Recovering German and Irish moorings Southwest of Ireland. A campaign on the new Irish Research Vessel (RV) Tom Crean.

Originally published at https://samueldi.github.io/.

The one-week long Aimsir/EirOOS survey ended a couple of weeks ago and was the first physical oceanography campaign of the new Irish Research Vessel (RV) Tom Crean. Our primary goal was to recover three moorings located southwest of Ireland, on an offshore underwater plateau known as Goban Spur. This campaign was carried out as a collaboration between three different ocean research institutions: 1) Maynooth University with scientists from the A4 project; 2) the Marine Institute; and 3) the Federal Maritime and Hydrographic Agency of Germany (in German, Bundesamt für Seeschifffahrt und Hydrographie, or BSH).

 

Image credit: Sam T. Diabaté

 

 

Moorings are instrument arrays anchored on the sea floor which sample the water column for an extended amount of time (from months to years). In recent years, a network of moorings has been measuring water properties at the Goban Spur (13°E, 49°N). In 2016, German scientists of BSH (the Federal Maritime and Hydrographic Agency of Germany) deployed three EB moorings on the deeper part of the Goban Spur, while in 2020, the Marine Institute filled in the gap between the German moorings and the Irish coastline with additional EBS moorings. The mooring geographical locations, reminding of the ‘OMEX’ mooring array deployed in the mid-90s, were chosen to close the eastern boundary of the NOAC line, a basinwide mooring array measuring the North Atlantic conveyor belt circulation.

(a) General bathymetry map of the region Southwest of Ireland, showing also the mooring locations as colour filled circle) as well as the planned and effective CTD stations displayed as light and dark crosses. The mobilisation and demobilisation ports, respectfully Cork and Galway, are also indicated. Despite being indicated here, EBS5 was not recovered. (b) Zoom in on the Goban Spur, where most of the action took place. Markers are the same as on (a), only planned CTD stations are not shown. Image credit: Gerard D. McCarthy.

While moorings EB2 and EBS3 were lost, possibly due to trawling activity, three Goban Spur moorings (EB3, EB1 and EBS1) and one shallow mooring (EBS5) sampled the ocean for an extended period. Recovery of these moorings was the primary goal of our cruise. These mooring locations are shown on the map above. The campaign was conducted on the RV Tom Crean between September 24th and 30th, and the principal investigator was Dr. Gerard McCarthy, my PhD supervisor.

The Maynooth University team, which was composed of Dr. Gerard McCarthy, Dr. Levke Caesar, Dr. André Düsterhus, Dr. Samantha Hallam, Dr. Stephen Ogungbenro and myself, met up with Dr. Manuela Köllner and Tobias Svensson from BSH on the Friday 23/09. We embarked the RV Tom Crean on the following day, joining Dr. Eoghan Daly, Alan Berry and Conall O' Malley from the Marine Institute as well as the ship’s crew. We set sail on that day. Mooring EB3 was recovered on Monday 26/09. Rougher weather hindered mooring recovery until the Thursday 29/09, and the elapsed time was used as best as possible to conduct CTD profiles (Don’t know what CTD stations are? Find out more info here).

Dr. Gerard McCarthy and Dr. Eoghan Daly on a coffee break. Image credit: Sam T. Diabaté.

Mooring EBS1 and EB1 were recovered on the Thursday 29/09, and it was decided to sail towards land immediately after because of the sea condition worsening. We fled ahead of the storm and reached — not without trouble — Galway Bay on the evening of Friday 29/09. We disembarked on the following morning.

Together with Dr. Samantha Hallam, I cleaned up the moored instruments recovered from the mooring lines, downloaded the data from the MicroCATs, set up the instruments for calibration dips, and more broadly facilitated the smooth running of the mooring operations headed by Dr. Manuela Köllner (for EB1 and EB3) and Conall O' Malley (for EBS1).

