From: "Martin" To: Subject: aus-wx: National Climate Centre predicts warm and dry winter for South Eastern Australia Date: Wed, 17 May 2000 22:44:11 +0930 X-Mailer: Microsoft Outlook Express 5.00.2014.211 Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com The National Climate Centre has predicted a fairly strong chance of dry and warm conditions over the next 3 months ( June - August). I cannot understand how this prediction is made. We are not entering an El-Nino phase but rather a decaying La Nina and I would have thought this would have caused the dry conditions to be around Eastern and Northern Australia. The prediction of dry conditions for SE Australia is particularly surprising and alarming given the fact that SE Australia has not had a decent winter for years and currently many areas are having record dry 36 month period. Surely we are due for a boomer wet Winter! Martin +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ Date: Thu, 18 May 2000 03:16:50 +1000 From: Don White X-Mailer: Mozilla 4.5 [en] (Win98; I) X-Accept-Language: en To: aussie-weather at world.std.com Subject: Re: aus-wx: Unusual morning in Canberra Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com Blair, In the new AWS at Dinner Plain operational yet? I have not seen any data through from it so far. Have you ever looked at Parkes v Parkes AP in NSW? Some unusually high minimum temp variations occur here - up to 7-8 degrees on the 6 am obs at times. Don White Blair Trewin wrote: > > > > > Throughout the night, Canberra AP has been 6 to 8 degrees warmer than > > Tuggeranong, in the SW suburbs of the city and only a few kilometres as > > the crow flies from the airport. > > currently of -2 at tuggeranong and + 6 at the airport. > > Hard to forecast?? > > > > Don W > > It's definitely unusual. It seems to be related to the wind; Canberra > Airport was reporting light winds (4-7 knots) most of the night, > whereas Tuggeranong was calm all night. The two weren't too far apart > for the first part of the night, but Canberra Airport then rose from > 3.5 at midnight to 6.8 at 0330, whilst Tuggeranong kept falling. > (Canberra Airport did eventually fall to 1, probably sometime between > 0700 and 0730 based on the half-hourly obs - which is unusually late > for a minimum there). > > Even a comparatively light wind can break down the low-level inversions > which are critical to low minimum temperatures under clear-sky > conditions. This is even more true over snow cover; I've just been > looking at some Scottish observations from late December 1995, when > Altnaharra equalled the British record low (-27.2) - on the previous > night it went from -24 to -5 and back again during the course of a few > hours, all of it in darkness, in response to the commencement and > cessation of a light SE wind. Perisher Valley also rose from a minimum > of -18.0 to an 0900 temperature of 0.0 in similar circumstances on > 29 June 1994 (the day Charlotte Pass set the Australian record of -23). > > In regions with reasonably homogeneous terrain and a reasonably dense > station network (for example, central western NSW and interior SW WA), > the upper limit of variation of daily max/min temperature anomalies > between adjacent stations is around 4 degrees. (I use anomalies, rather > than actual temperatures, here to take into account sites which are > consistently warm or cold, e.g. town v airport sites). This number > increases considerably in complex topography or near the coast. > I'm currently wrestling with the issue (in my extremes verification > work) of whether or not a minimum of -12.8 at Mount Hotham was > reasonable when Mount Buffalo (340m lower and similarly exposed) only > managed -4. Hopefully the new AWS at Dinner Plain (potentially a very > cold site) will get something lower than that this winter and save > us the trouble of working out whether -12.8 is really a legitimate > Victorian record :-) > > Blair Trewin > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com > with "unsubscribe aussie-weather your_email_address" in the body of your > message. > -----------------------jacob at iinet.net.au------------------------------ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ From: Blair Trewin Subject: Re: aus-wx: National Climate Centre predicts warm and dry winter for South Eastern Australia To: aussie-weather at world.std.com Date: Thu, 18 May 2000 11:22:50 +1000 (EST) X-Mailer: ELM [version 2.5 PL2] Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com > > The National Climate Centre has predicted a fairly strong chance of dry and > warm conditions over the next 3 months ( June - August). I cannot understand > how this prediction is made. We are not entering an El-Nino phase but rather > a decaying La Nina and I would have thought this would have caused the dry > conditions to be around Eastern and