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#1440877 - 09/11/2017 11:18 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
_Johnno_ Offline
Weatherzone Addict

Registered: 08/11/2009
Posts: 1694
The BOM keep saying that this La Nina or close La Nina conditions will have little impact over the summer period mainly due to the Indian ocean but have I missed something? Has anyone seen the big warm up in the IOD regions the last week or two?

The last time the ssts looked like this north west of Oz, north of oz and the Pacific was August, September last yr and we all know what happened to large parts of Australia then! (away from the east coast east of the ranges).

I know we are now at the tail end of the IOD season but surely with this set up with both the Indian and Pacific on our favour it is a little naive and premature to say that the current set up with have little impact for rainfall this Summer across the country.

http://www.weatherzone.com.au/climate/indicator_sst.jsp?c=ssta


Edited by _Johnno_ (09/11/2017 11:19)
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#1440878 - 09/11/2017 11:22 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 1266
Loc: Wollongong, NSW, Aus
True, I think we've seen the lingering IOD's influence last week with the outbreak of severe storms and Tasman Low.

Also another tongue of tropical moisture is making its way across the country. Pity it isn't May.

EC & GFS in the longer term also look very unstable with a deep thermal trough fed by decent ne'erlies. So things are a changing, and hopefully for the moister.

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#1440883 - 09/11/2017 12:20 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: GringosRain]
GringosRain Offline
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Registered: 19/06/2007
Posts: 1331
Loc: Quorrobolong NSW
is this a forum or an ignorum...because I dont seem to get responses in here.

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#1440884 - 09/11/2017 12:22 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Locke Offline
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Registered: 27/12/2007
Posts: 4361
Loc: Brisbane
I still think the MJO is one of the final key ingredients for above average rainfall through early Summer.

Currently the MJO signal is weak and predicted to remain so when it cycles through phases 5 and 6 during November.

I think the critical timing will be the next pass in December. I think if were seeing MJO values > 2 at that time then there is going to be a high likelihood of a major rainfall event during the period in combination with other favorable ingredients.
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This post and any other post by Locke is NOT an official forecast & should not be used as such. It's just my opinion & may or may not be backed by sound meteorological data. For official information, refer to Australian Bureau of Meteorology products.

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#1440887 - 09/11/2017 13:18 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: GringosRain]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 1266
Loc: Wollongong, NSW, Aus
Originally Posted By: GringosRain
What are peoples thoughts on when we get enhanced rainfall chances in the SE of the country (lets say NSW generally) with reference to the MJO..... During the active phase of the MJO or inactive phase? Ive heard some say that in the peak monsoon season, the MJO keeps the moisture north and precipitates it, so by default it would seem then we may be more likely to get better rainfall in the south between active periods of the MJO when tropical moisture is activated by triggers further south?? thoughts?


Sorry Gringos, didn't see your post.

The question is does the MJO really impact the SE of Aus? It does facilitate, when deep, the monsoon trough slipping further south and cyclogenisis, so maybe it does? I would say more indirectly than directly.


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#1440888 - 09/11/2017 13:35 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Kino]
GringosRain Offline
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Registered: 19/06/2007
Posts: 1331
Loc: Quorrobolong NSW
My suspicion is we might do better between phases especially in favourable years like this one is shaping up to be. by memory we have to get a very active southern dipping monsoon trough to get the big events down here, and they seem to be relatively few and far between.
I recall at other (most)times seeing plenty of monsoonal activity in the north during an active MJO and no rain coming further south, in fact it can be quite dry (sinking stable air?)
As an example the last two events in NSW have been between phases.
I guess we can watch this season to see if there is any noticeable correlation with NSW rainfall, if nobody has further comments on this.

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#1440889 - 09/11/2017 15:01 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Locke Offline
Weatherzone Addict

Registered: 27/12/2007
Posts: 4361
Loc: Brisbane
The event last month corresponded with a strong active phase as did major rainfall events in Oct 2010 and January 2011.

May 1996 and Feb 1999 flood events both coincided with strong active phases.

Would love to know what the MJO was doing in late January 1974 but I suspect it was either in phase 5 or 6 and the value was over 2.
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This post and any other post by Locke is NOT an official forecast & should not be used as such. It's just my opinion & may or may not be backed by sound meteorological data. For official information, refer to Australian Bureau of Meteorology products.

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#1440893 - 09/11/2017 18:40 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Chris Stumer Offline
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Registered: 28/01/2010
Posts: 1609
Loc: Kingaroy
The trades are still blowing along nice and healthy.

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#1440903 - 09/11/2017 22:04 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Locke]
GringosRain Offline
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Registered: 19/06/2007
Posts: 1331
Loc: Quorrobolong NSW
Originally Posted By: Locke
The event last month corresponded with a strong active phase as did major rainfall events in Oct 2010 and January 2011.

May 1996 and Feb 1999 flood events both coincided with strong active phases.

Would love to know what the MJO was doing in late January 1974 but I suspect it was either in phase 5 or 6 and the value was over 2.


You are referring to the event in QLD earlier in October? My question isnt in reference to QLD as it is obviously more affected by the active phase. There was a major storm outbreak a few days ago in NSW and there was a bigger rain event/storm/squall line early in the last week of October. Im pretty sure we werent in an active MJO phase then?

Models are indicating a rain event down this way in about 10 days time too which looks to me to be after the MJO passes through also.

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#1440909 - 10/11/2017 07:18 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Locke Offline
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Registered: 27/12/2007
Posts: 4361
Loc: Brisbane
I'm not so sure of the connection between MJO phases and rain events in NSW although I suspect there would still be some form of correlation in the long term data.

Big rainfall events can occur for a variety of reasons but often require multiple sets of factors to combine (otherwise they would occur with a far greater frequency).

Tropical moisture infeed is certainly one factor and looking at what seems to be a correlation between the MJO and such events in South East QLD you could argue that under favourable circumstances the MJO provides larger amounts of tropical moisture to feed South.

But certainly only one piece that fits a variety of different puzzles.
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This post and any other post by Locke is NOT an official forecast & should not be used as such. It's just my opinion & may or may not be backed by sound meteorological data. For official information, refer to Australian Bureau of Meteorology products.

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#1440911 - 10/11/2017 07:39 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Mike Hauber Offline
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Registered: 13/07/2007
Posts: 2755
Loc: Buderim
According to BOM the impact of mjo is mostly north Australia.



Some research into MJO links with rainfall finds statistically significant relationships with rainfall outside the tropics, but the relationship is not strong. Generally rainfall can increase around phase 4, whereas the peak rainfall in the tropics is phase 5/6. The increased rainfall is due to remotely forced low pressure systems, and changed wind direction, with more northerly winds as the MJO approaches Australia feeding more tropical moisture into the extra-tropical regions.

edit:

I'd also add that influence on severe flood events might not be the same as that on average rainfall. In particular it would seem that a leftover tropical system late in the MJO cycle could cause severe flooding in southern Australia during a period when rainfall is on average reduced.
Quote:

a. Summer (DJF)

In summer (Fig. 8), enhanced tropical convection, as indicated by negative OLR anomalies, shifts from the Indian Ocean in phase 2 to the Australian–Indonesian monsoon region by phase 5. In the Indian Ocean, the OLR anomaly is bounded between about 12°N and 20°S, which is as far south as it extends for any season (cf. Figs. 9 –11). Over Australia, however, a negative OLR anomaly appears at extratropical latitudes in phases 3 and 4, preceding the main tropical convective signal in phase 5. This is the same signal highlighted in the rainfall in the previous section (e.g., Fig. 3). Thus, the enhanced rainfall in the extratropics occurs in conjunction with increased high-level clouds, which in phase 4 are linked continuously back to the tropics as a relatively narrow band oriented toward the northwest. This OLR signature bears a close resemblance to what is commonly known as a northwest Australian cloud band. Northwest cloud bands may occur in any season, each event typically lasting over several days, although they have been shown to be more frequent in winter (Tapp and Barrell 1984).

