Observations from aircraft of temperatures and humidities near stratocumulus clouds

James, D. G.

doi:10.1002/qj.49708536405

Cited by 24 publications

(7 citation statements)

References 4 publications

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“…Such waves have been observed by aircraft, rockets and reported by Kuettner et al (1987) above convective boundary layers in continental mid-latitudes and by James (1959) and P®ster et al (1993) above deep convection in the tropics. These waves have earlier been studied numerically with two-dimensional simulations by Clark et al (1986) above shallow cumulus and by Fovell et al (1992) above a squall line.…”

Section: Introductionsupporting

confidence: 52%

Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution

1998

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Systematic westerly biases in the southern hemisphere wintertime ¯ow and easterly equatorial biases are experienced in the MeÂ teÂ o-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a signi®cant deceleration of the mean ¯ow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a signi®cant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the MeÂ teÂ o-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the ®rst, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere), and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere); the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the ®ner tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the vertical resolution .

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Section: Introductionsupporting

confidence: 52%

Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution

1998

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“…Interestingly, a systematic overall increase in LWP with AI as indicated by TMI LWP in Fig. 2a was also noticed in previous observational and modeling studies, e.g., Johnson et al (2004), Wilcox (2010), Randles and Ramaswamy (2010), Adebiyi et al (2015), and Adebiyi and Zuidema (2016). While this could partly be explained by the fortuitous spatial correlation between higher aerosol loads and thicker clouds in this Sc region, these studies argue that strong atmospheric absorption by the smoke warms the 700 hPa air temperature and increases upward motion.…”

Section: Effect Of Biomass Burning Smoke On Seviri and Modis Retrievalssupporting

confidence: 82%

Evaluating the diurnal cycle of South Atlantic stratocumulus clouds as observed by MSG SEVIRI

et al. 2018

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Abstract. Marine stratocumulus (Sc) clouds play an essential role in the earth radiation budget. Here, we compare liquid water path (LWP), cloud optical thickness (τ), and cloud droplet effective radius (re) retrievals from 2 years of collocated Spinning Enhanced Visible and Infrared Imager (SEVIRI), Moderate Resolution Imaging Spectroradiometer (MODIS), and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) observations; estimate the effect of biomass burning smoke on passive imager retrievals; and evaluate the diurnal cycle of South Atlantic marine Sc clouds.The effect of absorbing aerosols from biomass burning on the retrievals was investigated using the aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI). SEVIRI and MODIS LWPs were found to decrease with increasing AI relative to TMI LWP, consistent with well-known negative visible/near-infrared (VIS/NIR) retrieval biases in τ and re. In the aerosol-affected months of July–August–September, SEVIRI LWP – based on the 1.6 µm re – was biased low by 14 g m−2 ( ∼ 16 %) compared to TMI in overcast scenes, while MODIS LWP showed a smaller low bias of 4 g m−2 ( ∼ 5 %) for the 1.6 µm channel and a high bias of 8 g m−2 ( ∼ 10 %) for the 3.7 µm channel compared to TMI. Neglecting aerosol-affected pixels reduced the mean SEVIRI–TMI LWP bias considerably. For 2 years of data, SEVIRI LWP had a correlation with TMI and MODIS LWP of about 0.86 and 0.94, respectively, and biases of only 4–8 g m−2 (5 %–10 %) for overcast cases.The SEVIRI LWP diurnal cycle was in good overall agreement with TMI except in the aerosol-affected months. Both TMI and SEVIRI LWP decreased from morning to late afternoon, after which a slow increase was observed. Terra and Aqua MODIS mean LWPs also suggested a similar diurnal variation. The relative amplitude of the 2-year-mean and seasonal-mean LWP diurnal cycle varied between 35 % and 40 % from morning to late afternoon for overcast cases. The diurnal variation in SEVIRI LWP was mainly due to changes in τ, while re showed only little diurnal variability.

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“…Moeng et al [2005] analyzed their large-eddy simulation (LES) results and found that a cloud free and turbulence layer of several tens of meters is always present in the inversion due to local wind shear events. Both early and more recent observations have shown that the cloud top is indeed not the limit of the turbulence mixing [e.g., James, 1959;Lenschow et al, 2000]. These studies clearly demonstrate the importance of the wind shear in the stratocumulus dynamics; they also raise the question: what is the funda-mental difference between the strongly sheared and the shear-free stratocumulus convection?…”

Section: Introductionmentioning

confidence: 83%

Effect of intense wind shear across the inversion on stratocumulus clouds

Wang

Golaz

Wang

2008

Geophysical Research Letters

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[1] A large-eddy simulation model is used to examine the impact of the intense cross-inversion wind shear on the stratocumulus cloud structure. The wind shear enhanced entrainment mixing effectively reduces the cloud water and thickens the inversion layer. It leads to a reduction of the turbulence kinetic energy (TKE) production in the cloud layer due to the weakened cloud-top radiative cooling and the formation of a turbulent and cloud free sublayer within the inversion. The thickness of the sublayer increases with the enhanced wind shear intensity. Under the condition of a weaker inversion, the enhanced shear mixing within the inversion layer even lowers the cloud-top height and reduces the entrainment velocity. Finally, increasing wind shear or reducing inversion strength tends to create an inversion layer with a constant bulk Richardson number ($0.3), suggesting that an equilibrium value of the Richardson number is reached. Citation: Wang, S., J.-C. Golaz, and Q. Wang (2008), Effect of intense wind shear across the inversion on stratocumulus clouds, Geophys. Res. Lett., 35, L15814,

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Observations from aircraft of temperatures and humidities near stratocumulus clouds

Cited by 24 publications

References 4 publications

Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution

Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution

Evaluating the diurnal cycle of South Atlantic stratocumulus clouds as observed by MSG SEVIRI

Effect of intense wind shear across the inversion on stratocumulus clouds

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