Northern Australia. The prediction of > dry conditions for SE Australia is particularly surprising and alarming > given the fact that SE Australia has not had a decent winter for years and > currently many areas are having record dry 36 month period. Surely we are > due for a boomer wet Winter! > > Martin A few points here: 1. The seasonal forecast is based on sea-surface temperature patterns in both the Pacific and Indian Oceans - it's not just a simple ENSO- based system. The Pacific, averaged over the year and country as a whole, has more influence than the Indian, but there are certain seasons and regions where the Indian Ocean is the more significant of the two. 2. There is very limited forecast skill arising from ENSO at this time of year. In essence, this is because marked deviations from neutral conditions characteristically begin and end in the southern autumn, and hence near-normal SSTs in the eastern Pacific in April (the current situation) don't imply the likelihood of near-normal conditions several months down the track, in the way that they would later in the year - near-normal conditions in April could mean the start of an El Nino/La Nina, the end of an El Nino/La Nina, or a prolonged period of near-normal conditions, and at that time of year it's hard for a forecast scheme to tell which is which. This is known as the 'autumn predictability barrier'. 3. As a result of the lack of persistence in ENSO in autumn, whilst there are strong simultaneous correlations between tropical Pacific temperatures and eastern Australian winter rainfall (and minimum temperature), the lag correlations (which is what you need for a forecast, because you don't have the winter SSTs to hand when you're trying to make a winter forecast) are weak to non-existent. This means that at this time of year the forecast skill in SE Australia is limited (and what there is comes mainly from the Indian Ocean). The ENSO influence on the forecast picks up considerably from July onwards. One of the problems we face in making seasonal forecasts is that, in any given season, there will be parts (sometimes large parts) of the country where we have little forecast skill, but we don't have the option of just leaving those bits of the map blank. You'll notice references to skill (or lack thereof) in some of the media releases, but that sort of subtlety rarely makes it into the media (except perhaps for the specialist rural papers). The current drought is extremely localised by normal standards (although I suspect it would be far more widespread if we had capacity to measure rainfall over the oceans south of Victoria); it is essentially confined to Tasmania, southern Victoria and south-eastern SA. It has also persisted through just about every possible state of ENSO. The main synoptic driving force behind it is that the high- pressure belt has been persistently south of its normal position for three years now, but it is far from clear why this is happening. Blair Trewin +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ From: Blair Trewin Subject: Re: aus-wx: Unusual morning in Canberra To: aussie-weather at world.std.com Date: Thu, 18 May 2000 12:00:18 +1000 (EST) X-Mailer: ELM [version 2.5 PL2] Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com > > Blair, > In the new AWS at Dinner Plain operational yet? I have not seen any data > through from it so far. I don't think so. I expect it will open when the airport does, which I presume will be at the start of the ski season. It isn't yet listed in the stations table of the database here. > Have you ever looked at Parkes v Parkes AP in NSW? Some unusually high > minimum temp variations occur here - up to 7-8 degrees on the 6 am obs > at times. Parkes is the most extreme example, but big differences are actually quite common at town centre/airport combinations. This can be partially attributed to urban heat islands, but bigger factors are topography and the state of the town centre site. Many of the old town centre sites are/were in poor condition (Parkes was certainly no exception, with the instruments within a metre or two of a corrugated iron fence) and were hence fairly unrepresentative of the surrounding region. Cobar and Glen Innes are other places in NSW where this happens regularly, whilst in other cases there has been a marked apparent drop in temperatures when a station has moved (with few or no overlapping observations) to the airport - Cootamundra, Young and Bendigo are good examples here. Back in about 1992 someone from the Tasman Institute wrote (and had published, which doesn't say a lot for the standard of the reviewing) a paper in which he used such unadjusted data to claim that Australian temperatures exhibited a falling trend. Blair Trewin +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ X-Sender: disarm at braenet.com.au (Unverified) X-Mailer: Windows Eudora Pro Version 3.0 (32) Date: Thu, 18 May 2000 14:41:24 +1000 To: aussie-weather at world.std.com From: Matthew Smith Subject: aus-wx: warm fronts Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com The latest synoptic has a warm front on it for those interested... http://www.bom.gov.au/difacs/IDX0894.gif?92694921 its to the far SW of WA... Matt Smith +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ X-Sender: carls at ford.ace-net.com.au Date: Thu, 18 May 2000 15:56:08 +1000 To: Aussie Weather List From: Carl Smith Subject: aus-wx: FWD: A light moment Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com >From: Dosidicus at aol.com >Date: Thu, 18 May 2000 01:00:37 EDT >Subject: OFF - T: A light moment > >NHC Unveils Revolutionary New Model > >Miami (AP)--In time for the beginning of the 2000 hurricane season, >the National Hurricane Center revealed the latest model for hurricane >intensity forecasting Tuesday. The model itself was not present at >the press conference, but the staff of the NHC were on hand to >answer questions. Other hurricane specialists from around the world >were present as well for the occasion. > >The model, which the NHC calls FLIPER, uses a revolutionary new >technique to forecast hurricane intensification. "Hurricane >intensity forecasting has always been a thorny problem for >meteorologists," says Max Mayfield, the new director of the NHC. >"This model will give us the upper hand in forecasting for the first >time." Dr. Jack Beven emphasized the magnitude of the improvement, >saying "This will improve intensity forecast accuracy from zer--by >exactly fifty percent." > >The model works by "estimating the statistical probability of the >presentation of one side of a circular metallic object when rotated >rapidly along a horizontal axis for a duration of one to three >seconds," said Lixion Avila. He responded to allegations that it was >in fact a coin with "That's ridiculous, and an insult to the people >who invested their time an energy into this. We make better use of >tax dollars than that." > >Other hurricane specialists were skeptical. "They [the NHC] are >behind the curve," said Dr. Greg Holland of the Australian Bureau >of Meteorology. "We've been using a crystal ball for years with >fine results." > >The full description of the FLIPER model will appear in next month's >issue of the Monthly Weather Review. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ From: "W.A. (Bill) Webb" To: "Wx Aus" Subject: aus-wx: Cold fronts and warm fronts Date: Thu, 18 May 2000 16:18:09 +1000 X-Mailer: Microsoft Outlook Express 5.00.2615.200 Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com Hi All, Some interesting discussion on this subject. Although I'm sure I miss some as I'm concentrating on weather in north Queensland when I look, not uncommonly I see warm fronts marked on the BoM MSL synoptic charts. As Matthew pointed out, there was one just recently - easily overlooked way down in the SW corner as I remember. I gather also that, as the charts are hand drawn by various forecasters, some forecasters add features and some don't bother because of their lack of significance ?? On the question of the monsoon trough and its arrival and departure - I am under the impression that its location at any time is driven by the seasons - ie, wherever the area of greatest direct incidence of solar radiation is - in our summer time, around about the latitude of Darwin/tip of Cape York (at the Tropic of Capricorn, Rockhampton in Qld, the sun is directly overhead at mid day in Dec, but it doesn't get the most "direct" radiation - hence less heating). The highs to the south of the continent move north and south in sync with this system (the Hadley Cell). Having said that, there are influences on the trough which enhance and suppress its activity during its presence off northern Australia - the MJO for instance, which we constantly watch for up here - in ALL seasons. I do not know if it has any "influence" on the monsoon as such, but the heat low referred to in posts, which sits over about the Kimberly, is a typical pre-monsoon feature. It makes life very uncomfortable up there - the "troppo" season. There's much more - but that's my 2 bobs worth. See ya, Bill, Proserpine. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ Date: Thu, 18 May 2000 19:18:06 +1000 From: Keith Barnett X-Mailer: Mozilla 4.6 [en] (Win95; I) X-Accept-Language: en To: aussie-weather at world.std.com Subject: Re: aus-wx: National Climate Centre predicts warm and dry winter for South Eastern Australia Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com Seems pretty odd given that the previous outlook had huge areas of eastern or southeastern Australia going for 50-60%+ chance of above-median rainfall. The encouraging thing about the latest one is that forecast skill is low for this time of the year in the area concerned. And given that there has been 2 months of below average rainfall in Sydney to date, and the propensity for June to be a wet month with its 1040mb highs near Tasmania and east coast lows not an uncommon occurrence, I'd be surprised if we don't get heavy rain in the next few weeks. Martin wrote: > > The National Climate Centre has predicted a fairly strong chance of dry and > warm conditions over the next 3 months ( June - August). I cannot understand > how this prediction is made. We are not entering an El-Nino phase but rather > a decaying La Nina and I would have thought this would have caused the dry > conditions to be around Eastern and Northern Australia. The prediction of > dry conditions for SE Australia is particularly surprising and alarming > given the fact that SE Australia has not had a decent winter for years and > currently many areas are having record dry 36 month period. Surely we are > due for a boomer wet Winter! > > Martin > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com > with "unsubscribe aussie-weather your_email_address" in the body of your > message. > -----------------------jacob at iinet.net.au------------------------------ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ X-Sender: jdeguara at pop.ihug.com.au X-Mailer: QUALCOMM Windows Eudora Pro Version 4.2.2 Date: Thu, 18 May 2000 20:43:31 +1000 To: aussie-weather at world.std.com From: Jimmy Deguara Subject: aus-wx: Amos Weatherwatch meeting Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com AUSTRALIAN METEOROLOGICAL & OCEANOGRAPHIC SOCIETY, A.M.O.S. SYDNEY CENTRE - WEATHERWATCH GROUP NEWSLETTER NUMBER 00-05 - MAY 2000 The Next Meeting of the AMOS Weatherwatch Group will be on Wednesday 24th May 2000 at 7:30pm (19:30) at Macquarie University, Building E5A, Room 143 (E5A-143). Expensive Parking is available in University Car-Parks see notes below. This meeting will be an opportunity to hear Dr. John Lowke, speaking on Many Aspects of Lightning (Including Ball Lightning). MAKE A NOTE IN YOUR DIARY NOW - DO NOT MISS THIS CHANCE! Dr. Lowke is a retired professional scientist who was the chief research scientist in the C.S.I.R.O., Division of Applied Physics, shortly before his retirement last year. John's principle research was in the field of electrical discharges in gases. He has worked on lasers, plasma physics, the physics of welding, and is a member of the Standards Australia Committee for the formulation of standards for the protection of buildings from lightning strikes. This background in physics, and interest in the cause of Ball Lightning, led him to work for the United States Airforce in Vietnam. He is a contributor to the latest book on Ball Lightning. People should arrive promptly at the venue, and you are assured of a fascinating evening. Questions are invited, but there may also be time for you to present your experiences of ball lightning, or near misses. Visitors are very welcome. Discussion will follow the presentation, and light refreshments will be available during the meeting. Dinner with the Speaker will be held at the 'Middle of Nowhere' Restuarant at the end of Culloden Road, off Talavera Road, North Ryde, at 6:00pm(18:00). Please RSVP by Tuesday 23rd May 2000 to Alan Williams at 9488.9975, or e-mail :-alanjwilliams at ozemail.com.au At this meeting of Weatherwatch be careful about your parking, fees have increased to be $2.00 for the first hour, then one dollar for each subsequent hour, to a MAXIMUM OF $4.00 (If you let it run out it will start at $2.00 again) Four dollars gives you until 23:59. IF YOU HAVE EXPERIENCE OF BALL LIGHTNING PLEASE PARTICIPATE. PHOTOS OF INTERESTING LIGHTNING DISPLAYS WELCOME. (WARNING - THIS IS NOT AN OPPORTUNITY FOR STORM CHASING) Enquiries to Alan Williams (02)9488.9975 Paul Graham (02)9888.2527 Jimmy Deguara (02)9627.1943 Future date of the next AMOS Weatherwatch Meeting is 26th July 2000 Other dates will be listed on the AMOS Web Site later in the year at http://atmos.es.mq.edu.au Click on AMOS Sydney Centre. Other 2000 Weatherwatch Meeting Dates will emerge later in the year, after the Olympics. Please bring any suggestions for future programmes to our May Meeting. Recent Weather Below average rain for April in Sydney, with a warm spell. Heavy rain across the Tropical North of Australia. Cyclone Tessi 1st-2nd April. Heavy rain on Queensland Coast. Cyclone Rosita 18th-20th April. Destruction at Broome and Cable Beach. Subsequent heavy rain across the centre of the Continent. Wishing all our members and friends a safe, interesting Autumn/Winter season. Today's Quiz Question. What is the difference in the headings between Newsletter 00-03 and 00-05? No prizes. Tell Roger or Alan. Regards Roger T. Nurse, News Editor 9th May 2000 Paul Graham (Convenor)(AMOS Committee) 9888.2527 Alan Williams(Scribe)(AMOS