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ERA5 reanalysis is used to examine extreme precipitation using a spatially dependent precipitation threshold applied within a cyclone compositing framework. This is used to account for regional variation in precipitation generating processes within Southern Hemisphere mid‐latitude cyclones across the cyclone lifecycle. The spatial extent of extreme precipitation is limited to a smaller region around the cyclone center compared to non‐extreme precipitation, though extreme precipitation displays a good spatial correlation with non‐extreme precipitation. Extreme precipitation occurs more often during the deepening phase of the cyclone before it reaches peak intensity. Precipitation occurrence at the 90th and 98th percentiles reduces to 46% and 30% of the deepening value across the cyclone lifecycle, averaged over the composite. Precipitation fraction at the 90th and 98th percentile reduces to 80% and 60% of the deepening value. Our methodology provides a quantitative assessment of precipitation extremes both spatially and temporally, within a cyclone compositing framework. Plain Language Summary: Extra‐tropical cyclones play a major role in the circulation within the atmosphere, acting to transfer heat toward the poles. Here we assess the representation of extreme precipitation within extra‐tropical cyclones. By applying a threshold for precipitation that changes with geographic location, we are able to determine how extreme precipitation varies within a cyclone‐centered coordinate system. When breaking cyclones into lifecycle stages representing deepening, peak intensity and decay, we find that extreme precipitation occurs most often as the cyclone is developing. The area of the cyclone relevant for extremes reduces toward the cyclone center as the threshold for determining extreme precipitation increases. Extreme precipitation weakens at a higher rate as cyclones becomes more intense, highlighting the importance of extremes in the growth phase of the cyclone. Key Points: We detail a new methodology to assess precipitation extremes within cyclone composites using a spatially dependent precipitation thresholdExtreme precipitation occurs preferentially and makes up a larger fraction of total accumulation before cyclones reach peak intensityExtreme precipitation is more constrained around the cyclone center and weakens more rapidly over time compared to moderate precipitation [ABSTRACT FROM AUTHOR]

Extreme temperature events (ETEs) have evolved alongside the warming climate over most parts of the world. This study provides a statistical quantification of how human influences have changed the frequencies of extreme temperatures in New Zealand, depending on the synoptic weather types. We use the ensembles under pre‐industrial conditions (natural scenarios with no human‐induced changes) and present‐day conditions (anthropogenic scenarios) from the weather@home regional climate model. The ensemble simulations under these two scenarios are used to identify how human influences have impacted the frequency and intensity of extreme temperatures based on their connection to different large‐scale circulation patterns derived using self‐organizing maps (SOMs). Over New Zealand, an average two to three fold rise in frequencies of extremes occurs irrespective of seasons due to anthropogenic influence with a mean temperature increase close to 1°C. For some synoptic situations, the frequency of extremes are especially enhanced; in particular, for low‐pressure centres to the northeast of New Zealand where the frequency of occurrence of daily temperature extremes has increased by a factor of 7 between anthropogenic and natural ensembles for the winter season, though these synoptic patterns rarely occur. For low‐pressure centres to the northwest of New Zealand, we observe high temperatures frequently in both anthropogenic and natural ensembles which we expect is probably associated with warm air advection from the Tropics. The frequency of occurrence of high temperatures in these synoptic patterns has also increased by a factor of 2 between the natural and anthropogenic ensembles. For these synoptic states, the extremes are observed in the North Island and along the east coast of the country with the highest temperature along the Canterbury coast and Northland. The change between the natural and anthropogenic ensembles is largest on the west coast along the Southern Alps for all the synoptic circulation types. [ABSTRACT FROM AUTHOR]

