Matthew A. Janiga

M.S. Student, DAES, University at Albany

Earth Science and Mathematics, 330

 

 

 

 

 

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Master's Research

My research focuses on the mesoscale convective systems (MCSs) observed over West Africa during the AMMA field program. I am examining the two-way interaction between convection and synoptic features within the West African monsoon. One focus is the role of mesoscale convection in the genesis and life-cycle of African easterly waves. These are the main weather systems in Sahelian Africa and are important for tropical cyclogenesis.

(a) Multi-scale study of the MCS over Niamey, Niger on August 11, 2006

A multi-scale case study of an intense MCS that passed over the MIT radar on August 11, 2006 was performed. This was one of the largest convective events during the 2006 season as well as one of the best observed. This MCS also occurred during AMMA SOP-3 (Redelsperger et al., 2006) when there were eight soundings a day were being launched from Niamey Airport.

 

On Aug. 9, 1200 UTC convection began north of the Cameroon highlands, associated with orographic lift, as is common in this region (e.g. Laing et al. 2008). This convective cluster reached maximum size and intensity on Aug. 11, 1200 UTC just east of Niamey. Time-height radiosonde plots from the Niamey Airport indicate a robust intensification of the AEJ and a cyclonic feature at mid-levels associated with the MCS. This MCS was associated with production of mid-level potential vorticity (PV) of around 1 PVU, several times higher than the background state. As the MCS approached Niamey a decrease in reflectivity, rainfall rate, and warming cloud tops were observed. Consistent with this, the descending rear inflow was intensifying and a fine-line was observed at increasing distances ahead of the leading convective line.

 

Radar reflectivity at 1 km from the MIT C-band radar in Niamey, Niger at 0251 UTC. Range rings are every 50 km. Reflectivity is overlaid onto 10.9 μm IR.

 

Meteogram of zonal and meridional wind from radiosondes being launched every three hours from Niamey Airport. The dashed line indicates the passage of the MCS. The African easterly jet (AEJ) is indicated by the maximum in easterly flow at ~ 4km.

 

(b) Seasonal Characterization of MCS Structures and their Environment

 

At the heart of this research are the MIT radar observations taken during the summers of 2006 and 2007. Profiles of divergence were obtained from the radial velocity (Mapes and Lin, 2005). This combined with the high frequency sounding data allow for estimates of the diabatic heating.

 

      July 22, 2006 at 0700

    July 22, 2006 at 0800

     July 22, 2006 at 1000

Raw volume scan base reflectivity, the radius of the range is 150 km (left), divergence at several radii with error bars (center), and a contour frequency altitude diagram (CFAD) of reflectivity. Note the increasingly stratiform appearance of all three diagrams.

 

References

 

Laing, A.G. and coauthors, 2008: Diurnal cycles of deep convection in northern tropical Africa. Quarterly Journal of the Royal Meteorological Society, 134, 93-109.

 

Mapes, B.E., and J. Lin, 2005: Doppler Radar Observations of Mesoscale Wind Divergence in Regions of Tropical Convection. Mon. Wea. Rev., 133, 1808–1824.

 

Mohr, K.I. and C. Thorncroft, 2006: Intense convective systems in West Africa and their relationship to the African easterly jet. Quarterly Journal of the Royal Meteorological Society, 132, 163-176.

 

Parker, D.J.; Thorncroft, C.D.; Burton, R.R.; Diongue-Niang, A., 2005: Analysis of the African easterly jet, using aircraft observations from the JET2000 experiment, Quarterly Journal of the Royal Meteorological Society, 131, pp.1461-1482.

 

Redelsperger, J.L. and coauthors,. 2006: African Monsoon Multidisciplinary Analysis: An international research project and field campaign, B.A.M.S, 120, 1739-1746

 

Acknowledgments

 

This material is based upon work supported by the National Science Foundation under grant ATM0507976. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

 

Based on a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, UK, US and Africa. It has been the beneficiary of a major financial contribution from the European Community's Sixth Framework Research Program. Detailed information on scientific coordination and funding is available on the AMMA International web site http://www.amma-international.org.

This Site is maintained by Matthew Janiga. This page would not have been possible without significant contribution from the following individuals: Ademe Mekonnen, Kevin Tyle, Chris Thorncroft, Gareth Berry, Brian Mapes, and Susanna Hopsch.

 

 

 

 

 

 

 

Last updated 4/6/09

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