Cloud Development and Distribution Around Khartoum

Hammer, Richard M.

doi:10.1002/j.1477-8696.1970.tb04131.x

Cited by 16 publications

(8 citation statements)

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“…Furthermore, modeling studies on the effects of irrigation on precipitation have shown that precipitation enhancement caused by irrigation occurs in regions that are quite distant from the irrigated fields [ Segal et al , 1998]. The formation of mesoscale circulations initiated by surface soil moisture heterogeneity [ Hammer , 1970; Eltahir and Bras , 1996; Avissar and Liu , 1996; Pielke et al , 1997; Georgescu et al , 2003] is a mechanism by which irrigation could promote an enhancement of precipitation closer to the boundaries of irrigated land. In summary, precipitation enhancement caused by irrigation is likely to be strongest from the boundaries of the Ogallala Aquifer to downwind regions.…”

Section: Introductionmentioning

confidence: 99%

Evidence of enhanced precipitation due to irrigation over the Great Plains of the United States

DeAngelis¹,

Domínguez²,

Fan³

et al. 2010

J. Geophys. Res.

258

247

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[1] At the end of World War II, there was a rapid increase in irrigation over the Ogallala Aquifer in the Great Plains of the United States via groundwater withdrawal, and we hypothesize that this disruption of the local hydrological cycle has enhanced the regional precipitation. We examined station and gridded precipitation observations for the warm season months over and downwind of the Ogallala over the 20th century. Increases in precipitation of 15-30% were detected during July from the easternmost part of the aquifer to as far downwind as Indiana. The timing (1940s, July) and spatial pattern of the precipitation increase are consistent with the history of Ogallala irrigation and mechanisms by which increases in evapotranspiration can affect convection. Additionally, we conducted a vapor tracking analysis and found that evapotranspiration over the Ogallala Aquifer contributes to downwind precipitation and that the contribution is greater when the evapotranspiration is higher. This makes it hydrologically possible that the irrigation development was associated with the observed precipitation increases. Finally, there is no clear evidence that atmospheric circulation changes or modes of internal climate variability increased the July precipitation. Further analysis of the influence of Ogallala irrigation on precipitation will include the controlled analysis of climate model simulations that explicitly include irrigation.

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Section: Introductionmentioning

confidence: 99%

Evidence of enhanced precipitation due to irrigation over the Great Plains of the United States

DeAngelis¹,

Domínguez²,

Fan³

et al. 2010

J. Geophys. Res.

258

247

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“…Correct predictions of surface sensible and latent heat fluxes can help the prediction of mesoscale circulations (Segal et al 1988), localized convection (Hammer 1970;Segal et al 1995;Freedman et al 2001), and boundary layer characteristics (Monteith 1995). Although some detailed land surface models are available for ecological applications, usually at river basin domain sizes (e.g., Simunek et al 2005;Marletto et al 2007), global numerical weather prediction models still lack an adequate representation of surface processes.…”

Section: Discussionmentioning

confidence: 99%

“…Observational evidence shows that the intensity and spatial distribution of surface sensible heat fluxes can drive mesoscale circulations, such as sea breezes or thermally induced upslope flows (Segal et al 1988), and can trigger and sustain localized convection (Hammer 1970;Segal et al 1995). The prediction of such localized phenomena is difficult even for a regional weather forecasting system with a resolution scale approaching a few kilometers.…”