Extreme temperature events (ETEs) have evolved alongside the warming climate over most parts of the world. This study provides a statistical quantification of how human influences have changed the frequencies of extreme temperatures in New Zealand, depending on the synoptic weather types. We use the ensembles under pre‐industrial conditions (natural scenarios with no human‐induced changes) and present‐day conditions (anthropogenic scenarios) from the weather@home regional climate model. The ensemble simulations under these two scenarios are used to identify how human influences have impacted the frequency and intensity of extreme temperatures based on their connection to different large‐scale circulation patterns derived using self‐organizing maps (SOMs). Over New Zealand, an average two to three fold rise in frequencies of extremes occurs irrespective of seasons due to anthropogenic influence with a mean temperature increase close to 1°C. For some synoptic situations, the frequency of extremes are especially enhanced; in particular, for low‐pressure centres to the northeast of New Zealand where the frequency of occurrence of daily temperature extremes has increased by a factor of 7 between anthropogenic and natural ensembles for the winter season, though these synoptic patterns rarely occur. For low‐pressure centres to the northwest of New Zealand, we observe high temperatures frequently in both anthropogenic and natural ensembles which we expect is probably associated with warm air advection from the Tropics. The frequency of occurrence of high temperatures in these synoptic patterns has also increased by a factor of 2 between the natural and anthropogenic ensembles. For these synoptic states, the extremes are observed in the North Island and along the east coast of the country with the highest temperature along the Canterbury coast and Northland. The change between the natural and anthropogenic ensembles is largest on the west coast along the Southern Alps for all the synoptic circulation types. [ABSTRACT FROM AUTHOR]

Weather types (WTs) are often used to assess the relationships between synoptic‐scale atmospheric dynamics and local scale climate anomalies. We focus here on Aotearoa New Zealand (ANZ) where pre‐existing WTs have recently been characterized using a set of descriptors monitoring the daily location and intensity of their main atmospheric centres of action (ACAs). We show here that the precipitation and temperature anomalies associated with the WTs in ANZ are more complex than previously thought. They do not solely depend on type occurrence, but are also strongly modulated by within‐type changes in the location and intensity of ACAs, and their interaction with surface terrain. Thus, the mere analysis of WT occurrence is not sufficient to explain climate variability over ANZ. The magnitude and sign of daily minimum and maximum temperature anomalies are strongly driven by meridional advection of temperature, which is also driven by within‐type changes in ACAs. The amplitude of precipitation anomalies is likewise strongly variable within WTs. Associated mechanisms involve interactions between the underlying terrain and atmospheric fluxes modulated by ACAs, modifying the strength and location of orographic uplift. Finally, daily extreme precipitation can occur under several cyclonic WTs, more particularly when their low‐pressure ACAs are significantly more intense than normal. This situation is associated with more intense moisture transport towards ANZ, promoting heavy precipitation there. These results provide a detailed assessment of within‐type variability in temperature and precipitation patterns at both synoptic and local scales. They also help to improve understanding of local effects of larger scale synoptic patterns, thereby allowing for more accurate use of analogues in forecasting. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a detailed comparison of ten precipitation products over the central southwest Asia ( CSWA) region. The spatial characteristics and temporal variations of wintertime precipitation over CSWA region are assessed using four gauge-only [Asian Precipitation - Highly Resolved Observational Data Integration Towards Evaluation of Water Resources ( APHRODITE), Climate Prediction Center Unified Rain gauge ( CPC-uni), Global Precipitation Climatology Center Full Data Reanalysis ( GPCC) and Climate Research Unit ( CRU)]; three satellite-derived ( 3B42-V6, 3B42-V7 and GPCP-1DD) and three reanalysis [Climate Forecast System Reanalysis ( CFSR), ERA-Interim and Modern-Era Retrospective Analysis for Research and Applications ( MERRA)] precipitation products. The analysis is performed for two different periods: (1979-2007) for the gauge-only/reanalyses and (1998-2007) for the satellite-derived products. Using an ensemble average of four gauge-only observational data sets as our reference, we carry out comprehensive qualitative assessment of the uncertainties/biases associated with each data set. Additionally, we examine the relationship pattern between CSWA wintertime precipitation and El Niño-Southern Oscillation ( ENSO) phases. In the gauge-only category, APHRODITE and GPCC perform better than CPC-uni and CRU data sets in terms of the spatial and temporal variations of skill matrices. Overall, GPCC shows the best performance (including the precipitation sensitivity to ENSO events) and is the preferable observational data set for long-term climatological analysis over the CSWA region. Among the satellite-derived precipitation products, 3B42-V7 displays the most realistic wintertime precipitation distribution pattern when compared to 3B42-V6 and GPCP-1DD; however, efforts are needed to further improve the accuracy of satellite-derived products over the dry arid and semi-arid areas of CSWA. In the reanalysis category, MERRA's performance is relatively better than CFSR and ERA-Interim, although significant biases exist in all of the reanalyses due to overestimation of precipitation over the mountainous regions of CSWA. [ABSTRACT FROM AUTHOR]

