes in the boundary layer dynamics; T Max represents the significantly greater daytime vertical connection to the deep atmosphere, whereas T Min often represents only a shallow layer whose temperature is more dependent on the turbulent state than on the temperature aloft.Because the turbulent state in the stable boundary layer is highly dependent on local land use and perhaps locally produced aerosols, the significant human development of the surface may be responsible for the rising T Min while having little impact on T Max in East Africa. This indicates that time series of T Max and T Min should become separate variables in the study of long-term changes.

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Section: ) General Discussionmentioning

confidence: 99%

Surface Temperature Variations in East Africa and Possible Causes

2009

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“…Corresponding damping of model sensitivity has been demonstrated at high-latitudes (Beesly et al, 2000;Byrkjedal et al, 2008). Nevertheless, at present, the primary attention of climatologists is still focused on the daytime PBL (Stone and Weaver, 2003;Walters et al, 2007). This study consists of two distinct sections.…”

Section: Introductionmentioning

confidence: 99%

On the role of the planetary boundary layer depth in the climate system

Esau

Zilitinkevich

2010

Adv. Sci. Res.

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Abstract.The planetary boundary layer (PBL) is a part of the Earth's atmosphere where turbulent fluxes dominate vertical mixing and constitute an important part of the energy balance. The PBL depth, h, is recognized as an important parameter, which controls some features of the Earth's climate and the atmospheric chemical composition. It is also known that h varies by two orders of magnitude on diurnal and seasonal time scales. This brief note highlights effects of this variability on the atmospheric near-surface climate and chemical composition. We interpret heat capacity parameter of a Budyko-type energy balance model in terms of quasi-equilibrium h. The analysis shows that it is the shallowest, stably-stratified PBL with the smallest h that should be of particular concern for climate modelling. The reciprocal dependence between the PBL depth and temperature (concentrations) is discussed. In particular, the analysis suggests that the climate characteristics during stably stratified PBL episodes should be significantly more sensitive to perturbations of the Earth's energy balance as well as emission rates. On this platform, h from ERA-40 reanalysis data, the CHAMP satellite product and the DATABASE64 data were compared. DATABASE64 was used to assess the Troen-Mahrt method to determine h through available meteorological profile observations. As it has been found before, the shallow PBL requires better parameterization and better retrieval algorithms. The study demonstrated that ERA-40 and CHAMP data are biased toward deeper h in the shallow polar PBL. This, coupled with the scarcity of in-situ observations might mislead the attribution of the origins of the Arctic climate change mechanisms.

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“…Qualitatively similar behavior has been reported in stratified wind-tunnel experiments by Ohya et al (1997), who found dramatic changes in boundary layer characteristics in response to decreasing mechanical forcing. Likewise, regime transitions have been modeled with simple 1D models (Estournel and Guedalia 1985;Revelle 1993;McNider et al 1995;Derbyshire 1999a; Van de Wiel et al 2002a;Walters et al 2007;Acevedo et al 2012) in large-eddy simulation (LES) studies (Jimé nez and Cuxart 2005;Zhou and Chow 2011) and in studies using direct numerical simulations (Nieuwstadt 2005;Flores and Riley 2011).…”

Section: Introductionmentioning

confidence: 99%

The Minimum Wind Speed for Sustainable Turbulence in the Nocturnal Boundary Layer

Wiel

Moene

Jonker

et al. 2012

Journal of the Atmospheric Sciences

130

120

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The collapse of turbulence in the nocturnal boundary layer is studied by means of a simple bulk model that describes the basic physical interactions in the surface energy balance. It is shown that for a given mechanical forcing, the amount of turbulent heat that can be transported downward is limited to a certain maximum. In the case of weak winds and clear skies, this maximum can be significantly smaller than the net radiative loss minus soil heat transport. In the case when the surface has low heat capacity, this imbalance generates rapid surface cooling that further suppresses the turbulent heat transport, so that eventually turbulence largely ceases (positive feedback mechanism). The model predicts the minimum wind speed for sustainable turbulence for the so-called crossing level. At this level, some decameters above the surface, the wind is relatively stationary compared to lower and higher levels. The critical speed is predicted in the range of about 5-7 m s 21 , depending on radiative forcing and surface properties, and is in agreement with observations at Cabauw. The critical value appears not very sensitive to model details or to the exact values of the input parameters. Finally, results are interpreted in terms of external forcings, such as geostrophic wind. As it is generally larger than the speed at crossing height, a 5 m s 21 geostrophic wind may be considered as the typical limit below which sustainable, continuous turbulence under clear-sky conditions is unlikely to exist. Below this threshold emergence of the very stable nocturnal boundary layer is anticipated.

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Positive surface temperature feedback in the stable nocturnal boundary layer

Cited by 52 publications

References 24 publications

Surface Temperature Variations in East Africa and Possible Causes

Surface Temperature Variations in East Africa and Possible Causes

On the role of the planetary boundary layer depth in the climate system

The Minimum Wind Speed for Sustainable Turbulence in the Nocturnal Boundary Layer

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