Jump to content


  • Content count

  • Joined

  • Last visited

Community Reputation

598 Exceptional

About sebastiaan1973

Profile Information

  • Gender
  • Location
  1. Oh dear. What a terrible forecast. A Central Pacific La Nina in full effect.
  2. Yes, we have to wait and see. https://www.clim-past.net/13/1199/2017/cp-13-1199-2017.pdf Abstract The impact of solar variability on weather and climate in central Europe is still not well understood. In this paper we use a new time series of daily weather types to analyse the influence of the 11-year solar cycle on the tropospheric weather of central Europe. We employ a novel, daily weather type classification over the period 1763–2009 and investigate the occurrence frequency of weather types under low, moderate, and high solar activity level. Results show a tendency towards fewer days with westerly and west-southwesterly flow over central Europe under low solar activity. In parallel, the occurrence of northerly and easterly types increases. For the 1958–2009 period, a more detailed view can be gained from reanalysis data. Mean sea level pressure composites under low solar activity also show a reduced zonal flow, with an increase of the mean blocking frequency between Iceland andScandinavia. Weather types and reanalysis data show that the 11-year solar cycle influences the late winter atmospheric circulation over central Europe with colder (warmer) conditionsunder low (high) solar activity.
  3. https://www.researchgate.net/publication/271737956_Impacts_of_two_types_of_La_Nina_on_the_NAO_during_boreal_winter There seems to be two types of La Nina with different implications for our weather. We - the winter lovers- need an Eastern Pacific La Nina. E.g. 2006-1996-1985.
  4. Mother nature has a lot of tricks to get the mild air to us
  5. Some of the latest CFS-runs shows record low windspeeds.
  6. Old news. http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean available for everybody
  7. http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0259.1 Abstract Over the last decades, the stratospheric polar vortex has shifted towards more frequent weak states which can explain Eurasian cooling trends in boreal winter in the era of Arctic amplification. The extra-tropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the stratospheric polar vortex, is predominantly zonal and centered around the pole; however, it does exhibit large variability in wind speed and location. Previous studies showed that a weak stratospheric polar vortex can lead to cold-air outbreaks in the mid-latitudes but the exact relationships and mechanisms are unclear. Particularly, it is unclear whether stratospheric variability has contributed to the observed anomalous cooling trends in mid-latitude Eurasia. Using hierarchical clustering, we show that over the last 37 years, the frequency of weak vortex states in mid to late winter (January and February) has increased which were accompanied by subsequent cold extremes in mid-latitude Eurasia. For this region 60% of the observed cooling in the era of Arctic amplification, i.e. since 1990, can be explained by the increased frequency of weak stratospheric polar vortex states, a number which increases to almost 80% when El Niño/Southern Oscillation (ENSO) variability is included as well.
  8. Interannual variation of seasonal-mean tropical convection over the Indo-Pacific region is primarily controlled by El Niño–Southern Oscillation (ENSO). For example, during El Niño winters, seasonal-mean convection around the Maritime Continent becomes weaker than normal, while that over the central to eastern Pacific is strengthened. Similarly, subseasonal convective activity, which is associated with the Madden–Julian oscillation (MJO), is influenced by ENSO. The MJO activity tends to extend farther eastward to the date line during El Niño winters and contract toward the western Pacific during La Niña winters. However, the overall level of MJO activity across the Maritime Continent does not change much in response to the ENSO. It is shown that the boreal winter MJO amplitude is closely linked with the stratospheric quasi-biennial oscillation (QBO) rather than with ENSO. The MJO activity around the Maritime Continent becomes stronger and more organized during the easterly QBO winters. The QBO-related MJO change explains up to 40% of interannual variation of the boreal winter MJO amplitude. This result suggests that variability of the MJO and the related tropical–extratropical teleconnections can be better understood and predicted by taking not only the tropospheric circulation but also the stratospheric mean state into account. The seasonality of the QBO–MJO link and the possible mechanism are also discussed. http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-16-0620.1
