NASA Image of the Day

NASA Image of the Day The latest NASA “Image of the Day” image.

  • Behold the Southern Lights!
    on April 19, 2019 at 1:43 pm

    As the International Space Station orbited 265 miles above the southern Indian Ocean about halfway between Madagascar and Antarctica, the crew snapped this image of the Aurora Australis. […]

  • A Rainbow and the Cygnus Launch
    on April 18, 2019 at 1:00 pm

    A rainbow is seen at launch Pad-0A after the Northrop Grumman Antares rocket launched, Wednesday, April 17, 2019 at NASA’s Wallops Flight Facility in Virginia. […]

  • Northrop Grumman Engineers Load Final Cargo for Cygnus Launch
    on April 17, 2019 at 1:02 pm

    Mission engineers load the final cargo into the Cygnus resupply spacecraft onboard the Northrop Grumman Antares rocket, Tuesday, April 16, 2019. […]

  • Northrop Grumman’s 11th Cargo Launch Prepares to Launch to Station
    on April 16, 2019 at 1:04 pm

    A Northrop Grumman Antares rocket carrying a Cygnus resupply spacecraft is seen during sunrise on Pad-0A, Tuesday, April 16, 2019, at NASA’s Wallops Flight Facility in Virginia. […]

  • NASA Takes Advantage of Innovative 3-D Printing Process for SLS Rocket
    on April 15, 2019 at 2:07 pm

    America’s powerful new deep space rocket, NASA’s Space Launch System, will face harsh conditions and extreme temperatures in flight when launching NASA’s Orion spacecraft and potential cargo to lunar orbit, and for that, it’ll need strong protection. […]

Diana Francis

Welcome to my personal website!

I would be honoured and happy to connect and collaborate. Please visit also my ResearchGate page and let’s stay in touch!

 

PhD Defense presentation  PhD Thesis Manuscript

 

Peer re-viewed journal publications:

2018

Francis D., C. Eayrs, J-P. Chaboureau, T. Mote, D. Holland (2018), Polar jet associated circulation triggered a Saharan cyclone and derived the poleward transport of the African dust generated by the cyclone, Journal of Geophysical Research: Atmospheres, DOI:10.1029/2018JD029095.

 

2017

Bou Karam Francis D., C. Flamant, J.-P. Chaboureau, J. Banks, J. Cuesta, H. Brindley, L. Oolman, 2017: Dust emission and transport over Iraq associated with the summer Shamal winds, Aeolian Research, Volume 24, February 2017, Pages 15-31, ISSN 1875-9637.

 

2014

Bou Karam D., E. Williams, M. Janiga, C. Flamant, M. MacGraw-Herdeg, J. Cuesta, A. Auby, C. Thorncroft, 2014: Synoptic-scale dust emissions over the Sahara desert initiated by a moist convective cold pool in early August 2006, Quarterly Journal of the Royal Meteorological Society, DOI: 10.1002/qj2326.

 

2013

Kravitz B., K. Caldeira, O. Boucher, A.Robock, P.J. Rasch, K. Alterskjær, D. Bou Karam et al., 2013: Climate model response from the Geoengineering Model Intercomparison Project (GeoMIP), Journal of Geophysical Research Atmospheres, VOL. 118, 1–13, doi:10.1002/jgrd.50646, 2013.

 

Tilmes S., J. Fasullo, J.-F.Lamarque, D. Marsh, M. Mills, K. Alterskjær, O. Boucher, J. N. S. Cole, C. Curry, J. Haywood, P. Irvine, D. Ji, A. Jones, D. Bou Karam et al. 2013: The Hydrological Impact of Geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP), Journal of Geophysical Research Atmospheres, VOL. 118, 1–13, doi:10.1029, 2013.

 

2012

Kok J., E.J.R. Parteli, T.I. Michaels and D. Bou Karam (2012, Solicited): The physics of wind-blown sand and dust, Rep. Prog. Phys. doi:10.1088/0034-4885/75/10/106901.

 

Schmidt H., K. Alterskjær, D. Bou Karam, O. Boucher, A. Jones, J. E. Kristjánsson, U. Niemeier, M. Schulz, A. Aaheim, F. Benduhn, M. Lawrence and C. Timmreck (2012): Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models, Earth Sys. Dyn. doi:10.5194/esdd-3-63-2012.

