Tropical Weather & Forecasting Final Exam
convective scale:
-1 km -minutes to hours -tornado, dust storm, lightning
mesoscale
-100 km -hours to days -MCCS, mountain and lake disturbances
synoptic
-1000 km -days to weeks -fronts and TC's
planetary
-10000 km -months to years -AMO, NAO, MJO, etc.
what is the TAFB warning area?
-37-95W and 7-31N
how do CCKWs influence AEWs
-CCKWs impact environmental like moisture, wind shear -can enhance AEWs and modify their convection -tropical cyclogenesis is favored in the 2-3 days following convectively active phase
radiation feedback mechanism
-Deep clouds absorb IR -Warmer than surroundings -Warmer clouds enhance overturning circulation Strengthens -More convection means more deep clouds -Causes a feedback loop
what is ENSO and what is it characterized by?
-El Niño southern oscillation -characterized by SST and pressure anomalies in the pacific
ENSO and the tropics:
-La Niña increases Atlantic hurricane activity and vice versa
deep convection:
-Strong precipitation/thunder/lightning, extends well above freezing level, anvils of ice crystals -strong updrafts and downdrafts
what does a negative NAO mean?
-above normal heights and pressure across high latitudes -below normal heights and pressures across low latitudes in the Central North atlantic -cooler winter in the USA -more northern Azores high --> more tracks recurving in the Western North Atlantic
passive vs. active sensors
-active sensors send out pulses to be reflected, absorbed or transmitted by the atmosphere -passive sensors receive emissions from constituents in earth's atmosphere
phases of the MJO
-active: lots of convection, divergence aloft, upward motion and convergence, stormy and wet -suppressed: more sinking motion and subsidence, generally dry and sunny
what is an equatorial wave and what can they do?
-atmospheric oscillations that are confined to the equator due to the Coriolis force and its change with latitude -they can influence global circulation, organize equatorial precipitation, interact with other waves and modulate TC formation and intensification
project STORMFURY and findings
-attempted to weaken a hurricane -didn't work --> proved that second eyeballs are already common in hurricanes and seeding in hurricanes does not work well because hurricanes contain a lot of natural ice and very little supercooled water
what does a positive NAO mean?
-below normal heights and pressures across high latitudes -above normal heights and pressures across low latitudes in the Central North Atlantic -warmer winter in the USA -more southern Azores high --> more zonal TC tracks into the Gulf of Mexico
microwave imagery
-can penetrate through clouds, can show PWAT, brightness temperatures, SST and wind speeds (scatterometer)
MJO and its impacts on TC
-convectively enhanced phase of MJO increases TC activity in the Indian Ocean, Australian, NW and NE Pacific Basins
what is an offshore waters forecast?
-designed for mariners -warnings are issues for conditions up to 48 hours from issuance time
maximum potential intensity
-difference in temperatures near the surface and at the outflow
what happens to a TC at landfall
-differences between land and ocean -friction causes a spin down -dry air near the surface intrudes the TC circulation -decrease in surface evaporation rate and condensational heating
limitations of SLOSH
-doesn't include normal river flow and rain -breaking waves
dynamical vs. statistical models
-dynamic: use equations of fluid dynamics and physics of the atmosphere -statistical: use parameters based on intensity change to make numerical predictions
walker circulation
-easterly trade winds on either side of the ITCZ -increased over the western pacific "warm pool" -depth of warm waters much greater over the warm pool (deep thermocline) on the west
what is the madden Julian oscillation
-eastward moving anomalies of precipitation and westerly wind -traverse the planet in the tropics -intraseasonal -period is 30-60 days
what are convectively couples kelvin waves?
