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  • Miscellaneous Research Papers (e.g. blocking, past severe winters and heatwaves)

    Blessed Weather

    Here are the current Papers & Articles under Miscellaneous. Click on the title of a paper you are interested in to go straight to the full paper.

    Current likelihood and dynamics of hot summers in the UK
    Published Sept 2020
    Summer 2018 in the United Kingdom (UK) was its joint hottest on record and the associated impacts raise questions over societal resilience to extremes of this magnitude or greater occurring in upcoming years. Better information on the current likelihood of extreme and unprecedented events feeds into improved understanding of risk, relevant for policy and contingency planning. However, making robust estimates of likelihood is difficult given that extremes in the historical record are few by definition. We overcome this by using a large ensemble of initialised climate model simulations to assess the chance of exceeding summer 2018 temperatures in the current climate and find it to be ∼11% each year, although a weak circulation bias may mean this estimate is conservative. This likelihood has increased sharply over the last few decades. A one in 100-year event would bring summertime temperatures to the UK of approximately 1 °C above 2018, an anomaly similar to that of the notable hot summer of 1976. Subsetting the large ensemble enables characterisation of the dynamics around hot summers, and investigation of possible remote influences. Several circulation patterns bring warm temperatures to the UK, and it is likely that influences from different remote regions are active or dominant in different years. We present evidence suggesting roles for tropical precipitation anomalies via extratropical wave trains. Circulation anomalies associated with wet conditions in the Caribbean project particularly strongly onto the hot UK summer conditions, with a weaker signal from the tropical Pacific consistent with developing La Niña. We also highlight possible influence in some years from springtime high sea ice anomalies in the Sea of Okhotsk and low anomalies in the Barents/Kara seas. Building on this, we use new experiments that isolate the effects of opposing springtime sea ice anomalies in the two regions and find a causal relationship with the summertime circulation over the North Atlantic and northern Europe.

    Thunderstorms and extreme rainfall in south Norfolk, 16 August 2020: meteorological analysis
    Published July 2021
    A multicell thunderstorm cluster affected parts of the Breckland region in south Norfolk on the afternoon of 16 August 2020, producing as much as 240mm of rain. A detailed mesoanalysis is constructed to analyse the meteorological conditions present using conventional observations, reanalysis and privately owned automatic weather station observations. While the instantaneous rain rates observed are not unprecedented, when maintained over several hours result in this event ranking as the highest August daily rainfall on record in the United Kingdom.

    Contraction of the Northern Hemisphere, Lower-Tropospheric, Wintertime Cold Pool over the Past 66 Years
    Published May 2015.
    Employing reanalysis datasets, several threshold temperatures at 850 hPa are used to measure the wintertime [December–February (DJF)] areal extent of the lower-tropospheric, Northern Hemisphere, cold-air pool over the past 66 cold seasons. The analysis indicates a systematic contraction of the cold pool at each of the threshold temperatures. Special emphasis is placed on analysis of the trends in the extent of the −5°C air.
    Employing three different reanalysis datasets, the analysis presented here demonstrates that the 850-hPa wintertime cold pool has systematically contracted, at each of several threshold temperatures, since the mid-twentieth century.

    An easy read of the above report is in the coverage by the Washington Post.

    Exploring recent trends in Northern Hemisphere blocking
    2014 paper. Abstract:
    Observed blocking trends are diagnosed to test the hypothesis that recent Arctic warming and sea ice loss has increased the likelihood of blocking over the Northern Hemisphere. To ensure robust results, we diagnose blocking using three unique blocking identification methods from the literature, each applied to four different reanalyses. No clear hemispheric increase in blocking is found for any blocking index, and while seasonal increases and decreases are found for specific isolated regions and time periods, there is no instance where all three methods agree on a robust trend. Blocking is shown to exhibit large interannual and decadal variability, highlighting the difficulty in separating any potentially forced response from natural variability.

    Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern.
    2019 paper. Abstract:
    The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wave number 7 circulation pattern. We show that this pattern constitutes an important teleconnection in Northern Hemisphere summer associated with prolonged and above-normal temperatures in North America, Western Europe and the Caspian Sea region. This pattern was also observed during the European heatwaves of 2003, 2006 and 2015 among others. We show that the occurrence of this wave 7 pattern has increased over recent decades.

    Ocean and atmosphere influence on the 2015 European heatwave
    2019 paper. Abstract:
    During the summer of 2015, central Europe experienced a major heatwave that was preceded by anomalously cold sea surface temperatures (SSTs) in the northern North Atlantic. Recent observation-based studies found a correlation between North Atlantic SST in spring and European summer temperatures, suggesting potential for predictability. Here we show, by using a high-resolution climate model, that ocean temperature anomalies, in combination with matching atmospheric and sea-ice initial conditions were key to the development of the 2015 European heatwave. In a series of 30-member ensemble simulations we test different combinations of ocean temperature and salinity initial states versus non-initialised climatology, mediated in both ensembles by different atmospheric/sea-ice initial conditions, using a non-standard initialisation method without data-assimilation. With the best combination of the initial ocean, and matching atmosphere/sea-ice initial conditions, the ensemble mean temperature response over central Europe in this set-up equals 60% of the observed anomaly, with 6 out of 30 ensemble-members showing similar, or even larger surface air temperature anomalies than observed.

