south biscay gales

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1 SOUTH BISCAY GALES: 2013, JULY 31 st CASE STUDY Isabel Lete Lombardero, 2016. [email protected] PhD candidate; Master in Spatial Science and Technology (2012) Graduate in Navigation and Maritime Transport (2011). EHU/UPV University of the Basque Country. Abstract South Biscay coastally trapped disturbances known as gales (galernas, enbatak, galarrenak, bruilartak) are adverse phenomena that send along the Cantabrian and Basque Coast a narrow jet of sudden and violent gusts of wind that do not follow a hydrostatic balance parameterization, being faster, stronger and of a Western-North- Westerly component, and accelerate as they rush Eastward enduring their speed and intensity. These gales run the coast line from West to East strengthening in Eastern Cantabrian Seashore line from May to October. Well known by the death people and disasters induced 7 , Gales are dangerous for the difficultness in predicting them: both the direction of the violent gusts and their displacement along the coast line are ageostrophic, that is, perpendicular to the mesoescalar pressure gradient. In this paper the pure ageostrophic gale happened on the noon of 2013 July 31st is analysed; more than for its strength - the wind gusts only raised to 40 km h -1 - it is important for the scholastic behaviour of atmospheric and oceanographic variable as for the absolute independence from any other phenomenon whatsoever (i.e. Cold Front) Keywords: Upwelling, downwelling, mesolow, gale, ageostrophic wind jet, coastally trapped disturbance, wind reversals, air-sea interaction. Acknowledgements Thanks to Dr. Agustin Sanchez la Vega who choose this topic for me as Master Thesis and has since become devotion. Thanks to Dr. Jon Saenz who patiently led me to understand mesoescalar coastal disturbances, and thanks to those whose comments and suggestions helped to improve this research. I have not received any support, funding or grant neither from state institutions nor from private organization. INTRODUCTION Enclosed into Coastally Trapped Disturbances (CTD) these sudden, violent and dangerous phenomenon may happen from May to October along the eastern coast of South Biscay throwing gusts of wind higher than 40 knots due to the confrontation of very different air masses enhanced by the orographic effect of the mountain chain that runs along the coast line and that acts as a wall 18 . The strongest gales are linked to a cold front or to a turbulence line 12 , thus predictable to a certain point; these winds can raise over 100 km h -1 . In contrast, pure ageostrophic

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Page 1: South biscay gales

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SOUTH BISCAY GALES: 2013, JULY 31st CASE STUDY

Isabel Lete Lombardero, 2016. [email protected]

PhD candidate; Master in Spatial Science and Technology (2012) Graduate in

Navigation and Maritime Transport (2011). EHU/UPV University of the Basque

Country.

Abstract

South Biscay coastally trapped disturbances known as gales (galernas, enbatak,

galarrenak, bruilartak) are adverse phenomena that send along the Cantabrian and

Basque Coast a narrow jet of sudden and violent gusts of wind that do not follow a

hydrostatic balance parameterization, being faster, stronger and of a Western-North-

Westerly component, and accelerate as they rush Eastward enduring their speed and

intensity. These gales run the coast line from West to East strengthening in Eastern

Cantabrian Seashore line from May to October.

Well known by the death people and disasters induced7, Gales are dangerous for the

difficultness in predicting them: both the direction of the violent gusts and their

displacement along the coast line are ageostrophic, that is, perpendicular to the

mesoescalar pressure gradient.

In this paper the pure ageostrophic gale happened on the noon of 2013 July 31st is

analysed; more than for its strength - the wind gusts only raised to 40 km h-1

- it is

important for the scholastic behaviour of atmospheric and oceanographic variable as

for the absolute independence from any other phenomenon whatsoever (i.e. Cold Front)

Keywords:

Upwelling, downwelling, mesolow, gale, ageostrophic wind jet, coastally trapped

disturbance, wind reversals, air-sea interaction.

Acknowledgements

Thanks to Dr. Agustin Sanchez la Vega who choose this topic for me as Master Thesis

and has since become devotion. Thanks to Dr. Jon Saenz who patiently led me to

understand mesoescalar coastal disturbances, and thanks to those whose comments and

suggestions helped to improve this research. I have not received any support, funding or

grant neither from state institutions nor from private organization.

INTRODUCTION

Enclosed into Coastally Trapped Disturbances (CTD) these sudden, violent and

dangerous phenomenon may happen from May to October along the eastern coast of

South Biscay throwing gusts of wind higher than 40 knots due to the confrontation of

very different air masses enhanced by the orographic effect of the mountain chain that

runs along the coast line and that acts as a wall18

.

The strongest gales are linked to a cold front or to a turbulence line12

, thus predictable to

a certain point; these winds can raise over 100 km h-1

. In contrast, pure ageostrophic

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gales, typical gales are not linked to any other storm and even if their winds speed do

not often raise over 60 km h-1

they sweep the coast at a speed of 40 knots and are more

difficult to predict, much more dangerous indeed.

Although typical gales are especially dangerous for merchant vessels in coastal

manoeuvring, ports approach and docking operations for there is not yet a mathematical

model8 that could advise the arrival, strength and lasting of the event, small recreational

vessels are most affected and sent to the rocks without any manoeuvring possibilities.

People at beaches are also potential victims for these events occur on beautiful summer

days.

The atmospheric conformation previous to a gale is well known by meteorologists1,2

,

but it is yet under debate what triggers them. In this situation weather forecasters advise

a “possible gale” almost every good summer day!

Based on my personal experience sailing this wonderful coast, I can say that previous to

gale wind gusts another remarkable anomaly happens on sea surface. Being able to

notice this alteration early enough may lead us to prevent coastal population and activity

of the advent of a gale, if not to determine its intensity and burst time.