Section: Introductionmentioning

confidence: 99%

Leaf Area Index Specification for Use in Mesoscale Weather Prediction Systems

Knote

Bonafè

Giuseppe

2009

Monthly Weather Review

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The energy budget at the surface is strongly influenced by the presence of vegetation, which alters the partitioning of thermal energy between sensible and latent heat fluxes. Despite its relevance, numerical weather prediction (NWP) systems often use only two parameters to describe the vegetation cover: the fractional area of vegetation occupying a given pixel and the leaf area index (LAI). In this study, the Consortium for Small-Scale Modelling (COSMO) limited-area forecast model is used to investigate the sensitivity of regional predictions to LAI assumptions over the Italian peninsula. Three different approaches are compared: a space-and time-invariant LAI dataset, a LAI specification based on Coordination of Information on the Environment (CORINE) land classes, and a Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-retrieved dataset. The three approaches resolve increasingly higher moments both in time and space of LAI probability density functions. Forecast scores employing the three datasets can therefore be used to assess the required degree of accuracy needed for this parameter. The MODIS dataset is the only one able to capture the expected vegetative cycle that is typical of the Mediterranean ecosystem and noticeably improves the 850-hPa temperature and humidity forecast scores up to 172 h forecast time. This suggests that accounting for LAI temporal and spatial variability could potentially improve the prevision of lower-level variables. Nevertheless, model biases of 2-m screen temperatures are not substantially reduced by the more detailed LAI specification when comparisons to synoptic observing stations are performed. Using long-term measurements collected by the CarboEurope project, a detailed verification of sensible and latent heat flux predictions is also presented. It shows that the desirable positive impact arising from a better LAI specification is nullified by the large uncertainties in the initialization of the soil moisture, which remains a crucial parameter for the reduction of screen-level biases.

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“…Soil initialization has the primary aim of integrating water and energy fluxes into the soil and snow buffers, and effectively determines the partitioning of surface fluxes between latent and sensible heat. It therefore has an immediate effect on the structure of temperature and humidity in the boundary layer, controlling the model prediction of the diurnal cycle, the timing and intensity of convection, and mesoscale circulations (Hammer 1970;Segal et al 1995;Segal et al 1988).…”

Section: The Problem Of Soil Initializationmentioning

confidence: 99%

Soil Initialization Strategy for Use in Limited-Area Weather Prediction Systems

Giuseppe

Cesari

Bonafè

2011

Monthly Weather Review

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Three diverse methods of initializing soil moisture and temperature in limited-area numerical weather prediction models are compared and assessed through the use of nonstandard surface observations to identify the approach that best combines ease of implementation, improvement in forecast skill, and realistic estimations of soil parameters. The first method initializes the limited-area model soil prognostic variables by a simple interpolation from a parent global model that is used to provide the lateral boundary conditions for the forecasts, thus ensuring that the limited-area model's soil field cannot evolve far from the host model. The second method uses the soil properties generated by a previous limited-area model forecast, allowing the soil moisture to evolve over time to a new equilibrium consistent with the regional model's hydrological cycle. The third method implements a new local soil moisture variational analysis system that uses screen-level temperature to adjust the soil water content, allowing the use of high-resolution station data that may be available to a regional meteorological service.The methods are tested in a suite of short-term weather forecasts performed with the Consortium for Small Scale Modeling (COSMO) model over the period September-November 2008, using the ECMWF Integrated Forecast System (IFS) model to provide the lateral boundary conditions. Extensive comparisons to observations show that substantial improvements in forecast skills are achievable with improved soil temperature initialization while a smaller additional benefit in the prediction of surface fluxes is possible with the soil moisture analysis. The analysis suggests that keeping the model prognostic variables close to equilibrium with the soil state, especially for temperature, is more relevant than correcting the soil moisture initial values. In particular, if a local soil analysis system is not available, it seems preferable to adopt an ''open loop'' strategy rather than the interpolation from the host global model analysis. This appears to be especially true for the COSMO model in its current operational configuration since the soil-vegetation-atmosphere transfer (SVAT) scheme of the ECMWF global host model and that of COSMO are radically diverse.

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Cloud Development and Distribution Around Khartoum

Cited by 16 publications

References 0 publications

Evidence of enhanced precipitation due to irrigation over the Great Plains of the United States

Evidence of enhanced precipitation due to irrigation over the Great Plains of the United States

Leaf Area Index Specification for Use in Mesoscale Weather Prediction Systems

Soil Initialization Strategy for Use in Limited-Area Weather Prediction Systems

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