Atmospheric Science and Weather Analysis Flashcards

The Foehn effect, observed on the lee side of mountain ranges, produces warming primarily due to:

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.

In the context of Numerical Weather Prediction (NWP), what is 'data assimilation'?

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.

The Madden-Julian Oscillation (MJO) primarily affects weather on which time scale?

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.

Which atmospheric feature is characterized by a narrow corridor of strong upper-level winds and is critical for mid-latitude weather development?

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.

The term 'precipitable water' (PW) refers to:

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.

A mesoscale convective system (MCS) is best defined as:

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.

Which synoptic-scale process most directly causes large-scale rising motion ahead of an approaching trough at the 500 hPa level?

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.