Some hours before the event, sea surface shows some changes, anomalies in

temperature, salinity and currents that are observable in oceanographic buoys, with the

available satellite remote sensing technology and even to the naked eye from the beach

or sailing boats along the coast. One just has to be aware of these anomalous alterations

and get to safety. On live data are of utmost importance10

.

We know how and when South Biscay Gales develop; it is yet under debate why or

what triggers them. Movements and/or geo-magnetic energy alterations at the bottom of

Aviles canyon induced by outer space energy waves (sun and galactic waves’ activity)

should be investigated thoroughly.

This study consists of four field campaigns to collect data. Atmospheric: sea level

pressure (SLP), Air temperature (SLT) and relative humidity (SLH); wind direction

(WDIR), wind speed (WSP), gusts direction (gust dir), intensity of the gusts (gust sp);

air composition and ionization (Ion), and oceanographic: sea surface temperature (SST)

and salinity (SSS), tide, currents and sea conditions, waves, clouds, rain and visibility,

all data from different sources as well as from a station placed on board the "Lete V"

sailing vessel that provides minutely data at different spots of the Basque coast to

further analyze them. Other public data have been obtained from land and buoy stations

and from satellite remote sensors.

Due to the nature of the phenomenon, the fact that these gusts of ageostrophic wind do

not correspond to the geostrophic balance neither in intensity nor in direction or speed,

the data obtained on board the sailing vessel "Lete V" are of utmost value since there

are no other records with the frequency adapted to the length of the gusts (2 to 5

minutes) in which wind intensity changes from 0 to 100 km h-1

in a few seconds to

gradually decrease afterward. The frequency of data collection in our station is of 5

minutes, while that of EUSKALMET is 10 minutes and AEMET fixed stations every 30

minutes. Nevertheless, magnetic alterations are out of reach onboard for the lack of

appropriate devices, as well as sea-air heat and evaporation transfer rates.

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1. A PURE AGEOSTROPHIC GALE, “THE CANTABRIAN TYPICAL GALE”

Known locally as “Galernak, galarrenak, enbatak, bruilartak” South Biscay Gales are

Marine Boundary Layer adverse and anomalous meteorological phenomena that happen

suddenly in the lowest atmosphere along the Cantabrian Coast from May to October6.

Cantabrian typical gales are adverse for the violence and destructive capacity and

harmfulness of its consequences and they are anomalous for the rarity of its genesis and

development due to the fact that they do not follow the atmosphere hydrostatic

equilibrium, algorithms and rules. Neither gales source nor their development are yet

parameterised due to the lack of accurate data and a multidisciplinary working team,

resulting in a situation where typical gales are advised to “might happen” at almost

every good summer day!

1.1. COASTAL LAYOUT

These kinds of phenomena occur along coasts where a mountain chain exists which

extends very close and parallel to the coast line and where the continental layer is very

close to the coast: in a distance off shore of about 12 miles the depth drops dramatically

in less than 1 mile from -100 m to -4000 m (Figure 1).

Figure 1 - Coastal layout. Continental layer. Heights and distances

in Cantabrian Coast.

Encompassed in “Coastally Trapped Disturbances” (CTD)3, The Bay of Biscay

ageostrophic gale is an adverse phenomenon that throws along the Cantabrian Coast

(figure 2) a jet of sudden and violent burst of gust wind with a WNW component that

moves from West to East between the months of May to October (Figure 3) intensifying

in the Eastern Bay of Biscay; its danger is given by the difficulty of its prediction as

both: the violent gusts of wind and its movement are ageostrophic, that is, perpendicular

to the gradient of mesoscale pressure.

Source: Author, Lete, I. 2015

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Figure 2 - Ageostrophic gale development area.

Figure 3 - South Biscay Gales: set of sudden ageostrophic gusts.

Californian disturbances known as "southerlies", "Californian Eddies" or "Wind

Reversals" have been widely studied in recent decades14

and after several hypotheses,

scientific community has concluded that these disturbances spread like a Kelvin wave

with three atmospheric layers16

involving as well the marine surface layer and including

the deep water upwelling (upwelling / downwelling system) that happens before the

Source: Author, Lete. I. 2014. Base Map Google Earth

Source: Author, Lete, I. 2014

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atmospheric disturbance (Figure 4). This deep colder and saltier water mixing but not

dissolving with sea surface warmer and fresher water interacts with the adjacent marine

boundary air layer inducing the advection of the gale. This interaction is of utmost

importance in a conceptual level to understand the genesis of the phenomenon. This

instability provoked by the upwelling system, makes the previous warm sea surface

water mass issue to the atmospheric marine boundary interface layer the latent heat by

means of the evaporation and enhanced by the land winds1

Figure 4 - Three Kelvin wave layers: free atmosphere, inversion,

MBL and sea surface with temperatures and heights.

Gales are very typical in the Bay of Biscay South Coast and appear as a sudden change

in wind direction, speed and intensity usually in summer, in days with high heat and

humidity.

1.2. CONCEPTUAL MODEL

Mesoscale convective systems, as gales, include an abrupt leading-edge gust front and

associated temperature drop. The thick anvil affects on surface temperature, and the

trailing mesohigh impacts on surface winds13

.

The advection of individual cells within the line and the triggering of new cells

determine the overall propagation speed of the entire squall line which tends to be

controlled by the speed of the system cold pool with new cells being constantly

triggered along its leading edge gust front15

. An average cold pool speed is on the order

of ~ 20 m/s (40 knt). Under certain circumstances, these cool, refreshing and gusty

winds become much stronger and potentially damaging. (Figure 5).

1

Source: Author, Lete, I. 2015

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Figure 5 - A conceptual model of a mesoscale convective system

(Smull and Houze, 1987).

