MFE 658 Lecture 2a /Winter Storms MFE 658 Lecture 2a ...

MFE 658 Lecture 2aMidlatitude Cyclones/Winter Storms

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MFE 658 Lecture 2aMidlatitude Cyclones, Fronts, and Related Hazards

• Source of energy

• Formation of Fronts

• Jet Streaks/Short Waves

• Interaction with Planetary Waves

• Hazards associated with Winter Storms

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Energy Source for Midlatitude Cyclones

• Potential energy of the mean state is converted to kinetic energy as cold air sinks and warm air rises.

• Winter storms derive their energy from temperature gradients in the form of baroclinic instability, an instability of the sheared zonal wind.

• The energy source for baroclinic instability is the potential energy in the environmental flow. As the instability grows, the center of mass of the fluid is lowered.

• In growing waves in the atmosphere, cold air moving downwards and equatorwards displaces the warmer air moving polewards and upwards.

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The Definition of EnergyEnergy – the ability to do workTwo familiar types

1. Kinetic energy – the energy of motion: K = 1/2mV2

2. Potential energy – stored energy: P = mgh

KE = 1/2 x mass x velocity2 4

Baroclinic Instability

Distribution of geopotential height (solid) and temperature (dashed) on a constant pressure surface in a developing baroclinic wave in the Northern Hemisphere. The pressure surface is located near the level where the speed of the wave is the same as the speed of the mean zonal flow.

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Baroclinic Instability

Cross section through a developing storm (baroclinic) wave showing slope of typical air parcel trajectories (arrows) in relation to the slopes of the temperature contours. Note: warm air rises and cold air sinks.

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Midlatitude Storm Winds

Surface winds show confluence of cold and warm air, causing a front to form.

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Norwegian Cyclone Model

The Norwegian cyclone model describes how fronts evolve and interact in a winter storm.

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Idealized Norwegian Cyclone Model

Incipient Mature

Occluded Dissipating

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Model Midlatitude Cyclone

This schematic shows relationship of surface and upper-level winds.

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Wave Growth and Propagation

Wave growth and propagation are the result of thermal advection. Warm advection leads to troughing and cold advection leads to ridging. This is the essence of baroclinic instability.

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http://www.atmos.washington.edu/~ovens/loops/

Short Waves/Jet Streaks

• Short waves in the jet stream provide the initial perturbation that allows midlatitude cyclones to deepen.

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Schematic depiction of the propagation of a mid-tropospheric jet streak through a Rossby wave over 72 h. Solid lines: height lines, Thick dashed lines: isotachs, Thin dashed lines: isentropes

Time = t0

J

Conceptual Model of Jet Streak – Planetary Wave Interaction

JJ

JTime = t0 + 24 h

Time = t0 + 48 h

Time = t0 + 72 h

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Short Waves: Alberta Clipper

Short wave troughs aloft form over and downwind of major mountain ranges.

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Surface Cyclone Development

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Short-rangestorm/jet streakon order of days

Medium-range Rossby Wave Train downstream wave-energy transferon order of week(s)

Sub-seasonal - Rossby Wave Propagation slow retrogression of wave axison order of weeks to a month+

Jet Streak – Planetary Wave InteractionThree Interacting Time Scales

Planetary WaveWave TrainWinter Storm

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UK Japan UKCal.

9-27Nov.

Time/Long. Diagram: 250-mb Meridional Wind (m s-1) 35-60 N, 6-28 November 2002

Planetary WaveWave TrainWinter Storm

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Time/Long. Diagram: 250-mb Meridional Wind (m s-1)Latitude Belt ( 35-60 N) 6-28 November 2002

UK Japan UKCal.

Cyclogenesis

TornadoesOil Tanker

Alps Flood/Wind

Cyclogenesis

Snow/Ice Storm

Shuttle Launch DelayMoroccan Flood

Alps flood

Cyclogenesis

India/T.C.

Cyclogenesis

Cold-Air

Cold-Air

6 Nov.

28 Nov.

Flood

Flood

Winter Weather Hazards

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Weather Hazards

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Hazards associated with Midlatitude Cyclones

Winter Storm Hazards

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Hazards in Midlatitude Cyclones

What is the distribution of hazards around a strong winter storm?

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Weather Hazards in Winter Storms• High Winds• Large Ocean Swell and Surf• Storm Surge• Blizzards• Freezing Rain, Sleet, Snow• Heavy Rains and Flash Flooding• Severe Thunderstorms

– Lightning, Flooding, High Winds, Tornados

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High WindsWhere do we find the strongest winds in a midlatitude cyclone?• Surface

– Where the pressure gradient is largest, often on NW side of storm.

