Sub-Synoptic scale process - Climatology Flashcards
Mesoscale phenomena
Part of a continuum of atmospheric motion - spatial size range is 10 - 200km, with a time scale of a few hours to a few days
Mesoscale phenomena can be separated into two broad groups depending on their origin
- Free atmosphere processes
- Thermal and mechanical effects of the surface - surface induced processes
Two aspects of earths surface that lead to development of mesoscale weather processes
- Physical character of the surface - Orographic forcing
- spatial variability of the surface energy balance - Thermal forcing
In stable situations air tends to get blocked and flows around an obstacle.
What happens with decreasing stability.
More and more air passes over the obstacle and forms lee waves
Measure for the amount of blocking:
Froude number
Froude number equation
Froude number = pi(horizontal wind speed/stability of the atmosphere x width of the obstacle
Four types of foehn effect
- Stable foehn
- Unstable foehn
- Low-level blocking
- The typical bora
Bora
Cold, dry gusty wind that occurs when cold air is trapped below an inversion
Most common dynamic mesoscale feature created by mountains
Foehn effect
Temperature change with height for non-saturated air (1 degree per 100m)
Dry adiabatic lapse rate (DALR)
Temperature change with height for saturated air (0.4 - 0.8 per 100m)
Saturated (moist) adiabatic lapse rate (SALR)
Foehn effect results
Precipitation on the windward side of a mountain range and a drying effect on the leeward side
Foehn effect process
- Moisture lost through precipitation on the windward side
- Consequently, the condensation level on the lee side is at a higher level
- This results in longer dry adiabatic warming on the lee side
- Therefore, at the same altitude, air on the lee side is warmer than on the windward side
Two thermal effects on horizontal airflow
- Land-sea breeze system
- Mountain valley winds
Boundary layer
The region of the atmosphere that is directly influenced by the surface beneath it
Layers of the atmospheric boundary layer (ABL)
- Outer layer
- Turbulent surface layer
- Roughness layer
- Laminar boundary layer
- Sub surface layer
Outer layer (ABL)
The remaining turbulent layer that extends to the top of the ABL
Turbulent surface layer
Immediately above the surface elements, small-scale turbulence dominates
Roughness layer
Strongly influenced by the roughness elements, complex 3-d flows around them
Laminar boundary layer
Molecular diffusion
Sub surface layer
Molecular diffusion of heat away from the ground
Four primary forms of energy
- Radiant energy (electromagnetic waves)
- Thermal energy (energy possessed by a body as a consequence of its sensible/latent heat content)
- Kinetic energy (energy of motion)
- Potential energy (energy that a body possesses as a result of its position in gravity
Flow rate of mass
Mass flux
Flow rate of mass per unit (surface) area
Mass flux density
Rate of work/flow rate of energy
Power,heat flux
Flow rate of energy per unit (surface) area
Heat flux density
Flow rate of radiative energy per unit (surface) area
Radiant flux density
Three modes of energy exchange
- Radiation - electromagnetic waves
- Conduction - molecular motion
- Convection - mass movement in a fluid
Net all-wave radiation
The amount of all-wave radiant energy that is available at a surface, which is then partitioned into different energy balance components
Net all-wave radiation equation
Net all-wave radiation = net shortwave radiation + net longwave radiation
Most important link between energy and water balance
Latent heat flux - evaporation and condensation at the surface results in mass loss or gain of water
Input/output of a glacier terms:
Accumulation -
Ablation -
Accumulation -
Snow/ice gain e.g snowfall, rainfall, superimposed ice
Ablation - Snow/ice loss e.g Surface melt, basal and englacial melt, evaporation, sublimation, calving and avalanching
How does ice and snow compare with radiation exchanges on glaciers
Albedo of snow is higher than ice, meaning once a glacier loses its snow in the summer, it absorbs more energy and melts faster.
How much melting occurs in summer on a glacier in the ablation zone
30-40mm
High and low ablation events are associated with which wind direction
North-west
South west