1.3. AIR MASSES

Tornadoes form when cold, dry, high-pressure air from the North blows over land

colliding with warm, moist, low-pressure air coming from the South. This warm air

spins upward explosively, forming a tornado (Figure 6).

Figure 6 - Tornado formation.

Cantabrian Gales instead, form when a hot, dry, relative-low-pressure air from land at

South reaches the coast line. This negatively buoyant “dry” air forms the inversion layer

which acts as a “ceiling” under which a colder moist air from the ocean at North enters

in towards the coast. Water evaporates from the ocean surface and comes into contact

with the mass of cold air forming clouds. Evaporation from the warm ocean surface

supplies the system’s fuel. A mesolow pressure center develops which form winds. As

the mesolow spot weakens the speed of the wind increases. The warm humid air tries to

raise rapidly in the thunderstorm updrafts. As the hot and dry air of the inversion acts as

a cap and the mountain chain prevents the oceanic moist air from entering land, it

Source: Smull and Houze, 1987

Source: George Tuggle illustrator.

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escapes eastward in a leading edge gust front form, against Coriolis force influence.

(Figure 7).

Figure 7 - Cold and wet sea air advection (MBL) beneath warm

air mass from land (INV) trapped between the inversion and

coastal mountains.

The ageostrophic gale happens at a time when a mass of cold and damp air (Marine

Boundary Layer, MBL) enters from the sea to the coast line and above it, from ground,

another mass of hot and less humid air acts as a ceiling stopping the sea air from rising.

As the mountain chain acts as well as a wall. In the case that certain factors are present

generators disturbance develops in the MBL. (Figures 4, 7, 13).

1.4- ENERGY

The energy that drives thunderstorms comes primarily from the latent heat that is

released when water vapor condenses to form cloud drops. For every gram of water that

is condensed, about 600 calories of heat are released to the atmosphere. When water

drops freeze in the upper parts of the cloud, another 80 calories per gram are released13

.

The release of latent heat energy in an updraft is converted, at least in part, to the kinetic

energy of the air motions. This is what happens over Matxitxako when cirrus-stratus

form and dissipate as the hot and dry air mass that forms the inversion layer reaches sea

shore.

On another hand, colder sea air mass sinks under the warmer land air mass and

evaporates sea water gaining latent heat as well. Not only is the sinking cold air denser

than its surroundings, but it carries a horizontal momentum that is different from the

surrounding hot air reaching a horizontal velocity much higher than the previous wind

at the lowest level. When such air hits the ground, it usually moves outward ahead of

the storm at a higher speed than the storm itself. This is why before a gale a gust of cool

air is developed “announcing” the gale.

There is a distinct boundary between the hot, dry air and the cold, humid air mass in

which the gale develops. The passage of such a gust front is easily recognized as the

Source: The comet program.

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wind speed increases and the air temperature suddenly drops. Over a five-minute period,

a cooling of more than 5°C happens and cooling 12 to 20 C in twenty-minutes is not

unusual. (Figure 8).

Figure 8 - Temperature drop at a gale: 14 C in 1h.

1.5. FORCES

Gales are very low atmosphere phenomena that happen under the inversion layer

situated around 600 m high decreasing intensity drastically with height and seaward.

Due to the fact that gales only happen at sea surface level, Coriolis force does not act.

Neither does act friction or dragging force for the wind jet is preceded by a suction low

pressure area. Geostrophic balance then cannot be applied (Figure 9) and a different

parameterization must be applied. Corresponding algorithms are yet to be developed.

Several attempts have been done with no good results. It is necessary first to fully

understand the phenomenon to integrate the corresponding factors proportionally.

Source: Author, Lete, I. 2014

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Figure 9a - Geostrophic Balance.

Figure 9b - Ageostrophic Wind.

Source: Author, Lete, I. 2014

Source: Author, Lete, I. 2014

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Figure 9c – Formulation.

1.6. PRESSURE GRADIENTS

Gale wind is an ageostrophic stream that responds to the intense mesoescalar pressure

gradients occurring along the coast4: positive at West and negative at East (higher

pressure values over Galicia (i.e. 1008mb) and lower pressure over the Basque Coast

(i.e. 994mb). This opposing pressure tendency is due to synoptic scale flow at 850 mb

and to the NW cold moist air mass advection and SW warm dryer air with strong

thermal contrast at the interface, on the Bay of Biscay. (Figure 10).

Source: Author, Lete, I. 2014

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Figure 10 – Pressure gradients: West to East and offshore inland.

The regions of highest winds occur just downwind of coastal topographic headlands and

points where the coast tends to turn away from the flow direction. This effect can be

enhanced by mesoscale effects that lead to mesoscale regions of reduced pressure along

the coast5. For example, patchy fog dissipation and adiabatic warming of downslope

winds can lead to small-scale variations in surface temperature, which will drop sea

level pressure locally. The vertical distance or thickness between pressure surfaces is

directly related to the mean temperature in the vertical layer. (Figure 11).

Source: Author, Lete, I. 2015

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Figure 11 – Mesolow.

Therefore, the strong horizontal temperature gradient at the surface is associated with a

strong horizontal pressure gradient force (PGF), from high pressure over the cold ocean

to low pressure over the warm land. This is reflected by the steep slope of the 1000-hPa

pressure surface. Cold ocean response (COR).

The coastal jet is due to the persistence of the baroclinic structure at low levels and its

structure a function of the slope of the strong inversion which indicates the thickness

between the layers. Putting the two layers (MBL: sea surface to 850 hPa and inversion:

850-to-500 hPa) back-to-back, it is evident that there is a thermal gradient aloft that

turns the wind down coast bringing NE breeze. However, it is really the low-level

thermal gradient that transforms this flow into a jet, and this low-level thermal structure

is definitely the coastal effect called gale.