I was also in charge of the Vessel Mounted Acoustic Doppler Current Profiler (VmADCP), which is an instrument designed to measure the water velocity (currents) of the water column below the ship keel. The VmADCP aboard the RV Tom Crean is a Pinnacle 45 from Teledyne RDI, a particularly modern instrument which allows to perform a novel acquisition method referred to as ‘interleaved’. This new method comes with new processing challenges, which I was able to circumvent with help of Pr. Jules Hummon of University of Hawaii who was contacted by mail. Next month, Gerard and I will be taking part in a workshop organised by Dr. Eoghan Daly on VmADCP acquisition and data processing.

The RV Tom Crean in Galway harbour on demobilisation day. Image credit: Sam T. Diabaté.

The RV Tom Crean is a very modern ship, with a range of new assets to help scientists conduct research at sea. I was in particular impressed by the features of the dry laboratory. Scientists can now operate the CTD winch from a designated desk in the dry lab, provided the bridge has granted us control. The different screens in the lab are all connected to a central PC unit, and everything is accessible from a server, allowing researchers to quickly work on different ongoing measurements at a time (VmADC Profiling, but also swath bathymetry measurements, underway systems, CTD monitoring, etc.). The ship design makes life aboard comfortable and easy, with a gym, a TV space, a very comfortable dining room facing the galley, and plenty of room to work.

As on previous cruises I took part in, pods of common dolphins and pilot whales were common encounters. A camera was installed on the hull and allowed to see dolphins having great fun right beneath us. Colleagues Dr. Samantha Hallam and Alan Berry shared some wonderful footages on their social media, some of which can be seen below. Dr. Eoghan Daly also put together a video of our campaign which was shown during the RV Tom Crean commissioning ceremony, and it can be found below too.

Sam

Sam Tiéfolo Diabaté

Doctoral researcher in Physical Oceanography

My research focuses on ocean currents and sea level.

International Women's Day 2022

The A4 and ROADMAP teams are proud to support International Women’s Day 2022. Our Group is 50% female, each with diverse backgrounds and a variety of interests including ocean sciences, coding, modelling and statistics. Below, we present the range of different research topics that inspire us to discover more in these areas and outline the paths that we have taken into the field. 

 

Modelling Sea Level Change

Dr Niamh Cahill

 

Niamh Cahill is an applied statistician with interests in developing statistical models for the analysis of time dependent, compositional and/or spatial data. She uses a Bayesian approach to statistical modelling, which is suitable for developing complex hierarchical models, accounts of uncertainties related to model parameters, incorporates prior knowledge, and shares information across data sites. Her research covers a range of statistical disciplines including: stochastic processes; time series analysis; computation and simulation; and multivariate analysis.

 

Niamh completed her PhD in University College Dublin in 2015. Following this she spent two years as a postdoctoral researcher in UMASS Amherst. Niamh joined the Mathematics and Statistics department at Maynooth University in 2018. One aspect of her research focuses on the development of statistical models to assess and interpret indicators of climate change, specially sea-level change. 

 

Rising seas increase the vulnerability of cities and associated infrastructure that line the coastline of Ireland because of higher extreme sea levels (and flooding), coastal erosion, salinization of surface and ground waters, and degradation of coastal habitats. Armed with statistical knowledge of how sea levels have been changing in the 20th and 21st century, future links between mean sea-level and sea level extremes due to storm surges and wave climate can be established, which are vital to inform decision making related to flood risks. Dr Cahill has recently been awarded funding from Science Foundation Ireland/ Frontiers for the Future Project. This project will focus on predicting Sea Levels and Sea Level Extremes for Ireland

Statistical Models for sea level change

Maeve Upton

 

 

In 2021, the Intergovernmental Panel on Climate Change (IPCC) released their AR6 report which stated with “high confidence” that the “global mean sea level has increased by 0.2 m between 1901 and 2018”. However, understanding how sea level has varied globally and local, and the main drivers of this change is crucial for predicting future rise. The influence of different sea level drivers, for example thermal expansion, ocean dynamics and glacial – isostatic adjustment (GIA), has changed throughout time and space. Therefore, a useful statistical model requires both flexibility in time and space and have the capability to examine these separate drivers, whilst taking account of uncertainty.