-enourage or suppress convection with vertical motion -convection interacts with waves in complicated ways which is why they are called convectively coupled
ET process
-erosion of warm core -inner core loses symmetry -asymmetries increase in the area -fronts develop -increase in forward motion
fast intensification
-favorable environmental conditions -vortex alignment -well defined inner core -axisymmetric convection and precipitation -more convective bursts -strong upper level outflow
cone of uncertainty:
-forecasters examine the latest model forecasts and make a track prediction for 120 hours -circles are then drawn representing the 67th percentile of all NHC track errors in the past 5 years and then tangent lines of the circle are drawn which reveal the cone
difference between geostationary and low earth orbit satellites:
-geostationary monitors a limited area -low earth orbits have high resolution coverage each day but only goes to the same location twice a day
(dynamical) global vs. regional model
-global: coarse resolution, parameterized physics such as clouds -regional: higher resolution, resolving clouds and thunderstorms
primary circulation in a tc
-gradient wind balance -PGF= CoF + CeF
cold clouds
-ice crystals and supercooled water droplets -ice nucleation is hard -growth through condensation -ice crystals grow faster than water droplets
secondary circulation in a tc
-in-up-out -thermal wind balance -winds change sharply with height -warm core means wind speeds increase as you go down the TC
impacts of clouds on radiation
-infrared is long; from ground it can be reflected back or absorbed or escape -visible is short (sun); can be reflected or absorbed through -infrared from surface; most gets absorbed
infrared and its drawbacks
-infrared measures the brightness temperature of clouds (cold and high are colorful) -drawback because it can't penetrate through clouds
factors that affect storm surge:
-intensity (stronger=more surge) -size (larger=more surge) -forward speed (slower storm= surge further inland) -angle of approach -width and slope of shelf (gradual shelf slope = more surge)
phase transition between la nina and el nino
-la nina to el nino is faster than El Niño to la nina because easterly trades need to re establish and drive upwelling off the S American coast for the second transition
MEOWs
-maximum envelope of water -shows the max. storm surge for all simulations for a given parameter -used as guidance for planning and operations
MOMs
-maximum of the meows -used to design evacuation zones and when uncertainty is high
oceanic nino index
-measures ENSO by averaging SST in regions -values > +0.5 mean el nino -values < -0.5 mean La Niña
diurnal cycle and its impact on tropical cyclones:
-more convection is observed at night because high clouds in a TC radiate out energy which cools the layer of clouds below and makes the atmosphere more unstable for convection -less convection is observed during the day because high clouds absorb radiation which causes the top layer to warm making the atmospheric column more stable
hovmoller diagram
-moves eastward and down so arrows point diagonal -green: above average rainfall -brown: below average rainfall
SLOSH forecast model (sea, land, and overland surges from hurricanes)
-numerical model used to estimate storm surge heights for historical, hypothetical or predicted hurricanes -includes: flow through barriers/gaps/passes and overtopping of levees, tides and inland inundation
RMM Index of 8 Phases:
-phases 1 and 2 have the most TC formations, most RI cases and highest level of accumulated cyclone energy (ACE) -phases 1-3 are negative and have lower shear than normal
classical criteria for monsoons:
-prevailing wind shifts greater than 120 degrees between January and July -average frequency of prevailing wind is greater than 40% -speed of mean wind exceeds 3 m/s -pressure patterns satisfy a steadiness criterion
what is a high seas forecast?
-primarily for winds 25 knots or greater and/or seas 8 feet or higher -high seas forecast is a text forecast issued primarily for large ocean going vessels
p surge
-probabilistic storm surge -accounts for uncertainty -probabilities based on NHC official advisory
potential storm surge flooding
-provides risk assessment for decision makers -shows height above ground that the water could reach -depicts the reasonable worst case scenario at any individual location -shows inundation levels that have a 10% chance of being exceeded
visible imagery
-radiation from the sun that is reflected from Earth and clouds -large thick clouds are white -thinner clouds are gray
TC decay
-reverse WISHE -decrease in intensity -reduced heat and moisture fluxes
Carnot engine
-reversible thermodynamic process that converts heat into work -heat added from ocean, rising air and condensation of water vapor, air loses energy through radiation back to space, air brought back down to starting point
what is the NAO?
-sea level pressure difference between subtropical (Azores) high and the sub polar low
asymmetrization
-storm loses symmetry due to shear -strongest updrafts downshear side of eye
southern oscillation
-strength of easterly trade winds modulated by "swings" of mass/pressure across basin -higher pressure in east means stronger easterlies -higher pressure in west means weaker easterlies
what are the scales of airborne sampling?
-synoptic: variation in moisture content -vortex: highest rain in eyewall & mostly convective, lighter rain in areas outside eyewall -microscale: ice pellets and snowflakes
warm clouds
-temperature above freezing throughout -cloud droplet nucleation -droplets grow through condensation -droplets grow by collision coalescence and become heavy then fall out
characteristics of CCKWs
-travel eastward and faster/smaller than MJO -defined by their impacts on convection (active/suppressed) -use 200 hPa or OLR to visualize
what is the difference between the tropics and mid latitudes?
-tropics: weak CF, PGF weak, small temp contrasts higher tropopause -mid latitudes: strong CF, PGF strong, strong temperature and density gradients, lower tropopause
slow intensification:
-unfavorable environmental conditions -vortex misalignment -poorly defined inner core -asymmetric convection
what is the Atlantic Multidecadal oscillation?
