CCM Atmospheric Science and Weather Analysis 3 — Questions and Answers
Question 1: The Foehn effect, observed on the lee side of mountain ranges, produces warming primarily due to:
- Radiative heating from reflected sunlight off snow
- Adiabatic compression of descending air and latent heat release on the windward side (Correct answer)
- Advection of warm maritime air over the barrier
- Increased surface sensible heat flux from bare rock
Correct answer: Adiabatic compression of descending air and latent heat release on the windward side
Foehn warming results from net latent heat released during condensation on the windward ascent, so the descending air on the leeward side is warmer than at the same altitude on the windward side.
Question 2: In the context of Numerical Weather Prediction (NWP), what is 'data assimilation'?
- The process of removing erroneous observations before model initialization
- The mathematical technique to merge observations with a background forecast to produce the best initial state (Correct answer)
- Converting satellite radiances to surface temperature values
- Downscaling coarse global model output to high-resolution grids
Correct answer: The mathematical technique to merge observations with a background forecast to produce the best initial state
Data assimilation (e.g., 3D-Var, 4D-Var, EnKF) combines observational data with a prior model state to create an optimal analysis that minimizes errors in the model initial conditions.
Question 3: The Madden-Julian Oscillation (MJO) primarily affects weather on which time scale?
- Hours to days (synoptic scale)
- Days to weeks (intraseasonal, 30-60 day) (Correct answer)
- Months to years (interannual)
- Decades (interdecadal)
Correct answer: Days to weeks (intraseasonal, 30-60 day)
The MJO is an eastward-propagating tropical convective anomaly with a characteristic period of 30-60 days, making it the dominant mode of intraseasonal variability in the tropics.
Question 4: Which atmospheric feature is characterized by a narrow corridor of strong upper-level winds and is critical for mid-latitude weather development?
- Planetary boundary layer
- Jet stream (Correct answer)
- Intertropical Convergence Zone (ITCZ)
- Hadley Cell subsidence zone
Correct answer: Jet stream
Jet streams are narrow ribbons of fast-moving air (often exceeding 100 knots) at tropopause level that steer mid-latitude storm systems and influence cyclogenesis through upper-level divergence.
Question 5: The term 'precipitable water' (PW) refers to:
- The precipitation rate at a given location
- The total column water vapor if condensed into liquid at the surface (Correct answer)
- The fraction of cloud liquid water that reaches the ground
- The temperature at which dew begins to form
Correct answer: The total column water vapor if condensed into liquid at the surface
Precipitable water is the depth of liquid water that would result if all water vapor in a vertical atmospheric column were condensed, typically measured in inches or millimeters.
Question 6: A mesoscale convective system (MCS) is best defined as:
- A single isolated thunderstorm cell with a rotating updraft
- An organized complex of convection with a contiguous precipitation area spanning at least 100 km (Correct answer)
- A non-precipitating stratiform cloud deck at mid-levels
- A tropical cyclone with organized deep convection
Correct answer: An organized complex of convection with a contiguous precipitation area spanning at least 100 km
An MCS is a cluster of thunderstorms organized over a horizontal scale of at least 100 km, exhibiting a coherent precipitation structure often including both convective and stratiform regions.
Question 7: Which synoptic-scale process most directly causes large-scale rising motion ahead of an approaching trough at the 500 hPa level?
- Surface friction divergence
- Upper-level divergence associated with jet streak diffluence (Correct answer)
- Radiative cooling of the mid-troposphere
- Downslope orographic flow
Correct answer: Upper-level divergence associated with jet streak diffluence
Ahead of a 500 hPa trough, upper-level divergence (especially in jet streak exit regions and areas of diffluence) removes mass from the column, lowering surface pressure and forcing ascent.
CCM Atmospheric Science and Weather Analysis 3
The Foehn effect, observed on the lee side of mountain ranges, produces warming primarily due to: