NZ Climate Flashcards
Describe the orographic influences that affect Auckland airport?
IMMEDIATE area: LOW ROLLING HILLS and EXTENSIVE MUD FLATS at LOW TIDE;
COROMANDEL ranges EAST: Provide some SHELTER from EASTERLY winds PREVENTS LOW CLOUD BASE and HEAVY PRECIPITATION;
WAITAKERE ranges NORTHWEST: Provide SHELTER from WNW and STRENGTHEN WEST and SW WINDS
Describe the orographic influences that affect Wellington airport?
HIGH GROUND to NORTH and SOUTH produce OROGRAPHIC FUNNELLING through COOK STRAIT that acts NNW or SSE;
RIMUTAKA RANGES EAST and HILLS WEST provide ADDITIONAL FUNNELLING which influence LAND and SEA BREEZE;
HARBOUR area of PORT NICHOLSON NORTH and FITZROY BAY SOUTH airport UNOBSTRUCTED to wind
Describe the orographic influences that affect Christchurch airport?
PORT HILLS 15KM SOUTHEAST up to 2000ft;
SOUTHERN ALPS 90KM WEST;
CANTERBURY PLANE LARGE and FLAT;
COOK STRAIT
Describe the surface winds at Auckland airport?
Most COMMON: SOUTHWEST and NORTH-NORTHEAST(less);
SOUTHWEST: SPRING and SUMMER, 20KTS up to sustained 30KTS during PASSING of COLD FRONT;
NORTH-NORTHEAST: Throughout WHOLE YEAR;
GUSTS over 50KTS occur TWICE a YEAR
TROPICAL CYCLONE: SOUTHERN EDGE MOVES NORTHWEST to SOUTHEAST causing NORTHEAST WINDS which turn EAST and SOUTHEAST
Describe the surface winds at Wellington airport?
TERRAIN means SURFACE WINDS do NOT follow GRADIENT WINDS ABOVE FRICTION LAYER;
NORTHERLY and SOUTHERLY 98% of time;
NORTHERLIES: Associated with SOUTHERN TROUGHS or DEPRESSIONS moving EAST during SPRING/SUMMER. Accompanied COLD FRONT is PRECEDED by NW wind 50-60 KNOTS;
SOUTHERLIES: Associated with RIDGES of HIGH PRESSURE over SOUTH ISLAND and LOWS OVER or EAST of NORTH ISLAND, not as common but STRONG (30 KNOTS);
SUDDEN SOUTHERLY occurs when LINE SQUALL PASSES region, LASTS 30-40 minutes up to 50 KNOTS
Describe the surface winds at Christchurch airport?
North-east/east Most frequent in summer – Seabreeze is the major contributing factor When 3000 feet wind blows north north-west through to North Northeast, surface wind will be Northeast East. Most common when anticyclone to east or south-east of Canterbury North-west Hot dry fohn wind – hot and dry bringing turbulence Most likely occurrence – ahead of cold fronts moving from the south-west When 3000 feet wind between South Southeast and Southwest surface wind – Southwest. Strength – exceed 20 kn approximately 3% of the year. Marginally less than 50% below this speed are from the south or south-west, the remainder from north-west or north east.
Describe the sea breeze at Auckland airport?
MOST COMMON is SSW from late OCTOBER to late MARCH;
AVERAGE SPEED is 5-10 knots;
If PREVAILING WIND is SOUTH WEST breeze may INCREASE to 20-25 knots and VERTICALLY extend to 2000-3000ft AGL;
If PREVAILING WIND is N/NE breeze WEAKENS and becomes SHALLOW with STRONG SHEAR at 500-600ft
Describe the sea breeze at Wellington airport?
MOST COMMON between late OCTOBER and early APRIL, during hours of 0900 and 1800, SSW 6-12 knots;
REQUIRES small PRESSURE DIFFERENTIAL between LAND and SEA which means it is NOT UNCOMMON to have SOUTHERLY and NORTHERLY at EITHER end of RUNWAY if PREVAILING is slight NORTHERLY;
If wind ABOVE FRICTION LAYER E/NE an established breeze will INCREASE to 12-14 knots due to SHIELDING from RIMUTAKA and TAURUA ranges to EAST and NORTH EAST of airport
Describe the sea breeze at Christchurch airport?
STRONGEST between OCTOBER and APRIL, NNE at 15 knots;
REQUIRES WEAK PRESSURE GRADIENT;
Establishes 1-2 HOURS AFTER SUNRISE, PEAKS 1 HOUR later, till 1-2 HOURS AFTER SUNSET
Describe the land breeze at Auckland airport?
COMMON in SUMMER and WINTER but STARTS LATER and is WEAKER in WINTER;
Blows ENE at 10-15 KNOTS starting at MIDNIGHT
Describe the land breeze at Wellington airport?
Occurs during ALL SEASONS as a NNE during WEAK PRESSURE GRADIENTS;
STRONGEST during COLD, STABLE, NIGHTS with assistance from KATABATIC winds from the EASTERN RANGES;
NOT UNUSUAL for land breeze to form, from MIDAFTERNOON in WINTER
Describe the land breeze at Christchurch airport?
Occurs on CLEAR NIGHT with a WEAK PRESSURE GRADIENT 1-2 HOURS AFTER sea breeze has SUBSIDED;
KATABATIC flow from ALPS CONTRIBUTES to STRENGTH;
Describe the turbulence at Auckland airport?
