Oscillations, Ensemble Prediction, and Ocean Waves Lectures (ENSO slides and Figures not included!) Flashcards
To Graduate.
The ____ is an intraseasonal fluctuation or wave occurirng in the global tropics.
MJO
TheMJOisresponsibleforthemajorityofweathervariabilityintheseregionsandresultsinvariationsinseveralimportant
atmosphericandoceanicparameterswhichinclude:
- Lower and Upper Level wind speed and direction.
- Cloudiness and rainfall
- Surface Pressure
- Sea surface temperature
The typical length of the MJO is ___.
30-60 Days
Characteristics of the MJO are:
- eastward propagation of regions of enhanced and suppressed tropical rainfall
- primarily over the Indian and Pacific Oceans
- typically evident over the Indian Ocean first and propagates eastward to the tropical Pacific
- Over the eastern Pacific, the pattern of tropical rainfall becomes nondescript, but reappears over the Atlantic and Africa.
More Characteristics of the MJO include:
- distinct patterns of lower and upper level divergence and circulation anomalies in the tropics and subtropics
- these features can extend across the globe and provide important information regarding the regions of ascending and descending motion of particular phases of the oscillation
The active convection _______ as it moves into the western hemisphere.
weakens
Upper level and Lower Level Features when the convection (MJO) is active in the Indian Ocean and Indonesia:
Upper-Level:
- Anomalous easterlies exit the area of enhanced convection associated with anti-cyclonic gyres straddling the equator to the west of the convection. - cyclonic gyres straddle suppressed convection to the east
Lower Level:
- Anomalous easterlies are evident to the east of the area of enhanced convection (anti-cyclonic gyres) - Anomalous westerlies are evident within and to the west of the area of enhanced convection (cyclonic gyres)
Low level gyres are generally (weaker/stronger) than those at upper levels.
weaker
As the MJO propagates eastward through the central and eastern Pacific, the circulation anomalies become (less/more) recognizable.
Less
Enhanced rainfall accompanies the Upper Level (Convergent/Divergent) phase of the MJO. However rainfall may still be suppressed across portions of the equatorial ______ due to colder water.
Divergent
Eastern Pacific Ocean
Anomalously strong 850 mb easterlies occur in the tropics within the low level (convergent/divergent) phase of the MJO.
Divergent
Anomalously strong 850 mb westerlies occur in the tropics within and immediately west of the low level (convergent/divergent) phase of the MJO.
Convergent
During the MJO, 850mb westerlies south of Mexico are:
associated with an enhanced monsoon trough over the NW Caribbean and Southern Gulf of Mexico.
these areas also have cyclonic shear and are favorable for tropical cyclone formation
The MJO can substantially modulate the intensity of monsoon systems around the globe including:
- The Australian Monsoon(SH Summer)
- The Asian Monsoon (NH Summer)
- The South American Monsoon (SH Summer)
- The North American Monsoon (NH Summer)
The divergent (wet) phase of the MJO can affect the _____ and _____ of the monsoon.
timing and intensity
The convergent(dry) phase of the MJO can ______ and also ________ during already existing monsoons.
prematurely end
initiate breaks
The MJO also seems to influence the _______ cycle.
El Nino/La Nina
The MJO does not cause the El Nino but can contribute to the _______.
Speed of development and overall intensity
The MJO is known to modulate tropical cyclone activity in the _____, _____, ______, and _____.
Indian Ocean
Pacific Ocean
Gulf of Mexico
Atlantic Ocean
_________ at the surface in and just behind the MJO’s area of ________ may generate mirror-image cyclonic gyres straddling the equator.
At the same time in the upper levels, mirror-image anticyclonic gyres develop along and just behind the ______.
The net result is:
- westerly wind anomalies
- enhanced convection
- area of convection
- a reduction of U/L wind shear for westward-moving tropical cyclones and an increase in U/L divergence.
The strongest tropical cyclones tend to develop during the U/L (divergent/convergent) phase of the MJO.
divergent (wet)
As the MJO progresses eastward, the favored region for tropical activity shifts (east/west).
east
Enhanced tropical rainfall in the western and central Pacific can contribute to extreme rainfall events in ________.
