Meteo 452 Final (Cumulative)
Explain key concepts and outcomes of Held-Hou model of the Hadley Cell
-Held-Hou model predicts basic aspects of Hadley Cell Assumptions: 1. 2-layer atmosphere 2. Frictionless upper-layer 3. Conservation of angular momentum 4. Thermal wind balance 5. Assume θ_E is known 6. Radiative heating equals radiative cooling across cell -Hadley cell strength defined as the difference between temperature with the Hadley cell (θ_m0) and equilibrium temp (θ_E0) at the equator -Equilibrium temp is the temperature achieved in the absence of a Hadley circulation -Zonal wind defined to increase with latitude (y) -Hadley cell extent (Y) directly proportional to potential temperature gradient -------- (from other card) -The Earth's surface moves faster than the atmosphere at the tropics. This creates a net momentum flux from the surface to the atmosphere at the tropics. -After getting to the upper-atmosphere, the air then travels poleward, conserving angular momentum. -When it reaches 30° latitude, it gets deflected to the right, due to the Coriolis force. The air then sinks dry adiabatically, ending up warmer than when it started. -Momentum in transferred from the atmosphere to the surface in the subtropics because the Earth's surface now moves slower than the atmosphere
Understand how convection changes the temperature and moisture profile
-In convective precipitation, heating is "bottom heavy" -In stratiform precipitation, heating is "top heavy"
Describe the difference between in-situ and remote sensing observations
-In-situ observations are taken by instruments that are in direct contact with the medium that they are "sensing" (Aircraft and satellites) -While dropsondes and flight level data are "in-situ", remote sensing observations utilize electromagnetic (or sound) waves to observe a medium not directly in contact with the instrument.
Understand the evolution and changes of the Walker circulation and Pacific Ocean during positive and negative phases of ENSO
-La nina keeps high 200mb vector winds even more confined to the west
Describe the characteristic weather patterns of the West African monsoon
-Larger precip amounts associated with larger θe (shifts north during summer months) -African Easterly Waves • Undulations of the AEJ form localized low-level vorticity maxima • Convection becomes organized into mesoscale convective complexes • African Easterly Waves propagate
Define latent heat and sensible heat
-Latent heat is associated with phase change associated with vapor flux -Sensible heat is energy required to change the temperature of a substance with no phase change
Describe the difference in energy sources
-Mid-latitudes energy comes from baroclinicity, or temperature gradients that gets converted to kinetic energy by thermally direct circulations. -Energy in the tropics arises from latent heating (barotropic), or evaporation over warm oceans, which feed moist convection release.
Explain sensible and latent heat fluxes in ocean-air exchange
-Ocean-air fluxes provide entropy input -Fluxes depend on wind speed and ocean-air temperature and moisture disequilibria -Re-entrant spray drops input sensible energy to TC -Spray droplets rapidly cool to equilibrium temperature, giving off sensible heat -Latent heat flux is of larger magnitude -Andreas et al. 2008: sensible and latent heat fluxes from spray -Andreas 2010: combined enthalpy flux from spray
Describe diurnal cycle of tropical convection
-Steeper upper-level lapse rates at night than during the day, due to radiational cooling -During the day, the sun heats up the upper-atmosphere, weakening upper-level lapse rates
Explain how conservation of angular momentum contributes to global circulation pattern
-The Earth's surface moves faster than the atmosphere at the tropics. This creates a net momentum flux from the surface to the atmosphere at the tropics. -After getting to the upper-atmosphere, the air then travels poleward, conserving angular momentum. -When it reaches 30° latitude, it gets deflected to the right, due to the Coriolis force. The air then sinks dry adiabatically, ending up warmer than when it started. -Momentum in transferred from the atmosphere to the surface in the subtropics because the Earth's surface now moves slower than the atmosphere
Explain the wind, moisture, pressure, and precipitation distribution of a neutral Walker circulation
-Trade winds bring moist surface air to the west -Moist air rises and becomes drier as it feeds rain -Dry air returns to the east, sinks as it cools -Lower pressure to the west, higher pressure to the east