 

Schmidt H., K. Alterskjær, D. Bou Karam, O. Boucher, A. Jones, J. E. Kristjánsson, U. Niemeier, M. Schulz, A. Aaheim, F. Benduhn, M. Lawrence and C. Timmreck (2012): Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models, Earth Sys. Dyn. doi:10.5194/esd-3-63-2012.

 

2010

Bou Karam D., C. Flamant, J. Cuesta, J. Pelon, E. Williams (2010): Dust emission and transport associated with a Saharan depression: The February 2007 case, J. Geophys. Res., doi:10.1029/2009JD012390.

 

Schwendike J., D. Bou Karam, S. Crumeyrolle, C. Flamant, S. Jones, M. Schmidberger, F. Solmon, T. Stanelle, P. Tulet, H. Vogel, B.Vogel (2010), Mineral dust transport over West Africa in 2006, AMS 29th Conference on Hurricanes and Tropical Meteorology, Proceedings, P1. 101, May 2010.

 

2009

Bou Karam D., C. Flamant, P. Tulet, M. C. Todd, J. Pelon and E. Williams (2009a): Dry cyclogenesis and dust mobilization in the Inter Tropical Discontinuity of the West African Monsoon: a case study, J. Geophys. Res., 114, D05115, doi:10.1029/2008JD010952.

Bou Karam D., C. Flamant, P. Tulet, J-P. Chaboureau, A. Dabas, M. C. Todd (2009b): Estimate of Sahelian dust emissions in the Intertropical discontinuity region of the West African Monsoon ,J. Geophys. Res., 114, D13106, doi:10.1029/2008JD011444.

Pospichal B., D. Bou Karam, S. Crewell, C. Flamant A. Hünerbein, O. Bock, F. Saïd (2009): Diurnal cycle of the inter-tropical discontinuity over West Africa analysed by remote sensing and mesoscale modelling,Q. J. R. Meteorol. Soc. DOI: 10.1002/qj. 435.

2008

Bou Karam D., C. Flamant, P. Knippertz, O. Reitebuch, J. Pelon, M. Chong, A. Dabas (2008): Dust emissions over the Sahel associated with the West African Monsoon inter-tropical discontinuity region: a representative case study, Q. J. R. Meteorol. Soc. 134: 621–634.

Bou Karam D., C. Flamant, P. Knippertz, O. Reitebuch, M. Chong, A. Dabas, J. Pelon (2008): A newly identified mechanism for dust emissions over the Sahel associated with the West African Monsoon inter-tropical discontinuity, 24th International Laser Radar Conference (ILRC), 23-27 June 2008, Boulder, Colorado, USA.

Todd M.C., D. Bou Karam, C. Cavazos, C. Bouet, B. Heinold, G. Cautenet, P. Tulet, C. Perez, I. Tegen, and R. Washington (2008): Quantifying uncertainty in estimates of mineral dust flux: an inter-comparison of model performance over the Bodélé Depression, Northern Chad, J. Geophys. Res., 113, D24107, 2008, doi:10.1029/2008JD010476.

Pelon, J., M. Mallet, A. Mariscal, P. Goloub, D. Tanré, D. Bou Karam, C. Flamant, J. Haywood, B. Pospichal, S. Victori (2008): Characterisation of biomass burning aerosol from microlidar observations at Djougou (Benin) during AMMA-SOP0/DABEX,J. Geophys. Res., 113, D00C18, doi:10.1029/2008JD009976.

News


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Sharav dust storm

Bou Karam D., C. Flamant, J. Cuesta, J. Pelon, E. Williams (2010):

Dust emission and transport associated with Saharan depressions: The February 2007 case.

Abstract


The dust activity over North Africa associated with the Saharan depression event in February 2007 is investigated by mean of spaceborne observations and ground based measurements. The main characteristics of the cyclone as well as the meteorological conditions during this event are described using the European Centre for Medium-range Weather Forecasts (ECMWF). The dust storm and cloud cover over North Africa is thoroughly described combining for the first time Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) images for the spatio-temporal evolution and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat observations for the vertical distribution.

The Saharan depression formed over Algeria in the lee of the Atlas Mountain on the afternoon of February 20 in response to midlatitude trough intrusion. It migrated eastward with a speed of 11 m s-1 and reached Libya on February 22 before exiting the African continent toward the Mediterranean Sea on February 23. The horizontal scale of the cyclone at the surface varied between 800 km and 1000 km during its lifetime. On the vertical the cyclone extended over 8 km and a potential vorticity of 2 PVU was reported on its centre at 3km in altitude. The cyclone was characterised by a surface depth of 9 hPa, a warm front typified at the surface by an increase in surface temperature of 5°C, and a sharp cold front expressed by a drop in surface temperature of 8°C and an increase in 10m wind speed of 15 m s-1.

The cyclone provided a dynamical forcing that led to strong near-surface winds and produced a major dust storm over North Africa. Heavy dust load was seen along the cold front and the southeastern edge of the cyclone accompanied by a deep cloud band along its northwestern edge. The dust was transported all around the cyclone leaving a clear eye on its centre. On the vertical, slanted dust layers were consistently observed during the event over North Africa. Furthermore, the dust was lofted to altitudes as high as 7 km, becoming subject to long range transport.

Key Words: Mediterranean cyclone, CloudSat, ECMWF, North Africa, Sharav cyclone, CALIPSO.

Bou Karam D., C. Flamant, J. Cuesta, J. Pelon, E. Williams (2010): Dust emission and transport associated with a Saharan depression: The February 2007 case , J. Geophys. Res., doi:10.1029/2009JD012390.

Quantification of Dust load in the ITD region

Bou Karam D., C. Flamant, P. Tulet, J-P. Chaboureau, A. Dabas, M. C. Todd (2009b): Estimate of Sahelian dust emissions in the Intertropical discontinuity region of the West African Monsoon, submitted to JGR.


Abstract

A three-dimensional mesoscale numerical simulation has been performed to investigate the dust emissions over Sahel associated with strong near-surface winds in the region of the West African Inter Tropical Discontinuity (ITD) during the summer, when the ITD is located over Niger and Mali around 18°N.

The study focuses on the period from 2 to 12 July 2006, in the framework of the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period 2a1. A comparison with space-borne observations from the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) as well as airborne lidar observations acquired on 7 July 2006 demonstrates that the model is able to reproduce the complex vertical structure of the dynamics and aerosol field associated with the monsoon-harmattan interface.

This suggests that the model can be used reliably to analyse and quantify the dust emissions associated with the strong monsoonal surface winds blowing over the Sahelian dust sources during the rainy season. A comparison with the surface observations in Niamey between 2 and 12 July period indicates that the near surface characteristics of the monsoon to the south of the ITD are realistically reproduced over the period of the simulation.

The dust load in the ITD region simulated by the model is compared to the estimates derived from satellite observations using the method of Koren et al. [2006]. The daily mean values of dust load related to the strong winds on both side of the ITD, estimated from the simulation within the model domain (2°W-16°E, 12-28°N), are in excess of 2 Tg on some days and are found to be underestimated with respect to the observational estimates.

In the present case, the dust load associated with the strong winds south of the ITD accounts for approximately 1/3 of the total load over the entire domain on a given day, and is simulated to range between 0.5 and 0.8 Tg on average.

This indicates that the mean daily dust load estimated in the ITD region is close to the estimated daily rate of dust emission from the Bodélé depression. This study suggests that emissions driven by strong surface winds occurring on both sides of the ITD while it lies across the Sahel may contribute significantly to the total dust load over West and North Africa observed annually.

Keywords: Dust, MesoNH, airborne lidar, density current, AMMA

Dry cyclogenesis and dust lofting over Sahara-Sahel

Diana Bou Karam, Cyrille Flamant, Pierre Tulet, Martin C. Todd, Jacques Pelon and Earle Williams: Dry cyclogenesis and dust mobilization in the Inter Tropical Discontinuity of the West African Monsoon: a case study, submitted to JGR.



Abstract

Three-dimensional mesoscale numerical simulations were performed over Niger in order to investigate dry cyclogenesis in the West African Inter Tropical Discontinuity (ITD) during the summer, when it is located over the Sahel. The implications of dry cyclogenesis on dust emission and transport over West Africa are also addressed. The study focuses on the case of 7th July 2006, during the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period 2a1.

Model results show the formation of three dry cyclones along the ITD during a 24-hour period. Simulations are used to investigate the formation and the development of one of these cyclones over Niger in the lee of the Hoggar-Aїr Mountains. They show the development of the vortex to be associated with (a) strong horizontal shear and low-level convergence existing along the monsoon shearline and (b) enhanced northeasterly winds associated with orographic blocking of cool air masses from the Mediterranean Sea. The dry cyclone was apparent between 0700 and 1300 UTC in the simulation and it was approximately 400 km wide and 1500 m deep. Potential vorticity in the centre of vortex reached nearly 6 PVU at the end of the cyclogenesis period (1000 UTC).

The role of the orography on cyclogenesis along the ITD was evaluated through model simulations without orography. The comparison of the characteristics of the vortex in the simulations with and without orography suggests that the orography plays a secondary but still important role in the formation of the cyclone. Orography and related flow splitting tend to create Low Level Jets (LLJs) in the lee of the Hoggar and Aїr mountains which, in turn, create conditions favorable for the onset of a better defined and more intense vortex in the ITD region. Moreover, orography blocking appears to favor the occurrence of a longer-lived cyclone.

Furthermore, model results suggested that strong surface winds (~11 m s-1) enhanced by the intensification of the vortex led to the emission of dust mass fluxes as large as 3 µg m-2 s-1. The mobilized dust was mixed upward to a height of 4-5 km to be made available for long-range transport.

This study suggests that the occurrence of dry vortices in the ITD region may contribute significally to the total dust activity over West Africa. The distribution of dust over the Sahara-Sahel may be affected over areas and at time scales much larger than those associated with the cyclone itself.

Key Word: AMMA, cyclone, dust emission, MesoNH, Intertropical Discontinuity.



A newly identified mechanism for dust emission over West Africa


Bou Karam, D., C. Flamant, P. Knippertz, O. Reitebuch, J. Pelon, M. Chong, A. Dabas (2008): Dust emissions over the Sahel associated with the West African Monsoon inter-tropical discontinuity region: a representative case study, Q. J. R. Meteorol. Soc. 134: 621–634.

Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/qj.244

Abstract:

Near dawn airborne lidar and dropsonde observations acquired on 7 July 2006, during the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period 2a1, were used to investigate dust mobilisation, lifting and transport in the inter-tropical discontinuity (ITD) region over western Niger.

Atmospheric reflectivity data from the LEANDRE 2 lidar system enabled us to analyse the structure of dust plumes in the context of wind and thermodynamic information provided by the WIND lidar system and dropsondes.

Dust mobilisation was mainly observed in two locations: (a) Within the monsoon flow as the result of the passage of a density current issued from a mesoscale convective system over southwest Niger. (b) At the leading edge of the monsoon flow where the near-surface winds and turbulence were strong, because the monsoon flow was behaving as an intrusive density current. The circulation in the head of the monsoon density current lifted the mobilized dust towards the wake, along an isentropic surface. Away from the leading edge, some of the mobilized dust was observed to mix across the monsoon-harmattan interface, due to the existence of mechanical shear above the monsoon layer, and to become available for long-range transport by the harmattan.

Because dust sources are widespread over the Sahel and presumably active on many days when the ITD is located in this region during summer, dust emissions associated with the described mechanism may influence the radiation budget over West Africa.

Key words: Monsoon, Harmattan, Density current, AMMA, Airborne lidars, Dropsondes, ECMWF analyses.

Model inter-comparisons of dust emission over the Bodélé Depression


M.C. Todd, D. Bou Karam, C. Cavazos, C. Bouet, B. Heinold, G. Cautenet, P. Tulet, C. Perez, I. Tegen, and R. Washington: “Quantifying uncertainty in estimates of mineral dust flux: an inter-comparison of model performance over the Bodélé Depression, Northern Chad”, J. Geophys. Res., 113, D24107, 2008, doi:10.1029/2008JD010476.

Abstract

Mineral dust aerosols play an important role in the climate system. Coupled climate aerosol models are an important tool with which to quantify dust fluxes and the associated climate impact.

In recent years, numerous models have been developed but to date there have been few attempts to compare the performance of these models. In this paper a comparison of five regional atmospheric models with dust modules is made, in terms of their simulation of meteorology, dust emission and transport.

The inter-comparison focuses on a 3-day dust event over the Bodélé depression in Northern Chad, the world’s single most important dust source. Simulations are compared to satellite data and in-situ observations from the Bodélé Dust Experiment (BoDEx 2005).

Overall, the models reproduce many of the key features of the meteorology and the large dust plumes that occur over the study domain. However, there is at least an order of magnitude range in model estimates of key quantities including, dust concentration, dust burden, dust flux and AOT.

As such, there remains considerable uncertainty in model estimates of the dust cycle and its interaction with climate. The paper discusses the likely sources of this model uncertainty.