HyMeX - Hydrological cycle in the Mediterranean EXperiment
The U.S. participation in HyMeX is a collaborative effort between R. Rotunno (NCAR) K. Friedrich (U. of Colorado) V. Grubišić (U. of Vienna)
Although much has been learned about orographic precipitation in recent years, the ability to predict its location and intensity with the desired accuracy remains elusive. A major obstacle in achieving such ability is that the location and amount of precipitation depend on the accurate prediction of multi-scale motions and microphysical transformations that have not been amenable to simultaneous measurement. The upcoming field campaign of the international program HyMeX (Hydrological cycle in the Mediterranean EXperiment; http://www.hymex.org/) in the fall of 2012 will attempt to obtain such information on the most extensive-to-date range of processes contributing to heavy precipitation events (HPEs) over the orography of the northwestern Mediterranean Sea Basin.
The overall scientific objective is to discover the weakest links in the chain between the ‘input’ (upstream flow and humidity) and the ‘output’ (precipitation amount and location with respect to the flood-prone area of southeastern France; Fig. 1) through study of the intermediate transformational steps (orographic flow modification, condensation and transformation of condensate to precipitation). We believe that this discovery will allow to better estimate the predictability limits of rainfall with respect to catchment size. Knowledge of such predictability limits directs the forecasting enterprise towards more fruitful approaches (e.g. a lower-resolution ensemble versus a higher-resolution deterministic forecast) and also informs the social-science research on the communication of forecast information/uncertainty to the end users.
Figure 1: Schematic diagrams of three flash-flood scenarios representing the typical synoptic scale flow during HPEs: Cevennes case: 13-14 October 1995, Gard case: 8-9 September 2002, and Aude case: 12-13 November 1999 (adapted from Fig. 17 in Ducrocq et al. 2008).
We propose to join this campaign to both aid in obtaining, and benefit from achieving, our shared goals which focus on four major questions:
- What are the mesoscale environments most conducive to Heavy Precipitation Events (HPEs)?
- What is the role of the complex orography on HPEs in the region?
- What are the cloud-scale dynamics and microphysics mechanisms leading to HPEs?
- What enhancements in the ability to predict HPEs can be achieved by assimilation of mesoscale environment data?
The existing meteorological observation networks will form the backbone of the observation strategy to characterize the HPE meteorological environment at the synoptic and mesoscales (Fig. 2). Essential in addressing the U.S. research objectives in HyMeX is the usage of the NRL-P3 aircraft with the airborne radar ELDORA
and a dropsonde system, two polarimetric Doppler on Wheels radars, the Doppler on Wheels rapid scan radar, and two MGAUS stations. Additional instruments such as the U. of Wyoming King Air with a Raman Lidar, the U. of Oklahoma mobile polarimetric C-band radar (SR-2 radar), the U. Connecticut mobile polarimetric X-band radar, and NCAR’s integrated sounding system (ISS) are desired to address more specific research objectives.
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