Explain the subtropical jet using thermal wind balance argument
-Tropopause latitude decreases at the subtropical jet, due to the thermal wind balance -Decreasing potential temperatures with latitude leads to increasing vertical wind shear, due to the thermal wind balance
Explain the different types of satellite imagery used for observing TCs
-Visible band (~0.65 μm) -Infrared band (~3.75 μm, ~10.7 μm) -Water vapor band (~6.5 μm) • Water vapor imagery generally shows mid-tropospheric moisture -89 GHz Microwave band (0.33 cm) • Emission from large concentrations of ice hydrometeors in mid-to-upper levels • Distinguishes deep convection • Upward bound radiation penetrates cirrus canopies • Unable to see most low-level circulations -36 GHz Microwave band (0.83 cm) • Emission from low-level clouds and rain • Distinguish heavy rain and low-level circulations • Upward bound radiation unaffected by ice particles
Explain the role of sensible and latent heat fluxes
-Warm water powers tropical cyclones through entropy import and export
Describe the characteristic weather patterns of the South Asian monsoon
-Winds switch to westerlies in July -Largest rainfall amounts in south and east India
Identify regions where each balance is dominant and explain
-cyclostrophic: R₀>>1 or ≈4 -gradient: R₀≈1 -geostrophic: R₀<1
Explain inversion layers within Hadley cell
1. Air ascends in deep cumulus convection at the ITCZ. 2. Air slowly subsides as it cools due to net longwave radiation loss to space. 3. Trade wind inversion, moistened by trade cumuli. 4. Increase of low-level and mid-level moisture due to boundary layer fluxes.
Explain the necessary dynamic conditions for TC development
1. Location >5° latitude from the equator 2. Relatively weak vertical wind shear 3. Pre-existing enhanced low-level vorticity
Explain the necessary thermodynamic conditions for TC development
1. Warm sea surface temperature ( > ~26°C) 2. Conditionally unstable atmosphere 3. Sufficient mid-level moisture
Describe analogous processes in the TC secondary circulation
AB -> Isothermal Expansion -Adiabatic cooling offset by surface fluxes CD -> Isothermal Compression -Adiabatic warming offset by radiational cooling BC -> Adiabatic Expansion -Cooling partially offset by latent heat release DA -> Adiabatic Compression -Adiabatic warming
Describe processes of a Carnot heat engine
AB -> Isothermal Expansion CD -> Isothermal Compression BC -> Adiabatic Expansion DA -> Adiabatic Compression
Define the El Niño/Southern Oscillation (ENSO)
An irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting much of the tropics and subtropics. The warming phase is known as El Niño and the cooling phase as La Niña. Southern Oscillation is the accompanying atmospheric component, coupled with the sea temperature change: El Niño is accompanied with high, and La Niña with low air surface pressure in the tropical western Pacific. The two periods last several months each (typically occurring every few years) and their effects vary in intensity. The two phases relate to the Walker circulation, discovered by Gilbert Walker during the early twentieth century. The Walker circulation is caused by the pressure gradient force that results from a high pressure system over the eastern Pacific Ocean, and a low pressure system over Indonesia. When the Walker circulation weakens or reverses, an El Niño results, causing the ocean surface to be warmer than average, as upwelling of cold water occurs less or not at all. An especially strong Walker circulation causes a La Niña, resulting in cooler ocean temperatures due to increased upwelling. Mechanisms that cause the oscillation remain under study. The extremes of this climate pattern's oscillations cause extreme weather (such as floods and droughts) in many regions of the world. Developing countries dependent upon agriculture and fishing, particularly those bordering the Pacific Ocean, are the most affected. Warm phase - El Niño • Lower pressures in central Pacific, higher pressures over western Pacific • Weaker easterly trade winds, presence of equatorial westerlies • Warmer waters across central and eastern Pacific Cold phase - La Niña • Lower pressures in western Pacific, higher pressures over central Pacific • Stronger easterly trade winds • Cooler waters across central and eastern Pacific
Define Mesoscale Convective Systems (MCSs)
Bands of zones of clouds and precip about 100km or larger which are generated by interacting convective cells (hot towers). These produce much of the precip in the tropics.
Explain difference between convective and stratiform precipitation
Convective Precip: localized, small scale, vigorous updrafts and downdrafts, intense precip & newer active convection. Stratiform Precip: older, less active convection, broad homogeneous precip, weaker vertical velocities, and cooling at melting level (cooling air more dense & produces downdrafts).
Define cyclostrophic, gradient wind, and geostrophic balance
Gradient Wind Balance: Centrifugal + Coriolis = Pressure Gradient Centrifugal: v²/r Coriolis: fv PGF: 1/ρ ∂p/∂r
Describe the temperature and equivalent potential temperature structure
Highest T at 600mb and 250mb in temperature anomaly, max when r is 0 and decreases as r increases
Define hot towers and explain the role of entrainment in hot tower growth
Hot Towers: tall tropical cumulonimbus clouds. Warm high-θe air bubbles rising from boundary layer to tropopause. Role of Entrainment: dry environmental air drawn into the rising bubble of high-θe air.
Define statistical, dynamical, ensemble, and consensus forecast models
I. Statistical models A. CLIPER (Climatology-Persistance) -Exploits historical relationships between storm motion and storm descriptors -Used as a benchmark: A forecast is "skillful" if it has lower mean track errors than CLIPER B. SHIPS (Statistical Hurricane Intensity Prediction Scheme) -Exploits historical relationships (multiple linear regression) between storm intensity and storm descriptors obtained from dynamical models and satellite data -Predictors include: • Climatology and persistence • Atmospheric environmental parameters (e.g. wind shear) • Ocean information (e.g. SST) -Often outperforms all other numerical models II. Dynamical models ---complex codes that use numerical approximations of the dynamic equations, in turn representing physical processes at all modeled locations and times a. Global models solve the governing equations over the whole globe (GFS, UKMet, NAVGEM, ECMWF) • Have no lateral boundary conditions • Most skillful at forecasting track • Performs well at long lead times • Are becoming useful for forecasting TC size and outer wind structure • Inadequate resolution to define the TC inner core (eye and eyewall structure, radius of maximum wind, etc.) or to capture intensity *Grid point model: • Gridboxes represent volume averages of the major physical variables • These are used to parameterize other atmospheric properties we can't resolve • Rain and cloud water drops, CCNs, dust, turbulent eddies, etc. b. Regional models solve the equations centered on the tropical cyclone (HWRF, GFDL, NAMM) • Are capable of representing inner core structure and intensity change • Models with higher resolution grids are "nested" within lower resolution grids of global models • Highest resolution grid follows the storm center • Performance degrades at longer lead times III. Ensamble Models -An ensemble is a set of dynamical model forecasts run with perturbed initial conditions, unlike a single "deterministic" run -Perturbed initial conditions represent uncertainty in the initial analysis -Model physics is the same for each ensemble member [so model is effectively assumed to be perfect, with forecast error deriving from initial analysis errors] -The average of all the ensemble member forecasts is the ensemble mean -Average distance of all forecasts from the ensemble mean is the ensemble spread IV. Consensus forecast models -Average of forecasts from multiple models is referred to as a consensus forecast -The forecasts from the various member models differ due to differences in both model initialization and model physics
Understand the environmental steering layer
I. Steering flow is primarily an average of 850-200 mb winds -500 mb winds are a good approximation of layer flow II. Steering layer depends on storm strength -Weaker storms have shallower steering layers -Stronger storms have deeper steering layers
Understand slantwise moist symmetric neutrality in the eyewall cloud