  9. Understanding the linkage between El Niño Southern Oscillation (ENSO) and Northern Hemisphere climate has found to be one of the key mechanisms to improve the predictability skill in extratropical regions. The El Niño signal propagates poleward via Rossby wave trains in the upper troposphere. In the North Pacific, this contributes to a deepening of the winter Aleutian low pressure system (AL), and hence to a strengthening of the Pacific North America (PNA) pattern. As a consequence, the strengthened wave anomaly interacts constructively with the climatological planetary wave and thereby enhances upward propagation of planetary waves into the stratosphere. This can lead to Sudden Stratospheric Warming (SSW) events, which can then have a lasting impact on the North Atlantic and Europe by projecting onto the North Atlantic Oscillation (NAO) pattern, thereby influencing weather over Europe. Pressure anomalies in the North Pacific can also propagate to the North Atlantic and Eurasia through the mid- and upper troposphere as a Rossby wave train, but the relative importance of the tropospheric and stratospheric pathways is still not resolved. In this study, we evaluate the relative importance and the role of both pathways. We use a 3D wave activity flux to identify the propagating Rossby waves in the troposphere and in the stratosphere. On the one hand, that the stratospheric pathway can be due to planetary wave reflection or absorption, exhibiting different surface responses and different time scales. On the other hand, when the stratosphere is less active, in neutral Vortex events, we show that the tropospheric pathway is dominant leading to a negative(positive) NAO during El Niño(La Niña) years. We also investigate the role of the synoptic eddies, which play a significant role in maintaining the southward(northward) shift of the storm track in the Atlantic during El Niño(La Niña) conditions. https://ams.confex.com/ams/21Fluid19Middle/webprogram/Paper318786.html Please notice the presentations of this conference https://ams.confex.com/ams/21Fluid19Middle/webprogram/Paper319446.html. E.g. https://ams.confex.com/ams/21Fluid19Middle/webprogram/Paper318618.html Or https://ams.confex.com/ams/21Fluid19Middle/webprogram/Paper319446.html The Madden-Julian Oscillation (MJO), also known as the 30-60 day oscillation, represents a major fraction of convective variability in the tropics and is the strongest of the intraseasonal climate oscillations. The MJO has important derivative effects on extratropical circulation and intraseasonal climate (e.g., Zhang [2013]). Recently, a number of authors, beginning with Yoo and Son [2016], have shown that the stratospheric quasi-biennial oscillation (QBO) modulates the amplitude of the boreal winter MJO such that MJO amplitudes are larger on average during the easterly phase (QBOE) than during the westerly phase (QBOW). A major possible mechanism is the decrease in static stability in the lowermost stratosphere under QBOE conditions resulting from relative upwelling associated with the QBO induced meridional circulation. Marshall et al. [2016] have further shown that the observed QBO influence on the MJO should result in improved predictability of the MJO and its convective anomalies in the Pacific during QBOE relative to QBOW. Here, evidence is presented that tropical upwelling changes related to the 11-year solar cycle also modulate the boreal winter MJO. Using outgoing longwave radiation (OLR)-based MJO index (OMI) amplitude data covering the 1979-2016.3 period (37.3 years), it is found that the increase in MJO occurrence rate and mean amplitude during December, January, and February (DJF) under QBOE conditions is especially large under solar minimum (SMIN) conditions while the decrease in MJO amplitude under QBOW conditions is largest under solar maximum (SMAX) conditions. Consistently, the DJF mean static stability calculated from ERA-Interim reanalysis data in the lowermost stratosphere over the warm pool region is especially high under QBOW/SMAX conditions and is lowest under QBOE/SMIN conditions. Specifically, while the mean MJO amplitude in DJF is ~ 42% larger in QBOE than in QBOW, it is ~ 88% larger in QBOE/SMIN than in QBOW/SMAX. Conversely, the mean MJO amplitude in DJF is only ~ 27% larger in QBOE/SMAX than in QBOW/SMIN. Similarly, while the occurrence rate of daily MJO amplitudes in DJF exceeding unity is ~ 34% larger under QBOE conditions than under QBOW conditions, it is ~ 88% larger in QBOE/SMIN than in QBOW/SMAX. On the other hand, it is only ~ 17% larger in QBOE/SMAX than in QBOW/SMIN. This dependence on the solar cycle is consistent with a solar-induced increase in relative tropical upwelling under SMIN conditions and a decrease (relative downwelling) under SMAX conditions (e.g., Matthes et al. [2004]). However, these results are based on a limited time record. For example, only 4 to 6 winters qualify for the QBOE/SMIN category while 7 to 9 winters qualify for the QBOW/SMAX category, depending on adopted limits for the QBO and solar phases. During the coming solar minimum, at least one additional winter in the QBOE/SMIN category should occur (possibly as early as the 2017/2018 winter), during which a larger-than-average number of higher-amplitude MJO events is to be expected and an initial test of the proposed relationship will be possible.
  10. Interesting Steve. Perhaps a trend. Thanks Don. An inverse relationship between aggregate northern hemisphere tropical cyclone activity and subsequent winter climate http://moe.met.fsu.edu/~rhart/papers-hart/2010HartGRL.pdf
  11. Latetst GLOSEA5 update shows a postive NAO/AO this winter. In the northern part of the Pacific pressure tends to be higher than normal. In the northern part of Atl. Ocean low pressure seems to be the king. Still time for a change.... http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean Thanks Recretos
  12. @Don, do you know some publications about this subject?