Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Thermodynamics and Convection > Midterm Unit One > Flashcards

Midterm Unit One Flashcards

1
Q

What is convection?

A

The vertical displacement of air-masses under the effect of buoyancy.

  • Air mass is warmed at the surface to the point that it becomes buoyant (heating at surface must be sufficient enough to remain buoyant) and rises.
  • Air is cooled at the mid-tropospheric levels to the point that it becomes negatively buoyant (sinks).

Produces an updraft that transports heat in the vertical and down gradient from a warmer location to cooler upper tropospheric levels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does vertical overturning refer to?

A

To the up and down vertical displacement of an air-mass to describe convection.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe moist convection.

A

Moist convection is easily observed as it often generates clouds and precipitation. Observed on the large scale and great intensity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe dry convection.

A

Not readily observed, weaker (confined horizontally and vertically).
Characteristic of the atmospheric boundary layer.
Thermal rolls, plumes.
Favoured over sites subject to localized intense heating (volcano…)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is temperature advection?

A

It is the transfer of heat though movement of air in the horizontal and vertical z direction.
Atmospheric flow: vertical component is much smaller so can usually be neglected.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Differ convection from vertical advection. (3)

A
  1. Vertical temperature advection unlike convection does not involve buoyancy.
  2. Convection seek to attain thermal equilibrium by redistributing heat in the downgradient. Vertical advection can result in strengthening or weakening of the temperature gradient (does not seek equilibrium).
  3. Vertical advection = product of the vertical wind speed and rate of change delta(T)/delta(z) which is much weaker than magnitude of convection.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is background flow?

A

The wind direction and wind shear.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Give examples of convective circulation.

A

Fair weather cumulus, shower producing cumulus, cumulonimbus, squall lines, supercell storms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe squall lines.

A

Critical to the maintain of the squall line organisation and long term maintenance is the cooperation between the updraft and downdraft.

  • updraft: maintained by the uplift of the advancing cold air of the downdraft (cold pool creating a sloping cold front)
  • downdraft: maintained by precipitation falling into it: precipitation evaporates as it falls ->cools the air-masses in mid-level and makes them sink.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Scale of convective circulations?

  • thermal plumes, cumulus clouds
  • squall lines, supercells -tropical cyclones, monsoons
A
  • scale of thermal plumes, cumulus clouds: Length<10km. t<1 hour
  • scale of squall lines, supercells (large convective development): 10km1000km, 1h
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Thermodynamic system of convective phenomenon:
equation? (1st Law of thermodynamics)
ideal gas law of moist
partial pressure law

A
  • DELTA U = Q - W
    change in system’s internal energy = (heat received @ surface) - (work = upward transfer of heated mass)
  • p = rho_m R_m T
  • p_m = p_d + e
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the mean environmental lapse rate?

A

In the lower 10km of the atmosphere, the global and annual mean rate of temperature decrease with height iis of 7.0 deg/km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the 3 possible transfer of heat in the atmosphere.

A
  1. Conduction: transfer of heat from molecules to molecules: for air (which is a bad conductor of heat) conduction happens only very near Earth’s surface.
  2. Radiation: heat transfer from the body that emits electromagnetic waves to the body that absorbs.
  3. Convection: from hot place to cold places (a circulation pattern that is continuous).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is convection triggered?

A

When excessive heating though conduction and radiation, convection seeks to return to thermal equilibrium (vertical exchange, mixing of air masses).

  1. Heating->destabilized lapse rate.
  2. Heated air masses vertically ascend -> mixing along the updraft. -> Progressive heating of mid & upper tropo
  3. Exhaustion of source of surface heating -> surface cooling
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the two important processes in play to reset thermal equilibrium. Describe the second.

A
  1. Exchange of air mass in the vertical.
  2. Mixing along ascend/descend and @ final position

Mixing is an essential process because:

  • mix of env into cloud = entrainment->turbulent flow captures non-turbulent air
  • mix cloud into env = detrainment->turbulent flow injected in non-turbulent air
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Give a definition of convection in terms of energy conversion.

A

Convection is a mechanism through which the creation of APE (available potential energy) (generated from the vertical gradient of heating) is converted to KE (kinetic energy) (resulting in the updraft/downdraft of air-masses) and eventually dissipated to micro-scale motions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the role of moisture through convective processes.

  • surface
  • ascent
  • mid-upper tropo
  • mid-lower tropo
A

@ Surface: Heated moist air mass can hold a higher amount of water vapour (when air mass is heated and thermal equilibrium perturbated)
@ascent: humid air is lighter and more buoyant than dry air at same T
@mid-upper: water vapour moved upwards condenses so
precipitation & condensational heating
@mid-lower: falling precipitation particules evaporate (latent heat absorbed) -> evaporative cooling -> sinking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where does convection happen?