1.7. MATHEMATICAL MODELING

Mesoescalar oceanic-meteorological models are required. Although high-resolution,

non-hydrostatic models are able to predict the details very realistically, the forecast of

convective initiation is still subject to considerable error! It depends on the quality of

the information feeding the boundary conditions.

2. LOCAL PHENOMENOLOGY

• Gales are sudden and violent gusts of sea air from WNW.

• The wind heads up sharply and rises to 60-100 km h-1

.

• Temperature drops to 15ºC in 20’.

• Relative humidity triggers from 40% to 100%.

Source: Author, Lete, I. 2014

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• Sea state changes from ripple to high with harsh swell.

• Visibility falls to less than 1 km.

• Clouds: stratus appears and disappears without displacement whose ceiling is

between 400 and 600 m.

• From 600m height weather conditions are constant, do not change and wind

blows the same existing synoptic wind.

• Gale wind does not follow geostrophic balance, this is:

• The wind is of a WNW component, parallel to the coast line and perpendicular

to the mesoescalar pressure gradient. (Figure 9b, 11).

• Wind displacement along the coast is faster and faster as it rushes eastward,

accelerating. (Figure 2).

• Wind intensity is stronger and stronger as it rushes eastward, intensifying.

• Wind does not penetrate beyond the narrow coastal strip, braking onshore along

the coastal mountain range and above the inversion layer around 600 m in

height. Seaward, at two miles from coastline, its intensity drops dramatically if it

is a pure typical gale; while if it is associated with a cold squall line front the

intensity extends along the front line.

Gales appear after a morning with air temperatures above 30 C before noon, and with

calm and soft, southerly gusty winds. The atmospheric pressure having been falling

during the morning and been of a negative tendency at the East and positive tendency at

the Western coast.

During the gale, humidity and atmospheric pressure increase, rising strong and sudden

gusts of winds from WNW (average 80 km h-1

), which produce rough seas, dangerous

for small boats and merchant vessels maneuvering near the coast or at ports. Low clouds

appear and air temperature can drop about 12 C in 20 minutes.

The danger of the phenomenon is not so much the wind strength as the speed with

which it rotates and rages. After the gale previous weather conditions are restored.

2.1. FÖEHN EFFECT

During the day the land heats and due to Föehn effect the air entering the bay of Cadiz

climbs up Iberian Plateau suffering a dry adiabatic cooling (-1 C/100m) and losing

moisture at reaching dew point where condensation and precipitation happen, to

continue its climbing up in a saturated adiabatic loosing process (-0.5°C/100m). This

mass of air crosses the Castilian plateau in a Bordeaux direction and at downing the

Cantabrian Coast, this air descends suffering a dry adiabatic warming, heating (+

1 C/100m) through which this air mass ends up warmer and less humid than when it

came into Cadiz. This process causes a convective mesoscale thermal low over land that

tends to be filled by a cold and wet air mass advection coming from the sea. This air

transport is the wind of gale. (Figure 12).

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Figure 12 - Föehn effect and cold and wet marine air advection.

MBL.

2.2. UPWELLING / DOWNWELLING

South Biscay Gales sea induction:

Prior to gale atmospheric anomaly development, another anomaly occurs at sea: the

immediate before days, deepwater outcrops "upwelling" and subsequent "downwelling"

can be clearly seen in the buoys located along the submerged continental cliff from Cap

Peñas to Cap Ferret, outcrops that are anomalous for this time of year. (Figure 13).

Source: Author, Lete, I. 2014

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Figure 13 - Gale inducing upwelling.

Well, this accused atmospheric pressure wave generator of the gale is induced by an

ocean wave upwelling and related anomalous subsidence that starts against the Avilés

Canyon.

While for the gale tripping the atmosphere has to be prepared.

Moreover, these anomalous upwellings are preceded by solar coronal mass anomalous

activity added to spatial galactic waves’ arrival. This electro-magnetic energy chock

may shake Earth core and move Earth crush enough to provoke a bottom sea pulse so

that deep sea water may start its way up Aviles Canyon. (Figure 14).

Source: Author, Lete, I. 2015

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Figure 14 - Historical gales and sun cycles.

As mentioned earlier in this section, these upwellings occur at coasts where a mountain

chain ranges parallel and close to the seashore and where the continental cliff drops

dramatically from -100 m to -4000 m in less than 1 mile and very close to the coast, at

about 12 miles away. In our Cantabrian coast upwellings begin to climb up the Avilés

canyon, the spot where this phenomenon starts.

These upwellings cause a wave on sea surface that induces, provokes the atmospheric

machinery to start working.

The anomalous upwelling carries to sea surface colder water of higher salinity and

density and filled in nutrients. This different mass of water does not blend well with sea

surface layer water and raises a swell whose surface wave induces in the MBL a Kelvin

wave triggering on gale winds. (Figure 13).

Well, this oceanic anomaly, this wave at sea surface caused by the anomalous upwelling

can be seen in remote sensing photographs of the outburst of plankton due to deep water

nutrients up going and measured, and thus predict the advent of a gale the following

day. (Figure 15).

Source: Author, Lete, I. 2014

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Figure 15 - Gale one day’s SST anomaly.

The variables that indicate that upwelling is occurring in the sea surface are the changes

in the values of sea water density provided by its temperature and salinity and changing

currents: U values [ms- 1

] = positive values for currents from East + E and negative for

currents from the West –W; V [ ms- 1

] = positive values for currents from North +N and

negative for currents from South –S; and UI [ m3s

-1 km

-1] = index of surface water

displacement along the coast that can cause an upwelling to fill the space created. And

these variables can be measured by sensors on buoys and satellites. (Figure 16).

Figure 16 - Upwelling currents: U, V, UI.