– Near convective clouds (including tornados)

– Near the fronts - SW side

• Upper Air– Where the height gradient is largest– In pulses, jet streaks, superimposed

on the jet stream

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Lost at Sea

Right now, as you read this, there are five to six million shipping containers on enormous cargo ships sailing across the world’s oceans. And every hour, on average, one is falling overboard never to be seen again. It’s estimated that 10,000 of these large containers are lost at sea each year, and our understanding of what happens to them afterwards is scant at best.

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Dr. Wolfgang Rosenthal, lead scientist for the MaWave Project convened in 2000 to investigate the disappearance of ships, stated “One large ship sinks every week on average worldwide, but the cause is never studied to the same detail as an air crash. It simply gets put down to ‘bad weather.’” A press release by the European Space Agency in 2004 claimed that "Severe weather has sunk more than 200 supertankers and container ships exceeding 200 metres in length during the last two decades. Rogue waves are believed to be the major cause in many such cases".

Lost at Sea

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The preceding numbers are exaggerated, but given the lack of survivors or evidence, exact statistics* of ships scuttled by giant waves are difficult to come by. The fact remains that every year large ships sink or otherwise go missing, taking their crews along with them. If you also consider smaller vessels, the numbers are sobering. *Response from Navy to my FOI request (2012-NSC-19) for data on ships lost at sea was, “I regret to inform you the requested documents do not exist within the files at this command.”

Lost at Sea

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Possible Causes of the LossesRouge Waves – (aka freak waves) are relatively large and spontaneous ocean surface waves that occur far out at sea, and are a threat even to large ships and ocean liners.

• Rouge waves are more precisely defined as waves whose height is more than twice the significant wave height (SWH), which is defined as the mean of the largest third of waves in a wave record.

• Rogue waves are not necessarily the biggest waves found at sea; they are, rather, surprisingly large waves for a given sea state.

• Rogue waves seem not to have a single distinct cause, but occur where physical factors such as extreme wind fields and strong currents cause waves to merge to create a single exceptionally large wave.

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Possible Causes of the Losses

Synchronous rolling – inversely proportional to the square root of the metacentric height and directly proportional to the beam of the ship – takes place because of resonance between, the natural period of roll of the ship & the natural period of the oscillation of the waves. The rolling will gradually increase to high capsizing values.

• Parametric roll – occurs when natural roll period is between 1.8 to 2.1 times the encounter period (normally associated with the pitching period)

*Stability Analysis of Parametric Roll Resonance. B.J.H. van Laarhoven DCT 2009.062

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Parametric Roll

The larger the flare on container ships the more likely is the parametric roll occurrence and wider the range of resonance. It requires a group of waves above a threshold or critical height for parametric roll to be initiated and sustained. The threshold depends on hull size and shape.

The cruise ship Voyager in Cyclone Valentina (Mediterranean Sea), on February 14th 2005.

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Parametric Roll

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Factors Affecting Wind Wave DevelopmentThe following factors control the size of wind waves: 1. Wind strength2. Wind duration3. Fetch - the uninterrupted distance over which the wind blows

without changing direction.4. Air-sea temperature difference5. Ocean depth

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Wave Steepness and Ship Hazard! Wave steepness= Wave Height/Wave Length = H/L! Young waves are steeper than older waves! Steep waves pose significant risk to marine vessels en route ! The wave steepness in 60% of the global ship accidents

ranged from .03 to .04.

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Swell and Wave LifecycleThree things happen to large waves when they leave the storm region.

1. Dissipation: Wave amplitude gradually dies out as the waves travel away from their source. Opposing wind enroute can accelerate the dissipation or decay of wave energy.

2. Dispersion: Swell disperse over the open ocean: longer wavelength swell move faster than shorter wavelength swell.

3. Angular spreading: Shorter wavelengths (steeper waves) have more angular spreading.

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Wave Decay

Dissipation

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Deep Water Waves and Dispersion

Graph of the relationship between wave speed and wavelength.

Depth > L/2, where L is wavelength - defines deep water waves.Longer waves move faster

C = (gL/2Π)1/2

C = wave speedg = gravity (9.8 m/s 2)

Dispersion of waves of differing wavelength leads to swell that run ahead of storm.

