Atmosphere I : Weather Flashcards
define atmosphere
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%.
what are the only components of the atmosphere that vary locally in concentration
carbon dioxide, ozone and water vapour
what are aerosols
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.
define the atmospheric layers
these are principally the troposphere, stratosphere, ozonosphere, mesosphere, thermosphere, ionosphere, exosphere
tell me about the troposphere
(or overturning layer) 0-10km above the earths surface
tell me about the stratosphere
(or layer of constant temperature) 10 - 25 km on its own, combined with the ozonosphere it is 10 -50 km though
tell me about the mesosphere
(some similarity with troposphere) 60 - 100km
tell me about the thermosphere, ionosphere and exosphere
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
what layer of the atmosphere does weather occur
the troposphere
where is the ozone layer
in the stratosphere
what is weather
it is the instantaneous state of the atmosphere, what we experience on a daily basis
what does type of weather depend on
location: latitude, altitude, terrain, water bodies
what is climate
the long-term average weather
define weather
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.
define climate
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.
what is air pressure
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.
how do you calculate atmospheric pressure
P = pgh
where P = pressure, pa
p = air density, kg/m^3
g = gravitational constant, 10 m/s^2
h = height above surface, m
what are the base units of pressure (pascals)
kg/ms^2
what is atmospheric pressure measured in
millibars (mb)
what is the conversion rate between pascals (air pressure) and millibars (atmospheric pressure)
1mb = 100pa = 1hpa
what is the average sea level pressure
1013mb
what happens to air density with altitude
air density decreases with altitude, most air molecules held tightly to surface (gravity), pressure decreases with altitude
what is a reference fram
a reference frame describes where we look at dynamics from, what the observer is looking at
what is a non-inertial reference frame
the reference frame is moving too (due to earths rotation), this is termed a non-inertial reference frame
what objects experience virtual force related to reference frames
objects in the earths reference frame experience virtual forces related to the movement of the reference frame.
tell me about inertial vs non-inertial reference frames
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
what is the Coriolis effect
it is a quasi-force or fictitious force exerted on a body when it moves in a rotating reference frame
what is the equation for the Coriolis force/effect
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
simply why does the Coriolis effect occur
equator is moving faster than the poles, air mass is going in the direction and speed of the equator, eg. deflection.
define Coriolis force
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 -2n 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.
define cyclone
(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.
what is cyclogenesis
the formation of cyclones. occurs in preferred areas and is usually most vigorous in wintertime.
how does cyclogenesis work
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.
what are cyclone associated with
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.
define Buys Ballot’s law
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.
which way is the deflection of the air parcel due to Coriolis effect
to the right in the northern hemisphere
to the left in the southern hemisphere
which way does air move
air moves along the gradient from high to low pressure and is deflected due to the coriolis effect.
in the southern hemisphere, air will move clockwise in a …..
low pressure area
in the northern hemisphere, air will move clockwise in a …….
high pressure environment
what is a cyclone
air spins into low pressure
- anti clockwise in northern hemisphere
- clockwise in southern hemisphere
- also called depressions or lows
what is an anti-cyclone
air spins outward from high to low pressure
define convection
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.
what is buys ballot law
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.
what is geostrophic wind
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
what are isobars
lines of constant pressure at a given height
what do closer isobar mean for surface winds
closer isobars -> stronger pressure gradient -> faster wind speed
what do wind ‘barbs’ show
wind speed
what happens to air directly along the equator and continuing to do so
it will not be deflected
what is an air mass
a large volume of air with similar temperature and moisture content
what are the moisture properties of air masses
maritime = wet continental = dry
what are the thermal properties of air masses
tropical
polar
arctic
define air parcel
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.
define front
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.
tell me about fronts between air masses
boundary between air masses of different types of origins. located along low pressure troughs.
what is a cold front
cold air mass catches up to warm air mass, forces warm air up, causing clouds, often associated with heavy thunderstorms, rain and hail.
what are warm fronts
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.
what is an occluded front
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.
what is cyclogenesis
development and formation of cyclone
what is cyclolysis
the opposite of cyclogenesis - weakening of cyclonic flow
describe the process of cyclogenesis
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)
what is anticyclogenesis
development or strengthening of anticyclonic flow around a high pressure system
what is anticyclolysis
weakening of anticyclone
characteristics of an anticyclone
no or low clouds, brings continental air masses to the uk, cold in winter, warm in summer
what are two examples of blocking
omega block and diffluent block
what is blocking
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.
what is the impact of blocking (two examples)
lower than average winter temperatures over europe, % of normal winter rainfall less than average over most of europe.