Source: Author, Lete, I. 2013

Source: Author, Lete, I. Based Buoy B096 Pasaia, Euskalmet, 2013

Page 18: South biscay gales

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In turn, the day that a gale is going to happen in the afternoon, an alteration in sea

surface temperature daily evolution (SST) can be measured: the usual temperature

evolution process is disturbed along the morning. Due to solar radiation and albedo

effect, the summer days usually suffer the SST warming of about 1,5°C for 1400 UTC,

well, the day of gale this heating does not occur, and instead we can appreciate

temperature alternating falls that clearly indicate the mixture (no dissolution) of the two

distinct masses of water: one from the deep, colder and saltier and another at surface

that is warmer and less salty. (Figures 15, 16). But what causes these upwellings is yet

subject of another study in depth; just to mention, we have to take into account small

earthquakes in the canyon of Avilés and its causes, as well as solar activity and

electromagnetic and gravitational variations in the days before a gale. (Figure 14, 17,

18).

2.3. GALE INDUCTION

In the historical study of the gales that I have recorded over the years, I have seen that

the most virulent gales have occurred when the sun was beginning to rise in its 11-year

cycle, which is precisely when there is less solar activity, when coronal mass ejections

are virtually non-existent or do not reach the Earth's ionosphere, thereby limiting its

action as a deterrent shield train wave cosmic rays energy which causes clumping of

particles in the troposphere developing storms.

Figure 17 - Gale’s spatial induction.

Source: Author, Lete, I. Based Various 2013

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Figure 18 - Sun Cycle & Cosmic Rays & Cloud formation.

3. CLASSIFICATION

This ageostrophic wind behavior can be seen in the following disturbances whose

classification is proposed:

1. Ageostrophic pure gale, which classically is being called Biscayan Gulf Typical Gale,

less intense.

2. Frontal Gale: with two subtypes in storm ageostrophic behavior:

2.1. Cold Front gales: with an increase in wind strength and

2.2. Prefrontal squall line Gales: with a drop in wind direction towards the W, WNW

and an increased intensity.

Typical gales

Typical Gales are very dangerous for their sudden arrival. Occurring from June to

September, more often in July and August, usually in the afternoon and evening and

rarely at night they can extend along 400 km of the coast and affect only the coastal area

close to the sea shore. No storms are often associated.

Front gales

Front Gales are intense because they are associated to the passage of a Cold Front, and

therefore they are accompanied by rain and storms. They occur from April to October,

most often in July and August, at any time of the day and night with greater risk in the

afternoon or evening. They occur in the western Cantabrian rushing from West to East,

Source: Marsh & Svensmark, 2003

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worsening as they develop to the East and affecting as well open sea and inland areas,

with the extension of the Cold Front.

4. CASE STUDY

The event happened on the noon of July 31, 2013 from 23:53 to 00:48 has been chosen

for being a pure ageostrophic gale, even if it was a low intensity South Biscay Gale

“galernilla”. The wind response to the atmospheric variable evolution did not fit to

geostrophic balance. Not being linked to a cold front or a turbulence line made it

develop later by night and softer, blowing wind gusts of only up to 14 knots in Zumaia,

but local atmospheric variable evolution measured at Zumaia port and wind gust

behaviour were purely gale-type, thus this is a perfect example of gale event to study.

This was preceded by decreases of the atmospheric pressure and solar radiation,

reaching values below 1008 hPa and100 W m-2

, respectively (Fig. 28). With the arrival

of the gale, the wind direction turned from South to West, with a peak of wind speed

around 15-16 m s-1

.

This typical gale was not important for its strength or caused damage but for it was the

first “Pure Gale” ever measured, not linked whatsoever to any other adverse

phenomenon as Cold Fronts: neither previous to, nor during nor after.

In Donostia, temperature dropped 12.5◦C in 20 minutes. In Zumaia, air temperature had

risen to 39,9 C at 18:15z and fell 16 C in 4 hours.

Propagation speed was about 50 kmh−1. (Figure. 2). At sea, the maximum wave height

increased from values below 1 m to up to 3.5 m, with a decrease of the mean wave

period from 8s to 5s, typical period of wind-generated sea waves (Figure. 16).

Synoptic and mesoscale scale data have been collected from different sources: satellite

images, oceanographic buoys along Cantabrian coast, fixed land stations belonging to

AEMET and EUSKALMET and atmospheric soundings.

Local data have been collected from the WS-1090-SOLAR (915MHz)

WEATHERWISE INSTRUMENTS meteorological station installed onboard the vessel

“Lete V”.

4.1 RADAR IMAGERY

EUMESAT images: 31072013 12:00z (left) and 01082013 12:00z (right). The gale

event happened from 23:53 to 00:48 (local time) so no link to cold front or turbulence

line whatsoever existed. (Figure 19).

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Figure 19 - Radar imagery.

4.2 SPATIAL ACTIVITY PREVIOUS TO GALE DAY

ERUPTING MAGNETIC FILAMENTS: During the late hours of July 26th, two

filaments of magnetism erupted on the sun. The first to blow was a loop on the sun's

southwestern limb. A second filament connecting sunspots AR1800 and AR1805

erupted shortly thereafter. Both blasts were captured in a movie, recorded by NASA's

Solar Dynamics Observatory.

The explosions hurled coronal mass ejections (CMEs) into space: One of them (the one

propelled by the filament connecting AR1800 and AR1805) might be heading in the

general direction of Earth. (Figure 20).

Figure 20 - Sun activity.

Source: NEODAAS. Dundee Satellite receiving Station

Source: SPACEWEATHER, NASA

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4.3 SEA SURFACE ANOMALIES

Sea Surface upwelling / downwelling anomalies can be measured by satellite remote

sensors and ocean buoys. The variables taken into account are Salinity, Temperature

and currents.