NO SURFACE FRICTION turbulence;
THERMALLY INDUCED turbulence in and AROUND nearby HILLS
Describe the turbulence at Wellington airport?
LANDING:
NORTHERLY: THROUGHOUT APPROACH and LANDING phase;
SOUTHERLY: THROUGHOUT APPROACH with SMOOTHER LANDING phase;
TAKE OFF:
NORTHERLY: TO 3000ft
SOUTHERLY: LITTLE/NIL CLIMBING out of LYALL BAY;
SEVERE TURBULENCE LOW LEVEL when COOK strait wind is 240°-290° which comes with significant SHEAR at 500-1000ft due to TERRAIN;
TURBULENCE is PROPORTIONAL to DEGREE of FLUCTUATIONS in WIND DIRECTION
Describe the turbulence at Christchurch airport?
Relatively FREE from turbulence with EASTERLY SEA BREEZE;
Turbulent if SEA BREEZE changes to NORTH WESTERLY;
With NORTH WEST PREVAILING, wind loses MOISTURE over ALPS and is VERY ENERGETIC causing LOW LEVEL wind SHEAR and MODERATE/SEVERE turbulence to GROUND LEVEL;
CONVECTIVE HEATING can produce MODERATE turbulence with associated CB ACTIVITY and HAIL
Describe the fog at Auckland airport?
Mainly RADIATION FOG between APRIL and late AUGUST when there is a HIGH over the area;
FORMS from 0300 and CLEARS by 0900 but can persist when formed over HARBOUR to MIDDAY;
If PREVAILING WIND is NNE LESS FOG as it is blown away;
If PREVAILING WIND is W/NW WAITAKERE’S provide shelter and it may form EARLIER 2200 and may CLEAR AFTER SUNRISE but a FOG BANK may linger in the CHANNEL;
When the LAND WARMS and GENTLE SW SEA BREEZE sets in the fog may be PUSHED back OVER AIRFIELD
Describe the fog at Wellington airport?
Uncommon — five days per year on average Normally see fog originating off the east coast of South Island during southerly wind. Most occurrences January – March Radiation fog formed in Hutt Valley can be pushed by light north-east wind to the airport — very rare
Describe the fog at Christchurch airport?
Relatively high incidence – fortyfive days per year on average Radiation most common Clear nights with weak pressure gradient – north-east wind reduces to less than 5 kn and changes to light Northwest drift just prior to fog formation. Evening fog clears around midnight and redevelops prior to sunrise Advection fog, origin Pegasus Bay to north-east of the airport or the Waimakariri River to the north of the airport - slight lifting off the surface during the advection as it approaches airport Occasionally, advection fog sourced from Lake Ellesmere to the south, less likely to lift off the ground
Describe the low cloud at Auckland airport?
Most common cause – moist north-east airstream – cloud base of 5 – 600 feet and sometimes as low as 300 feet. Can persist up to 24 hours. Cloud over the Manukau heads than the airport. Slow-moving or stationary front with a moist north-north-east flow in advance, may have clout to 300 feet with persistent and heavy precipitation. Could last 12 hours. No garden precipitation from a west or south west wind flow usually requires the passage of a wave depression or a lowpressure area lying to the south and south-east of Auckland. This is often an unstable flow so that Cb activity and low cloud bases can be expected
Describe the low cloud at Wellington airport?
Moist southerly air stream Light or moderate strength Low pressure system lies to North or north-east of Wellington with higher pressures over Canterbury area, but not a large pressure differential. A weakening tropical depression moving down the east coast of North Island can produce long periods of low cloud. Moist northerly air stream Covers Cook straight with low cloud but high ground north of Wellington Shields airport and its immediate environment – cloud base generally higher than Cook straight. Hills to the north sometimes produce wave effect so that low cloud bases are found only side – not uniform. If northerly flow due to front or trough from the west low cloud 8 oktas over airport and South – on the approach side of runway. Strong wind, poor visibility and rain
Describe the low cloud at Christchurch airport?
high-pressure Ridge to East/south-east easterly drift advects low cloud or sea fog from Ocean and Pegasus Bay. 200 to 300 feet base is common depression to east/north-east surface wind south-west overland and south-east over sea – cloud base normally 1000 to 1500 feet. Airport may be kept free by shielding from Banks Peninsula. After passing of cold front south-westerly winds have commenced. Low cloud base – 1000 feet – lower ceiling towards East due to Port Hills
Describe the visibility at Auckland airport?
Due to low cloud: Almost totally absent in summer Great frequency May to August North to North East with winds less than 20 kn most common cause Due to showers Of short duration – may affect visibility 1 to 2 hours during a frontal passage Pollution Significant impact when winds are light, and air is stable
Describe the visibility at Wellington airport?
Low Cloud Generally due to southerly with a strength of less than 20 kn January to March has poorest conditions May to July generally optimal Reduced visibility due to precipitation is less likely than that of low cloud Heavy showers – visibility 1000 to 3000 m for short periods of time
Describe the visibility at Christchurch airport?
Northwest or Southwest winds – no reduction in visibility East/north-east or South Southwest – less than 20 kn Significant reduction due to low cloud and drizzle Excess of 20 kn, low cloud and poor visibility in South or Southwest wind May to September – highest incidences of low cloud and – or poor visibility
