meteorology Flashcards
(103 cards)
1
Q
what are the weather observations?(6)
A
- Atmospheric pressure, barometer. Mean sea-level atmospheric pressure on earth.
- Air temperature, thermometer
- Wind speed and direction, anemometer
- Humidity, hygrometer
- Rain fall, rain gauge
- Clouds, cloud ceiling instrumental, cloud cover, visual estimate, and cloud type.
2
Q
what are wind speed keys?
A
Wind speed keys showing direction and how many knots.
3
Q
what is a wather station report?
A
Typical weather station report- shows the pressure, temperature, current weather, wind direction, weather since last measurement, dew point, and wind speed.
4
Q
what is Sonde?
A
• Sonde: instrumented weather balloon, global coverage since 1950’s. .
5
Q
what was the NASA 1991?
A
• NASA upper atmosphere research satellite includes laser-doppler anemometry. Deployed 1991. crashed into pacific in 2011.
6
Q
what is Dropsonde?
A
Dropsonde- dropped from aircraft above tropical cyclones, and hurricanes to improve prediction.
7
Q
what des red mean on global weather stations?
A
- Global weather stations. Red is silent stations, which are war zones.
- Satellite coverage of all types. Very important. Increase in satellite data
8
Q
what is water in the atmosphere?
A
Water vapor colourless, clouds and fog are condensed water droplets.
The transitions of water either releases heat into the environment, or takes in heat from the environment.
9
Q
what role does humidity have?
A
- Several ways of giving atmospheric water vapour content.
- Behaviour of rising and descending air: a rising parcel will always expand due to the decreasing pressure. Loses energy as molecular speed slow so loses temperature. As pressure increases air parcel contracts again, and the molecular speed increases, t increases.
10
Q
what is absolute humidity role?
A
• a parcel of air will expand as it rises due to decreased pressure, and compress as it descends- due to increased pressure.
11
Q
what is absolute humidity?
A
Absolute humidity: mas of water vapour/ volume of air = water vapour density.
12
Q
how does absolute humidity change with air rising?
A
Since absolute humidity, mass/volume, then it will decrease as air rises and increases as air descends. Therefore, even though airs vapour content remains constant, the absolute humidity changes.
Need to express in a way not influences by changes in air volume.
13
Q
what is specific humidity?
A
mass of water vapour/total mass of air.
14
Q
what is the specific and mixing ratio?
A
Both specific humidity and mixing ratio remains constant as long as water vapour not added to or removed from the parcel.
15
Q
what is vapour pressure?
A
Moisture content of the air also quantified by measuring the pressure exerted by the water vapor in the air.
16
Q
what does the total pressure in an air parcel show?
A
Total pressure in an air parcel is due to collision of all molecules against edge of parcel. The sum of all pressures of the individual gases.
17
Q
what is the actual vapur pressure?
A
The “actual vapour pressure” is an estimate of the total amount of water vapour in the air.
18
Q
what is the saturation vapour pressure?
A
The “saturation vapour pressure” is the maximum amount of water vapour that can be in the air at a given pressure and time.
19
Q
what happens in a closed container to evaporation?
A
In closed container, evaporation will continue until as man molecules return to the liquid as they escaped.
20
Q
when is there an equilibrium with vapour?
A
At this point, there is an equilibrium. And the vapour is saturated.
Since the energy of the molecules increases with T, more molecules escape and so the saturation vapour pressure increase with increasing temperature.
21
Q
what happens to vapour at boiling point?
A
At the boiling point: saturation vapour pressure= atmospheric pressure.
Evaporation vs boiling: evaporation is a surface process, vapour pressure in liquid too low to form bubbles
22
Q
what is boiling?
A
Boiling, is a volume process, saturation vapour pressure= atmospheric pressure, so bubbles can form.
Boiling point varies with atmospheric pressure. Boiling point lower with lower pressure, higher altitude.
Phase diagram for H2O. There is a critical point.
23
Q
what does the saturation vapour pressure depend on?
A
The saturation vapour pressure depends manly on the air temperature. Saturation vapour pressure is less for ice than for water at the same tempertaure, because harder for water molecules to escape in ice surface.
24
Q
what is absolute humidity?
A
Absolute humidity: the mass of water vapour in a fixed volume of air
25
what is actual vapour pressure?
