Atmosphere I : Weather

Question 1

define atmosphere

Answer 1

the gaseous envelope of air surrounding the earth and bound to it by gravitational attraction. Up to a height of about 80km the relative proportions of the major constituent gases (apart from water vapour) are more or less constant. The percentage volume of water vapour varies between less than 1% and more than 3%.

Question 2

what are the only components of the atmosphere that vary locally in concentration

Answer 2

carbon dioxide, ozone and water vapour

Question 3

what are aerosols

Answer 3

natural pollutants in the form of aerosols, dust and smoke from volcanoes, forest fires, soil erosion etc, and man made pollutants such as sulphur dioxide, smoke, nitrogen dioxide, nitric oxide, ozone, lead and carbon monoxide.

Question 4

define the atmospheric layers

Answer 4

these are principally the troposphere, stratosphere, ozonosphere, mesosphere, thermosphere, ionosphere, exosphere

Question 5

tell me about the troposphere

Answer 5

(or overturning layer) 0-10km above the earths surface

Question 6

tell me about the stratosphere

Answer 6

(or layer of constant temperature) 10 - 25 km on its own, combined with the ozonosphere it is 10 -50 km though

Question 7

tell me about the mesosphere

Answer 7

(some similarity with troposphere) 60 - 100km

Question 8

tell me about the thermosphere, ionosphere and exosphere

Answer 8

all between 100km -500km , thermosphere: (molecular conductivity balancing energy input)

the ionosphere : electrical charge on particles significant

the exosphere : molecules liable to escape into orbit

Question 9

what layer of the atmosphere does weather occur

Answer 9

the troposphere

Question 10

where is the ozone layer

Answer 10

in the stratosphere

Question 11

what is weather

Answer 11

it is the instantaneous state of the atmosphere, what we experience on a daily basis

Question 12

what does type of weather depend on

Answer 12

location: latitude, altitude, terrain, water bodies

Question 13

what is climate

Answer 13

the long-term average weather

Question 14

define weather

Answer 14

the overall state of the atmosphere on a time-scale of minutes to months, with particular emphasis on those atmospheric phenomena that affect human activity. thus sunshine, temperature, rainfall, wind, cloud contribute to weather whereas air density does not. in contrast to weather, climate is concerned with the long-term behaviour of the atmosphere.

Question 15

define climate

Answer 15

the long-term atmospheric characteristics of a specified area. contrasts with weather. these characteristics are usually represented by numerical data on meteorological elements, such as temperature, pressure, wind, rainfall and humidity. these data are frequently used to calculate daily, monthly, seasonal and annual averages, together with measures of dispersion and frequency.

Question 16

what is air pressure

Answer 16

the force per unit horizontal area exerted at any given level in the atmosphere by the weight of the air above that level. the air pressure decreases most rapidly with height near sea level where the air is most dense. it decreases by about 50% for every 5km of ascent.

Question 17

how do you calculate atmospheric pressure

Answer 17

P = pgh

where P = pressure, pa
p = air density, kg/m^3
g = gravitational constant, 10 m/s^2
h = height above surface, m

Question 18

what are the base units of pressure (pascals)

Answer 18

kg/ms^2

Question 19

what is atmospheric pressure measured in

Answer 19

millibars (mb)

Question 20

what is the conversion rate between pascals (air pressure) and millibars (atmospheric pressure)

Answer 20

1mb = 100pa = 1hpa

Question 21

what is the average sea level pressure

Answer 21

1013mb

Question 22

what happens to air density with altitude

Answer 22

air density decreases with altitude, most air molecules held tightly to surface (gravity), pressure decreases with altitude

Question 23

what is a reference fram

Answer 23

a reference frame describes where we look at dynamics from, what the observer is looking at

Question 24

what is a non-inertial reference frame

Answer 24

the reference frame is moving too (due to earths rotation), this is termed a non-inertial reference frame

Question 25

what objects experience virtual force related to reference frames

Answer 25

objects in the earths reference frame experience virtual forces related to the movement of the reference frame.

