Evaluation of Cloud Shading Effects on the Generation and Modification of Mesoscale Circulations

Segal, M.; Song, Jiayun; Pielke, Roger A.; Purdom, James F. W.; Mahrer, Y.

doi:10.1175/1520-0493(1986)114<1201:eocseo>2.0.co;2

Cited by 42 publications

(43 citation statements)

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“…The altered u Ã in 33L, compared to 31L, modified the surface wind convergence and local convection forcing, a feature that is consistent with the findings in Colle and Yuter (2007). Consequently, areas of convection further differed between the two simulations due to the convection processes, and could be affected by model-generated thermal circulations due to sensible heat flux gradients induced by cloud shading and soil wetness contrasts (e.g., Ookouchi et al 1984;Segal et al 1986). …”

Section: April 2009 a L I G O E T A Lsupporting

confidence: 70%

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Aligo

Gallus

Segal

2009

Weather and Forecasting

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Weather Research and Forecast (WRF) model exploratory sensitivity simulations were performed to determine the impact of vertical grid resolution (VGR) on the forecast skill of Midwest summer rainfall. Varying the VGR indicated that a refined VGR, while adopting the widely used North America Regional Reanalysis (NARR) for initial and lateral boundary conditions, does not necessarily result in a consistent improvement in quantitative precipitation forecasts (QPFs). When averaged over a variety of microphysical schemes in an illustrative case, equitable threat score (ETS) and bias values actually worsened with a greater overpredicted rainfall for half of the rainfall thresholds when the VGR was refined. Averaged over strongly forced cases, ETS values worsened for all rainfall thresholds while biases mostly increased, indicating a further overprediction of rainfall when the number of levels was increased. Skill improved, however, for all rainfall thresholds when the resolution above the melting level was increased. Skill also improved for most rainfall thresholds when the resolution in the surface layer was increased, which is attributed to better-resolved surface turbulent momentum and thermal fluxes. Likewise, a refined VGR resulted in improvements in weakly forced cases, which are governed mostly by thermodynamic forcing and are sensitive to vertical profiles of temperature and moisture. Application of the factor separation method suggested that the refined VGR more frequently had a negative impact on skill through the interaction between lower-atmospheric processes and microphysical processes above the melting level. KeywordsAgronomy, atmospheric process, equitable threat score, illustrative case, lateral boundary conditions, melting levels, microphysical process, negative impacts, quantitative precipitation forecast, reanalysis, sensitivity simulation, summer rainfall, surface layers, thermal fluxes, turbulent momentum, vertical grids, WRF model, atmospheric thermodynamics, climate prediction, rainfall, weather forecasting Varying the VGR indicated that a refined VGR, while adopting the widely used North America Regional Reanalysis (NARR) for initial and lateral boundary conditions, does not necessarily result in a consistent improvement in quantitative precipitation forecasts (QPFs). When averaged over a variety of microphysical schemes in an illustrative case, equitable threat score (ETS) and bias values actually worsened with a greater overpredicted rainfall for half of the rainfall thresholds when the VGR was refined. Averaged over strongly forced cases, ETS values worsened for all rainfall thresholds while biases mostly increased, indicating a further overprediction of rainfall when the number of levels was increased. Skill improved, however, for all rainfall thresholds when the resolution above the melting level was increased. Skill also improved for most rainfall thresholds when the resolution in the surface layer was increased, which is attributed to better-resolved surface turbulent momentum ...

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Section: April 2009 a L I G O E T A Lsupporting

confidence: 70%

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Aligo

Gallus

Segal

2009

Weather and Forecasting

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“…The earliest hydrostatic models used simple boundary-layer schemes and neglected moisture, latent heating, radiation, and land-surface parametrisations. Some later models included radiation, moisture and latent heating, with increasingly sophisticated schemes for surface heating and the turbulent Neumann andMahrer (1971, 1974) 5 , Pearson (1973) Pielke (1974a,b) 4 1975-1979 2D 2.5-8 9 Neumann and Mahrer (1975) 5 , Sheih and Moroz (1975) 1 , Estoque et al (1976) 1 , Pielke (1976, 1977) 3 , Physick (1976) 4 , Anthes (1978) 2 , Asai and Mitsumoto (1978) 1 , Ookouchi et al (1978) 3 1980-19842D 3-10 8 Physick (1980 4 , Estoque and Gross (1981) 1985-1989 2D 1-10 14 Garratt and Physick (1985) 2 , Mahrer and Segal (1985) 1 , Physick and Smith (1985) 3 , Neumann and Savijarvi (1986) 1 , Noonan and Smith (1986) 2 , Segal et al (1986) 3 , Arritt (1987Arritt ( , 1989 4 , Briere (1987) 1 , Anthes (1987, 1988) Freitas et al (2007) 8 , Srinivas et al (2007) 8 , Talbot et al (2007) 8 , Thompson et al (2007) 8 , Cheng and Byun (2008) transport of heat, moisture, and momentum. Through the 1970s, turbulence in the surface layer was generally treated using simple K-theory, assuming constant fluxes, and with empirical formulations for turbulent transport in the overlying transition layer.…”