 

That being said, Maeve Upton is a third year PhD candidate in Maynooth University, developing a series of statistical models to analyse historical sea level and the main drivers of this sea level change. Along with her supervisors Prof Andrew Parnell and Dr Niamh Cahill, Maeve investigates sea level change along the east coast of North America using tide gauge data and proxy records from salt marshes. Her statistical models use Bayesian Hierarchical spatial temporal techniques which can identify changes in sea level in time and across space. Also, the statistical approach uses extensions of Generalised Additive Models (GAMs), which allow separate components of sea level to be modelled individually. The Bayesian framework allows for the inclusion of other physical models to constrain the evolution of sea level change over space and time.

 

Upton’s models have demonstrated that GIA was the main driver of relative sea level change along North America’s Atlantic coast, until the 20th century when a sharp rise in rates of sea level change can be seen.

 

In the future work, Upton plans to extended her models to incorporate other drivers of sea level change . Finally, Maeve will collaborate with Earth Scientists in Trinity College Dublin, to produce Ireland’s first historic sea level record from Irish salt marshes and statistical models. 

It’s all about air-sea interaction

Dr Samantha Hallam

 

As a sailor, windsurfer, and diver I have been interested in air-sea interactions for many years. Following a BSC in Environmental Science at UEA, an MRes in Ocean Science, I undertook a PhD at the University of Southampton, looking at the impact of Atlantic Ocean variability on tropical cyclones and the northern hemisphere jet stream. Part of the research highlighted that on interannual timescales a slowdown in the Atlantic Meridional Overturning Circulation (AMOC) can cause active hurricane seasons in the Atlantic (Hallam et al. 2019)

During 2019, as part of my PhD, I was fortunate to undertake an internship at the Bermuda Institute of Ocean Sciences looking at how tropical cyclone intensity predictions can be improved using ocean heat content (Hallam et al. 2021). During my first week Hurricane Humberto brought winds over 100mph to Bermuda, causing significant damage and power outage to over 80% of the island. The first-hand experience of a major hurricane emphasised the importance of the research. 

 

Satellite image of Hurricane Humberto, west of Bermuda, U.S., September 17^th, 2019. Photo courtesy: NOAA/Handout via Reuters 

 

In February 2021 it was a delight to join the ICARUS team at Maynooth University as post-doctoral researcher, working on the EU funded ROADMAP project investigating the impact of ocean circulation variability (western boundary currents and AMOC) on atmospheric and climate dynamics in the North 

 

North Atlantic – Winter jet latitude (upper) and winter jet speed (lower)  1871-2011 (Hallam et al. 2022)

 

 

Atlantic and North Pacific. Initial results indicate that the jet latitude meridional range is at a minimum in winter along the western boundary of the North Pacific and North Atlantic, where the SST gradients are strongest.  Also, during the period 1871-2011, the winter jet latitude in the North Atlantic has migrated 3 degrees poleward and an increase in jet speed of 10mph is observed, both have implications for European Weather (Hallam et al. 2022).

 

 

References:

Hallam, S., M. Guishard, S. A. Josey, P. Hyder & J. Hirschi (2021) Increasing tropical cyclone intensity and potential intensity in the subtropical Atlantic around Bermuda from an ocean heat content perspective 1955–2019. Environmental Research Letters, 16, 034052.

Hallam, S., S. A. Josey, G. D. McCarthy & J. J. M. Hirschi (2022) A regional (land–ocean) comparison of the seasonal to decadal variability of the Northern Hemisphere jet stream 1871–2011. Climate Dynamics.

Hallam, S., R. Marsh, S. A. Josey, P. Hyder, B. Moat & J. J. M. Hirschi (2019) Ocean precursors to the extreme Atlantic 2017 hurricane season. Nature Communications, 10, 896.

 

 

Applications of Decadal Predictions

Catherine O’Beirne

Fishery sector is of vast importance to the Irish economy. In 2019 it has generated €577 million and employed 16 thousand. The ability to predict changes in the future stock will support adaptation and fish stock management. In decadal climate prediction, initialized predictions have demonstrated improved prediction skill for the North Atlantic. The different stages of fish development are dependent on oceanic variables like temperature and variability and investigating decadal prediction skill for those variables will allow me to make statements on potential changes in fish stock. 