    Origin of variability in Northern Hemisphere winter blocking on interannual to decadal timescales
    2015 paper. Abstract:
    Variability of mid-latitude blocking in the boreal winter Northern Hemisphere is investigated for the period 1960/1961 to 2001/2002 by means of relaxation experiments with the model of the European Centre for Medium‐Range Weather Forecasts. It is shown that there is pronounced interannual and decadal variability in blocking, especially over the Eurasian continent, consistent with previous studies. The relaxation experiments show that realistic variability in the tropics can account for a significant part of observed interannual blocking variability but also that about half of the observed variability can only be explained by extratropical tropospheric variability. On the quasi‐decadal timescale, extratropical sea surface temperature and sea ice, in addition to tropical variability, play a more important role. The stratosphere, which has been shown to influence interannual variability of the North Atlantic Oscillation in previous studies, has no significant influence on blocking according to our analysis.

    The climate in the UK from November 1994 to October 1995
    No abstract, but this paper looks at the exceptional warmth of this 12 month period.

    The meteorology of the exceptional winter of 2015/2016 across the UK and Ireland
    2016 paper. Abstract:
    The meteorological winter of 2015/2016 will be remembered as another exceptional winter across the UK and Ireland, with numerous climate records broken and high impact weather events causing considerable disruption from flooding and high winds. A succession of winter storms tracked across the region, bringing persistent and in places record‐breaking rainfall, including the highest 24 and 48 h rainfall accumulations on record, from storm Desmond on 4–6 December. Persistent rain, particularly through the first half of the winter, resulted in new records for both monthly and seasonal rainfall accumulations widely across Ireland, Scotland, Wales and northern England. Temperatures were also exceptionally high through much of December and in late January. In this paper we document the main meteorological and climate features that defined this exceptional winter season, and consider its wider historical context.

    The UK winter of 2009/2010 compared with severe winters of the last 100 years
    2010 paper. Abstract:
    When severe British winters of the last 100 years are considered, those of 1963 and 1947 are usually the first that come to mind. More recent candidates include 1979 and 1982. Should winter 2010 now also be added to this list? To assist with a ranking in terms of temperature (maximum, minimum and mean), we can analyse monthly series from 1910 and daily series from 1960, based upon 5km grids. These series were assembled using the methods of Perry and Hollis (2005) and have been used to create (i) areal values for the UK, England, Wales, Scotland, Northern Ireland and regions and (ii) colour‐shaded maps. The monthly Central England Temperature series from 1659 provides a longer‐term perspective (Manley, 1974). For snowfall, there are monthly 5km grids of days with snow lying from 1961 (based upon 0900 utc station observations), as well as station records of snow depth at 0900 utc, mostly digitised from 1959.

    The 1962/1963 winter as observed at Belstead Hall (Suffolk) and through investigation of the synoptic charts
    2013 paper. Abstract:
    When I was a schoolboy in Ipswich in the early 1960s, weather readings from the nearby Belstead Hall were reported in the local newspaper, the East Anglian Daily Times. Recently I was asked about preserving the records, and the whole of the archive material from the owner has now been passed to the Chilterns Observatory Trust, a charity set up by Philip Eden (2010). I have copied the data covering the severe winter of 1962/1963, and this article describes the highlights of it from those readings together with some of my personal recollections of that remarkable season.

    Tropical origin of the severe European winter of 1962/1963
    2014 paper. Abstract:
    A set of relaxation experiments using the European Centre for Medium‐Range Weather Forecasts (ECMWF) atmospheric model is used to analyze the severe European winter of 1962/1963. We argue that the severe winter weather was associated with a wave train that originated in the tropical Pacific sector (where weak La Niña conditions were present) and was redirected towards Europe, a process we suggest was influenced by the combined effect of the strong easterly phase of the Quasi‐Biennial Oscillation (QBO) and unusually strong easterly winds in the upper equatorial troposphere that winter. A weak tendency towards negative North Atlantic Oscillation (NAO) conditions in December, associated with extra-tropical sea‐surface temperature and sea‐ice anomalies, might have acted as a favourable preconditioning. The redirection of the wave train towards Europe culminated in the stratospheric sudden warming at the end of January 1963. We argue that in February the sudden warming event helped maintain the negative NAO regime, allowing the severe weather to persist for a further month. A possible influence from the Madden–Julian Oscillation, as well as a role for internal atmospheric variability, is noted.

    The Mid-Winter 1963 Stratospheric Warming and Circulation Change
    1964 paper. Abstract:
    The stratospheric warming and circulation change of January and February 1963 are discussed by means of constant pressure charts, time sections and cross sections. Rawinsonde data are combined with wind data from the Meteorological Rocket Network. The warming initially appeared at 10 mb over southeastern Canada as the contour field began its evolution from a pattern dominated by a circumpolar vortex to a nearly symmetrical bipolar pattern. The subsequent events, such as the northwestward spread of the warm air and destruction of the wintertime polar cyclone, are found to be strikingly similar to those of the 1957 warming.
    The circulation changes could be traced upward beyond the 55-km level, with an indication that maximum intensities occurred near 45 km. Contour charts of the 10-, 2-, and 0.4-mb surfaces give evidence that the entire atmospheric layer from about 25 km to at least 55 km belongs to the same regime, but with significant interlevel variations in the slope and intensity of the systems.


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