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isotach
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lines of equal WIND SPEED
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What balances out the vertical pressure gradient force?
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Gravity
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positive jet axis tilt
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*weak/neutral cyclone development
*small/neutral vorticity advection
*upper air cannot support storm development
*yields calm weather and weak vorticity advection
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Do shortwaves move faster than longwaves?
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Yes
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What is advection?
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When atmospheric properties are transported horizontally by the wind. Calculation of advection can be easily done for processes represented by isopleths. If isopleths move due to another process (i.e. surface heating), it is NOT advection. Positve advection contributes to the local increase in the advected quantity. The local change is entirely due to advection. Local change= horizontal + vertical advection. Advections are scalar, only the wind in the expression has direction.
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stretched vorticity
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decreases shearing effects in the atmosphere
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frontal inversion
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dew point temperature mimics temp profile
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What is sounding capability?
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Provides hourly, 19-channel operational soundings from geostationary altitude.
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When temperature decreases, what does relative humidity do?
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It increases
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More sophisticated treatment of the past weather can produce what?
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Statistical forecast
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What is geostrophic wind determined by?
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The height field
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What is the ratio of cyclones to anticyclones?
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1.8
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overshooting
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another CIN region above the EL where a parcel keeps traveling upwards --> indicative of very strong updrafts
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When winds diverge, what possible signature is happening?
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A mesocyclone signature
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What satellite imagery can't you use at night?
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Visible imagery
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How does a radiosonde measure wind speed and direction?
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A GPS
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Where are warmer cloud tops found?
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At lower levels
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What state is the atmosphere often in?
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Conditionally unstable
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What is geostrophic divergence?
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Evaluation of -∇*V ⃗ depends entirely on an estimation of the ageostrophic wind. The real wind is the sum of the geostrophic and the ageostrophic wind. Divergence due to the geostrophic wind alone is very small, due only to variation in f (the coriolis parameter) from south to north (f increases from South to North). Vertical motion is present in the atmosphere only if the flow is ageostrophic.
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What equation is derived from the hydrostatic equation?
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The hypsometric equation
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What causes an occlusion?
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The narrowing of the warm sector
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What satellite imagery can you usually see deformation taking place?
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Water vapor imagery
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How are observations transmitted?
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Through phone lines or satellite relays
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What can be converted to point upwards to measure wind speed and direction up to 16 km?
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Doppler radar
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What are keys to upper level development?
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Postion of shortwaves
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What type of data is usually wrong with extreme conditions, like heat waves etc.?
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MOS data
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Where is the greatest temperature contrast?
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Along the frontal zone
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What can measure the speed of winds toward and away from the radar by measuring the movement of particles?
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Doppler radar
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What is dilation (stretching)?
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Clouds will stretch, will spread out along this axis. Confluence is along the axis of dilation.
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What are the two most important things for an ageostrophic wind?
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Magnitude and current
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If the lines are heights, the arrows represent what?
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The geostrophic wind
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What is contraction (shrinking)?
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Clouds will shrink and contract along this axis. Diffluence is along the axis of contraction.
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What is vorticity?
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A measure of "spin" in the atmosphere. The spin moves around in the fluid atmosphere. Positive value= cyclonic (counterclockwise) and negative value= anticyclonic (clockwise).
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What is kinematic frontogenesis?
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There is no relationship between the isotherm deformation and the v component of the wind responsible for compressing the isotherms- in reality there is a feedback between the two. Fronts can double their intensity in a matter of several hours; kinematic frontogenesis suggests that it takes on the order of a day.
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Uses of Skew T Diagrams
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1. Air masses
2. Cloud layers
3. precipitation types
4. stability
5. vertical structure (location of "spheres"
6. non thermoddynamic propertis (like winds and jetstream)
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What is ground data processing system?
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Provides efficient dissemination data and products to users.
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What type of air mass is maritime tropical (mT)?
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Warm and moist
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Why is rawinsonde drift important?
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Data Assimilations Systems assume that there is no drift and the ascent is instantaneous. Given the resolution of today's models and satellite observing systems, rawinsonde drift may now have a greater impact. Errors are highly correlated between neighboring launch stations due to strong synoptic dependency. This would result in a structured error pattern.
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What type of air mass is continental tropical (cT)?
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Hot and dry
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What model should you look at first?
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GFS- Global Forecast System
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What is the Doppler dilemma?
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Combining the two previous equations gives the following. The speed of light and the radar wavelength are fixed. Thus there exists a trade off between the maximum range and the maximum velocity. There are some ways of dealing with this - varying the PRF from pulse to pulse, post-processing algorithms, but both types of folding appear often enough that we must know about them. V_max R_max=cλ/8
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What is remote sensing?
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The instrument is measuring the state of the variable at a location other than that of the instrument.
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What is Doppler velocity?
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The distance to target has changed from times T1 to T2, resulting in a phase shift between the two return signals, which Doppler radars are capable of measuring. By knowing the phase shift, the wavelength and the time interval from T1 toT2, the velocity the target has moved toward or away from the radar can be computed. If the target is moving sideways so that its distance relative to the radar does not change, the radar will record zero radial velocity for that target.