 

After completing a B.A. in Environmental Science at Trinity College Dublin in 2016 and an M.Sc. in Climate Change at Maynooth University in 2018. I am currently a 3^rd year PhD candidate at Maynooth University. The area of focus is on understanding Atlantic variability and its connection to the Irish shelf advancing knowledge of Irish sea-level change in an Atlantic context; development of predictive capacity on decadal timescales for the North Atlantic; and how these predictions be applied for stakeholder needs

 

With the aim being to improve decadal prediction skill in the Northeast Atlantic. For this we apply ensemble subsampling, a process that selects those ensemble members for creating a subsampled ensemble mean, which perform best under evaluation by physically based statistical predictors. Climate modes, like Subpolar Gyre (SPG) and the Atlantic Multidecadal Variability (AMV), interact with our region of interest and therefore we will use those to inform us about our subsampling decisions. Applying this methodology on seasonal scales has demonstrated improved prediction skill for other climate modes.

 

Historic Sea Level Change and Outreach

Dr Zoe Roseby

 

I am postdoctoral researcher at Trinity College Dublin, interested in reconstructing past environmental change using sediment cores and microfossils found within them. My current research focuses on producing sea level reconstructions from Ireland, as part of the A4 project. 

 

In addition to my research, I participate in outreach activities on the topics of climate change and sea level rise. I am the lead applicant on Línte na Farraige, a project funded by the Creative Ireland Programme, ‘Creative Climate Action’, which seeks to meaningfully connect people with profound changes happening in our environment, society and economy arising from climate change. Línte na Farraige is a collaborative project including a team of artists, scientists, the Climate Action Regional Offices, local authorities, community groups among others. The project consists of a set of visual light installations by artists Timo Aho and Pekka Niittyvirta, that will be placed across Irish coastal sites in the coming months. Check out the website https://www.creativeireland.gov.ie/en/blog/creative-climate-action-linte-na-farraige/

Prior to my appointment at Trinity College Dublin, I carried out a bachelors and integrated master’s degree in Geological Oceanography at Bangor University and a PhD with British Antarctic Survey (BAS), University of Southampton and Durham University. My PhD project reconstructed the deglacial history of the Anvers Trough, western Antarctic Peninsula shelf. 

My research interests stem from my childhood on the Cornish coast and curiosity about the sea. I am passionate about supporting equality and diversity in STEM and sit on the Athena SWAN self-assessment team in the School of Natural Sciences, Trinity College Dublin.

Predicting “Dancing water”

Ashly Uthaman

 

Waves, the dancing water, are both impressive and frightening. Ocean waves, primarily, generated by surface winds, travel thousands of kilometre from their place of origin. On reaching the shore they dissipate energy by breaking at the surf zone thus making it the most dynamic part. Extreme wave events threaten life, livestock and livelihoods and takes away large part of coast every year. Globally, melting glaciers and ice sheets are causing increase in sea-level rise and coastal extreme events are becoming more severe. Wave predictions can help to save lives and limit the damage caused by severe storms.

After completing my Master’s in Physical Oceanography from Cochin University of Science And Technology (2018), India, I worked as Project Associate (2018 -2020)  in National Institute of Oceanography, Goa, India. I was part of project aided by Space Application Centre, Ahmedabad, India. I developed an automated Rip current prediction system for the Goa (West coast of India) using numerical modelling. I am 1^st year Phd student at Maynooth University and my work focusses on the decadal wave prediction of Irish coast.

 

The ocean waves influence the atmosphere above and the ocean below, so it is important to include their effects in wave predictions.  Coupled atmospheric and wave model will be used to get complete idea of swells from North Atlantic and the waves near the Irish coast will be simulated by surf zone model.

  

The AMOC and Climate Change

Dr Levke Caesar

 

 

Dr Levke Caesar on a ship expedition in the North Atlantic.