Actual vapour pressure: amount of water vapour in terms of the amount of pressure that the water molecules exert
26
what is saturation vapour pressure?
Saturation vapour pressure: pressure that the water molecules would exert when in equilibrium with air at a given temperature.
27
what is relative humidity and when does it increase and decrease?
Relative humidity= water vapour content/ water vapour capacity
= actual vapour pressure/saturation vapour pressure x100
Increases with increase in vapour content. Decreases with increase in temperature, as warmer water has higher saturation.
28
what is dew point?
Dew point:
Temperature to which air needs to be cooled, with no change in air pressure our moisture content for saturation to occur. (to form cloud, fog, dew, frost) 10 degrees is saturated with water vapour
29
why should temperature in a parcel be cooled?
• Temperature to which a parcel of moist air must be cooled, with pressure and mixing ratio constant for a parcel to becomes saturated.
30
what is a high and low dew point?
* High dew point: high water vapour content
| * Low dew point: low water vapour content
31
why is dew point good for weather?
• Key measurement to predict formation of dew, frost or fog.
May be used to estimate cumulus clouds base.
32
what are dew point and night temperature differences?
• Dew point and night temperature differences- expected min. T lower with decreasing dew point.
Reason: lower dew point means less greenhouse water vapour near ground, so less heat radiated back to ground, more lost upwards.
33
what is the wet bulb thermometer?
The wet bulb thermometer:
• evaporation cooling cools wet bulb thermometer. Due to latent heat of vaporisation.
• Web bulb T is the lowest T that can be reached by evaporative cooling
• Form differences in temperature can calculate dew point and relative humidity.
• When air reaches saturation vapour pressure, evaporation = condensation
• No heat output so wet bulb same T as dry thermometer.
34
what percentage of the warming effect is due to water vapour?
Water vapour is 60% contribute to the warming effect
35
what is water vapour content of the atmosphere controlled by?
Water vapour content of the atmosphere is controlled by temperature. Sustained greenhouse effect is driven by non-condensable gases, mainly CO2.
36
what do the gases cause the temperature to do?
These gases cause the temperature to rise, and then leads to an increase in the water vapour that further increase the temperature, which is positive feedback.
37
how do the gases generate a positive feedback?
Generates positive feedback accelerating warming, in turn- leading to more water vapour in the atmosphere. On early venus, this led to a runaway greenhouse effect.
38
when does frost form?
If dew point T is at or below freezing and then frost forms.
39
when does dew form?
Dew forms when air in constant with these surfaces cools by conduction
If air cools to dew point water avaour condenses on surfaces
40
what forms the fog and clouds?
• Airborne particles are required for water vapour to condense or deposti on the produce cloud droplets
41
what are cloud condensation nuclei?
Cloud condensation nuclei: CCN. Also known as hydroscopic nuclei, water vapour rapidly condenses on their surfaces
42
what are sulphate aerosols?
• Sulphate aerosols act as CCN, these are the major sources of CCN in the atmosphere above the oceans
43
what is the role of plankton?
• role of plankton: coccolithophores and trichodesmium produce gas, which oxidised in atmosphere. The sulphate aerosols produced act as a CCN that helps generate more clouds, reflecting more radiation, which cause cooling.
44
what is the CLAW hypothesis?
• CLAW hypothesis. Ocean warms, enhanced phytoplankton growth, enhanced DMS production, elevated DMS concentration, elevated SO2 conc, more cloud condensation nuclei.
45
why does fog form best on clear nights?
• Radiation fog forms best on clear nights, thin layer of moist air near the ground, overlain by dry air. Thin moist air doesnt have much greenhouse effect, so cannot trap must outgoing longwave radiation.
46
what is advection fog?
Advection fog: when warm moist air moves over a surface sufficiently cooler in order to cool air to dew point. Typically forms along upwelling coasts in summer when upwelling is most intense/ warm moist sea air is carried, advected, over the cold coastal upwelled waters, forming fog.
Fog formation: valley fog and upslope fog.
47
what is the formation of clouds?
• Clouds form when moist air rises and cools, lifting mechanisms.
• Convection lifting, warmed air is buoyed upwards.
Clouds from un the troposphere, type is controlled by:
• Air stability, elevation at which moisture condenses, and wind conditions.
48
what is frontal lifting?
to do with cloud formation. Frontal lifting- air is carried upwards along fronts
49
what is convergence lifting?
to do with cloud formation.Convergence lifting- converging wind forces air upwards
50
what is orographic lifting?