Committee) 9488.9975 Roger Nurse (Publicity)(AMOS Member) 9449.1473 Jimmy Deguara(Storms)(ASWA Liaison) 9627.1943 ---------------------------------------------------------------------------- --------------- Jimmy Deguara from Schofields, Sydney President of Australian Severe Weather Association Inc. (ASWA) http://severeweather.asn.au e-mail: jdeguara at ihug.com.au homepage with Michael Bath note new URL http://australiasevereweather.com/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ From: "Michael Thompson" To: Subject: Re: aus-wx: National Climate Centre predicts warm and dry winter for South Eastern Australia Date: Thu, 18 May 2000 21:25:18 +1000 X-Mailer: Microsoft Outlook Express 5.00.2014.211 Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com It's these East Coast lows that make long range forecasts so unreliable during the winter months along the NSW coasts. A good guide to the rainfall variability is at http://www.bom.gov.au/climate/averages/variability.shtml bear in mind that the desert area variability's are extreme due to the low averages. Considering the NSW has high average rainfall, yet still has HIGH - VERY HIGH variability you can see why rainfall forecasts are so risky. Michael ----- Original Message ----- From: Keith Barnett To: Sent: Thursday, 18 May 2000 19:18 Subject: Re: aus-wx: National Climate Centre predicts warm and dry winter for South Eastern Australia > Seems pretty odd given that the previous outlook had huge areas of > eastern or southeastern Australia going for 50-60%+ chance of > above-median rainfall. > The encouraging thing about the latest one is that forecast skill is low > for this time of the year in the area concerned. And given that there > has been 2 months of below average rainfall in Sydney to date, and the > propensity for June to be a wet month with its 1040mb highs near > Tasmania and east coast lows not an uncommon occurrence, I'd be > surprised if we don't get heavy rain in the next few weeks. > > Martin wrote: > > > > The National Climate Centre has predicted a fairly strong chance of dry and > > warm conditions over the next 3 months ( June - August). I cannot understand > > how this prediction is made. We are not entering an El-Nino phase but rather > > a decaying La Nina and I would have thought this would have caused the dry > > conditions to be around Eastern and Northern Australia. The prediction of > > dry conditions for SE Australia is particularly surprising and alarming > > given the fact that SE Australia has not had a decent winter for years and > > currently many areas are having record dry 36 month period. Surely we are > > due for a boomer wet Winter! > > > > Martin > > > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com > > with "unsubscribe aussie-weather your_email_address" in the body of your > > message. > > -----------------------jacob at iinet.net.au------------------------------ > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com > with "unsubscribe aussie-weather your_email_address" in the body of your > message. > -----------------------jacob at iinet.net.au------------------------------ > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------ From: paulmoss at tpgi.com.au To: aussie-weather at world.std.com Date: Thu, 18 May 2000 21:12:10 +0930 Subject: aus-wx: (Fwd) Re: Monsoon triggered by Cold Fronts?? X-mailer: Pegasus Mail for Win32 (v3.12a) Sender: aussie-weather-approval at world.std.com Reply-To: aussie-weather at world.std.com Hey all. I had Peter Bate, Manager of Climate Services BOM Darwin have a look at the cold front / Monsoon debate. heres his reply. Paul in Darwin ------- Forwarded message follows ------- Date sent: Wed, 17 May 2000 11:44:45 +0000 To: paulmoss at tpgi.com.au From: Ian Shepherd Subject: Re: Monsoon triggered by Cold Fronts?? Paul, I forwarded your query to Peter Bate, Manager of the Climate & Consultative Services section in the Bureau's Darwin Regional Office. Here is his reply ... >X-Sender: pwbate at ntserver >X-Mailer: QUALCOMM Windows Eudora Pro Version 4.0.1 >Date: Wed, 17 May 2000 10:40:40 +0000 >To: Ian Shepherd >From: Peter Bate >Subject: Re: Fwd: Monsoon triggered by Cold Fronts?? >Cc: pwbate > >Ian, > >Anthony Cornelius makes some reasonable points. For monsoon onset you >really need broad-scale vorticity and this can come from W to NW'lies >on the north side as well as E to SE'lies to the south. Not sure that >the latter are necessarily associated with a cold front though. I >guess one can often argue that a SE surge from the ridge is often the >"tail end" of a cold front (perhaps this is where the BoM's alleged >conservatism comes in). You also need upper divergence of course, and >the appoach of a long-wave trough extended to low latitude sometimes >provides an avenue for this to get going. Timing is also important, >and is often the trickiest part. These things need to happen at a >favourable time, and need to be reasonably concurrent. A favourable >time could (but not necessarily) be provided by such things as the >approach of an active 30-60 day ISO phase (evident in upper div, >zonal wind, pressure, etc). As he also says, negative affects are >possible if they occur at the wrong time. A dry SE surge can have a >strong suppressing effect. > >As we know, cross-equatorial surges during the monsoon season are >something we look for in attempting to predict monsoon behaviour. >Such surges are generated by a strong sub-tropical ridge, are >manifested in the easterly trade wind belts then cross the equatorial >region where they begin turning into the monsoonal westerly belt. In >our own region it would be fair to say that a strong cold front >through E China/Japan may sometimes be a precursor to a good NE surge >through the S China Sea, which may subsequently give a boost to the >Indonesian/Australian monsoon. I believe it is drawing rather too >long a bow to call such a surge a cross-equatorial cold front though. > >Cheers, >Peter > >>>Date sent: Mon, 15 May 2000 20:55:52 +1000 >>>From: Anthony Cornelius >>>To: aussie-weather at world.std.com >>>Subject: Re: aus-wx: cold fronts and warm fronts >>>Send reply to: aussie-weather at world.std.com >>> >>>Hi Michael, >>> >>>Cold fronts are thought to be one the processes that trigger the >>>monsoonal onset. For example, the monsoon generally requires the >>>presence of the Pilbara and Cloncury lows to be present. This >>>draws in a moist inflow from the tropical oceans. However, it then >>> presents a sharp moisture discontinuity over the northern >>>Australia region (over land), as you have tropical maritime air, >>>and tropical continental air beside each other. However, there's >>>no real disturbance besides the two heat lows/troughs - and while >>>the atmosphere is unstable to about 700mb, due the to nature of >>>heat lows/troughs generally anti-cyclonic conditions occur above >>>700mb, thus adding subsidence to the area. So you have a >>>quasi-state equilibrium over the area, and no real trigger to spark >>>off convection. A cold front is thought to be one of three >>>triggers that allow the monsoon to fully develop. It displaces the >>>tropical continental air and since the heat trough is dependent on >>>heat, moves northwards into the moist (unmixed) tropical maritime >>>air. This adds further convergence to the air, and is thought to >>>be a trigger. Convection then breaks out on the northern side of >>>the trough. >>> >>>The other two methods are thought to be anticyclogenesis causing >>>barotropic instability (it is sometimes associated with a cold >>>front too, and is thought to have a similar effect...however >>>increases horizontal wind shear in the E'lies). And the other >>>method is considered to be an extension of a long wave trough. >>> >>>None the less...these methods (at least in my opinion), could also >>>have a negative effect should they occur at the 'wrong' time, or >>>have other systems associated with them. >>> >>>I'm curious about the cold fronts triggering monsoons on the other >>>side of the equator though! This is most difficult to >>>conceptualise... >>> >>>Anthony Cornelius >>>Queensland Coordinator of the Australian Severe Weather Association >>>(ASWA) (07) 3390 4812 14 Kinsella St Belmont, Brisbane QLD, 4153 >>>Please report severe thunderstorms on our Queensland severe >>>thunderstorm reporting line on (07) 3390 4218 or by going to our >>>homepage at http://www.severeweather.asn.au >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- >>> ++-+ >>> -+ To unsubscribe from aussie-weather send e-mail >>> to:majordomo at world.std.com with "unsubscribe aussie-weather >>> your_email_address" in the body of your message. >>> -----------------------jacob at iinet.net.au------------------------- >>> --- -- >>> >>>------- End of forwarded message ------- >>> >=============================================================== > Peter Bate, Regional Manager, Climate & Consultative Services > Bureau of Meteorology, PO Box 40050, > CASUARINA NT 0811 AUSTRALIA > Phone [Fax]: (08) (International: 61 8) 8920 3813 [8920 3832] > e-mail: p.bate at bom.gov.au >=============================================================== > Ian Shepherd, Senior Meteorologist, Severe Weather Section Northern Territory Regional Office Bureau of Meteorology, PO Box 40050, Casuarina, N.T. 0811 Ph (08) 8920 3821 Fax (08) 8920 3840 e-mail I.Shepherd at bom.gov.au ------- End of forwarded message ------- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ To unsubscribe from aussie-weather send e-mail to:majordomo at world.std.com with "unsubscribe aussie-weather your_email_address" in the body of your message. -----------------------jacob at iinet.net.au------------------------------