These are some of the data gathered that day. (Figures 21, 22).

Figure 21 - Sea Surface Salinity anomaly.

Figure 22 - Sea Surface Temperature / Salinity anomaly.

Source: Boya de Bilbao-Vizcaya. Puertos del Estado

Source: SMOS satellite

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4.4 ATMOSPHERIC STATE. SYNOPTIC SCALE

4.4.1 300 HPA LEVEL

The synoptic situation at 300 mb, at about 9 km of altitude, at 0.00 the day August 1,

2013, shows that the jet stream height was at abnormally low latitudes on the

Cantabrian coast, with a strong southwest flow, dragging a cold front and intensifying

the situation in the lower layers of the atmosphere. (Figure 23).

Figure 23 - Atmospheric State. Synoptic scale: 300 hPa. 2013,

August 1 0:00UTC.

4.4.2 500 HPA LEVEL

At the level of 500 mb (about 5500 m) a thermal low penetrating over Cadiz can be

appreciated, with synoptic flow from SSW (South-Southwest), as well as a strong

thermal contrast that crosses the Cantabrian coast. Twelve hours later, the thermal low

shifts clearly eastward, reaching the Gulf of Lion and the intensification of the trough to

the SW can be seen. The low pressure has deepened southwest of Ireland remaining

stationary and the thermal dorsal has deepened on the peninsula in NE (Northeast). The

strong thermal contrast of the atmosphere over the coastline of the Gulf of Biscay

increases (negative on the sea) and over Galicia, at West of the Cantabrian coast, with a

strong negative pressure gradient to the east and a strong flow from SW (Southwest) to

generate the hurricane gusts from WNW (West-Northwest); the gale . (Figure 24).

Source: Meteociel.fr

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Figure 24 - Atmospheric State. Synoptic scale: 500 hPa. 2013,

August 1. 0: 00UTC.

4.4.3 850 HPA LEVEL

At the level of 8500 mb (about 1500 m) a Southwest flow and a thermal dorsal, whose

axis passes through the Basque Country in a SE-NW (Southeast-Northwest) direction is

appreciated. The gale wind is an ageostrophic stream responding to the intense

mesoscale pressure gradients that occur along the coast: positive to the west and

negative to the east (the pressure in Galicia is at least 6 hPa higher than in Hondarribia).

This opposing pressure tendency is due to the flow at 850 hPa synoptic scale and to the

air mass advection of cold air coming from the NW and warm air coming from the SE

with a strong thermal contrast at the interface, over the Bay of Biscay.

The presence in the peninsular South of a warm air mass in middle layers of the

atmosphere (at 850 mb) from North Africa, favors a higher surface temperatures that

lead to the formation of a relative low over the peninsular center, situation that

generates a weak cyclonic flow, with southerly winds on the Bay of Biscay. This hot

terrestrial air flow at reaching the sea shore evaporates sea water and contrasts with the

much colder air mass over the sea, which collapses forming a mesolow on the

Cantabrian coastline due to the negative eastward barometric trend. This mesolow

moves towards the French coast accelerating and intensifying in the advance. The

strong thermal contrasts over the Cantabrian coast, negative at sea and positive eastward

increases the phenomenon which generates the gale.

(Figure 25): The level of 850 mb is characterized by a thermal ridge over the eastern

Bay of Biscay with a warm advection of southerly winds. The gray lines represent the

contours of the Temperature at 850 mb level and the white lines represent the heights in

Dm. The zonal temperature contrast is high particularly on the Cantabrian area. The axis

of the heat dorsal over the Iberian Peninsula moves to the Northeast, with its lower end,

which is associated with the maximum temperatures at 850 mb, pointing to the center of

the mesolow. At the same time, it appears that there are two large zones with different

Source: Meteociel.fr

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pressure tendency. Both in one as in the other zone the value of the pressure trend

intensifies. In the part of the Asturian coast, with positive pressure tendency, the wind

has already rolled west, which is consistent with the fact that the wind rolls almost

simultaneously with the pressure rise.

Figure 25 - Atmospheric State. Synoptic scale: 850 hPa. 2013,

August 1 0:00UTC.

4.4.4 SEA LEVEL

On the surface, at mesoscale level, there are also factors that increase the temperature

and pressure difference between the two adjacent air masses. On the one hand, a strong

mesoscale pressure gradient is formed due to the geographical configuration of the area,

and moreover, the overheated air mass coming from land, due to the Föehn effect, gets

to the coast giving rise to a strong thermal contrast between the two adjacent air masses.

(Figure 26).

Source: Meteociel.fr

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Figure 26 - Atmospheric State. Mesoscale: Sea Level Pressure and

Temperature. 2013, July 31.

A collapse of the local barometric pressure of about 12 mb in 12 hours had happened,

with warm southerly winds and a hot, muggy and sultry day on course, followed by a

rise of pressure in which process the gale unleashed. The sudden and strong gusts of a

WNW (West-Northwesterly) component wind intensified. The intensity of the gusts

reached 50 km h-1

as pressure suffered a micro-low, to later continue its ascent.

With the inlet marine air mass the preexisting temperature drops 18 C in 2 hours due to

the replacement of the overheated land air mass. (Figures 27, 28).

Source: Meteociel.fr

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Figure 27 - Atmospheric State. Local Scale: wind gusts, Absolute

pressure, Temperature, Relative Humidity. 2013, July 31.

Figure 28 - “Lete V” onboard data: gusts, P, T, h. 2013, July 31.

a) 23:13-01:08, b) 0:00-0:30h.

