Lecture 1-12

Question 1

History of Synoptic-scale circulations

Answer 1

1. Admiral Fitz-Roy in British Navy. obtained a good set of surface observations from ships and coastal stations in and around British isles. He proposed a model which accurately depicted the horizontal scale of mid-latitude cyclones.
2. Bjerknes and Solberg presented a cyclone model based on observations from Scandinavia. Their main contribution was their observation that cyclones grow from the energy contained within the polar front and proposed a reasonable model for the distribution of cloud and precipitation with respect to the cyclone.
3. Satellite and radar systems made structures that weren’t previously observed became evident.

Question 2

History of Planetary-scale circulations

Answer 2

1. Establishment of upper-air observing networks in the 1940s and 1950s made the systematic study of general circulation of the atmosphere possible.
2. Plots o horizontal wind and pressure revealed that flow in the middle and upper troposphere outside of the tropics takes the form of waves of various sizes.
3. Longwaves such as these are said these are said to exist on planetary scale.

Question 3

History of Mesoscale Circulations

Answer 3

-Radar showed that synoptic scale systems had smaller scale features embedded within them.
-subdivisions are often based on our understanding of the governing equations of motion of the atmosphere and the fact that certain terms in these equations are more important at certain scales than they are at others.

Question 4

History of small-scale circulations

Answer 4

-At smaller scales in the atmosphere, the effect of friction on the flow becomes important.

Question 5

History of Physical Basis of Scale Separation

Answer 5

-Is quantitative evidence from radiosondes and the analysed the KE of the east-west component of the wind.
-Spectrum shows that there is energy at all scales of motion, there are strong peaks at frequencies ranging from a few days (the synoptic scale) to a few weeks (the planetary scale). There are also peaks at one year (the annual cycle), one day (the diurnal tide), and a smaller peak at a few minutes which may correspond to gravity waves.
-3 important notes: 1. KE never completely vanishes since KE is converted from one scale to another. 2. Energy involved in the larger scales is much bigger in the free atmosphere than near the ground (frictional and turbulence effects are more prominent near the ground). 3. There is no peak in the energy spectrum at the mesoscale (“spectral gap”).

Question 6

Scale Interactions

Answer 6

-Constant cascade of energy from the planetary scale circulation driven by differential solar heating to the micro-scale at which the energy is dissipated by friction into heat.
-Energy is transported from smaller scales to larger scales. planetary scale mid-latitude westerly current at upper levels involves the synoptic-scale disturbances.
-lifespans are strongly correlated to their horizontal length scales.

Question 7

Implications of Scale Analysis

Answer 7

-For large-scale and synoptic-scale flows, the length and time scales are suuch that only terms that needed to be retained are those that involve the pressure gradient and the Coriolis force (quasi-geostrophic flow). The fluid is hydrostatic and incompressible and the flow is almost inviscid (frictionless), especially over time scales of about a day.
-small-scale motions, the quasi-geostrphic assumption doesn’t apply.

Question 8

Advection

Answer 8

-Advection: Basically means winds are able to move various properties of the atmosphere around with it. (i.e moves around temperature).

Question 9

The surface pressure decreases by 3 hPa. per 180km in the eastward direction. A ship steaming eastward at 10km/hr measures a pressure fall of 1 hPa per 3 hrs. What is the pressure change on an island that the ship is passing.

Answer 9

asked to find dP/dT. DP/Dt is the change following the motion of the ship is -1hPa per 3 hrs. The zonal velocity of ship is given and it is moving u=10km/hr eastward and v and w are zero in this case. Thus, we have:
dP/dt=DP/Dt-(udP/dx)
dP/dt=-1hPa/3hrs-(10km/hr)(-3hPa/180km)
dP/dt=-1hPa/6hrs

Question 10

POSITIVE ADVECTION IS ALWAYS…

Answer 10

Defined with a negative sign in front of it

Question 11

Circle:

Answer 11

is determined by the intersection of a sphere and a flat surface

Question 12

Great circle:

Answer 12

Great circle: if a plane intersects the sphere through the centre, the circle is a great circle

Question 13

The shortest distance between two points on a sphere…

Answer 13

determined by a great circle through these two points

Question 14

line of latitude:

Answer 14

The intersection of a plane perpendicular to the polar axis and the Earth

Question 15

longitude line:

Answer 15

is defined as a great circle which intersects the poles.
-reference longitude: is defined by the longitude line (meridian) which passes through Greenwich, England..

