Docstoc

FOG IN THE MEDITERRANEAN

Document Sample
FOG IN THE MEDITERRANEAN Powered By Docstoc
					          FOG IN THE
        MEDITERRANEAN


             or
How bad can weather become in
      CAVOKLAND
           FOG IN THE MED
   As everywhere, fog develops if three basic
    conditions are met
    – Moisture
    – Stability
    – Stagnation (fog trigger)
   How do these conditions work together in
    southern Europe?
           FOG IN THE MED
   Basic conditions favoring fog development
    – Moisture – no problem, it’s there in abundance,
      Med basin is a large water body
    – Stability – also no problem, area “enjoys”
      frequent Azores High ridging
    – Stagnation – the big problem, large local and
      regional differences under same type of ridging
           FOG IN THE MED
 Stagnation - the big problem of the area
 Reasons for stagnation
    – mountainous terrain with deep valleys keep any
      airmass “without escape”
    – airmass exchange basically by way of turbulent
      mixing which generally weakens in fall
    – once winds become generally weak, air doesn’t
      move except local valley/mountain winds
           FOG IN THE MED
 Stagnation - the big problem of the area
 Reasons for non-stagnation
    – mountainous terrain adjacent to open water area
    – airmass exchange also by way of turbulent
      mixing which often weakens in fall, but…
    – once winds become generally weak, local
      valley/mountain winds combine with land/sea
      breeze which keep area ventilated
   FOG IN THE MED

Favorable areas for
fog formation by
region
      FOG




FOG
                                            FOG
   FOG !!



   FOG




                            FOG
                                             FOG


Rough coastline in N & S Italy counteract
stagnation, but some wider valleys along
Tyrrhenian Sea coast favor fog formation
                          FOG




                        FOG
Coastline counteracts
stagnation
                                FOG
FOG

                                     FOG
 FOG


                               FOG




      Coastline south of Izmir
      does not favor stagnation!
         FOG IN THE MED
 There is a distinct fog/no fog line in the
  Mediterranean region
 Practically no fog along the coast, if
  adjacent to a mountain range
 Very foggy in valleys of mountain ranges
  bordering the Med or over plainland further
  north and east
        FOG IN THE MED
 The beginning of the fog season
 Later than in northern Europe due to more
  solar insolation and more instability???
This    is how it goes…..
     % Frequency cig/vis < 800 ft/ 1,000 m at Vicenza
80
70
60
50                                                      Sep
                                                        Oct
40
                                                        Nov
30                                                      Dec
20
10
 0
  00Z 03Z       06Z 09Z 12Z 15Z              18Z 21Z
           FOG IN THE MED
 Frequency is already high in September!
 Fog is persistent from November onwards
    – Vicenza is typical Po Valley, frequency is highest
      in area, but trend in Bosnia is similar
    – Tuzla, Banja Luka, and valley stations in MND-
      N/S begin the trend 2 weeks later than Po Valley,
      and from thereon are short of Po Valley’s
      frequency
          FOG IN THE MED
   Typical synopsis that lead to the combined
    effects of
    – Moisture
    – Stability
    – Stagnation
 Azores High ridging into area via Alps is
  probably the most obvious way
 Other possibilities?
                               Not cP yet,
                               more mPmm




Note moisture advection from
Adriatic into Po Valley
                                 Washing cold front
                                 over Bosnia
Moist air over Po   Air mass mix over Balkans
Valley stagnates!   comes under ridging
           FOG IN THE MED
 Northeasterly flow over Balkans pretend
  advection of dry continental air
 Not in autumn !
    – autumn is the Balkans and Po Valley’s prime
      rainy season, right after the summer dryness
    – Gulf of Genoa Lows moving northeast can soak
      the Po Valley before dumping all rain onto the
      Balkans, therefore, NE flow in wake of system
      has moisture-laden air waiting for the next ridge
           FOG IN THE MED
   Certainly, the combined effects of
    – moisture
    – stability
    – stagnation
 helps fog formation in the Balkans & Italy
 but state of the ground is also very
  important in the Med’s prime wet season
             FOG IN THE MED
   Evidently, the Med will soon be no longer
    CAVOK-land
    – however, the Mediterranean Sea also cools, but
        slowly
    –   adjacent land masses cool much faster
    –   latitude is still rather north
    –   Camp Bondsteel is further north than
        Milwaukee, Wisconsin
    –   which means think FZFG!!!
FREEZING FOG IN THE MED
   Occurs where?
    – Italy (Po Valley) does affect our stations
    – Balkans, with highest frequency in our theater;
      does affect all our stations
    – Turkey (interior) not affecting our stations
    – Spain (interior) not affecting our stations
FREEZING FOG IN THE MED
   Maximum frequency in the Balkans
    – Favorable area of air-mass mix
    – Favorable area for Azores High ridging or
      connection with the Siberian High
    – Strong cooling due to “bowl effect” (see
      Ramstein and Grafenwoehr)
   Conditions typically available by mid-
    November
                                    cP




This synopsis will clear the Balkans initially, but will create
FZFG 24 hours later as early as 15 October, even in Kosovo
           FOG IN THE MED
 There are different types of fog
 not all fog in the Med is radiation fog
    – Mixing fog
    – Advection fog
    – Upslope fog
   are fog types which do not require
    stagnation
           FOG IN THE MED
   Mixing Fog
    – develops locally, and instantaneously if colder
      air is mixed with warmer air and dewpoint
      temperature rises above ground temperature
    – happens frequently in the Balkans after a cold
      spell when air from the Med or Black Sea is
      sneaking in from SE or E
    – Happens in the Po Valley when Adriatic Sea air
      is sneaking westward
           FOG IN THE MED
   Advection Fog
    – Fog that has developed elsewhere is coming into a
      fog-free area, often with remains of a frontal
      system (moisture trapped under inversion, but air
      not yet stagnant)
    – Likewise, a stagnant air which is coming under
      motion and is expanding or being pushed out of
      area (losing stagnation)
    – Can happen anywhere at any time, but favorable
      areas are Aviano, Taszar, Tuzla, Camp Bondsteel
               FOG IN THE MED
   Upslope Fog
    – special sort of advection fog that is forced to lift
      (rising terrain)
    – also moist air short of fog which comes under
      upslope, but can not be further lifted due to strong
      inversion, air is cooled to condensation point, low
      stratus develops and touches the ground
    – favorable locations are Taszar, stations along NE
      side of Dinarics, also Aviano and San Vito
         FOG IN THE MED
 Conclusion
 Fog is a major problem in fall and winter
 Our Med desks handle areas that have the
  most fog frequency in the entire theater,
  some locations (Milan) are even worse than
  Fresno, CA
 Not all fog cases are radiation fog for which
  most of our tools have been developed!

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:7
posted:2/27/2012
language:
pages:28