Every second, billions of litres of warm water flow northward near the surface of the Atlantic, while the same amount of cold water in the deeper ocean flows back southward. In this way, an amount of heat equivalent to the energy production of a million nuclear power plants is brought into the North Atlantic. Since much of this heat is released into the atmosphere, it has a significant impact on Europe's climate. The circulation behind all this is called the Atlantic Meridional Overturning Circulation, or short AMOC. Climate models predict a weakening of the AMOC in response to global warming, and scientist have wondered for years whether this slowdown has already begun. One of these scientists is Dr Levke Caesar.

As a climate physicists Dr Caesar studies climatic changes in and around the North Atlantic with a special focus on the role and the past evolution of the Atlantic Meridional Overturning Circulation. Since direct continuous measurements of the AMOC only started in 2004, she looks at other climate variables, that can be linked to the strength of the AMOC, to learn more about its past. One example are the sea surface temperatures of the North Atlantic: they are highly affected by the northward heat transport associated with AMOC and reach back until the end of the 19^th Century. And indeed, a unique region of cooling temperatures south of Greenland suggests that the system has weakened by about 15 percent since the middle of the 20th century (Caesar et al., 2018). This is in line with the trends found in other proxy data like the grain sizes or the composition of coral shells found in ocean sediments, that all indicate that the AMOC in recent decades has been weaker than ever before in at least 1600 years (Caesar et al., 2021).These findings are particularly interesting for Ireland - not just because it profits from the heat brought northward by the AMOC but also because a such a slowdown of the AMOC has been linked to an enhanced sea-level rise at both sides of the North Atlantic as well as increased storminess in north-western Europe. 

 

Simplified scheme of the Atlantic Meridional Overturning Circulation and the fingerprint in the sea surface temperatures that is caused by a slowdown in AMOC strength.

 

 

 

 

References

 

Caesar, L., McCarthy, G. D., Thornalley, D. J. R., Cahill, N., & Rahmstorf, S. (2021). Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nature Geoscience, 14(3), 118-120. https://doi.org/10.1038/s41561-021-00699-z

Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., & Saba, V. (2018). Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature, 556(7700), 191-196. https://doi.org/10.1038/s41586-018-0006-5

 

 

Communication Climate Change - Discussion with three Nobel Laureates

As a climate physicist, I consider anthropogenic climate change to be the most serious known challenge of the 21^st century – and likely also of the 22^nd and the 23^rd century. Even though this thread has been known to scientist for several decades, policy makers are still reluctant to take the necessary steps to preserve our climate. Some even openly questions the integrity of climate scientist and the existence of a human made climate change. At the same time, the consequences of climate change become more and more visible: massive coral bleaching, melting polar ice shields and rising sea levels are changing the appearance of our planet; extreme weather events, like heat waves and flooding, endanger millions of people every year.
How can it be that one the one side the basic science of climate change with the emission of greenhouse gases, especially carbon dioxide, as the cause are very clear and other the other side the acceptance among public and politicians about the need to act are so low? Is it a problem of communication?
Together with three Nobel Laureates as well as another scientist I discussed this question during this year’s Lindau Science Days. Normally, the Lindau Nobel Laureate Meeting assembles once a year Nobel Laureates and young scientists of different science sectors to foster the exchange of ideas, cultures and disciplines. Due to the pandemic this year’s meeting was postponed and replaced with an online event. As a Lindau Alumni and climate scientist I was asked to join this discussion with Nobel Laureates Steven Chu (Nobel Prize in Physics 1997 for the development of methods to cool and trap atoms with laser light), Mario J. Molina (Nobel Prize in Chemistry 1995 for the research on the formation and decomposition of ozone) and Brian P. Schmidt (Nobel Prize in Physics 2011 for the discovery of the acceleration expansion of the Universe) as well as Georg Schuette from the Volkswagen Foundation that promotes the communication of science.

As all three laureates have extend experience in convening their findings to the public as well as policy makers (Steven Chu served as United States Secretary of Energy under the administration of President Barack Obama from 2009 to 2013, Brian Schmidt is a laureate of the Australian Research Council and it is due to Marion Molina and his colleague’s efforts of informing policy markers and news media of their findings and the dangers of CFCs, that these were effectively banned from use), the discussion was extremely interesting and divers.

