NZ Airport Climates Flashcards
What are the orographic influences at Auckland? What are their effects? (2)
- Coromandel Ranges to the east: shelter the easterly preventing low cloud bases and precipitation
- Waitakere Ranges to the north west: Influence the W/ SW wind
What are the orographic influences at Wellington? What are their effects? (2)
- North Is. and South Is. high ground create channelling through strait: prevailing wind is NNW or SSE
- Hills East and West of runway: additional channelling
What are the orographic influences at Christchurch? What are their effects? (4)
- Port hills 15km SE or airport at 2000ft
- Southern Alps 90km to the West
- Canterbury plain is large and flat
- Wind is normally affected most by alps and cook strait
Describe the characteristics of the surface wind at Auckland? (7)
- SW and NNE are most common
- SW occurs more in spring summer
- NE is evenly spread
- When strength is 20kts + it is probably SW direction.
- Sustained 30kts + is normally due to post cold front streams
- Gustiness not common (50kts + only 2 days per year)
- Southern edges of TC move through from NW to SE: winds start NE, then E, and then SE
Describe the characteristics of the surface wind at Wellington? (5)
- 98% is N or S direction
- Due to complex terrain winds do not necessarily follow gradient above friction layer
- Northerly winds associated with troughs or depressions moving east, most common in spring/ early summer. The accompanying cold front is always preceded by strong NW winds (50-60kts)
- Southerly winds associated with ridges of high pressure over South Is. or over/ to the east of North Is. (very strong)
- Sudden winds occurs when a squall line passes. light N winds can be replaced by strong S winds 50kts. Usually short lived (30-40min)
Describe the characteristics of the surface wind at Christchurch? (6)
- NE or E is most common
- Most frequent in summer due to the sea breeze
- When 3000ft wind is NNW to NNE, the surface wind will be ENE - most common when high is E or SE of Canterbury
- NW wind sis hot, dry föhn wind with turbulence - most likely ahead of cold fronts from the SW
- When 3000ft wind between SSE and SW, surface wind will be SW direction
- Winds in excess of 20kts occur 3% or year. slightly less than half blow from S/SW with rest from NW or NE
Describe the characteristics of the sea breeze at Auckland? (4)
- Main direction is SSW and most common Oct-Mar
- Average speed 5-10 kts
- SE wind will strengthen breeze up to 20-25 kts, and increase vertical extent to 3000ft
- NE wind will weaken the breeze and make it thin. (Strong shear between 5-600ft)
Describe the characteristics of the sea breeze at Wellington? (7)
-Generally Oct-Apr
-Normally SSE with strength of 6-12kts
-Good heating required overland in anticyclonic conditions
-Very small pressure differential is essential
-Normally between 0900-1800 but smaller window during autumn and spring
-Not uncommon to have southerly sea breeze at one end and a light northerly wind at the other
-If wind above friction layer is E/NE, breeze will strengthen to 12-14kts.
Shielding of Rimutakas and Tararuas to the E/NE will assist
Describe the characteristics of the sea breeze at Christchurch? (5)
- Strongest Oct-Apr
- Requires weak pressure gradient
- Strength is 15kts
- Direction is NNE
- Established 1-2 hrs after sunrise, peaks 1 hr later and weakens 1-2 hrs after sunset
Describe the characteristics of the Land breeze in Auckland? (3)
- Common in summer and winter, but starts late run winter
- Blows from E/NE
- 5-10kts starting about midnight
Describe the characteristics of the land breeze at Wellington? (4)
- Needs weak pressure gradients
- Light NNE blows year round at night
- Katabatic effects from N/ NE influence the strength as well as time of day
- Not unusual for land breeze in winter from mid afternoon onwards.