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Deep Water Waves: Dispersion & Swell

In deep water, waves of different wavelengths travel at different speeds. Waves with the longest wavelengths move the fastest and leave an area of wave formation sooner. Because of their different speeds, waves separate out from one another into groups with similar wavelength. This process is called dispersion. Dispersion causes groups of waves with the same wavelength to travel together, causing a very regular, undulating ocean surface called swell.

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Group Velocity

The group velocity is 1/2 the individual wave velocity.

•Individual waves within a set of waves move faster than the group of waves moves.

•The group velocity is 1/2 the individual wave velocity.

– Waves in the front loose energy in lifting an “undisturbed” ocean surface.

– Waves in the back benefit from the energy of waves ahead.

– The leading wave dissipates and the trailing wave grows, resulting in the slower group velocity.

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Angular Spreading

Angular spreading is proportional to swell energy.Swell from broad fetches experience less angular spreading.Steep waves dissipate more quickly through angular spreading.

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Swell and Wave LifecycleTwo things happen to large swell waves when they near shore.

1. Shoaling: As waves move into shallow water they slow and become steeper as they increasingly feel the bottom, until finally the top of the wave pitches forward and the wave breaks.

2. Refraction: As waves move into shallower water, they slow down and thus turn toward the shore.

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In the high-tech marine world of radar, distress radio beacons, GPS, and satellite surveillance, how can hundreds of enormous vessels just get swallowed up by the sea? And furthermore, how can this be happening with scarce media notice?

Lost at Sea

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80+% of storms that produce hurricane force winds undergo a period of explosive cyclogenesis (aka “bombs”). A bomb is defined as a midlatitude cyclone that deepens 1 mb/hr for 24 hours (at 60˚N equivalent).

Background: Explosive Cyclogenesis

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Distribution of pressure falls in 24 hours (Sanders and Gyakum 1980)

Distribution of Pressure Falls in Bombs

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Explosive cyclone density [contour interval 4×10−5 explosive cyclones (°lat-2), 1979-1999 (From Lim and Simmonds 2002).

Distribution of Bombs

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Distribution of bomb events in the North Pacific Ocean 1974-1984 with SST (Chen and Fu 1997).

SST and Distribution of Bombs

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Surface Sensible Heat Fluxes

Distribution of sensible-heat fluxes45

Forcing by Shortwaves

Short waves aloft provide strong mid-tropospheric forcing where needed across the East Coast.

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Deep Convection in HF Storms

Northeast Pacific Storm 18-20 December 2002was under forecast by more than 10 mb by NCEP.

Pessi, A. T., and S. Businger, 2009: Mon. Wea. Rev., 137, 3177-3195.

Surface analysisValid 1200 UTC19 December 2002

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The Perfect Storm

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Animation of the “Perfect Storm”

The perfect storm absorbed Hurricane Grace in October 1991. The Andea Gail swordfish boat sank in this storm on 10/28/91.

Sea-level Pressure/Winds 500-mb Heights

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Hurricane-like Core in Perfect Storm

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SEATTLE - 2/4/06

Hurricane force winds cut power to nearly 200,000 homes and businesses in Western Washington on Saturday, forced the closure of the floating bridge on Lake Washington for the first time in nearly seven years, and resulted in at least one fatality when a tree fell on a car.

West Coast Windstorms

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SEATTLE - 12/15/06

Fierce winds cut power to nearly 800,000 homes and businesses in Western Washington on Friday. This home in Redmond had ten fallen trees on it when the winds died down.

West Coast Windstorms

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Mother of all NW WindstormsColumbus Day Storm of 1962

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Mother of all NW Windstorms

Columbus Day Storm of 1962

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NW Windstorms and Bridges

Hood Canal Bridge sinks on 13 Feb. 1979

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NW Windstorms and Bridges

Tacoma Narrows Bridge 7 November 1940

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Hawaii: Two Epic Wave Events

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Hazards – Large Waves

• Peggotty Beach, Massachusetts February 9, 1978

Oahu, North Shore January 1998.

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December 1969 HF Storm

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1969 Wave Damage on Oahu

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HF Storm of December 1969

NCAR/NCEP Reanalysis Data for 8 AM 30 November 1969

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Animation of SLP Analyses Dec. 1969

A captured fetch occurs when the swell travel at the same speed as the storm, so that high winds remain over the swell region.

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HF StormJan. 1998

Photos by S. Businger

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HF Surface Winds on 26 January 1998

NCAR/NCEP Reanalysis Data for 8 PM 25 January 1998

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Animation of SLP Analyses Jan. 1998

Note the captured fetch that again occurred in this case.