Source: Author, Lete, I. 2014

Source: Author, Lete, I. 2014

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4.4.5 TIDAL EFFECT IN SEA SURFACE PRESSURE

Most gales happen with high tides due to the inverted barometric effect which lowers

atmospheric pressure a range of 1 mbar for every 1 cm of sea level growth.

Figure 29 - Tidal inverted barometric effect.

4.4.6 AIR COMPOSITION

During the summertime gale days a sharp meteorological contrast is established in

South Biscay coast between the Cantabric High pressure system offshore and the

thermal low of Castilian’s plateau. The resultant along-shore winds and colder ocean

waters along the coast are very important components of the local climate. Another

atmospheric consequence of this contrast is the presence of a very strong temperature

inversion separating warm and dry air subsiding aloft from the cool and moist, turbulent

air near the ocean surface. This well-mixed layer over the ocean is known as the marine

atmospheric boundary layer (MABL), and its vertical structure, depth, and temporal

variability are important to a range of scientific interests. These include the dynamics

of the alongshore winds and their consequent impact on ocean upwelling; the upwelling

nutrient supply’s influence on the bountiful marine food web; the transport of chemical

compounds from the ocean to the atmosphere; and the development of marine

stratocumulus cloud layer below inversion layer (Figure 30). As SST lowers with the

upwelling, the thermal difference is higher thus low stratus formation is easier. Of

course, the environmental consequences of this meteorological setting are also

important to operational interests such as to fishing vessels, small craft, merchant

vessels maneuvering and aviation at landing. The height of the MABL is defined as the

altitude of the base of the temperature inversion, and generally demarcates the depth to

which atmospheric constituents are effectively mixed on short time scales.

This transport of chemical compounds from the ocean to the atmosphere can be

measured at environmental coastal stations (and even some sensitive people are able to

Source: Author, Lete, I. Based Tides Puertos del Estado, 2013

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smell) and is subject of another study in deep. Only to mention, abnormal levels of SH2

and SO2 are noticeable the morning before the gale and abnormal levels of O3 and NOx

with the entrance of the marine air. (Figure 31).

Figure 30 - Marine stratocumulus cloud.

Figure 31 - NOx and O3 gale anomaly.

Source: RIST Tokyo University of Science, 2012

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Source: Ingurumena. ejgv. euskadi.net

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5. GALES PREVENTION HANDOUT

This hand out was made with de intention of helping recreational boats users with the

analysis of the situation cat can lead to as unsuspected gale event.

Marine boundary layer state on a gale day: before, during and after a gale, at a coastal

location.

The cold and wet sea air advection (MBL) blows beneath the warm air mass from land

(INV) and is trapped between the inversion and coastal mountains rushing eastward.

Ageostrophic gale starts to develop when a cold and wet Marine Boundary layer (MBL)

moves inland over the Sea Surface and above this MBL there is another colder and less

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humid air mass coming from land (by Föehn effect) that acts as a ceiling, the so called

Inversion (INV). In the case that certain generating factors converge (upwelling at sea

surface) a perturbation will develop in the MBL.

The gale wind is an ageostrophic stream that responds to the intense mesoescalar

pressure gradients occurring along the coast, positive at W and negative at E. This

opposing pressure tendency is due to synoptic scale flow at 850 mb and to the NW cold

air mass advection and of cold and SW warm air with strong thermal contrast at the

interface, on the Bay of Biscay.

Interinfluence of the marine surface layer and the atmospheric boundary layer:

Gales can be predicted early enough to avoid coastal disasters. Sea surface suffers some

changes in temperature, salinity and currents that are observable in oceanographic buoys

with the available satellite technology and even to the naked eye from the beach, and

bathing, surfing or sailing along the coast. One just has to be aware of these anomalous

alterations and get to safety.

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Some tips and recommendations if trapped in one gale:

FUTURE RESEARCH

It is absolutely necessary to obtain accurate sea surface data on live to detect anomalies

in sea surface temperature, salinity and currents in order to settle an alarm system, as

well as sea-air heat transfer and vaporization.

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Changes in two air masses composition should be well understood as well to

parameterize the adverse phenomenon.

With a mathematical modeling systematization in mind, a multidisciplinary work team

is required.

CONCLUSION

Below the inversion layer, at about 600 meters high, and as narrow as 4 nautical miles,

from the mountains that surround the coast line seaward, sudden and unexpected raffles

of wind up to 80 knots are sent strengthening and accelerating as the phenomenon

advances eastward, toward the Atlantic French Coast where they disappear.

This narrow jet of wind runs the Cantabrian Sea coast line from west to east from May

to October and is due to the collision of two air masses: one warm and less humid

(h 40%, T>30ºC) incoming from the plateau that stays over the coast in an inversion

manner and the other cold and wet (h 100%, T<15ºC) coming from the sea that enters

under the inversion layer and rushes along the coast in front of the coastal mountains

and under the inversion giving a sudden and violent end to a hot and sultry day.

South Biscay Gales are a set of gusts of strong and sudden winds that last a few

minutes starting from 0 km h-1

rising to 100 km h-1

in a few seconds and decreasing

quickly to start another gust and repeat the set like this for around 2 hours.

Well known for the damage caused, one of the most harmful ones happened at midnight

the 12th

of August, 1912 when 143 fishermen sank in Biscayan Gulf waters leaving 225

orphans, 75 parents, 12 younger brother and sisters, 40 brides about to be married in 3

days and 75 widows in charge of the entire population with no support and resources at

all and in the most absolute misery and desolation, in whose honor I have written a

historical novel entitled “La galerna y la mar” end edited by the editorial Desclée De

Brouwer. This work is an attempt to try to understand this adverse phenomenon and

give some advices so that any seaman or woman can foresee the signs of an incoming

gale.

