Urban climate - lectures 16-19

Question 1

Landscapes modified by human agency, buildings

Answer 1

Urban environment

Question 2

The localised warming exerted by an urban area

Answer 2

Urban Heat Island

Question 3

Heat added to the atmosphere by human activities

Answer 3

Qf

Question 4

Road transport, power generation, domestic heating, air conditioning

Answer 4

Examples of Qf

Question 5

Heat stored within the urban canopy

Answer 5

Qs

Question 6

Advection (from surrounding areas)

Answer 6

Qa

Question 7

Is Qe important in UHI

Answer 7

less important - little surface water available for transpiration and evaporation. For local climate with parks or irrigated areas may cause oasis effect!

Question 8

Is Qg important in urban areas

Answer 8

Yes, an enhanced role

Question 9

Why is Qg more important in urban areas

Answer 9

Increased heat storage during the day caused by urban materials, increased heat emission in evening and night, low sky view factors

Question 10

Where is Qg less important

Answer 10

Mediterranean settlements

Question 11

What heat flux is most important in suburbs

Answer 11

Qh

Question 12

Suburban Qh lags rural Qh

Answer 12

diurnal variation

Question 13

Urban radiation & energy fluxes lead to the generation of…

Answer 13

urban boundary layer

Question 14

Multiple reflective surfaces (urban canyon), changed albedo, particulate matter - reflects and absorbs incoming SW radiation

Answer 14

SW radiation

Question 15

Particulate matter reflects and absorbs incoming SW radiation, as a result is a source of downwards LW radiation, reduced LW emission (sky view factor)

Answer 15

LW radiation

Question 16

Additional source of energy Qf, reduced Qe, increased Qg and Qs, reduced Qa

Answer 16

Surface energy balance

Question 17

High Qh and Qs, low Qe

Answer 17

City centre energy balance

Question 18

High Qe, low Qh and Qs

Answer 18

Rural energy balance

Question 19

Slower to warm up in mornings (Qg) and low sky view factors mean reduced receipt of SW radiation

Answer 19

Urban cool island

Question 20

Urban areas often have slower heating and cooling rates than rural areas

Answer 20

Diurnal evolution of UHI

Question 21

Why are warming & cooling rates different?

Answer 21

Qg, outgoing LW radiation

Question 22

How are parks different from urban surroundings?

Answer 22

colour - albedo
water availability

Question 23

High proportion of available water

Answer 23

possible oasis effect Qe > Q*

Question 24

Only occurs when synoptic-scale pressure gradients light, more common at night, can be of great significance for pollutant dispersal

Answer 24

Urban breeze

Question 25

Increased drag and turbulence from urban surface results in a relatively deep zone of friction - reduced windspeeds in comparison to equivalent rural atmosphere

Answer 25

Urban Boundary Layer

Question 26

if wind is oblique to street =

Answer 26

corkscrew effect

Question 27

if wind is parallel =

Answer 27

no sheltering by buildings - channelling of wind may result in jetting effect so enhanced wind speed

Question 28

Speed increases with height, so tall buildings will deflect faster moving upper air down to ground level, so can be up to 3 times windier than over open ground

Answer 28

Impacts of tall buildings

Question 29

Weak synoptic flow / pressure gradient, clear skies, more prominent at night

Answer 29

Favourable synoptic conditions for UHI

Question 30

City located on a high mountain ridge, prone to UHI development - UHI > 11°C recorded. Entrainment of warm urban air into katabatic flow makes some valleys warmer than valley heads.

Answer 30

Johannesburg, South Africa

Question 31

Since mid 1970s, greater diurnal temp on _____ and ____ compared to rest of the week

Answer 31

Sunday and Monday

Question 32

small town east of Chicago, downwind of steel mills, with increased annual precipitation from 990 mm to 1450 mm in 1930-1945. at nearby stations precipitation decreased from 990 to 900mm. rise in precipitation kinked to rise in steel production - but little investigation

Answer 32

The La Porte Anomaly

Question 33

positive correlation between UHI intensity and vapour pressure - so warmer nights associated with more moisture in air, difference in vapour pressure

Answer 33

Urban moisture excess (UME)

Question 34

Urban Plume - meso or micro?

Answer 34

Meso

Question 35

Canopy Layer - meso or micro?

Answer 35

Micro

Question 36

Line & point pollution sources

Answer 36

Canopy Layer/ microscale

Question 37

Areal pollution source

Answer 37

Boundary layer/ mesoscale

Question 38

Warm air overlying cold air

Answer 38

inversion

Question 39

occurs in a stable atmosphere, vertical motion is suppressed causing a relatively thin, concentrated plume

Answer 39

fanning

Question 40

occurs during the development of a surface radiation inversion

Answer 40

lofting

Question 41

If turbulent eddies are smaller than the pollutant cloud / plume

Answer 41

Will diffuse it

Question 42

if turbulent eddies are larger than the pollutant cloud / plume

Answer 42

Will transport it