Describe the characteristics of the land breeze at Christchurch? (4)
- Needs weak pressure gradient
- Occurs on clear nights
- Katabatic flow from alps a common factor
- Starts 1-2 hours after sea breeze has subsided
Describe the turbulence characteristics of Auckland? (2)
- Surface friction turbulence not normally present
- Thermally induced turbulence is often experienced in and around nearby hills
Describe the turbulence characteristics of Wellington? (4)
- In Northerly: Throughout approach and landing phase, and from takeoff to 3000ft
- In southerly: turbulent approach with smooth landing phase, little-none shortly after becoming airborne. smooth on climb out
- Low level severe turbulence can occur when cook strait wind is SW-NNW. Strong shear at 500-1000ft
- Degree of turbulence is directly proportional to the amount of fluctuation in wind direction
Describe the turbulence characteristics of Christchurch? (5)
- Relatively little when prevailing Easterly
- Turbulence if sea breeze turns to NW’er
- NW can have very strong low level shear with mod-sev turbulence
- Established NW will have turbulence down to ground
- Convective heating can create localised moderate turbulence and Cb and associated hail.
Describe the characteristics of fog at Auckland? (6)
-Radiation fog common Apr-Aug when a high prevails
-Prevailing wind will affect onset and persistence of fog
-Generally form 0300 and gone by 0900, may be slower when thicker fog
-Less of a problem when winds blow from the NNE
-When wind is W/ NW more likely to form fog, forms around 2200 and is difficult to predict duration.
-Substantial fog can remain over Papakura Chanel
When gentle sea breeze sets in from SW the fog can reform and last all day
Describe the characteristics of fog at Wellington? (4)
- Very uncommon - 5 days per year
- Normally sea fog from South Is. east coast in S wind
- Most occurrences are Jan-Mar
- Radiation fog from Hutt valley can very rarely be blown to airport in light NE wind
Describe the characteristics fog at Christchurch? (6)
- Quite common - 45 days per year
- Radiation type most common
- Clear nights with weak pressure gradient, NE wind drops to >5kts and changes to light NW
- Evening fog will clear around midnight and reform before sunrise
- Advection fog can form over Pegasus Bay or Waimakariri river to North but will lift slightly off the surface
- Advection fog off lake ellesmere less likely to lift off surface but also less common
What are the characteristics of low cloud formation at Auckland? (3)
- Most common cause is moist NE airstream (500-600ft, sometime 300ft) - will last 24 hours
- Slow moving or stationary front with moist NNE flow in advance may have 300ft cloud with persistent heavy rain lasting 12 hours
- Rain from the SW/W is usually due to passage of wave depression or low pressure lying to S/SE of AA, so Cb and low bases expected
What are the characteristics of low cloud formation at Wellington? (6)
- Moist southerly with light or moderate strength (most restrictive)
- Low to the N/NE with high over Canterbury (not large pressure difference)
- Weakening tropical depression down east coast of North Is.
- Moist northerly will cover cook strait but terrain will shelter airport
- Can produce wave effect on lee side-not uniform
- If northerly flow is due to front/trough to the west low cloud will form on approach side of runway, with strong wind, rain and poor vis.
Describe the characteristics of low cloud formation at Christchurch? (6)
- High pressure ridge to E/SE
- Easterly drift advects low cloud/fog from ocean & pegasus bay (200-300ft bases)
- Depression to E/NE
- Surface wind SW overland and SE over sea with cloud base to normally 1000-1500ft, due to shielding from banks peninsula
- Occurs after passing cold fronts
- SW winds 1000ft bases can be present, lower to the E around port hills.
What conditions can affect visibility at Auckland? (4)
- Low cloud: No problems in summer, High frequency May-Aug
- N - NE winds >20kts normally cause
- Showers can cause, short duration during a front
- Pollution when winds light and air is stable
What conditions can affect visibility at Wellington? (5)
- Low cloud: generally southerly with strength >20kts
- Jan-Mar has poorest conditions
- May-Jul generally optimal
- Precipitation less likely to cause than low cloud
- Heavy showers can reduce to 1000-3000m for short period
What conditions can affect visibility at Christchurch?
- No change in NW or SW winds
- E/NE or SSW winds >20kts will reduce vis
- Low cloud and drizzle will significantly reduce
- 20+kts from S/SW can bring low cloud and poor vis
- May-Sep have highest incidence of low cloud or reduced vis.
