Thickness of the dry convection and large-scale subsidence above deserts

Gamo, Minoru

doi:10.1007/bf00119441

Cited by 107 publications

(67 citation statements)

References 5 publications

(5 reference statements)

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“…Gamo (1996) showed that the lapse rates over deserts tend to be closer to neutral than in the ECMWF global model and that the ability of global models to represent SABL processes should be further evaluated.…”

Section: Discussionmentioning

confidence: 99%

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Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer

Cuesta

Marsham

Parker

et al. 2009

Atmospheric Science Letters

132

143

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The Saharan atmospheric boundary layer (SABL) plays a significant role in the atmospheric global circulation and directly affects the vertical redistribution of dust originated in the Sahara, the world's largest dust source. Recent measurements have revealed a variety of new dynamical mechanisms that control the structure of the SABL, which are responsible for exchange between the Saharan convective and residual boundary layers. Using new spaceborne laser remote sensing data (CALIPSO) and recently published results, we provide an overview of the following known dynamical mechanisms: diurnal vertical mixing, dynamical lifting (density currents and cold air outbreaks) and topographic effects (mountains and albedo anomalies).

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Section: Discussionmentioning

confidence: 99%

“…Over the Sahara, dust is transported by dry convection and it is mostly located in the Saharan atmospheric boundary layer (SABL), which is up to 6 km deep (Gamo, 1996). Three typical situations have been observed: freshly uplifted dust with clearer air above (e.g.…”

Section: Introductionmentioning

confidence: 99%

Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer

Cuesta

Marsham

Parker

et al. 2009

Atmospheric Science Letters

132

143

View full text Add to dashboard Cite

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“…Over the Sahara, large surface sensible heat fluxes and deep dry convection can result in a summertime boundary layer that is up to 6 km deep (Gammo, 1996). However, profiles from the Sahara in summer typically show a shallower active convective boundary layer (CBL), with a near neutrally stratified residual layer above (the Saharan Residual Layer, SRL).…”

Section: Introductionmentioning

confidence: 99%

Observations of mesoscale and boundary-layer scale circulations affecting dust transport and uplift over the Sahara

et al. 2008

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Abstract.Observations of the Saharan boundary layer, made during the GERBILS field campaign, show that mesoscale land surface temperature variations (which were related to albedo variations) induced mesoscale circulations. With weak winds along the aircraft track, land surface temperature anomalies with scales of greater than 10 km are shown to significantly affect boundary-layer temperatures and winds. Such anomalies are expected to affect the vertical mixing of the dusty and weakly stratified Saharan Residual Layer (SRL). Mesoscale variations in winds are also shown to affect dust loadings in the boundary layer.Using the aircraft observations and data from the COSMO model, a region of local dust uplift, with strong along-track winds, was identified in one low-level flight. Large eddy model (LEM) simulations based on this location showed linearly organised boundary-layer convection. Calculating dust uplift rates from the LEM wind field showed that the boundary-layer convection increased uplift by approximately 30%, compared with the uplift rate calculated neglecting the convection. The modelled effects of boundary-layer convection on uplift are shown to be larger when the boundary-layer wind is decreased, and most significant when the mean wind is below the threshold for dust uplift and the boundary-layer convection leads to uplift which would not otherwise occur.Both the coupling of albedo features to the atmosphere on the mesoscale, and the enhancement of dust uplift by boundary-layer convection are unrepresented in many cliCorrespondence to: J. H. Marsham (jmarsham@env.leeds.ac.uk) mate models, but may have significant impacts on the vertical transport and uplift of desert dust. Mesoscale effects in particular tend to be difficult to parametrise.

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“…Gamo (1996) showed that a mixed layer develops up to 3-4 km above the ground level (AGL) during the daytime over the northwest China desert in August. Figure 1 shows mean thermodynamic vertical profiles at Zhangye, located at 100.26E, 38.56N in the HEIFE region, at 2000 BST (BST; Beijing Standard Time which is 8 hour plus UTC) in August 1991.…”

Section: Equationsmentioning

confidence: 99%

Evaporation of Rain Falling Below a Cloud Base Through a Deep Atmospheric Boundary Layer Over an Arid Region

Takemi

1999

Journal of the Meteorological Society of Japan

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The evaporation of rain falling through a dry subcloud layer was investigated by using a onedimensional, time-dependent model only including sedimentation and evaporation. The model assumed a stratiform-type; weak rain under a condition of a dry, deep atmospheric boundary layer typical of the northwest China desert region in summer. Two kinds of experiments were conducted. In the first experiment, the air was assumed to be at rest. With a medium rain intensity (9.5 mm h-1) surface rain occurred at about 1h after rain started at the model top, whereas with a light rain intensity (0.97mm h 1) surface rainfall occurred at about 11.5 h. The amount of rain depleted by evaporation varied widely according to the fall distance from the top and rain intensity. With a constant amount of total rain provided at the top, the amount of evaporated rain increased with rain intensity. In the second experiment, constant downward vertical velocity was prescribed to examine the effect of subsidence warming on the rain evaporation. Only a descent of a few tens of cm s-1 significantly enhanced the rain depletion. Compared with the surface observations in the desert, it was suggested from the model results that evaporation of rain is a dominant cause of the observed changes typical of a desert rain event.

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Thickness of the dry convection and large-scale subsidence above deserts

Cited by 107 publications

References 5 publications

Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer

Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer

Observations of mesoscale and boundary-layer scale circulations affecting dust transport and uplift over the Sahara

Evaporation of Rain Falling Below a Cloud Base Through a Deep Atmospheric Boundary Layer Over an Arid Region

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