Question 16

1 degree latitude=

Answer 16

60 nautical miles or 111km

Question 17

A map is conformal…

Answer 17

when the angles between two intersecting lines on the globe are similar on the map projection

Question 18

Scale of a map:

Answer 18

The scale of a map is the ratio between the distance on the map and the distance on the globe. This ratio may vary across the map because of the distortions of the map projection.

Question 19

Great circles:

Answer 19

are curved lines with the exception of meridians.

Question 20

Four letter identifier systems

Answer 20

-First letter identifies the area of origin: C- Canada, K- United States, E-Northwestern Europe, L- Southwestern Europe, and M - Mexico and Caribbean.
-2nd, 3rd, and 4th letters are the 3-letter station identifier

Question 21

Scaling the Momentum Equations

Answer 21

-Horizontal speed = U is approximately 10m/s
-Vertical speed = W is approximately 1cm/s
-Length scale = L is approximately 10^6 m
-Depth Scale = H is approximately 10^4
-Pressure fluctuation= SigmaP/rho =10^3m^2s^(-2)
-Time = L/U is approximately 10^5 s
-Friction coefficient = 10^-4 (weird v).

Question 22

Mean Sea Level Pressure:

Answer 22

Mean Sea Level Pressure: is computed from the station pressure and reported in observations so that the barometric pressures at stations of different elevations can be compared at a common level for synoptic purposes.

Question 23

Altimeter Setting:

Answer 23

Altimeter Setting: is a computed value of mean sea level pressure expressed in inches and hundredths of mercury.

Question 24

How is wind direction described?

Answer 24

Wind direction (N=0, E=90, S=180, and W=270)

Question 25

Anemometer level:

Answer 25

A height of 10m. The height is so that is is above the wakes that form behind individual surface roughness elements such as nearby trees, houses, etc.
-Wind direction and speed reported in hourly observations are a two-minute mean. The direction is determined to the nearest ten degrees and the speed to the nearest knot.

Question 26

Wind Character:

Answer 26

is reported when there are significant variations in the wind speed, during the ten minute period ending at the time of the observation. The character will be reported as a Gust or Squall depending on the magnitude and duration of the variation

Question 27

Gust:

Answer 27

-Gust are sudden, rapid, and brief changes in the wind speed. They are characterized by the more or less continual fluctuations between the high (peak) and low (lull) speed.
-Gusts are reported when: (a) the highest peak speed is at least 5 kt higher than the current two minute average and (b) the highest peak is at least 15 kt.

Question 28

Squalls:

Answer 28

are essentially gusts with a longer duration of higher speeds. Squall speeds are reported when the following criteria are recorded: (a) the wind speed increases by 15 kt over the two minute average speed that preceded the increase (b) the duration of the peak speed period is at least two minutes (c) the wind speed attains a one minute mean of at least 20 kts (c) the wind speed attains a one minute mean of at least 20 kts, during the peak speed period (d) the wind speed diminishes by at least 5 kt.

Question 29

Prevailing visibility:

Answer 29

the greatest horizontal visibility that is equalled or surpassed throughout half of the horizon circle. It need not be a continuous half.

Question 30

Obscuration:

Answer 30

Aka obscured sky cover. The designation for the sky cover when the sky is compltely hidden by surface-based obscuring phenomena.

Question 31

Partial Obscuration:

Answer 31

A situation when a part of the celestial dome is hidden by a weather phenomenon.

Question 32

Layer amount:

Answer 32

The amount in tenths or oktas of the whole sky that is observed to be covered by a layer of cloud aloft or concealed by a surface-based layer.

Question 33

Summation amount:

Answer 33

At any level is the amount of the whole sky that is covered by layers at and below that level.

Question 34

Layer Opacity:

Answer 34

represents the portion of the whole sky that is observed to be concealed by the layer. If a layer doesn’t conceal any part of the sky, its opacity is zero.

Question 35

Ceiling:

Answer 35

is defined as lesser of:
(a) the height above ground of the base of the lowest layer aloft at which the summation opacity is 6/10 or more of the whole sky;
(b) the vertical visibility in a surface -based layer which completely obscures the whole sky. For obscurations, the ceiling height represents the vertical visibility into the obscuring phenomena rather than the height of the base, as in the case of clouds or obscuring phenomena rather than the height of the base as in the case of clouds or obscuring phenomena aloft.