-variability of SST over decades -it is positive when there is higher SST meaning more TCs
WISHE
-warm core builds due to condensation of water vapor -central pressure drops, which increases the radial pressure gradient -making stronger tangential winds intensify, enhancing more water vapor exchange from the ocean. -heat and moisture induces stronger inflow and updrafts
la nina
-warm pool and convection is concentrated in the west -cooler SST in the east pacific -thermocline sloped across the pacific increases --> increased upwelling along the South American coast
difference between a watch and warning
-watch: the POSSIBILITY of life-threatening inundation within 48 hours -warning: the DANGER of life-threatening inundation generally within 36 hours
ventilation
-weakens the TC by how shear injects dry air into the core at mid levels
El Nino
-weaker easterlies so warm pool spreads out -warmer SST in East Pacific -increases surface convergence over the central and eastern parts of the basin, hence, increasing precipitation -thermocline depth shoals in west and deepens in east
rapid intensification
-when a hurricane strengthens at least 30 knots in 24 hours -almost half of all tropical cyclone's are undergoing RI when they begin an eyewall replacement cycle
how can we measure ENSO by the atmosphere?
-when its positive, there is higher pressure over Tahiti, meaning stronger Easterlies -when its negative, there is higher pressure over Darwin, meaning weaker Easterlies
what are theoretical dry kelvin waves?
-without moisture, they would just be areas of zonal winds propagating along the equator on one single level only -in the vertical motion, there are regions of rising motion and the zonal winds are in different directions near the surface versus high in the troposphere
what is needed for a tropical cyclone to develop?
1. high instability 2. high humidity 3. vorticity 4. Substantial potential intensity 5. low vertical wind shear 6. divergence aloft
favorable conditions for intensification
1. warm ocean 2. low vertical wind shear 3. moist middle troposphere 4. Vorticity 5. upper level divergence
what triggers tropical cyclone genesis?
African easterly waves (AEWs)
CISK intensification process theory
Frictional convergence of warm, moist air into center fuels latent heat release
Caribbean peak of storms
October
definition of a tropical cyclone
a warm core non frontal synoptic scale cyclone, originating over subtropical or tropical waters, with organized deep convection and a closed surface wind circulation about a well defined center
vertical wind shear:
any change in wind speed and direction with height
what is significant wave height?
average of the highest 1/3 of waves
tropical weather outlook
based on deterministic and ensemble model predictions of whether a tropical cyclone will form
why doesn't the North American monsoon meet the criteria for monsoons?
because there is no opposite wind shift in the winter
what causes a warm core?
condensational heating
what are tidal datums
different levels as to which the tide is labeled
structure of tropical cyclones
eyewall slopes radially outward, eye has hot dry air above and warm moist air below which creates an inversion at the top boundary layer
aircraft wind probes
flight level measurements ONLY
how do different satellites work
for the GOES-16 geostationary satellite, there is an an advanced baseline imager instrument used for imaging Earth's weather, oceans and environment
APHEX Goals
forecast nowcast research
causes for monsoons
fundamental mechanisms: -the seasonal heating in the summer hemisphere, equatorial trough and the ITCZ change -differential heating between the land and ocean creates pressure gradient -the swirl introduced to the winds by the rotation of the Earth -moist processes and convection
wind speed probabilities
graphic of probabilities show the chances that winds exceeding the value shown
MHHW
mean higher high water
MLLW
mean lower low water
MSL
mean sea level
dropsondes
measure a orofile of winds, temperature, moisture and pressure
what is the radiation budget for the tropics and mid latitudes?
more radiation in tropics and less in mid latitudes
tail doppler radar
needs ice and rain for measurements and takes measurements
Atlantic peak of storms:
peak in mid early September
storm surge
rise of water generated by a storm, over and above the predicted tide
stepped frequency microwave radiometer (SFMR)
surface wind speeds ONLY
convection:
upward motion due to an air parcel being more buoyant than its environment
what is the structure of the tropical atmosphere?
vertical: temperature and wind changes with height horizontal: SST, wind, pressure, precipitation
storm tide
water level due to storm surge and the astronomical tide
what is extratropical transition
when a tropical cyclone moves into the mid latitudes and transforms into an extratropical cyclone which increases forward motion with heavy rainfall and strong winds remaining
how are wind shear vectors written?
with a (westerly component, southerly component) and easter/northerly is negative