• Orographic lifting- air must rise to pass over mountains
51
what are names used to describe different clouds?
* Cirrus- wispy, thin, feathery
* Cumulus- puffy, cottony
* Stratus- stable, layered
52
what do the prefixes mean to cloud types?
* Cirro- high latitude
* Alto- mid latitude
* Nimbo- rain producing
53
how is rain formed and when does it fall?
Rain forms by collision and coalescence- smaller droplets collide to create larger drops.
Drops fall when too large to suspend. Typical are 2mm. Drops larger than 5mm break up
Cold air near ground turns rain into sleet.
54
what is the Bergeron process?
Bergeron process- cold clouds contain water and ice.
• Water evaporates faster than ice, fueling crystal growth.
• Ice grows as delicate hexagonal flakes
Snowflakes may change as they fall- cold air, flakes remain a powder. Near melting T- flakes form clumps.
Above melting temperature- flakes form rain.
55
what is diurnal change in atmospheric stability?
• Mornings= air is most stable, resists vertical motions.
• By afternoon, surface heats, air rises as thermals, mixes and pulls down air from higher levels causing surface gusts.
Diurnal heating generates thermals, clouds and convections. Typical cumulus clouds bubble up, convection cells are initiated
56
what is adiabatic lapse rate?
• Adiabatic lapse rates, no heat exchanged from air parcel. May be dry, or moist, depending on saturation.
57
what is the average low temperature for diural change?
* Environmental lapse rate: actual temperature as measured by sonde. Average for lower atmosphere is 6.5 degrees celcius.
* Dew point lapse rate- approx 2 degrees
58
waht is dry adiabatic lapse state?
• Dry adiabatic lapse rate- as long as air parcels is unsaturated, it expands and cools by 10 degrees
As air cools it approaches its dew point.
59
what is moist adiabatic lapse state?
* Moist adiabatic lapse rate- if air is saturated, as it cools further get condensation and cloud formation.
* Latent heat of condensation is released so T loss rate decreases
* Likewise, heating on descent is offset by latent heat of vaporisation.
60
how are cumulus cloud developed?
Cumulus cloud development: will continue to rise through conditionally unstable zone, until stable zone is reached.
Development dependent on stability/instability of troposphere. This may lead to thunderstorms
Clouds don't penetrate far above tropopause as stratosphere is stably stratified.
61
what is the Fohn effect?
* Occurs with strong air flow over topography
* Importance of latent heat of condensation
* Can generate sudden temperature increase in alpine valleys known as Fohn.
* Lost all its moisture when its on the other side, so it warms at a much faster rate. 8 degrees higher.
* Strong northerly winds
* Snow only on northern side due to the Fohn effect.
* In USA, westerly winds over Rockies- chinook. Chinook native American tribe means snow eating.
62
what are mountain waves and rotors?
* Distinct cloud patterns.
* Above fohn clouds, there is a mixture of moist and dry air. The wave type motion brings moist air higher up, and it condenses to form patterns of clouds. Lenticular clouds.
* Rotor clouds- generated in lee of mountain. Because of the wave like processes, there are lots of turbulence.
* Large topography, can reach the top of the troposphere, and into the stratosphere.
* Major sources of turbulence, in rotor and also clear air turbulence.
* Can cause airplanes to lose wings etc due to wind turbulence.
63
what do air pressures start with?
* Air pressure is simply the mass of air above a given level.
* Starts with 2 identical air columns, cool one and heat the other.
* Column two will be warm so its expands.
64
air pressure and winds with air mass: how does the pressure gradient set up columns?
* But if we take a higher reference level, there is more air above the reference level, this sets up a pressure gradient force so that the upper level air flow will be from the warm column to the cold
* Warm air aloft is normally associated with high u.l. Atms pressure
* Cold air aloft is associated with low u.l. Atmospheric pressure.
65
how does the air move in columns?
• The high level movement of air now puts more air in the cold column and this sets up a pressure difference at ground level which results in a circulation cell being established.
66
what is the unit of atmospheric pressure?
Meteorologists are so conservative atmospheric pressure are still quoted in millibars. SI unit of pressure the Pascal is in hecto-pascal. Standard sea-level pressure
67
what are pressure charts?
Pressure charts show sea-level pressure charts. In the lower part of the atmosphere, pressure changes by about 10 mb for every 100 m of elevation change.
68
what are sea level pressure charts?
This produces sea level pressure charts. Initially, each observation is taken into account, then the sea level isobars are soothed. Sea level pressure charts are called constant height charts because they represent atmospheric pressure at a constant level.
69
what are the contours to sea level pressure charts?
Met Office output, sea level pressure charts and contour in 4 hPa intervals. Dominant features on a NE Atlantic Europe weather charts are Icelandic low pressure area and Azores high pressure area.
70
what do sea level pressure charts represent?
Sea-level pressure charts are called constant height charts because they represent atmospheric pressure .sea level pressure charts are the only commonly used height charts. Height levels are a better basis for analysis so constant pressure charts are used or upper levels.
71
what are upper level pressure charts?
• Upper level pressure charts: isobaric charts (=constant pressure)
72
why is cold air denser than warm air?
• Cold air is denser than warm air, it causes pressure surface to be lower in colder air masses, less dense warmer air allows the pressure surfaces to be higher. Heights are higher in warm air masses, and lower in cold air masses.
73
what are isobaric surfaces?
• Wave like patterns on an isobaric surface reflect changes in air temperature. An elongated region of warm air aloft shows up on an isobaric map, as higher heights and a ridge.
74
what is a cyclonic flow?
• Cyclonic flow is anticlockwise in the north hemisphere, and clockwise in the southern hemisphere.
75
what is the role of friction?
• Role of friction, the effect of friction on wind is dominant near the surface, in the planetary boundary layer. The boundary layer extends from the surface of about 1-1.5 km above ground level. Friction slows wind and so reduces CF Coriolis force, PGF pressure gradient force, is now stronger, so wind cuts across isobars. Contrast upper level and lower level winds.
76
what is Ballots law?
• Buys Ballot's law- stand with back to the upper level wind in the N. Hemisphere then low P to left. You can also start to construct your own pressure chart. Surface wind direction is about 30 degrees to the left of the upper wind direction.
77
what is the effect of the lower level convergence or divergence?
• The effect of the lower level convergence or divergence, air slowly rises above convergences (surface lows), air slowly sinks above divergence (surface highs)
78
what are areas of the geostrophic winds?
Holds doldrums and horse latitudes. Ferrel cell, Hadley cell.
Upper level geostrophic winds (N. Hemisphere) directional change until PGF and CF balance.
79
what are isobars and contours?
Isobars and contours on upper level chart like banks of stream, when narrowly spaced, flow is stronger. Increase in wind speed results in stronger coriolis force, that balance the larger pressure gradient force.
80
what is air mass?
* Large body of air with similar temperature and moisture characteristics in any horizontal direction
* Key to weather forecasting is determining air mass properties, modifications, trends and movements.
81
what are air mass source regions?
* Flat, uniform and extensive with light winds.
* Subtropical oceans in summer.
* Snow and ice covered artic plains in winter.
82
how do air masses influence UK?
* Arctic maritime is cold and dominant in winter in north. Scotland rarer in summer but brings cold and showers.
* polar maritime is cold and dry but collects moisture from warmer ocean showery, snow in winter, hail and thunder in summer.
* Returning polar maritime- moist but passes over cooler waters so stable often cloud cover but less rain.
* Polar continental: beast from the east 2018.
* Tropical maritime, warm and moist. Clash of air masses, moist air meets cold air.
83
what happens when polar continental and trpical maritime meet?
When a polar continental and tropical maritime meets, there is a rad danger to life weather warming in England.
Tropical continental has the source of North Africa and Sahara, brings heat waves, dust and pollutants from Europe.
84
what is in a jet stream?
* Hadley cell and the subtropical jet. At smaller radius of rotation, the velocity increases to conserve angular momentum.
* Polar and subtropical jet streams
* The jet streams mark the boundaries between the convection cells.
85
what happens to a jet stream at high altitudes?
• At high altitudes over the polar front and horse latitudes, air masses of different temperatures come in contact. Steep pressure gradient forms. Results sin fast flowing, high altitude westerlies, the jet streams. Speeds up to 200 to 400 km/hr.
86
what are meanders?
• "meanders" in jet streams drives N/S motion of warm and cold air masses
Velocity and temperature structure of Polar Front and jet stream. Shows a core with the most power.