Section: Historymentioning

confidence: 99%

Sea and Lake Breezes: A Review of Numerical Studies

Crosman

Horel

2010

Boundary-Layer Meteorol

279

225

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Numerical studies of sea and lake breezes are reviewed. The modelled dependence of sea-breeze and lake-breeze characteristics on the land surface sensible heat flux, ambient geostrophic wind, atmospheric stability and moisture, water body dimensions, terrain height and slope, Coriolis parameter, surface roughness length, and shoreline curvature is discussed. Consensus results on the influence of these geophysical variables on sea and lake breezes are synthesized as well as current gaps in our understanding. A brief history of numerical modelling, an overview of recent high-resolution simulations, and suggestions for future research related to sea and lake breezes are also presented. The results of this survey are intended to be a resource for numerical modelling, coastal air quality, and wind power studies.

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“…These simulations are essentially similar to those described in (Segal et al, 1986), except that the speed of the cloudy region is much larger here (up to 15 ms −1 compared with 1.7 ms −1 ). Results from (Segal et al, 1986) suggest that convergence and uplift should be generated at the edges of the cold anomaly, and that this uplift should be maintained or enhanced at the leading edge of the anomaly, but reduced on its trailing edge.…”

Section: Modelled Effects Of Moving Negative Surface-flux Anomaliesmentioning

confidence: 99%

“…In general, variations in cloud cover, or other parameters such as soil wetness or vegetation, can also induce such circulations (called 'nonclassical mesoscale circulations' by Segal and Arritt (1992)). Segal et al (1986) described idealized two-dimensional simulations of circulations driven by variable cloud cover. The contrast between an extensive clear area (about 80 km across) and an extensive cloudy area was shown to induce a circulation comparable to a sea breeze, when the clouds reduced solar fluxes by 60%.…”

Section: Introductionmentioning

confidence: 99%

Variable cirrus shading during CSIP IOP 5. I: Effects on the initiation of convection

Marsham

Morcrette

Browning

et al. 2007

Quart J Royal Meteoro Soc

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ABSTRACT:Observations from the Convective Storm Initiation Project (CSIP) show that on 29 June 2005 (Intensive Observation Period 5) cirrus patches left over from previous thunderstorms reduced surface sensible and latent heat fluxes in the CSIP area. Large-eddy model (LEM) simulations, using moving positive surface-flux anomalies, show that we expect the observed moving gaps in the cirrus cover to significantly aid convective initiation. In these simulations, the timing of the CI is largely determined by the amount of heat added to the boundary layer, but weak convergence at the rear edge of the moving anomalies is also significant.Meteosat and rain-radar data are combined to determine the position of convective initiation for all 25 trackable showers in the CSIP area. The results are consistent with the LEM simulations, with showers initiating at the rear edge of gaps, at the leading edge of the anvil, or in clear skies, in all but one of the cases. The initiation occurs in relatively clear skies in all but two of the cases, with the exceptions probably linked to orographic effects.For numerical weather prediction, the case highlights the importance of predicting and assimilating cloud cover. The results show that in the absence of stronger forcings, weak forcings, such as from the observed cirrus shading, can determine the precise location and timing of convective initiation. In such cases, since the effects of shading by cirrus anvils from previous convective storms are relatively unpredictable, this is expected to limit the predictability of the convective initiation.

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Evaluation of Cloud Shading Effects on the Generation and Modification of Mesoscale Circulations

Cited by 42 publications

References 0 publications

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Sea and Lake Breezes: A Review of Numerical Studies

Variable cirrus shading during CSIP IOP 5. I: Effects on the initiation of convection

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