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What is channel 2 imagery?
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Responds to both emitted terrestrial radiation and reflected solar radiation.
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What type of front has a higher chance of producing bad weather?
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Cold front
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What is the most basic way to measure humidity?
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Sling psychrometer
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What is the Trend Method?
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Weather systems won't change movement or direction unless something impacts them to do so.
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How accurate is model forecasting?
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On average models predict reasonably well 4 to 6 days out, meaning they will at least mimic the overall pattern. Accurate forecasts of sensible weather are still only good 2 days out.
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Why do the winds blow?
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Because there is a horizontal pressure gradient force.
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If the lines are isotherms, the arrows represent what?
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The geostrophic wind shear.
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What is cold, dry flow?
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Most cold air entering system comes from the west (at G&H)—a deeper layer. Air is dry—history of descent, perhaps in a tropopause fold—might be rising as it approaches the cold front. May have a "split front".
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Why does kinematic frontogenesis fail?
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Because temperature is treated as a passive scalar. As the thermal gradient changes the thermal wind balance is upset,therefore there is a continual readjustment of the winds in the vertical in an attempt to re-establish geostrophic balance.
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When are cyclones and anticyclones more numerous?
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January. In general, cyclones and anticyclones are more numerous, more intense, and displaced further south in January than in July.
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What are numerical weather prediction models?
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They are mathematical models. Dozens of mathematical equations that describe how temperature, pressure, winds, and moisture will change with time.
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What do clouds at all levels have the same of?
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The same albedo
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How are the weather models different?
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The way the models represent atmospheric processes or in the distance between grid points.
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What is the atmospheric window?
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The atmosphere absorbs no radiation in these windows- all radiation from the earth and the atmosphere reaches the satellite.
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What happens to the beam as the scan gets higher?
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It gets smaller
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What imagery is the number one tool in synoptic meteorology?
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Water vapor imagery
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How is infrared imagery useful?
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Radiation at this wavelength is not absorbed by atmospheric gases. Se we "see" the actual temperature of the object we are viewing- cloud, land, water, which is used to determine cloud top heights, ID of cloud top features, tracking synoptic and mesoscale features at night. Useful in conjunction with water vapor. Infrared shows cloud movement at all levels, water vapor shows cloud movement at upper levels.
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When do we use the GFS model?
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To start the NAM model.
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What are two precipitation processes?
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Curvature and solute effect and the Bergeron process
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What is a frontal boundary?
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The boundary between two different air masses
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What does this model do?
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It helps us fill in the gaps.
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How is advection different than divergence?
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It is nearly impossible to evaluate the amount of divergence by eye.
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Why is the wind approximately geostrophic in the first place?
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If the flow is stationary, no accelerations are present, and the wind is equal to the geostrophic wind. If accelerations are present, the wind will not be exactly geostrophic. But for the large-scale flow aloft (no friction and synoptic scale motions on the order of 2000 km), accelerations will be very small. So we can assume that large scale motions are approximately geostrophic.
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What are the units for potential vorticity?
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PVU (potential vorticity units), 1 PVU= 10^-6 m^2 s^-1 K kg^-1
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If the geostrophic wind speed is proportional to the height gradient then the geostrophic wind shear is proportional to what?
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The horizontal gradient of the vertical derivative of height.
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If we assume ∂z/∂p≈∆z/∆p then ∆z=-RT/pg ∆p which would be used for what?
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To calculate the thickness of a given layer.
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Where is a katatfront type cold front found?
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Downstream from mid-level diffluent troughs.
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What is the frontogenesis function dependent on?
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The changes in the parcel perceived temperature gradient, which is not necessarily the changes in the frontal temperature gradient. Really need to know the front relative flow to determine which and how parcels are interacting with the imposed thermal gradient- difficult to measure.
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How is frontolysis related to total deformation?
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The wind separates isotherms as cos(>90) is negative.
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What do we use to provide info on the movement of the air when there are no clouds present?
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Water vapor imagery
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What is ensemble forecasting and how does it hurt and help us?
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This approach runs several models, each with slightly different initial conditions. If the forecasts out to 24 hours agree, there is greater confidence in the forecasts- this particular weather situation is more predictable. The less agreement among the forecasts, the less predictable the weather.
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What is the ninth key to meteorology?
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Moisture, lift, and instability are needed for significant precipitation; no one is more important than the other.
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What will divergence aloft lead to?
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A net removal of molecules in the column, and rising motion below, in the absence of compensating convergence at lower levels.
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What does the hypsometric equation represent?
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The distance (in m) between 2 pressure surfaces will be proportional to the average temperature in the layer.
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What are the tracks of cyclones and anticyclones dictated by?
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The long term radiation balance, land/water distributions, and orographic features.
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What are sloping warm conveyor belts?
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Main WCB flow is parallel to cold front. Small component (often ageostrophic) is perpendicular to cold front (system relative) and the nature of this flow affects frontal structure. Rearward sloping ascent is relative to moving front, some flow to rear and forward sloping ascent is relative to moving front, some flow forward.
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What is one great use of satellites?
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That we can help monitoring the weather over the oceans, like watching hurricanes.
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What is the seventh key to meteorology?
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Clouds and precipitation are caused by rising air, while clear weather is caused by sinking air.
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What effects does ground clutter have on the radar scan?
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Reflections caused by objects on the ground- buildings, towers, mountains, etc and aircraft, birds, insects and these will show up as small, random echoes.
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What is the output from the computer know as?
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Guidance because the forecaster must determine how good the computer forecast is and how it applies to his/her area.
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How do we use water vapor imagery?
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The satellites can detect the movement of water vapor in the mid- to upper- troposphere.
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What is "The Butterfly Effect?"
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If a butterfly flaps its wing in South America, could that small change in the air lead to a tornado in Texas weeks later?
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What is veering of the winds with height?
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They are changing direction in a clockwise direction which indicates warm air advection occurring in the layer; i.e. warm air is being advected north.
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What usually blocks the cyclones and anticyclones from propagating any further on their treck?
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The Rocky Mountains are a barrier to cyclones penetrating eastward from the Pacific, while anticyclones tend to dissipate along the eastern coast of the U.S.
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What is a split front?
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When you have a cold front aloft and a cold front at the surface.
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What is the cold conveyor belt (CCB)?
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Actually as wide as WCB, just shown narrower. Flow just north of warm front (in cold air), and it travels underneath the WCB and rises and loops back around to east. Moisture causing comma head (mostly scattered) is from precipitation associated with WCB. Mixing aids in cloud development. Cold belt may merge with WCB in upper levels. Contrasting cloud tops near warm front seen in satellite imagery (especially in IR images).
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What are the six steps in the polar front theory?
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Stationary front, frontal wave, open wave, maturing phase, mature-occluded, and dissipated stage.
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What is ASOS and what does it stand for?
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It stands for Automated Surface Observing System. Observations updated every minute for pilots, but routinely on the hour for weather purposes and more frequently if conditions warrant (called a "special" observation). Most major ASOS sites feature a supplemental observer who is employed by an FAA contractor. This person ensures that ASOS is operating appropriately, serves as a backup should an instrument go down, and edits unrepresentative observation.
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In ASOS, what do we use to determine visibility?
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A visibility sensor. Visibility is determined by measuring the amount of light from a pulsed Xenon flashlamp that is scattered into a photodiode receiver. Experiment has shown that the amount of light scattered at approximately 45 degrees gives a good measure regardless of the type or size of the scattering particles. The 'light' is primarily in the blue and ultraviolet. About 10 ft above ground, samples a volume about the size of a basketball. Reports up to 10 miles in varying increments from < ½ to 1 mile and was designed to respond quickly to decreases in visibility and more slowly to increases. Will not be representative if a single patch of fog covers the sensor, or if a very low layer of fog is present. Will give visibilities too high if you have haze or fog along with bright sunshine.
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What is ACU and what does it stand for?
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It stands for Acquisition Control Unit. In a cabinet in the terminal building lies the master computer of the ASOS, the ACU. Maintains communication with the sensors by radio contact with the DCP. Requests data and orders self tests throughout the ASOS system and makes the results of self-tests of the system available to the observer or technician.
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What is the fourth key to meteorology?
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Since cool air can "hold" less water vapor than warm air, rain and other form of precipitation are caused by cooling the air.
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On water vapor imagery, what does red and green mean?
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Red implies sinking air and green implies rising air.
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What effects does the atmosphere have on the radar scan?
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Small echoes can be returned, even on a clear day. Clouds, smoke, fog, even turbulence or density variations can backscatter a pulse. These echoes are characteristically by large, uniformly colored areas centered around the radar.
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How does this data get presented to the public?
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Some private companies and TV stations have professional meteorologists that interpret the data, and others have broadcasters that present the interpretation of a professional meteorologist.
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What are the winds normal to the anafront like?
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They are weaker and moving slower than the front.
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What are the three cells called in the three cell model?
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Hadley cell, ferrel cell, and polar cell
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What is precipitation mode and what do we use it for?
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The radar goes into this mode when precipitation is detected. This scan is more focused on the big picture of the storms etc, not things like bugs and stuff. There are more scans per minute and at more elevations.
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What are the assumptions that we make to simplify the three-dimensional frontogenesis equation?
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y' axis is set normal to the frontal zone, with y' increasing towards the cold air (note: y' might not always be normal to the isentropes- i.e., the frontal zone might be oriented at an angle to the isentropes, as we'll later see). x' axis is parallel to the frontal zone and neglect vertical and horizontal diffusion effects.
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In ASOS, what do we use to measure dewpoint?
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It is determined by cooling a mirror located under the hood until condensation forms and measuring the temperature of the mirror with an embedded precision thermal sensor, and this is called a hygrothermometer. The presence of condensation is detected by reflecting an infrared beam off the mirror. Two photodetectors are used, but only is situated to pick up the direct reflection. The second will pick up IR scattered in its direction by the condensation. The presence of condensation is sensed by the drop in IR reaching the direct sensor and the increase at the second (indirect) sensor. Another thermal sensor (thermistor) detects the air temperature.
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