87
what are in the upper level pressure charts?
Upper level pressure charts- ECMWF, North Atlantic view.
• Upper level pressure charts
• The jet stream
• And planetary waves
88
what are the atmospheric fronts?
* A boundary or transition zone between 2 air masses of different densities (different temperatures, pressure and humidities)
* Large horizontal and vertical extents
* Frontal boundary zone highly variable from 1 km to 100 km
89
what is a cold front?
* Marked by a relatively narrow band of precipitation
| * Cumulonimbus clouds- may include thunderstorms.
90
what is a warm front?
• Very broad belt of cloud and precipitation. Includes temperature inversion, and frontal surface is much smaller slope than the cold fronts. Often with widespread nimbostratus precipitation near front
91
what is a occluded front?
• Cold front catches up with and overtakes a warm front. Forms an occluded front.
• Cold occlusion cause warm rides over cold, and cold occluded front and initial occlusion.
Warm occlusion: cold rides overwarm.
92
what are mid latitude cyclones?
Mid latitude cyclones, depression, brings storms. Develops in a wavelike manner, storm called a wave cyclone. A wavelike kink forms in from front.
An open wave forms then an initial occlusion.
93
what is the polar front theory?
Develops according to "polar front Theory", develops in a wavelike manner.
Weather map view of mid latitude cyclones is like breaking wave.
The low trough along front in between 2 highs, a kink forms and waves develop. The occlusion develops from the wave, and it advances until it becomes a cut-off cyclone.
94
what are mid latitude cyclones relation to Rossby waves?
Relation to Rossby Waves: as the parcel of air moves south, it gains relative counter-clockwise spin. As the parcel of air moves north, it gains relative clockwise spin. Convergence and divergence occurs, and the flow spins down and spins up in different areas.
95
what happens to mid latitude cyclones when the upper level divergence is stronger than the lower level convergence?
Mid latitude cyclones- vertical structure, cold air aloft associated with low pressure. When upper level divergence is stronger than lower level convergence (more air is taken out at top than is brought in below), surface pressure drop and the low intensifies.
96
how is the fliud flow on rotating earth affected by this?
Vorticity- may be regarded as the spin or rotation of a parcel of water or air. Like the coriolis force, the vorticity is zero at the equator, and maximum at the poles.
This covers changes in depth/height, in relative vorticity and in latitude. If a column of air or water moves equatorward, frequency decreases the relative vorticiy (or spin) must increase.
97
what rotation does the parel show near the pole?
Parcel retain rotation it had near the pole, so it appears to rotate counter-clockwise.
98
what are short waves roles in cyclongenesis?
* When isotherms parallel to contour lines, atmosphere is barotropic (winds blow parallel to isotherms)
* When isotherms cross contour lines, atmosphere is baroclinic (winds low across isotherms)
* In region of baroclinicity winds blow across isotherms and cause temperature advection.
* Cold advection: occurs on troughs west side. Isotherms are also shown.
* Warm advection, occurs on troughs east side.
* Baroclinic wave theory of developing cyclones.
99
what are Rossby waves important for?
Key to cyclogenesis. What happens when Rossby Waves get stuck.
100
what does summer show with cyclonegesis?
Blocking patterns, blocking high weather. Summer is a large area of warm, dry and fair weather forms. High pressure aloft causes sinking. Downwards motion compresses and warms air. Traps heat rising from surface. Cut off lows greater equatorward movement of cold high latitude air, greater poleward movement of warm low latitude air. With stronger pole-ward movement of warm air.
101
what seasons show flooding?
Summer- may lead to flooding near lows.
| Winter- may lead to anomalous cold plus snow, depending on position.
102
what cuases blocking?
Wave activity increase with more energy in atmosphere. Warming makes blocking more frequent.
More hotter extremes with warming? Dramatically increasing chance of extremely hot summer since 2003 European heatwave.
103
weather forecasting: how is it affected by cyclogenesis?
* Origins of the jet stream and their location, polar and subtropical jets may be separated or may coalesce
* Mid latitude cyclones: origins along the polar front, development and progression
* Rossby Waves: origins and relation to vorticity, relation of upper level patterns to surface circulation and fronts. Baroclinic wave theory of cyclogenesis, progression around the earth
* Atmospheric blocking: implications of stationary Rossby Waves, typical weather patterns arising from blocks in summer vs winter.