-Air parcel is neutral to buoyant or radial forces along the slantwise trajectories (m is absolute angular momentum) m1<m2<m3 θes1>θes2>θes3 I. If parcel moves up or left -mp>m1 so vp>v1, no longer in gradient wind balance, cont+cf are too large and act to accelerate parcel radially outward. -θesp<θes1, negatively buoyant downward acceleration II. If parcel moves down or right -mp<m3 so vp<v3, pgf too large, inward acceleration -θesp>θes3, positively buoyant upward acceleration -No matter where parcel is moved, it returns to its initial slantwise line, except for slantwise motions
Identify the most used metrics for monitoring ENSO
-Also Southern Oscillation Index (SOI)
Understand how temperature changes affect the buoyancy and saturation point of an air parcel
-As T rises, es rises (clausius), more evap -> more vapor, then get more condenstation -Parcel does work until e=es(T) -Higher T diff with env favors stronger buoyancy force since buoyancy is proportional to density differences
Understand processes of heat transport from tropics to higher latitudes
-Atmosphere and ocean are primary agents for earth's heat transport -Ocean heat transport peaks in the tropics -Primarily driven by warm currents along eastern continental shores -Atmosphere heat transport peaks in the mid-latitudes -Begins with latent heat flux from ocean surface to the atmosphere in the tropics -Ends with Hadley cell convection and/or baroclinic mixing -Intense solar radiative heating near equator creates belt of surface low pressure -Low-level moist air converges and rises at the Inter-tropical Convergence Zone (ITCZ) -Upper-level air returns to higher latitudes and subsides to create surface high pressure -Near the equator, moist air rises along moist adiabats -Traveling poleward, air cools by emitting longwave radiation -Around 30° latitude, air subsides along dry adiabats -Subtropical surface air warmer than initial tropical surface air (latent heat converted to sensible heat)
Describe the impact of ENSO on the Pacific midlatitude jet stream and on TCs globally
-El Nino extends Pacific midlatitude jet stream and amplifies storm tracks
Describe distribution and characteristics of incoming solar radiation and outgoing longwave radiation
-Energy surplus in tropics -Energy deficit at higher latitudes -For the earth to achieve radiative balance, heat must be transported away from the tropics and towards the poles.
Explain the Beta effect and the Fujiwhara effect
-Govern TC motion -TC circulation, combined with variation in the Coriolis parameter induces a wavenumber-1 asymmetry. -The vortex circulation advects lower (higher) planetary vorticity northward (southward) on the east (west) side of the storm. -β-gyres are produced around vorticity maximum and minimum. -β-gyres induce an additional steering flow across the TC (β-drift). -relative vorticity minimum northeast of storm, maximum southwest of storm, opposite in southern hemisphere. -see vorticity equation -Fujiwhara effect has to do with the interaction between two or more vortices
Define and explain Maximum Potential Intensity
The maximum intensity a TC can achieve is related to the efficiency (E; the thermal disequilibrium) multiplied times the ratio of two empirical coefficients (enthalpy and drag) Uses of MPI: -Calculates maximum intensity a TC can achieve from SST and environmental conditions -Comparison against observed TC intensity -As an upper-limit in statistical forecast models -Studying effects of climate change on TC intensity
Describe the primary circulation
The primary circulation encompasses the tangential winds moving cyclonically around the surface low pressure. The winds are highest near the center of the low and decrease with height. They become anti-cyclonic at troposphere.
Define the TC boundary layer
The region closest to the ocean where the transfer of sensible and latent heat occur. In intense hurricane conditions, the sharp ocean-air boundary disappears. In-situ measurements of the TC boundary and surface layer are at best...challenging.
Describe the secondary circulation
The secondary circulation encompasses the radial motion inward toward the center of the storm, and the rising motions that occur throughout the storms. This air sinks typically 4-6 degrees of latitude away from the center.