ABSTRACT New insight is provided regarding 21st century projections of synoptic scale atmospheric circulation over the New Zealand region. Daily mean sea level pressure patterns from a number of general circulation models ( GCMs) participating in the 5th Coupled Model Intercomparison Project ( CMIP5) were analysed through a self-organizing map ( SOM) technique. In terms of simulating the synoptic climatology found in reanalyses, an initial model evaluation revealed quite substantial differences in model skill. Generally, those models with relatively high horizontal atmospheric resolution skilfully simulated the historical frequency and mean lifetime of large scale synoptic patterns over this region. Analysing future projections under this smaller subset of better-performing models indicated robust and quite substantial increases in the annual frequency of widespread anticyclonic conditions over New Zealand, accompanied by a general decrease in widespread low pressure. These projected changes in frequency of synoptic occurrences become the most pronounced towards the end of the 21st century and for winter, whereas changes in the average synoptic pattern lifetime remain small. While not robust for all models in this subset, significant 21st century trends in the intensification of geostrophic westerly flow conditions within certain synoptic patterns were also found. Linking synoptic patterns to surface climate variables has also provided evidence that these circulation changes may collectively manifest as a significant non-uniform climatic change across New Zealand. These findings should encourage further focused studies on circulation-relevant applications and impacts in a climate change context. [ABSTRACT FROM AUTHOR]

ABSTRACT Black Saturday ( BS), 7 February 2009, is recognized as Australia's most severe bushfire event on record. The meteorology that day, although extreme, was typical of southeast Australian bushfire events, characterized by gusty northerly winds before a cool change brought strong southerly winds and a dramatic temperature drop. This study investigates a range of extra-tropical atmospheric (pressure, temperatures) and oceanic temperature anomalies that occurred on or leading up to BS. Results show several parameters were within the top 5% or were record breaking for the satellite era. Of particular note are the anomalies that occurred over the Antarctic region, having the strongest signal and appearing in unison with the pre- BS heatwave. We suggest that a combination of a warm polar ocean and an enhanced mid-latitude thermal contrast in the Indian Ocean aided in triggering sub-polar blocking and an intense cyclone, which brought the catastrophic cold front on BS. [ABSTRACT FROM AUTHOR]

ABSTRACT A cluster analysis-based synoptic classification scheme, known as the Kidson types, was applied to reanalyses and Coupled Model Inter-comparison Project phase 3 ( CMIP3) general circulation model ( GCM) output over New Zealand to identify the potential for future changes in regional circulation. Results indicate that a number of GCM 20th century control runs reproduce the type frequencies observed in reanalysis data. Application to future scenario runs for the periods 2046-2065 and 2081-2100 displays little variation in the annual frequency of the synoptic types relative to the 20th century, especially when uncertainty associated with the model ensemble is considered. This is surprising in the context of previous work on possible future movements in jet position and subsequent impacts on weather patterns. A sensitivity analysis that mimics the movement of the jet position was performed, revealing that the annual type frequencies are relatively insensitive to change. To determine whether this is a problem with the synoptic typing scheme, a correlation-based classification technique was also used, but showed similar results. This work highlights issues with applying synoptic classification schemes to GCM output and indicates that if such schemes are to be used they should be designed and tested with this application in mind. [ABSTRACT FROM AUTHOR]