Question 26

tell me about inertial vs non-inertial reference frames

Answer 26

non-inertial (moving) reference frame (observer) looks like a black ball would follow a curved rather than straight path which it would on an inertial reference frame. The curved path is due to the Coriolis force/effect

Question 27

what is the Coriolis effect

Answer 27

it is a quasi-force or fictitious force exerted on a body when it moves in a rotating reference frame

Question 28

what is the equation for the Coriolis force/effect

Answer 28

F = ma = m x 2 x (weird _n_ symbol) = m x 2 x _n_ x v^1 where the force is at 90 degree angle with respect to the object u (m is the mass of object u) m = mass of u (kg) _n_ = earths rotation speed (radian/s) v^1 = air parcel velocity

Question 29

simply why does the Coriolis effect occur

Answer 29

equator is moving faster than the poles, air mass is going in the direction and speed of the equator, eg. deflection.

Question 30

define Coriolis force

Answer 30

also known as the geostrophic force. an apparent force on moving particles in a frame of reference which itself is moving, usually rotating. such a force is required if Newtons laws of motions are to be applied in the rotating framework. The Coriolis force is of major importance to the movement of both oceanic waters ad air. in meteorology the coriolis force per unit mass of air arises from the earths rotation and is equal to -2_n_ x V, where _n_ and v are vectors representing respectively the angular velocity of the earth and the velocity of the air relative to the earth. in practical terms the force 'deflects' air particles to the right in the northern hemisphere and to the left in the southern hemisphere. it affects only the direction, not the speed of the wind.

Question 31

define cyclone

Answer 31

(or depression), a region of relatively low atmospheric pressure, typically one to two thousand km across, in which the low level winds spiral counter clockwise in the northern hemisphere and clockwise in the southern. cyclones are common features of surface weather maps and are frequently associated with windy, cloudy and wet weather.

Question 32

what is cyclogenesis

Answer 32

the formation of cyclones. occurs in preferred areas and is usually most vigorous in wintertime.

Question 33

how does cyclogenesis work

Answer 33

the inward spiralling air ascends within the systems and flows out in the upper troposphere. in any atmospheric column, if more mass is exported aloft than is imported at low levels, the surface pressure will fall, while surface pressure will rise and the low will fill if there is a net gain of mass in the column.

Question 34

what are cyclone associated with

Answer 34

cyclones are highly transient features which are associated with disturbed weather and, if frontal, with strong horizontal gradients of temperature and humidity, and sharp changes in cloud cover and type. Across the extra-tropical ocean basins they carry out very important heat transport in a meridional direction which offsets to some extent the persistent equator to pole imbalance in the radiation budget. In frontal cyclones warm air is transported poleward and cooled while cold air moves towards the equator and is warmed.

Question 35

define Buys Ballot's law

Answer 35

an observer in the northern hemisphere, standing with her back to the wind, will have low pressure to her left and high pressure to her right, the converse is true in the southern hemisphere. this law was formulated in 1857 by the Dutch meteorologist Buys Ballot.

Question 36

which way is the deflection of the air parcel due to Coriolis effect

Answer 36

to the right in the northern hemisphere | to the left in the southern hemisphere

Question 37

which way does air move

Answer 37

air moves along the gradient from high to low pressure and is deflected due to the coriolis effect.

Question 38

in the southern hemisphere, air will move clockwise in a .....

Answer 38

low pressure area

Question 39

in the northern hemisphere, air will move clockwise in a .......

Answer 39

high pressure environment

Question 40

what is a cyclone

Answer 40

air spins into low pressure - anti clockwise in northern hemisphere - clockwise in southern hemisphere - also called depressions or lows

Question 41

what is an anti-cyclone

Answer 41

air spins outward from high to low pressure

Question 42

define convection

Answer 42

in general, mass movement within a fluid resulting in transport and mixing of properties of that fluid. in the atmosphere a class of fluid motion in which warmer air goes up while colder air goes down. Unfortunately fluid dynamicists sometimes use the word in place of advection. in the case of fair-weather convection, air at low levels is slowly warmed by sunshine absorbed at the ground until it can lift away from the surface to be replaced suddenly by comparatively cool air from above.