Western North America
Typical scenario linking the pattern of tropical rainfall associated with the MJO to extreme precipitation events in the Pacific Northwest is :
Eastward moving U/L divergent phase in the central or eastern tropical Pacific and a retrograding mid-latitude jet stream trof in the high latitudes of the NE Pacific (Pineapple Express)
There is (weak/strong) year-to-year variability in the MJO activity.
strong
The interannual variability of the MJO can be partially linked to the ______.
El Nino cycle
Strong MJO is often observed when _____.
La Nina is weak or El Nino/La Nina is absent.
Weak or absent MJO activity is typicall associated with _______.
Strong El Nino episodes.
The ____________ is a zonal direct circulation in the tropical Pacific.
Walker Circulation
During a normal Walker circulation regime, _____ over the west Pacific. Meanwhile, _____ over the cooler water of the east Pacific.
Warm air rises (Heavy rainfall)
Cooler air Sinks (dry)
During the Walker Circulation, at the surface, the west and east Pacific are linked by ______.
Conversely, the upper troposphere portions are linked by ______.
westward-directed trade winds
eastward-directed winds
If the Walker Circulation is strong:
- Low (High) Pressure resides over the tropical West (East) Pacific
- The trade winds are strong over the Pacific
- The West (East) Pacific is wet (dry) and stormy (tranquil)
_____ is a disruption of the ocean-atmosphere system in the tropical Pacific.
El Nino
El Nino is characterized by a major (cooling/warming) of waters in the tropical central and eastern Pacific Ocean.
warming
El Nino is called _______ because it occurs or was first noticed along ________ around Christmas time.
“The Child”
The west coast of South America
El Nino occurs every _____ years and is characterized by a major weakening or even total reversal of the ______.
2-10 years
Walker Circulation
El Ninos are numerically characterized by a negative Southern Oscillation Index (SOI).
SOI = _______ - _______
SOI = (Tahiti SLP) - (Darwin SLP)
The CPC has recently changed from using the SOI to the _____ which is based on ________.
ONI (Oceanice Nino Index)
a 3 month running mean of SST departures in the Nino 3.4 Region.
El Nino is characterized by a _____ ONI ____ than +0.5
La Nina is characterized by a _____ ONI ____ than -0.5
Positive and greater than
Negative and less than
ONI thresholds for El Nino/La Nina must be exceeded for a period of at least ______ overlapping 3-month seasons.
5 consecutive
When the Walker Circulation is weak or reversed:
- El Nino forms
- Great Havoc occurs in the world’s weather patterns
- Great hardship is experienced by many people and much wildlife
When El Nino is present
- Low pressure moves to the tropical Central and East Pacific
- High Pressure forms over the tropical West Pacific
- The trade winds weaken or reverse over the Pacific Ocean
- The West (Central/East) becomes dry( very stormy)
Formative Stages of El Nino (late summer and fall):
- Walker Circulation weakens
- Pressure falls (rises) in the east(west) pacific
- SOI becomes negative
- ONI becomes positive (>0.5)
- Equatorial Kelvin Wave moves from west to east pacific
- Warm SSTs whift eastward
- Upwelling in East Pacific weakens
- Convection and Precipitation shifts eastward.
Mature Stage of El Nino (winter and spring) :
- WC reverses
- Low(High) pressure resides in central/east(west) Pacific
- SOI(ONI) is strongly neg(positive)
- Trade winds calm or reverse
- Equatorial Kelvin Wave moves from west to east pacific
- Warm SSTs cover central/east Pacific
- Sea Level mound resides in east pacific
- Upwelling in East Pacific is absent
- Heavy thunderstorms in central/east pacific
Dissipating Stage of El Nino (late spring and summer):
- WC begins to strengthen
- Pressure Falls (rises) in west (east) Pacific
- SOI (ONI) becomes positive(negative)
- Trade Winds Strengthen
- Equatorial Kelvin Wave dissipates
- Warm SSTs slosh back to the west Pacific
- Sea Level mound dissapears in east pacific
- Upwelling in East Pacific resumes
- Heavy Thunderstorms move back to west Pacific
- Dry weather returns to east Pacific
Definition of La Nina
A major cooling of the tropical East Pacific Ocean generally following a strong El Nino event with an overly-strong WC
Relationship between MJO strength and El nino.
Anomalously strong MJO often precedes major El Nino by 6-12 months
How exactly does the MJO initiate an El Nino?
