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Synoptic climatology of cut-off low events that produced extreme precipitation in Valencia, Spain
1  Associate Professor of Atmospheric Science, Department of Geography, Planning and Environment, East Carolina University, Greenville, NC 28590, USA


A seasonal synoptic climatology of cut-off lows (COLs) that produced extreme precipitation in the Valencia region of Spain during 1998-2014 is presented. COLs were shown to be the main producer of extreme precipitation in the region, especially during the transition seasons. The strongest raining COL events occurred during September-November. Six-day composites of lower and upper tropospheric winds, geopotential, sea-level pressure and precipitation show that COLs that produce extreme rainfall in this region remain stationary over Spain for 2-3 days and produce rainfall over the Valencia region for at least two days. In the low levels these COLs are characterized by low pressure over the Mediterranean sea and winds with an easterly, onshore component. Another interesting aspect of the composites is that transition season COLs are characterized by the presence of a filament of moisture that extends from the tropical Atlantic to Spain suggesting a role for remote moisture transport to feed COL rainfall. Further analysis is needed to confirm this hypothesis.

Keywords: cut-off low, extreme precipitation, seasonal climatology
Comments on this paper
Raquel Nieto
COLs in Iberian Peninsula
This work presents a climatology of COLs over a region where these systems are really important. Most of the extreme events in terms of precipitation are associated with them.

As we know, the COLs are very difficult to predict due to their erratic movement and short lifetime. It would be very interesting know how the future warming affects these synoptic systems.

How did you exclude the precipitations due to frontal systems crossing the Iberian Peninsula?

In a future work, the author could use a new daily precipitation gridded data set with a regular 0.2° latitude-longitude resolution for peninsular Spain and Balearic islands: Herrera, S., J. Gutiérrez, R. Ancell, M. Pons, M. Frías, and J. Fernández (2010), Development and analysis of a 50-year high-resolution daily gridded precipitation dataset over Spain (Spain02), Int. J. Climatol., 31, doi:10.1002/joc.2256.

A map with the position of the COLs detected could be useful.

Nice work!
Rosana Nieto Ferreira
Thank you Raquel,

I looked at daily maps of rainfall, winds, temperature and geopotential to separate frontal systems that produced extreme rainfall from the COL events that produced extreme rainfall. I have produced a separate composite of frontal systems crossing the IP and they look quite a bit different than the COL composites presented in this paper.

I just read another paper in this conference (Liberato et al.) that shows that TRMM underestimates the precipitation when compared to the Spain02 dataset. I will read Herrera et al. (2010) with interest - thank you for the reference.

Thank you also for the suggestion to add a map.

Muchas gracias por todos tus comentarios!

Margarida L. R. Liberato
Validation of EPEs and rankings
Dear Rosana

I really enjoyed reading your article, as it complements the research on extreme precipitation events (EPEs) on the Iberian Peninsula (IP) that we have been pursuing over the last years. I wonder if you have performed any kind of assessment of the magnitude of these EPEs, using records over the Valencia box.

In view of future climate assessment of EPEs over the Valencia box, it would be important to know to what precipitation values corresponds the top 1% of the distribution (daily TRMM rainfall values over 20mm) on observations.

In what concerns the 46 events on your study, it would be interesting indeed to compare at which positions they occur on the ranking we have developed for the IP (Ramos A. M.; Trigo R. M.; Liberato M. L. R. A ranking of high-resolution daily precipitation extreme events for the Iberian Peninsula. Atmospheric Science Letters 2014, 15, 328-334 doi: 10.1002/asl2.507).

I will be looking forward to reading your work on simulations using the Weather Research and Forecasting (WRF) model.

Rosana Nieto Ferreira
Dear Margarida,

I will look up the events that fall at the top 1% of the distribution. The 20 mm threshold captures the top 5% or so.

Thank you for the reference to your 2014 study and thank you also for taking the time to read and comment on my work.