Understand the differences between global and regional dynamical models
a. Global models solve the governing equations over the whole globe (GFS, UKMet, NAVGEM, ECMWF) • Have no lateral boundary conditions • Most skillful at forecasting track • Performs well at long lead times • Are becoming useful for forecasting TC size and outer wind structure • Inadequate resolution to define the TC inner core (eye and eyewall structure, radius of maximum wind, etc.) or to capture intensity *Grid point model: • Gridboxes represent volume averages of the major physical variables • These are used to parameterize other atmospheric properties we can't resolve • Rain and cloud water drops, CCNs, dust, turbulent eddies, etc. b. Regional models solve the equations centered on the tropical cyclone (HWRF, GFDL, NAMM) • Are capable of representing inner core structure and intensity change • Models with higher resolution grids are "nested" within lower resolution grids of global models • Highest resolution grid follows the storm center • Performance degrades at longer lead times
Define vapor pressure, saturation vapor pressure, mixing ratio, saturation mixing ratio
e=ambient vapor pressure es=vapor pressure of a saturated environment (pressure of vapor in equilibrium with liquid form, maximum at a given temperature) w=amount of water vapor in the air ws=theoretical maximum amount of water vapor that air can hold at a specific temperature and pressure
Define the LCL, LFC, and Equilibrium Level
e=es(T) at LFC, bottom of cape, EL is at top of cape, LCL is cloud base
Thermal Wind Balance
relates horizontal temp grad (horizontal gradient of layer thickness) to vertical gradient of geostrophic wind, applies to jets.
Describe conditions of stability, instability, and conditional instability
γ<Γm, Absolutely stable γ=Γm, Saturated neutral Γm<γ<Γd, Conditionally unstable γ=Γd, Dry neutral γ>Γd, Absolutely unstable
Understand potential temperature, equivalent potential temperature, and saturation equivalent potential temperature
θ: T parcel would have if parcel adiabatically brought back down/compressed to 1000hPa θe: θ that parcel would have if all moisture condensed out, describes T+moisture of air, conserved for adiabatic θes: θ that SATURATED parcel would have if all moisture condensed out, conserved if no entrainment
Describe the wind, pressure, and precipitation characteristics of the MJO
• The MJO is a region of lower pressure, low- level convergence, and convection. • The convection propagates eastward and dissipates over the central Pacific. • As convection approaches, easterly (westerly) winds are enhanced at the low levels (upper levels). • Associated with the convection and after convection passes are enhanced westerly (easterly) anomalies at the low levels (upper levels). • Anomalous Cyclonic and Anticyclonic regions occur at both low and upper levels • The circulation circumnavigates the globe in 40-50 days. • The low-level signal weakens as it moves into the Western Hemisphere. • The upper-level signal remains notable.
Define the ITCZ and Tropical Tropopause Layer
ITCZ: area of low level converging air, area of surface low pressure due to intense solar radiative heating near equator. TTL: transition zone between troposphere and stratosphere. Convective tropopause (10-14km): point where lapse rates increase just beyond moist adiabat. Cold point tropopause (16-17km): point where lapse rate becomes zero or near zero.
Define inertial stability and explain its importance and distribution
Inertial stability is the measure of resistance of a vortex to external forcings (resistance to radial flow) -Storm contracts -> more I² -Upper-level anticyclone -> less I² Increases poleward and towards storm center
Define angular momentum and explain angular momentum distribution
M = earth relative + planetary -Conserved quantity of a rotating body -Increases radially, decreases with height
Define Moist Static Energy
MSE=Lᵥw+gz+cpT Latent Heat + Gravitational Potential + Sensible Heat
Distinguish between tropical and mid-latitude cyclones
Mid-latitude Cyclones: -Low-pressure rotating systems in the mid-latitudes -Extracts energy from temperature gradients -Cold core low ideally tilted with height -Generally 1500-5000 km in diameter Tropical Cyclones: -Low-pressure rotating systems in the tropics -Extracts energy from warm ocean water -Warm core low ideally vertically upright -Generally 200-800 km in diameter
Define potential vorticity
PV: the absolute circulation of an air parcel that is enclosed between two isentropic surfaces.
Explain how potential vorticity changes in convective and stratiform precipitation
Potential vorticity is directly proportional to heating rates which is connected to vertical velocity. As vertical velocity increases, the potential vorticity increases. In convective precip, heating is "bottom heavy" and in stratiform precip, heating is "top heavy".