Give two region and 2 examples each

A

Extra Tropical Regions:

  • Following insolation cycle: thunderstorms, squall lines, tornadoes, warm season phenomena
  • cold air moving from heat source: seen over polar regions because of cold continental air traveling over warmer ocean: polar lows

Air masses become buoyant because of lifting

  • frontal lifting
  • orographic lifting
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is a front?

A

Weather system that is the boundary separating two different types of air due to passing fronts.
Deep convection is favoured immediately ahead of the cold front.

20
Q

Give an example of experimental campaigns

A

Pecan (Plains Elevated Convection at Night): field campaign, mobile resources repositioned each night depending on where storms were expected to form.

21
Q

What are sounding arrays?

A

Instrument in the arrays measure T, moisture, wind profiles, launch weather balloons

22
Q

What is Radar imagery?

Target?

A

It provides measurement of cloud echo-reflectivity used to estimate cloud type, precipitation, distance and height.
Sends out directional pulses of microwave radiation.

Targets: rain, snow, grapple, hail, even cloud droplets and cloud ice.

23
Q

How is called the intensity of a return signal? Describe

A

Echo reflectivity: It is a function of the particle’s diameter, dielectric constant and size distribution.
Gives info about type of particle, distribution.

High reflectivity = presence of water/ice of large size, high density
Low reflectivity = presence of water/ice of small size, low density

24
Q

PPI vs CAPPI?

A

PPI: Plan position indicator, rotates around the radar site @ fixed elevation angle
CAPPI: Constant altitude plan position indicator: extract from each PPI an annular ring of data for particular height

25
Q

What are radar imagery composites?

A

Results from several radars of the network put together

26
Q

Describe special feature of radar displays:

  • radar profiler
  • hook echo
A

Radar profiler: white horizontal band at altitude of melting layer in a cloud
Hook echo: tornado debris signature (anthropogenic or biomass debris lofting in violently rotating air)

27
Q

Describe doppler radars

A

estimate the in cloud wind speed and direction by assessing the doppler frequency shift on the condition that rain is present

28
Q

What is a geostationary orbit?

A

Circular orbit that follows direction and speed of Earth’s rotation

29
Q

What is the VIS for satellite imagery?

A

Visible imagery: images obtained using reflected sunlight

  • > high reflectance object = white
  • > low reflectance object = dark gray/black

Only visible during daytime
Higher resolution that IR (distinguish smaller features)

30
Q

What is the IR for satellite imagery?

A

Radiometers on the satellite sense the intensity of the heat emissions of the Earth components -> produce infrared images.
Cloud tops can be determine as = function of heat they emit = function of temperature

  • Low intensity (colder emitter) = white/red 0->high cloud tops
  • High intensity (warmer emitter) = dark gray/blue ->low cloud tops
31
Q

What is ITCZ?

Describe how its movement is affected (asymmetry)

A

Intertropical Convergence zone (Convection in the tropics)
It is a large scale feature that follows the seasonal cycle of insolation. I.e. it is a long band of clouds that circules the globe near the equator which shifts across from North to South as it follows the sun’s zenith angle (Tropic of Capricorn -> Tropic of Cancer)

Movement is affected by the distribution of land and ocean

  • over land: follows sun’s zenith
  • over ocean: linked to SST’s (determined by ocean Temperatures)

–> asymmetry in Southern and Northern H since more continental mass in NH so ITCZ is further away in NH summers)

–>development is organized in clusters with presence of weak equatorial waves that propagate westwards along ITCZ, experienced as erratic weather

32
Q

How does Trade winds affect ITCZ

A

Trade winds of NH and SH come together where ITCZ form as they pick up moisture as traveling over warm ocean surface.
ITCZ = tracer of ascending branch of Hadley circulation:
1. Trade winds Southward trajectory in NH transport heat flux from warm ocean surfaces
2. radiative cooling @ anvil tops
3. strong ascent in convective development along equatorial zone/gentle descent (descending branch of Hadley cell)

33
Q

Give a definition for summer monsoons

A

Seasonally reversing large-scale circulations
-winter (wind flows from continent to ocean): sunny and dry weather
-summer (wind flows from ocean to continent): torrential rains
Driven by asymmetric heating/cooling between an extensive land surface and neighbouring sea surfaces.

34
Q

What is the most extensive monsoon. Describe the processus.

A

Summer Asian Monsoons:
1. Temperature surface over land rises faster than that of ocean so T_oc Δz_oc reduction of air-mass over land
->decrease surface pressure over land
->formation of surface low pressure center
= thermal low

  1. Pressure gradient develops because of the thermal low in low troposphere in opposite direction than upper
    - >air drown in from ocean to continent @ low levels
    - >convergence of flow @ low levels over land
  2. Humid air mass become rapidly heated over continent
    lapse rate > lapse_equi = favourable condition for convective development
  3. Moisture rich convective air mass rise condense which lead to precipitation + latent heat release -> further rising of pressure surfaces and stronger upper divergence.