Vigorous bursts of Equatorial westerly winds, associated with the frequent positive phases of the MJO, may develop an oceanic Kelvin wave which forces a dome of warm water eastward from the West Pacific. This Kelvin wave would help suppress cold upwelling in the east pacific, helping to lower SLP, relax the zonal SLP gradient across the Pacific, and relax the trade winds, thus initiating El Nino.
What does ENSO stand for?
The El Nino Southern Oscillation
What is the North Atlantic Oscillation(NAO)?
NAO = (Azores SLP) - (Iceland SLP)
What is dictated by the NAO?
Climate variability from the Eastern Seaboard of the US to Siberia and from the Arctic to the subtropical Atlantic. (Especially during the NH Winter)
_______ is associated with a net displacement of air from the arctic and icelandic regions towards the subtropical belt near the azores and the iberian peninsula. This mass displacement strengthens the Icelandic Low near the southeast coast of Greenland and also strengthens the subtropical high in the atlantic, resulting in more intense westerlies in the atlantic and more intense westerlies over the North Atlantic
high index NAO
Stronger (easterlies/westerlies) bring more warm moist air over the European continent and gives rise to milder maritime winters.
Westerlies
During a Positive NAO, (warmer/colder) temperatures are also observed over the western Atlantic and eastern US
warmer
The stronger Atlantic Subtropical High also strengthens the _______. This causes _____ to be blown across the tropical Atlantic toward the Caribbean and Florida. Increased upwelling of cold water off the northwest coast of Africa helps to keep surface temperatures cooler in the tropical Atlantic and enhances ______.
- trade winds over the tropical Atlantic
- African Dust
- Dry Weather
A negative NAO is associated with a net displacement of air from over the subtropical belt near _____ and ____ northward to the Arctic and Icelandic regions.
This mass displacement weakens the _____ and increases the variability of its location.
Also is weakens the ______ in the Atlantic, resulting in less intense ______ over the North Atlantic Ocean.
_____ often develop in the Atlantic Jet Stream pattern.
- The Azores and Iberian Peninsula
- Icelandic Low
- Subtropical High and westerlies.
- Blocking patterns
During a negative NAO, Arctic High Pressure is better developed in _____ and often invades into northern and central ____ when significant blocking patterns develop over the Atlantic. During this time, colder temperatures are observed over the _____ and _______.
- the polar regions
- Europe
- western Atlantic and Eastern US
A weaker subtropical high contributes to weaker _____ and ______ off the northwest coast of Africa. This keeps SSTs ____ over the tropical eastern atlantic.
-trade winds/upwelling/warmer
The link between El Nino in the tropical Pacific and the NAO, is ______.
relatively weak
Influences leading to NAO:
- Stochastic interaction between storms, climatological stationary eddies, and time-mean jet pattern
-Long-term stratospheric influences on the troposphere
A. volcanic ash =PNA
B. Ozone depletion=PNA
C. Greenhouse gas accum=PNA
-intensity and distribution of tropical convection
-long-term feedback from oceanic circulation patterns and sea ice changes
____ is the dominant pattern of non-seasonal SLP variations north of 20N, and it is characterized by SLP anomalies of one sign in the Arctic and anomalies of opposite sign centered in the mid-lat.
Arctic Oscillation (AO)
AO index = _______ - ______
(SLP Mid-Lat) - (SLP Arctic)
Positive (Warm) AO is associated with higher pressure in _____ and lower pressure _____.
This is often associated with:
-the mid-lat/near the north pole
A. Fast-Strong zonal flow of westerlies across the mid-lat
B. Mild winter weather in the US and Europe
C. Melting arctic sea ice
Negative (cold) AO is associated with higher pressure in _____ and lower pressure in ______.