Question 43

what is buys ballot law

Answer 43

with your back to the wind, you can determine the location of high and low pressure. in a frictionless atmosphere and due to the Coriolis effect, the angle between the wind and pressure gradient is at 90 degrees. in the northern hemisphere: atmosphere pressure is low to the left and high to the right. opposite for southern hemisphere.

Question 44

what is geostrophic wind

Answer 44

the theoretical wind due to balance between the Coriolis and pressure gradient forces - ignores friction - geostrophic wind flows parallel to isobars - friction and coriolis effect deflect wind

Question 45

what are isobars

Answer 45

lines of constant pressure at a given height

Question 46

what do closer isobar mean for surface winds

Answer 46

closer isobars -> stronger pressure gradient -> faster wind speed

Question 47

what do wind 'barbs' show

Answer 47

wind speed

Question 48

what happens to air directly along the equator and continuing to do so

Answer 48

it will not be deflected

Question 49

what is an air mass

Answer 49

a large volume of air with similar temperature and moisture content

Question 50

what are the moisture properties of air masses

Answer 50

``` maritime = wet continental = dry ```

Question 51

what are the thermal properties of air masses

Answer 51

tropical polar arctic

Question 52

define air parcel

Answer 52

an imaginary body of air to which may be assigned any or all of the dynamic and thermodynamic properties of the atmosphere. investigation of the stability of the atmosphere is made most simply by the parcel method in which it is hypothesised that a test parcel of air moves vertically with respect to its environment as represented by an ascent curve on a tephigram.

Question 53

define front

Answer 53

a sharp transition zone separating air of different temperatures and origins. the term was introduced by the bergen school of meterology in 1918 as part of their work on extra-tropical cyclone structure. the front has a 3d form. it extends into the atmosphere as a gently sloping surface of about 1 in 100 so that the cold, denser air appears as a wedge shape beneath the warmer air. the front lies in a trough of lower pressure accompanied by changes in wind velocity, pressure and temperature as the front passes a site. the intensity of change varies greatly from one front to another. Horizontal convergence and associated vertical motion are a necessary feature of a well-defined front.

Question 54

tell me about fronts between air masses

Answer 54

boundary between air masses of different types of origins. located along low pressure troughs.

Question 55

what is a cold front

Answer 55

cold air mass catches up to warm air mass, forces warm air up, causing clouds, often associated with heavy thunderstorms, rain and hail.

Question 56

what are warm fronts

Answer 56

located at the leading edge of a warm air mass, warm air slowly overtakes cold air ahead of the front, warm air climbs over the cold air, stratiform clouds (sheets of clouds) form and rainfall increases as front approaches.

Question 57

what is an occluded front

Answer 57

cold air overtakes warm air, usually forms around mature cold fronts, cold and warm fronts curve poleward into the point of occlusion (triple point), wide range of weather along this front.

Question 58

what is cyclogenesis

Answer 58

development and formation of cyclone

Question 59

what is cyclolysis

Answer 59

the opposite of cyclogenesis - weakening of cyclonic flow

Question 60

describe the process of cyclogenesis

Answer 60

the development of cyclonic circulation leads to convection and clouds, starts by disturbance along a stationary front, distorts the front. cyclonic flow intensifies as pressure within disturbance decreases, forces warm air poleward and cold air equatorward. opposite is cyclolysis (weakening of cyclonic flow)

Question 61

what is anticyclogenesis

Answer 61

development or strengthening of anticyclonic flow around a high pressure system

Question 62

what is anticyclolysis

Answer 62

weakening of anticyclone

Question 63

characteristics of an anticyclone

Answer 63

no or low clouds, brings continental air masses to the uk, cold in winter, warm in summer

Question 64

what are two examples of blocking

Answer 64

omega block and diffluent block

Question 65

what is blocking

Answer 65

large high pressure air mass remains stationary over the same period for a long time (week or more) blocks or redirect migratory cyclones and fronts, can cause sustained heatwaves or cold conditions over the uk.

Question 66

what is the impact of blocking (two examples)

Answer 66

lower than average winter temperatures over europe, % of normal winter rainfall less than average over most of europe.