Monsoons are intensified through contribution of convective heating
*barrier effect of Himalayas: further force humid air to rise

35
Q

What is a thermal low?

A

It is a thermally driven low pressure center (e.g. in monsoons since heating over land lead to generation of low pressure center)

36
Q

What is the first theory of the creation of tropical cyclones and hurricanes.

A

Clusters of thunderstorms over the equatorial ocean

It is a large scale heat source generated by a number of thunderstorms Ts clustering together over warm ocean = the added effect of the condensational heating in each thunderstorm.

Similar to thermally driven monsoonal circulation:
convective heating by the cluster of thunderstorm over warm ocean
-> gradient in upper tropospheric levels
->divergence in mid & upper levels above heating source
->thermal low at surface
->convergence in boundary layer towards the convective cluster.

37
Q

Draw and describe the structure of a tropical cyclone.

A

outflow @ mid-upper levels from center-outwards
subsidence @ large radius, gentle
ascent @ convective towers near pressure low center, intense
inflow @ low levels (atmospheric boundary layer), flow inwards into thermal low

38
Q

What is the second theory of the formation of tropical cyclones and hurricanes?

A

Considered that latent heat (emphasis) is from the start of the driving force as it provides heat source to induce upper level divergence -> low pressure center at surface -> surface convergence.

Latent heat transfer from ocean to atmosphere:

  • > depends on wind speed (controls evaporation rate)
  • > presence of small initial disturbance critical (provides winds necessary for strong evaporation)
  • > strong evaporation = strong intensity of convection
  • > increases strength of converging winds
39
Q

Summarize what characterize strong rotational motion of tropical cyclones.

A
  1. Intense evaporation induced strong surface winds (induced by a pre-existing wave disturbance) -> provide thermal energy for deep convective developments over equatorial ocean and their organisation in clusters.
  2. Convective heating by a cluster of thunderstorms over warm ocean -> pressure gradient force in the upper levels that drive divergence in mid-upper levels above heating source
  3. Outflow of air because of divergence in upper levels -> pressure low at the surface -> convergence of flow in boundary layer towards convective cluster

Result: CCW circulation in lower levels that intensify exponentially with time

40
Q

Tropical cyclone spiral bands:
Cyclonic circulation @ low levels is associated with what?
Anticyclonic circulation @ upper levels is associated with what?
The rate @ which pressure is falling in the tropical cyclone center is a function of what?

A

with low level convergence
with upper level divergence

It is a function of the divergence in the atmospheric column which is a function of the amount of heating generated by convection

41
Q 
Energetics of Tropical cyclone
@ Boundary
@ convective towers near center
@ thin outflow layer @ top
@subsidence region
A
  • sensible fluxes of heat and water vapour from ocean to air mass flowing in wards
    • > heated, saturated air mass (lapse rate>lapse equi)
    • > potential energy increases

-updrafts: APE->KE

  • Radiative cooling @ anvil top as air travels radially outwards. Air mass cooled in upper levels (lapse rate>lapse equi)
    • > potential energy increases

-downdrafts: APE->KE

42
Q

What is a heat engine?

How does it resemble tropical cyclones?

A

It is a system that converts heat to mechanical energy by bringing a substance from a higher state temperature to lower state temperature.
-very efficient when ΔT is large and no loss of energy in any form

It resembles the ascending branch of a tropical cyclone:
->heat gained at low levels which is used for upwards displacement of air masses (~mechanical work)->transferred out of the system at the top through radiative emission from cloud top

43
Q

What is a Carnot cycle?

How does it resemble tropical cyclones?

A

It is a cyclic process where fluid undergoes series of change (volume and mechanical work) which is the theoretical limit to the fraction of the heat absorbed that can be converted into work. Does not return to initial conditions

Similarly, Tropical cyclones is a cyclic thermodynamic process with little loss of energy:
->Air masses involved undergo changes (phase and volume) and do mechanical work (updraft/downdraft) BUT returns to initial conditions

44
Q

Describe the eye of a tropical cyclone.

Explanation for it?

A

size: 35-65km of diameter
calm conditions, no rain practically, may be completely cloud free/few scattered clouds @mid-low/central dense overcast
–> all cases: stark contrast with surrounding of the eye wall

The divergent flow in upper levels cannot transport all the accumulated mass away from center

  • > redundant mass makes the upper level high pressure strengthen
  • > weight of excessive mass counteracts the strength w of updraft in the center
  • > @some point updraft is prohibited and the redundant mass starts descending
  • > descending air prohibits condensation
  • > rain free area = the eye
45
Q

Describe the positive feedback cycle of a tropical cyclone

A

As surface low deepens -> low level convergence intensifies -> more humid/warm air is drown into center by convergent flow -> convection more intense ->mid-upper level divergence intensifies ->surface pressure falls further
surface low becomes even deeper ->convergence into it intensifies further ->goes on and on

Thermodynamics and Convection (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions