A summary of the broadscale tropical circulation from 70°E to 180°, for the six months May to October 2005, is presented. The previous season (Nov 2004 - April 2005) was described as ENSO – neutral, although it did have some of the characteristics that are typical of weak El Niño events. Some of these indicators lingered for a short while into this period, but overall the period May to October 2005 is best described as being in a neutral ENSO phase. Towards the end of the period, there was some evidence of the Maritime Continent region becoming the broad focus of tropical convection. Throughout the season, sea-surface temperatures in the eastern near-equatorial Pacific were near average. The warmest waters of the Pacific were located close to the near-equatorial date-line, rather then the climatological location of the northwest Pacific. Most of the Northwest Pacific and Australian continent mean sea-level pressures were above average, with mostly close to average tropical convection. Outgoing long wave radiation and mean sea-level pressure over India indicate above average convection associated with the monsoon. Several active convective phases of the Madden-Julian Oscillation (MJO) were observed in the region during the season. The periodicity remained close to 45 days. A total of 18 tropical cyclones (13 typhoons) developed during the period, less than the mean (27) for the Darwin Regional Specialised Meteorological Centre (RSMC) area. All of these formed in the northwest Pacific.
A summary of the broadscale tropical circulation from 70°E to 180°, for the six months from November 2007 to April 2008, is presented. A mature La Niña state of ENSO (El Niño Southern Oscillation) prevailed early in the season, weakening towards the end of the season. The SST (sea-surface temperature) cool tongue pattern in the near equatorial far eastern Pacific near the South American coast extended west, past the date-line. The warmest waters in the equatorial Pacific remained close to their climatological location in the northwestern Pacific. The SOI (Southern Oscillation Index) remained positive throughout the season with a record high of +21 in February. Onset of the Australian monsoon over northern Australia occurred around 27 December 2007, close to the climatology. The signal of the MJO (Madden-Julian Oscillation) showed a regular periodicity of around 40–45 days during most of the season. A total of 23 tropical cyclones, close to the long-term average, developed in the RSMC area during the period.
A summary of the broadscale tropical circulation from 70°E to 180°, for the six months May to October 2007, is presented. During this period the Southern Oscillation developed from El Niño–Southern Oscillation (ENSO) neutral conditions to a La Niña (cold ENSO) state by the end of the period. The Southern Oscillation Index (SOI) remained within one standard deviation and positive from August, with the mean for the season being +1.3. Mean sea-level pressure (MSLP) anomalies for the season remained close to zero over much of the Darwin Regional Specialised Meteorological Centre (RSMC) region, except overAustralia where they were positive. The east Pacific sea-surface temperature (SST) cool tongue became cooler than normal. Convection over the southern Indian Ocean and Australia was generally below average while it was close to normal in the northern hemisphere monsoon. Several active convective phases of the Madden-Julian Oscillation (MJO) were observed in the region during the season. A total of 21 tropical cyclones (including 10 typhoons) were analysed during the period, less than the mean of 27 for the RSMC area.
This report presents verification results for the operational seasonal forecasts issued by the Australian Bureau of Meteorology from 2003 to 2005. It updates the results given in an earlier paper, which describes the methods used for operational verification of these forecasts. The poor performance of the seasonal minimum temperature forecasts in southwestern Western Australia is explored.
Fifteen tropical cyclones (TCs) formed in the South Pacific and southeast Indian Ocean during the 2005-06 TC season. This total was below the long-term average of 19 and is the seventh consecutive year of below average TC occurrence, although numbers were about average in the Australian region. Significantly there were five intense TCs, all in the Australian region. TC Monica reached a peak intensity of 69 m s-1 (135 kn) mean winds, the equal highest on record in the Australian region, as it crossed the Northern Territory coast. Most notably, TC Larry peaked in intensity at 56 m s-1 (110 kn) prior to crossing the Queensland coast, devastating the area around Innisfail. There were another four TCs that crossed the Australian coast. All of these crossed the Pilbara coast of northwest Australia, having a significant economic impact on the industry-rich region. The season occurred during a neutral El-Niño Southern Oscillation (ENSO) phase, whilst sea-surface temperatures (SSTs) remained warmer than normal over much of the region. Active phases of the intraseasonal Madden-Julian Oscillation (MJO) coincided with the development of eleven of the fifteen TC events.
The 2007 Antarctic ozone hole is reviewed from a variety of perspectives, making use of various Australian data and analyses. The 2007 ozone hole was relatively modest, particularly in comparison to that of 2006, due in part to a disturbance to the polar vortex in early September that led to an influx of ozone-rich air. Ozone depiction was still severe however in the lower stratosphere. The long-term outlook for recovery is described, with Antarctic ozone currently forecast to return to 1980 levels around the period 2055-2080.
Accurate prediction of low-level winds is an important research area for wind farm forecasting applications. The Centre for Australian Weather and Climate Research has extended its existing numerical weather prediction (NWP) capabilities to develop and implement a mesoscale assimilation and prediction system (named WLAPS for research purposes) which is shown to be all improvement on the Bureau's existing mesoscale model, mesoLAPS (denoted MLAPS). The usefulness of WLAPS as a tool for wind forecasting stems mainly from the fact that it has its own 10 kin resolution data assimilation scheme, in contrast to earlier Bureau of Meteorology mesoscale models which were initialised by interpolation from 37.5 km assimilation analyses.WLAPS performs well against several verification criteria, including: verification scores of gridded output that compare forecasts to model analyses, observation statistics which verify the forecast and analysis against observations, and event-based case studies. Where relevant forecasts are available, the performance of WLAPS is compared with that of its similar to 12.5 km resolution predecessor MLAPS.As part of the WLAPS project, the model has also been extensively verified against observational data from 53 hub height (40-80 m) wind towers across southern Australia. After bias corrections, WLAPS is shown to have a root mean square error (RMSE) of around 2 in s(-1) (depending on site type and season) for 1 to 12-hour forecasts, with bias close to zero. The inclusion of direction and stability information in the bias correction procedure is shown to have a positive impact on the forecasts. Verification against low-level winds is suggested as a useful criterion for mesoscale verification, since we expect the full range of scales of atmospheric motion to be present in low-level wind observations.
This study investigates the spatial and temporal variability of precipitation over northeast Victoria from 2000 to 2005. Using observational data for each month of the year, the elevation dependence of precipitation is analysed over the two distinct mountain ranges (the Strathbogie Ranges and the High Country) that characterise the region. It is found that the rate of increase of precipitation with terrain elevation is proportional to the rainfall at a reference station, representative of the mountain range. Therefore, extreme precipitation events result in pronounced increases in precipitation at the higher elevations. A synoptic classification is also applied to determine which systems are responsible for the precipitation over the region. This classification shows that interacting fronts produce the majority of the precipitation during the cooler months of the year, while cold lows dominate during the warmer months of the year. The consequences of this pattern is briefly investigated in terms of the Southern Annular Mode (SAM), and during 2000-2005 the precipitation from cold lows showed positive correlation with the SAM index, suggesting important large-scale influences on the regional precipitation.
Operational Consensus Forecasts (OCF) and official forecasts of daily maximum and minimum temperature in 2006 are verified for 107 locations where both forecasts are available. At eight capital cities the forecasts extend from one to six days ahead but for the remaining 99 locations the official forecasts usually extend only one day ahead. Over all sites combined, the next day's forecast from OCF is better than official forecasts for both maxima (61 per cent of sites; mean absolute error (MAE) 1.28 degrees C compared with 131 degrees C) and minima (75 per cent; MAE 1.48 degrees C compared with 153 degrees C). The comparative verification results revealed detailed systematic differences between the two forecasting schemes. For example, the official forecasts of capital city maxima were usually more accurate than OCF whereas for forecasts of capital minima OCF were more accurate.Forecasters at the three capital cities where official forecasts of maximum temperatures were clearly better than OCF provided summaries of their perceived weaknesses in OCF that enables them to improve on OCF guidance. The relative weaknesses of OCF and official forecasts are discussed with a view to improving future performance.\ The main suggestions arising from this study are that OCF may be improved by: (a) basing OCF bias-correction on wind analogues or developing an OCF model output statistics scheme; and (b) rationalising the number of numerical models used in OCF to reduce the over-representation of the Australian regional numerical model in its one to two days ahead forecasts and increasing the number of numerical models that contribute beyond two days ahead. Official forecasts should benefit from documentation of the meteorological situations where OCF performs both well and poorly then using that information when formulating official forecasts. Official forecasts of minimum temperature generally and maximum temperature at most locations would be more accurate if store weight were given to the OCF guidance.
Trends in warm season thunderday incidence are examined over southeastern Australia. There has been a significant increase in the number of thunderdays from 1941-2004, but much of this increase may have been a result of changes in observing practices in the mid 1950s. When data earlier than this are removed, some significant trends remain. There have also been smaller increases since 1970, mostly in the early part of the warm season (October-December). These increases may have been caused by changes in the atmospheric processes that affect this region. Examination of temporal trends in surface and 500 hPa temperatures and several instability indices since 1970 showed an increase in temperature and an increase in the number of days that instability is present in the atmosphere, as measured by the Total Totals index. It is unclear whether these increases are caused by localised phenomena or changes in some larger scale meteorological processes caused by climate change or other large-scale processes. Significant issues remain regarding the homogeneity of the thunderday record.
Extreme summer temperatures have a significant impact on Australasia, and these are expected to intensify with global warming. The simulation of these extremes, particularly near coasts, is limited by the modest resolution of global climate models such as the CSIRO Mk3.0. We examine the temperatures simulated by the regional model CCAM, at a resolution of around 0.5 degrees, downscaled from Mk3.0 simulations. Extremes for three periods, from monthly to decadal, are presented. The distribution of daily temperatures in summer is characterised by a large variation of standard deviation (SD) across the region, peaking along the southern Australian coast. The distribution is positively skewed along most coasts, and negatively skewed in the interior. There are strong correlations with daily winds.The projected mean warming over the 21st century for the A1B greenhouse gas scenario reaches 3 degrees C in the Australian interior, but barely half that on the south coast, as anticipated from the smaller rate of warming of the surrounding seas. There is rather little moderation of warming on the cast and west coasts, however. Warming over New Zealand and New Guinea is typically 2 degrees C, for both means and extremes, some 50 per cent larger than that of the oceans. The SD of temperature anomalies increases over much of Australia, while skewness increases on some coasts. Both SD and skewness decrease in the southeast. Changes in the extremes, relative to the means, relate to those in both measures. This is demonstrated using a beta distribution fit to local daily temperature distributions. At many location, changes in extremes cannot be accurately estimated from a simple shift of the distribution. Much of the pattern of change is related to the effect of wind variability over the enhanced land-sea contrasts, as shown using a simple model for the influence of wind.
A summary of the broadscale tropical circulation from 70o E to 180o, for the six months May to October 2010, is presented. During this period the El Nino/La Nina-Southern Oscillation (ENSO) state shifted gradually from neutral conditions to La Nina conditions by July 2010. The Southern Oscillation Index (SOI) remained mostly above +10 during the season and reached a peak value of +25 in September. The mean SOI for the season was +15.8. Above average convection persisted throughout the season south of the equator between 90°E and 140°E and the South Pacific Convergence Zone (SPCZ). Mostly weak mean sealevel pressure (MSLP) anomalies persisted in the Darwin Regional Specialised Meteorological Centre (RSMC) analysis area except over parts of Australia, where it remained higher than normal. Easterlies in the tropical western Pacific remained stronger than normal. Sea Surface Temperatures in the tropical western Pacific gradually shifted from a warm to cooler pattern during the season and in the tropical Indian Ocean were warmer than their long-term mean. Weak active convective phases of the Madden-Julian Oscillation (MJO) were observed in the the beginning of each month during the season with a periodicity of 30 to 35 days. However, it was difficult to analyse the eastward propagation of the MJO signal mainly due to the developing La Nina conditions. A total of sixteen tropical cyclones (including eight typhoons/severe cyclones) were analysed during the period, less than the mean of 30 for the Darwin RSMC analysis area.
An overview of the Australian Bureau of Meteorology's end-to-end Thunderstorm Forecasting System is presented. This system relies substantially on three components: (a) the National Thunderstorm Forecast Guidance System (NTFGS), a software package that specifically displays those output fields from the 0.125 degrees Australian operational Numerical Weather Prediction (NWP) model (MesoLAPS) that are particularly relevant to diagnosing thunderstorm potential out to 48 hours, (b) a nowcasting visualisation tool called 3D-Rapic, which displays volumetric radar data as well as output from radar-based algorithms, and (c) the Thunderstorm Interactive Forecast System (TIES) for the dissemination of thunderstorm forecasts and severe thunderstorm warnings. TIES can ingest algorithm-diagnosed thunderstorm positions and tracks which are automatically diagnosed from the radar data.An Australian supercell hailstorm case study is then presented to showcase how forecasters can use the system outputs to facilitate decision making at various stages of the severe thunderstorm forecast process. Training and assessment issues associated with implementation of the forecast systems are discussed. In particular, it is concluded that forecasters must have an in-depth understanding of the NTFGS and radar algorithms for them to be used meaningfully. Such algorithms can facilitate the warning and decision-making process when used carefully in conjunction with the base data and other data types.
Atmospheric and oceanic conditions in the southern hemisphere are reviewed for the austral spring of 2007. Particular emphasis is given to the Australian and Pacific regions. The transition from El Ni (n) over tildeo conditions in 2006 to La Ni (n) over tildea conditions in 2007 took approximately ten months, arriving in early to mid-spring. Sea-surface temperatures in the central to eastern equatorial Pacific were generally cool for the season, as was the subsurface, while the Southern Oscillation Index gradually rose, reaching near one standard deviation above normal by season's end. Despite the La Ni (n) over tildea conditions, mean temperatures remained warm over Australia, with spring 2007 being the third warmest since high-quality records commenced in 1950. Rainfall was very low early in the season, but by November central and eastern Australia received above-average totals. This rainfall did little to alleviate the six-year drought for the agriculturally vital Murray-Darling Basin. In the Antarctic, the sea-ice area of 15.2 million km(2) was the largest area observed for my month since the sea-ice pack was first observed in its entirety by satellites in 1979, and appeared consistent with changing circulation patterns. The Antarctic ozone hole reached an area of 25.1 million km(2); considerably less than the record 2006 area but still well above the 19792006 mean peak value of just under 21 million km(2).
Summary and conclusions The local estimation of real time operational MTSAT 1R AMVs and their impact on operational regional NWP has been described. Experiments using these data in a real time NWP trial have been summarized. Their benefit to current operational regional NWP, when used with a control employing NMOC’s full op-erational data base (including JMA AMVs), has been recorded. These results were consistant with past trials with GMS-5 and GOES-9 and have resulted in a rein-troduction of local vectors into operations. This trial has been followed by new studies of the impact of 6-hourly visible image based AMVs and hourly AMVs in the current operational systems and a study of the use of continuous (at least hourly) AMVs in the next generation 4-D VAR United Kingdom Me-teorological Office Unified Model based system. Looking ahead, the continuing trend to space based observations with higher spatial, temporal and spectral resolution should enable improved estimation of at-mospheric motion and result in quantitative benefit to
Estimated tropical cyclone intensities for northwestern Australia over the period 1968/69 to 2000/01 obtained from a recent offshore oil and gas industry review are compared with the Bureau of Meteorology official tropical cyclone best track archive, a modified best track archive and another international reference data-set. Potential influences on the accuracy of estimating tropical cyclone intensity over time due to increasing technology, methodology, knowledge and skill are discussed. Historical Bureau of Meteorology practices in regard to estimating tropical cyclone intensity are also outlined and a method is described to potentially rectify the official track data archive to overcome some procedural issues. The methodology of the objective industry review process is then described, together with its expected limitations, and comparisons between the various data-sets are presented.It is shown that a bias towards lower intensities likely exists in earlier (mainly pre-1980) tropical cyclone central pressure deficit estimates of the order of at least 20 per cent in 1970, reducing to around ten per cent by 1980 and to five per cent by 1985. Inferred temporal trends in the estimated intensity from the original data-sets are therefore significantly reduced in the objectively reviewed data-set. Implications for detecting potential climate-change trends are discussed and recommendations are made for a detailed review of the tropical cyclone data-set for the entire Australian region as well as a call for improvements in the analysis and direct sensing of tropical cyclone intensity.