BIBLIOGRAPHY

[1] Arasti, E. (1999). “La galerna típica”, Biblioteca de módulos TEMPO,

AEMET. “Hipótesis acerca de la formación de una galerna típica”. Instituto

nacional de meteorología.

[2] Arteche, J. L. (2012). “La Meteorología de la Galerna del Cantábrico”. El

Puertuco nº 36, julio.

[3] Boé, J. et al. (2011). “What shapes mesoscale wind anomalies in coastal

upwelling zones?”. Climatology Dynamics (2011) 36:2037-2049

[4] Booth, J.F. et al. (2013). “Midlatitude storms in a moister world: lessons from

idealized baroclinic life cycle experiments”. Climate Dynamics 41: 787–802.

[5] Bond, N. et al.(1996). “Coastally Trapped Wind Reversal”. Monthly Weather

Review, 124, 430-445

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[6] Ed. Bermeoko Udala (2012). “GALARRENA 1912-2012 GALERNA”

[7] Ferrer, L. et al. (2008). "Gales along the Cantabrian coast”. GLOBEC

International Newsletter, Vol. 14, No. 2, pp. 62.

[8] García, M. et al. (2010). “Estudio de una galerna del Cantábrico con el modelo

WRF-ARW”. Grupo de Meteorología de Santander.

[9] Kerry A. Emanuel. (1985). “An air-sea interaction theory for tropical cyclones”.

Journal of the Atmospheric Sciences, vol. 43. No.6.pg. 585-603-

[10] Lete, I. (2016). “La galerna y la mar”. Ed. Desclée de Brouwer.

[11] Le Cann, B. and A. Serpette (2009). “Intense warm and saline upper

ocean inflow in the southern Bay of Biscay in autumn–winter 2006–2007”.

Continental Shelf Research. Vol. 29 (8), 1.14-125.

[12] Martín, M. (2012). Aproximación de una galerna en la costa vasca.

Donostia, AEMET Euskadi.

[13] Neumann, G. and W.J. Pierson (1966). Principles of Physical

Oceanography. New Jersey Prentice-Hall.

[14] Reason, C.J.C. et al. (1999). “The Dynamics of Coastally Trapped

Mesoscale Ridges in the Lower Atmosphere”. Journal of the Atmospheric

Sciences. 49(18) 1677-169

[15] Robert H. S. (2008). Introduction to Physical Oceanography.

Department of Oceanography Texas A & M University.

[16] Skamarock, W. C. et al. (1999). “Models of coastally trapped

disturbances”. Journal of the Atmospheric Sciences, 56, 3349–3365.

[17] Torres, R.; E.D. Barton, P. Miller and E. Fanjul (2003). “Spatial patterns

of wind and sea surface temperature in the Galician upwelling region”. Journal

of Geophysical Research, 108, 3130.

[18] Usabiaga, J. I. A. (1988). “Galerna típica”. Meteorología Hiztegia. UZEI,

Elkar S.A. San Sebastián, Donostia.

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Figure 1: Coastal layout. Continental layer. Heights and distances in Cantabrian Coast.

.......................................................................................................................................... 3

Figure 2: Ageostrophic Gale development area. .............................................................. 4

Figure 3: South Biscay Gales: set of sudden ageostrophic gusts ..................................... 4

Figure 4: Three Kelvin wave layers: free atmosphere, inversion, MBL and sea surface

with temperatures and heights. ......................................................................................... 5

Figure 5: A conceptual model of a mesoscale convective system (Smull and Houze,

1987). ................................................................................................................................ 6

Figure 6: tornado formation .............................................................................................. 6

Figure 7: cold and wet sea air advection (MBL) beneath warm air mass from land (INV)

trapped between the inversion and coastal mountains...................................................... 7

Figure 8: Temperature drop at a gale: 14 C in 1h. .......................................................... 8

Figure 9a: Geostrophic Balance ....................................................................................... 9

Figure 10: Pressure gradients: West to East and offshore inland. .................................. 11

Figure 11: Mesolow ........................................................................................................ 12

Figure 12: Föehn effect and cold and wet marine air advection. MBL. ......................... 14

Figure 13: Gale inducing upwelling ............................................................................... 15

Figure 14: historical gales and sun cycles ...................................................................... 16

Figure 15: Gale one day’s SST anomaly ........................................................................ 17

Figure 16: upwelling currents: U, V, UI. ........................................................................ 17

Figure 17: Gale’s spatial induction ................................................................................. 18

Figure 18: Sun Cycle & Cosmic Rays & Cloud formation ............................................ 19

Figure 19: Radar imagery ............................................................................................... 21

Figure 20: Sun activity ................................................................................................... 21

Figure 21: Sea Surface Salinity anomaly ....................................................................... 22

Figure 22: Sea Surface Temperature / Salinity anomaly ................................................ 22

Figure 23: Atmospheric State. Synoptic scale: 300 hPa. 2013, August 1 0:00UTC ...... 23

Figure 24: Atmospheric State. Synoptic scale: 500 hPa. 2013, August 1. 0: 00UTC .... 24

Figure 25: Atmospheric State. Synoptic scale: 850 hPa. 2013, August 1 00UTC ......... 25

Figure 26: Atmospheric State. Mesoscale: Sea Level Pressure and Temperature. 2013,

July 31 ............................................................................................................................ 26

Figure 27: Atmospheric State. Local Scale: wind gusts, Absolute pressure, Temperature,

Relative Humidity. 2013, July 31 ................................................................................... 27

Figure 28: “Lete V” onboard data: gusts, P, T, h.. 2013, July 31. a)23:13-01:08, b)0:00-

30h .................................................................................................................................. 27

Figure 29: Tidal inverted barometric effect .................................................................... 28

Figure 30: marine stratocumulus cloud .......................................................................... 29

Figure 31: NOx and O3 gale anomaly ............................................................................ 29