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Waves are Scale Invariant

Breaking waves are scale invariant; its difficult to tell how large they are without a surfer for scale.

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Sites providing in-situ ocean measurements cover a very small portion of the global oceans with a distinct bias toward the margins of the major basins (Cardone et al. 2005). Ships tend to avoid storms.

HF Wind Fields Data and Methods

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HF Wind Fields: Data and Methods

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Jan 2003 through May 2008

Hurricane Force Fetch Climatology

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Very Extreme Sea-State Events

Distribution of 12+m significant wave height events as measured by the TOPEX, ENVISAT and JASON Altimeters (Cardone et al. 2005).

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HF Storm Example: 28-29 Jan. 2007

QuikSCAT wind image and GFS wind analysis for same time.

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WWIII Wave Fields

Wave Height

Wave Period

Wave Steepness72

Comparison of Breaker Heights

Breaker height = wave height x periods x shoaling factorWave steepness reached .07 along the AK coast.

*

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QuikSCAT vs GFS Analyses

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WW3 vs Buoys: Significant Wave Height

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Storm of the Century

This storm in March 1993 caused >200 fatalities.

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Occluded Stage

• All time low pressure in Raleigh, NC.

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This storm in March 1993 caused >200 fatalities.78


This storm in March 1993 caused >200 fatalities.

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Storm Snow Totals

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Hazards – Heavy Snow

North Dakota: A March 1966 blizzard nearly buried utility poles.

I believe there is a train under here somewhere!

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• Red Cross workers search for victims buried in cars following heavy snowfall The Great Lakes area is subject to extremely heavy "Lake Effect" snowfalls (1977).

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Snowstorms leave a band of heavy snow in their wake.

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Blizzard conditions occur N and NW of surface-low center.

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Heaviest snow occurs where gradient in cloud top temp is greatest.

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Death in blizzards comes from exposure to cold.

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Heavy Snowfall in Complex Terrain

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Hazard – Snow Avalanche

Western U.S. mountains generally record over 100,000 avalanches every winter. Some avalanche slides can reach speeds of over 100 miles per hour.

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Hazard – Snow Avalanche

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Hazards – Sleet and Freezing Rain

The Rain – Snow Line

North of the warm front there is a transition from rain to snow called the rain-snow line.

Freezing rain and sleet fall on the warm side of this line.

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Hazard – Freezing Rain

Kansas City, MO, January 31, 2002.

Frozen precipitation causes significant disruption of transportation and resulting economic impact.

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Freezing Rain

Television Tower Raleigh, NC January 1990

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Freezing Rain


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Freezing Rain


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Freezing Rain


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Rising Air and Precipitation

Where is the precipitation in midlatitude cyclones?– Along the cold front and in areas of convection.– Downwind (north) of the warm front– Wrapping around the Low Pressure Center

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Precipitation Pattern

Where is the precipitation in midlatitude cyclones?– Along the cold front and in areas of convection.– Downwind (north) of the warm front– Wrapping around the Low Pressure Center

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An ice storm in New York also caused flooding of water front properties in the region, January 1998.

Hazards – Heavy Rain and Flooding

Arizona Flash Flood

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The greatest hazard is from flood waters crossing roads.

Hazards – Heavy Rain and Flooding

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Where do the Hazards Occur?

Severe Thunderstorms– Produce:– Tornados– Large Hail– High Straight-line Winds– (Floods and Lightning)

Occur where jet stream crosses the cold front.

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Severe Thunderstorms associated with a cold front.

Weather Hazards in Winter Storms

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Recap: Where are the hazards?

Weather Hazards

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Severe T-stormsTornadosHigh winds

Sleet and ZR

BlizzardHigh winds

Recap: Where are the hazards?

Weather Hazards

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Summary: Winter Storm - Hazards• Heavy Snow/Frozen precipitation Blizzard Conditions, Snow, Sleet and Freezing Rain, Aircraft Icing, Riming, Snow Avalanches• Heavy Rain Flooding, Flash Floods, Mud and Debris Slides• High Winds Nor’easter, Blizzard, Turbulence, Storm Surge• Large Ocean Swell and Waves High Surf, harbor surges• Severe Thunderstorms Tornados, Large Hail, High Winds, Lightning

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Questions?

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Hazards – Severe Thunderstorms

Large HailTornadosHigh Straight-line winds

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