The term “medicane” (short for Mediterranean hurricane) has been used for more than two decades to identify storms that develop over the Mediterranean yet appear similar to tropical cyclones. They do not tend to become as strong as the strongest hurricanes, but Medicane Ianos, the most intense ever recorded, attained one-minute wind speeds of 44 meters per second, similar to a Category 2 hurricane.
However, there has been no scientifically agreed-on definition of a medicane, hindering our ability to understand exactly how they develop and whether they are becoming more or less frequent. A working group of European experts has now proposed what they hope will become the official definition of a medicane:
“A medicane is a mesoscale cyclone that develops over the Mediterranean Sea and displays tropical-like cyclone characteristics: a warm core extending into the upper troposphere, an eye-like feature in its center with spiral cloud bands around an almost windless center surrounded by nearly symmetric sea-surface wind circulation with maximum wind speed within a few tens of km from the center.”
Author Q&A
Three of the paper’s authors, Mario Marcello Miglietta, Giulia Panegrossi, and Emmanouil Flaounas, provided responses to our questions about medicanes and what it’s like to try to reach consensus on a key scientific definition like this.
How much of a risk do medicanes tend to pose to life and property?
Medicanes develop mainly through a combination of baroclinic and air-sea interaction processes. When the latter dominates, the development becomes similar to that of hurricanes, possibly reaching comparable intensity and damage.
Unfortunately, the predictability of these cyclones in the models may be limited due to both limitations in the representation of air–sea interaction exchanges at high wind speed, and the presence of small-scale upper-level (baroclinic) features that large-scale initial and boundary conditions may sometimes misrepresent.
This was the case with Storm Daniel, a medicane that intensified unexpectedly just before landfall and caused catastrophic flooding in the city of Derna, Libya. Two dams burst, and 5,000–15,000 fatalities were estimated as buildings were swept away. Other medicanes produced some victims and huge damage to properties and infrastructures, although not comparable to what happened during Daniel.
What were some of the problems caused by not having a consistent definition of a medicane?
The absence of an official or commonly accepted definition has created some confusion within the scientific community. For example, it was not clear whether the term should refer only to air–sea interaction-driven cyclones (like hurricanes) or should also include warm seclusions, the last stage of evolution of midlatitude cyclones. Additionally, some known cases of medicanes do not fit clearly in either of those two categories.
Consequently, the results of scientific articles on medicanes’ physical development processes or climatological features may not be comparable with each other. Moreover, the lack of a definition inhibits clear communication within communities of atmospheric and climate scientists. Pluralism of criteria to identify medicanes also creates confusion among national weather services for issuing warnings of imminent high-impact weather. As a consequence of this confusion, social media sources, private and governmental weather services, or even individuals felt entitled to classify newly formed or forecast cyclones as medicanes.
What distinguishes this definition from other definitions of a medicane that have been used in recent decades?
Differently from some previous studies, the proposed definition recognizes the existence of a deep warm core regardless of the generation process, following the indications from early studies that air–sea interaction processes (responsible for hurricanes) are not expected to exclusively contribute to the development of a medicane.
Hence, the proposed definition assumes that medicanes do not correspond to systems of homogeneous physical characteristics and do not develop according to a unique physical mechanism. In fact, the definition includes warm-core cyclones that are structurally similar to tropical cyclones in several ways, such as tropical transitions, subtropical cyclones, and warm seclusions.
Consequently, our definition accommodates different subcategories, and does not exclude diagnostics widely used for the identification of structural characteristics of cyclones (e.g., cyclone phase space diagrams) as useful numerical tools for the diagnosis of medicanes in climatological model datasets or case studies.
Finally, the definition reconciles the phenomenological and structural approaches that were used in previous studies on medicanes. Phenomenological approaches are empirical, based on satellite data used for monitoring the oceans and the atmosphere, and are often employed not only for later analysis but also for real-time situations. In contrast, structural approaches are based on diagnostic quantities derived from numerical weather model outputs that identify structural characteristics of the cyclones (symmetry, thermal structure) and are often employed in the postevent analysis by research scientists.
How difficult has it been to settle on an official definition?
The debate about the definition of medicane lasted several decades. Since these storms were identified in the Mediterranean, two different perspectives were proposed: one that considered medicanes as real tropical cyclones, although of smaller dimension, intensity, and duration, and the other that proposed medicanes to be a specific category of cyclones developing through an interplay of baroclinic and air–sea interaction mechanisms. To reconcile these two different perspectives, some attempts have been made to reach a general consensus—for example, a similar initiative on the medicane definition started in the framework of the HyMex program, but it was unsuccessful.
A fundamental boost was the initiative proposed within the framework of the European Cooperation in Science and Technology (EU COST) Action CA19109 “European Network for Mediterranean Cyclones in Weather and Climate” (MedCyclones, 2020–24). For four years, MedCyclones has been fostering a community effort to discuss the medicane definition, to review the different criteria and tools used to classify cyclones as medicanes, and to propose a definition that reached a general agreement and which could be used to classify a storm solely based on satellite observations. This effort was later supported by the European Space Agency through the project “Earth observations as a cornerstone to the understanding and prediction of tropical-like cyclone risk in the Mediterranean (MEDICANES)”. Lastly, the Tropical Cyclones in Anthropocene: Physics, Simulations & Attribution (TROPICANA) program of the Institut Pascal at University of Paris-Saclay (with the support of the program “Investissements d’avenir”) promoted the debate on the topic in one full immersion week, allowing inspiring discussions with Kerry Emanuel (of MIT) and many experts in the field.
In other words, the effort was extremely challenging. Much of the existing research had already been conducted using inconsistent definitions, and many colleagues supported differing perspectives on the physical or phenomenological elements that should qualify a cyclone as a medicane. The greatest achievement of the long-term discussions was the ability to transform these divergent views into a shared understanding of the problem, to create a collective urgency to address it, and ultimately, to reach a consensus that not only identified the common ground among the differing perspectives but also met the research and forecasting needs for a universally accepted medicane definition.
Read the article in Bulletin of the American Meteorological Society.