This is often associated with:
-near the North Pole/the mid-lat
A. High lat blocking in the jet stream leading to greater meridional flow and weaker zonal flow of westerlies in the mid-lat
B. Severe cold winter weather in US and Europe
C. Expanding arctic seas ice
___ and ____ are highly unpredictable.
NAO and AO
______ is associated with a Rossby Wave pattern with centers of action over the North Pacific and over North America.
Pacific-North American (PNA) Pattern
A positive PNA is charcterized by:
A. low 500mb height anomalies over the norther Pacific and eastern North America/western Atlantic
B. High 500mb height anomalies over western North America
___________ is a long-lived El Nino-like pattern of Pacific climate variability.
The Pacific Decadal Oscillation (PDO)
The PDO index = _____ - _____
SST(east pacific) - SST(central Pacific)
PDO :Warm(Cold) Index periods contain ______-than-normal waters in the north central Pacific Ocean and _______-than-normal waters along the west coast of North America.
cooler(warmer)
warmer(cooler)
The two main differences between PDO and ENSO:
- PDO persists for 20-30 years while ENSO persists 6-18 months
- Climactic fingerprints of the PDO are most visible in the North Pacific/North American Sector with secondary signatures in the tropics. The opposite is true for ENSO.
Cool PDO regimes prevailed from _____, ______, and _______.
Warm PDO regimes prevailed from ____ and ____
(1890-1924, 1947-1976, 1999-now)
1925-1946 and 1977-1998
20th century PDO fluctuations were most energetic in two general periodicities:
15-25 years
50-70 years
The effects of PDO are most drastic in the _____. In this region :
A _____ generally correlates with dry conditions and warmer temperatures.
A _____ generally correlates with wet conditions and cooler temperatures.
Pacific Northwest
+PDO
-PDO
Warm eras in the PDO have seen enhanced _________ in Alaska and inhibited productivity off the west coast of the US.
The opposite is true for cold eras.
coastal ocean biological productivity
The Earth has shown no statistically significant warming in the last _____.
15-17 years
PDO was discovered in ___.
1997
What is the traditional method of making a weather forecast?
To take the best model available and run it until it loses it’s skill.
What causes a model to lose it’s skill?
Growth of small errors in the initial conditions.
Skill is typically lost after ____.
6 days or so.
An alternate method that produces forecasts with skill up to 15 days uses what is called ________.
Ensemble Forecasting
What is ensemble forecasting?
Utilizes many model runs with slightly different initial conditions. An Ensemble mean is created and is more likely to have more skill because it averages over the many possible initial states and smoothes the chaotic nature of climate.
The 0-hour forecast:
shows winds, pressures, moisture, and temperatures t multiple vertical levels in the atmosphere and at grid intersections of about 100km.
_______ provide the initial conditions for numerical models that integrate the equations of motion of the atmosphere forward in time to produce a forecast.
The 0-hour forecast.
Uncertainty in the initial conditions are attributed to :
Instrument error
Spatial/temporal sampling error
Lack of Data
First Guess Background Field
In order to sample more of the possible atmospheric states, NCEP makes:
many forecast runs of a model out to 15 days in which the initial conditions of the individual runs are slightly perturbed.
Between ________ numerical model runs are executed daily using slightly altered initial conditions. These model runs are known as ______.
12-30
The ensemble members
An example of a pressure perturbation:
P: [ (P + deltaP) or (P - deltaP) ]
Ensemble members can also be used to estimate______.
The probabilities of certain events.
The ensemble prediction approach attempts to define the ________.
Probability Density Function (PDF) of atmosphere variables.
NWP Process:
____->____->____->____->____
- Gather Obs
- Data Assimilation
- Numerical Weather Predictions
- Forecast Post-processing
- Issue forecasts, Evaluate
Two problems with Ensemble Predictions:
- Chaos
2. Model Error
Increasing smoothness in ensemble prediction reflects the fact that :
There is more uncertainty in the predictions at long lead times.
With ensemble prediction, a smoother damped wave pattern is sometimes caused by :
Troughs and Ridges being superimposed on one another from different ensemble members.
The two green lines added to spaghetti plots represent:
These change slightly every day and are based on :
The two climatological lines of 500mb height that correspond to the red and blue forecast lines.
30 years of global data
By comparing the high lat green line with the blue lines and the low lat green line with the red lines, one can :
Determine how far removed from climatology a particular region is observed of predicted to be.
If at the initial time the spread is small so that the distribution must be strongly peaked, there is ______ confidence about the current state of the atmosphere.
relatively high
As the forecast lead time increases, departures from climatology get _____ and the spread gets ____.
smaller
larger
At long lead times, the departures from climatology will become so minuscule that :
It will be no better than using climatology
_____ can systematically contaminate all the ensemble forecasts run on that model.
Individual Model Biases
A solution to Individual Model Biases is :
To generate ensembles from a cluster of different models.
The biggest contribution to Model Error is ______.
Parameterization
Examples of Parameterization
- Land surface characteristics and processes
- Cloud microphysics
- Turbulent diffusion and interactions with surface
- orographic drag
- radiative transfer
What is a Weather Analog?
A historical weather event which is very similar or closely parallel to the current event.
What is a current?
Movement of water in the main water bodies of the earth.
Conform to Continental Boundaries
What affects currents?
- cold and warm sources
- currents are modified by Coriolis
What role do currents play?
They contribute to the transport of warm water poleward and cold water equatorward.
List the 4 Atlantic Currents
- Gulf Stream Current
- North Atlantic Current
- Canary Current
- North Equatorial Current
What drives sub-surface currents?
- Upwelling/Downwelling
- sinking of cold and salty water/ rising of fresh and warm water.
Which local current creates a maximum in water temperature and is an important energy source for tropical storms?
The Gulf Stream Loop Current
Coastal winds contribute to ___.
Upwelling/Downwelling
Tides are effected by ___?
Lunar/Solar Effects
Ebb and Flood
Coastal water temperature changes caused by currents may lead to :
Low clouds/Fog
Convection
What are the three factors in wave formation?
Wind Strength
Fetch
Duration
Put the correct formation stage # next to each ocean wave formation stage:
__ Slight Ripples are pushed upward by wind.
__ Wave height increases based on speed and duration.
__ Microscopic capillary waves
2
3
1
______ of air creates potential energy in the water.
Kinetic Energy
Wave Height (H) =
.02*V^(2)
3 factors for wave energy transfer:
Wave Shape
Steepness
Wind Drag
Equation for Fetch to attain a fully developed sea (FDS) :
Fetch (nm) = 3.17xWind^(4/3)
Using wind in (kts)
Equation for Fetch for a Significant Wave Height (ft):
Fetch (nm) = 43*H^(2/3)
What error is there in the Fetch equations?
Assumption of a totally unperturbed sea
not useful for lakes or bays
The biggest waves for in (fast/slow) moving storms.
slow
Wind Duration Equation:
Time(hrs) = 6.4*Wind^(1/3) (kts)
Time = 12.3*H^(1/6)
Any water _____ is made up of several periodic waves.
perturbation
Significant Wave Height (Hs) :
in a fully developed sea
Hs (ft) = .02*Wind^2 (kts)
What is the most often-used wave forecasting parameter?
Significant Wave Height (allows mariners better prep)
What is the % probability of getting a wave twice as high as the Significant Wave Height ? (Rogue Waves)
1%
Wave Dispersion Speed Equation:
Speed = 1.34 SQRT(Length)
What happens is a wave height becomes 10% of the wave length?
it breaks
Wave Length Equation:
L = 0.15*Wind^(2)
Near shore waves break is H > ___ depth.
80%
Strong slow-moving lows, lows moving at certain speeds, currents with wave motion opposed, and waves breaking near land are all examples of :
Dangerous Wave Situations
Storm Speed = ?
Storm Speed = 0.6Wind = 0.5Wave Speed
What happens with wind opposing currents?
Water piles up much faster, wave heights build quickly, and waves become steep!
On a lake or bay waves happen (later/sooner) and grow (slower/faster).
sooner and faster
Wave Height on a Lake or Bay =
=0.020*Wind^(2) * (Fetch/Ffds)^(1/2)
=0.011* Wind^(4/3) * Fetch^(1/2)
On a Lake or Bay: Wind duration for fully developed waves is :
Time = Height
_____ form on sub surface density discontinuities and (increase/decrease) wave drag on surface ships.
Internal Waves
increase
Mean and Standard deviation of significant wave height and the wave period are based on 45 years of ____ and _____.
ship reports and wave model
True or False:
Wave Modeling solves spectral balance equations for wave frequencies for a number of propagation directions.
True
True or False:
Wave Modeling takes into account currents, refraction, breaking, and ice coverage.
True
True or False:
Wave Modeling does not have wave data assimilation but uses 12hr wave forecast from previous run.
True
How often do Wave Models run?
How far out is the lead time?
Every 6 hours
Out to 6 days