The anomalous winds at the 850-hPa level in association with the extratropical rainfall signal in phases 3 and 4 are predominantly northerly (Fig. 3). At the 500-hPa level, these northerlies are associated with a midlatitude wave train (Fig. 8); in phase 2 a weak negative geopotential height anomaly exists over the southwest Indian Ocean that subsequently shifts eastward, strengthens, and undergoes downstream development. Then, by phase 4 a positive height anomaly develops over the Tasman Sea, consistent with, and reinforcing, the lower-tropospheric northerlies highlighted in Fig. 3. These low-level northerlies suggest a possible role for moisture transport from the tropics for the enhanced extratropical rainfall. Also, a slow-moving “blocking high” to the south and east of Australia is characteristic of many summer (and early autumn) synoptic weather events producing widespread high rainfall in southern Australia (e.g., Zhao and Mills 1991).
b. Autumn (MAM)

Although the tropical circulation anomalies in autumn (Fig. 9) closely resemble those in summer (Fig. 8), the extratropical anomalies show some noticeable differences. Similar to summer, in phases 2 and 3 weak anomalously high geopotential heights exist over southern Australia and to its east in the Tasman Sea. In phase 4, however, the anomalous 500-hPa high that existed over the Tasman Sea in summer is now split to the west and east. The only statistically significant (at the ∼10% level) extratropical height anomaly during these phases in autumn is the high that exists to the south and west of Australia in phases 3 and 4. Thus, unlike summer, there are no significant low-level northerly anomalies across the center of the continent in phases 3 and 4. Consistent with the lack of northerly anomalies, there are comparatively weaker (although still statistically significant in phase 4) extratropical rainfall signals in these phases in autumn (Fig. 4). Compared with summer, enhanced rainfall and coincident negative anomalous OLR (Fig. 9) are focused farther east and north in phase 4. Like in summer, however, this OLR anomaly is placed between a high to its east and a low to its west indicative of northerly anomalies along the northeast coast and to eastern parts of Australia (Fig. 4).
c. Winter (JJA)

One of the more striking winter rainfall signals associated with the MJO is the relatively quick transition from dry conditions in southern Australia in phases 3 and 4 to wet conditions in phases 5 and 6 (Fig. 5). The circulation anomalies at the 500-hPa level (Fig. 10) show an almost stationary high geopotential height anomaly over southeastern Australia during phases 2–4, and associated easterly anomalies at mid- and low levels over eastern and southern Australia (Figs. 5 and 10). This situation rapidly changes, however, between phases 4 and 5, as low height anomalies move into the region from both the north and west and become established over southeastern Australia in phase 5. The enhanced (suppressed) rainfall in southern Australia in winter is thus more closely aligned with the center of a large-scale area of low (high) geopotential height, rather than with anomalous northerly (southerly) winds as occurs in autumn or summer.
d. Spring (SON)

Finally, we are interested in the origin of the reduced springtime rainfall in the southeast during phase 3 (Fig. 6). The springtime 500-hPa extratropical circulation anomalies (Fig. 11) resemble those occurring in winter (Fig. 10), although there are also some similarities with those in summer (Fig. 8). Such similarities between atmospheric anomalies across different seasons, being computed from completely independent data, help increase our confidence in the reproducibility of the results. Compared to winter, however, the anomalous high over southern Australia reaches its peak intensity in phase 3 instead of phase 4. Thus the dry signal in spring during phase 3 appears well explained by the implied large-scale subsidence existing within the extratropical high. Contrasting with this, phases 4 and 5 in spring show wet signals extending across a wide range of latitudes and longitudes (Fig. 6), and these appear best associated with northwesterly anomalies originating from the eastern Indian Ocean (Fig. 6), in a similar fashion to what occurs in summer in phases 3 and 4.


Edited by Mike Hauber (10/11/2017 07:44)

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#1440914 - 10/11/2017 08:14 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 65
Loc: Pinjarra Hills, Qld
The discussion on this topic is very interesting, even if a bit highly technical at times.

Sometimes we need the climate drivers explained more simply for those of us that want to learn. I like these climate dogs videos produced to explain key drivers for Australia's climate.
http://www.climatekelpie.com.au/understand-climate/climatedogs

Apologies if that information on the climate dogs videos has been posted before. I tried to check using the search function but could not find previous reference to the videos. Apologies also to the more knowledge people on this forum if you find the videos to basic, but I do think they are useful for those of us wanting to learn.
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#1440923 - 10/11/2017 09:45 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Chris Stumer Offline
Weatherzone Addict

Registered: 28/01/2010
Posts: 1609
Loc: Kingaroy
I wonder what ENSO conditions will 2018 bring, will it be a neutral year, La Nina or El Nino? If the cool neutral in the Pacific gets it's act together next month or January then 2018 could be a La Nina year depending on if the predicted -PDO eventuates.


Edited by Chris Stumer (10/11/2017 09:46)

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#1440926 - 10/11/2017 10:05 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Mike Hauber]
GringosRain Offline
Weatherzone Addict

Registered: 19/06/2007
Posts: 1331
Loc: Quorrobolong NSW
Originally Posted By: Mike Hauber
According to BOM the impact of mjo is mostly north Australia.



Some research into MJO links with rainfall finds statistically significant relationships with rainfall outside the tropics, but the relationship is not strong. Generally rainfall can increase around phase 4, whereas the peak rainfall in the tropics is phase 5/6. The increased rainfall is due to remotely forced low pressure systems, and changed wind direction, with more northerly winds as the MJO approaches Australia feeding more tropical moisture into the extra-tropical regions.

edit:

I'd also add that influence on severe flood events might not be the same as that on average rainfall. In particular it would seem that a leftover tropical system late in the MJO cycle could cause severe flooding in southern Australia during a period when rainfall is on average reduced.
Quote:




Yeah nice Mike....I think this fits with my general observation, being that generally the correlation is weak between active phases and rain in the south east. I feel that we can often get good average rain events in the inactive phase, and every now and then everything aligns to bring a flood triggered from the active phase. It clearly is impacted by the phase, the MJO strength and time of year. I think the tail end of one of the MJO passages between now and April could bring substantial floods south this year....the ingredients feel right. See what happens

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#1440934 - 10/11/2017 12:20 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
CoastalStorm22 Offline
Weatherzone Addict

Registered: 10/07/2006
Posts: 2701
Loc: Lane Cove, Sydney, NSW
Typical MJO effects rainfall are as follows

OND



NJD



DJF


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#1440937 - 10/11/2017 13:49 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
GringosRain Offline
Weatherzone Addict

Registered: 19/06/2007
Posts: 1331
Loc: Quorrobolong NSW
thanks CS. Think thats further confirmation....cheers

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#1440938 - 10/11/2017 14:24 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Locke Offline
Weatherzone Addict

Registered: 27/12/2007
Posts: 4361
Loc: Brisbane
Whilst overall averages are interesting I think the results would be different if you isolated periods when the MJO signal was over 2.

If this produced a measurably different result the question then is what is influencing the strength of the MJO when its in any particular phase.
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This post and any other post by Locke is NOT an official forecast & should not be used as such. It's just my opinion & may or may not be backed by sound meteorological data. For official information, refer to Australian Bureau of Meteorology products.

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#1440949 - 10/11/2017 21:07 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Chris Stumer Offline
Weatherzone Addict

Registered: 28/01/2010
Posts: 1609
Loc: Kingaroy
NOAA has just declared a La Nina, it will be interesting to see whether BOM will do the same.

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#1440951 - 10/11/2017 21:14 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
CoastalStorm22 Offline
Weatherzone Addict

Registered: 10/07/2006
Posts: 2701
Loc: Lane Cove, Sydney, NSW
Anyone know why NOAA measure AO at 1000mb but the SAM at 700mb?

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#1440956 - 11/11/2017 01:26 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Raindammit Offline
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Registered: 14/02/2002
Posts: 12616
Loc: Townsville & Bilyana NQ
Last 30 days:

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