Even though none of us had the key to convince policy makers or the public from the severity of the thread, we certainly all agreed that we have no choice but to keep trying to convince them.

If you are interested in finding out more, you can watch the whole discussion at the Lindau Nobel Laureate Meetings Mediatheque.


Impressium from the discussion (copyright Lindau Nobel Laureate Meetings).

About the author: Levke Caesar recently finished her PhD in Climate Physics at the Potsdam Institute for Climate Impact Research in Germany. Her research topic was the evolution of the Atlantic Overturning Circulation and its impact on the Earth System. In October 2019 Ms Caesar has joined the Irish Climate Analysis and Research UnitS at Maynooth University. There she works within the A4 project and studies how changes in the Atlantic region, in particular regarding the ocean circulations, will affect Ireland. 
A4 (Grant-Aid Agreement No. PBA/CC/18/01) is carried out with the support of the Marine Institute under the Marine Research Programme funded by the Irish Government, co-financed by the European Regional Development Fund.

2020: the driest spring in Dublin since records began in 1837

Simon Noone , Conor Murphy and Csaba Horvath

Irish Climate Analysis and Research units (ICARUS), Maynooth University, Maynooth , Ireland.

Introduction

These are exceptional times. While the fine weather has served to make Covid-19 lockdown more bearable for many, the dry conditions themselves have been exceptional, especially in the east and in the Dublin region in particular. With 2 days left until the official end of spring, no rain is forecast so this is unlikely to change. Here we analyse precipitation records for the Phoenix Park station dating back to 1837, one of the longest continuous records in Ireland. We show that 2020 has returned the lowest spring [March, April and May (MAM)] rainfall total since at least 1837 and resulted in the development of drought conditions more extreme (and earlier in the year) than in summer 2018. The month of May, with a total rainfall of 8.3 mm (reported on Met Éireann’s website) ranks in the top 1% of driest months in the entire Phoenix Park record. However, truly remarkable is the fact that combined rainfall totals for April and May 2020 rank as the driest consecutive two months ever recorded at Phoenix Park, the longest running continuous series in the Republic. These are remarkable statistics on their own, however, long range forecasts and seasonal outlooks show little sign of significant rain at this stage.

The Phoenix Park Rainfall Record

 Phoenix Park is the longest continuous meteorological station in Ireland, with observations starting in 1837 and running through to present. Apart from some instrumentation changes over time, the site has always stood in the grounds of Ordnance Survey Ireland and the surrounding environment has remained largely unchanged (Figure 1). For this analysis we pieced together the Phoenix park record using monthly totals transcribed from the 10-year rainfall books for the period 1837-1940 and from quality assured records downloaded from the Met Éireann website from 1941-2020. For those not familiar with them, the 10-year books contain monthly rainfall reports, collated into ten years of data per sheet. The records are held at the Met Office in the UK and have recently been scanned and made publicly available here https://www.metoffice.gov.uk/research/library-and-archive/archive/ten-year-rainfall-books. For the most recent months, we take reported rainfall totals from Met Éireann’s monthly data website, which provides an up to date running total for the month. We note that this data has not yet been subject to final quality control by Met Éireann, which may change the final total for May, but would have to be considerable to change results much.

Figure 1. Phoenix Park site photo sourced from Met Éireann. 53°21‘50” N, 06°20’00’’ W, 48 m above mean sea level.

Figure 2 plots the annual rainfall totals for Phoenix Park over the full period of record for complete years (1837-2019). To check the quality of the data we applied the Pettit test and Standard Normal Homogeneity Test (SHNT) to the annual series. Both tests identify a statistically significant (p < 0.05) break point in 1913. However, we find no evidence from available metadata for any significant changes in the gauge, measurement practice or site at this time. Notes on the ten-year books highlight a change from an 8-inch gauge to a 5 inch gauge for some months in 1913, but reverts back to an 8 inch gauge before the end of the year. We note that Noone et al. (2016) also highlight a break point around this time at a number of other long-term gauges in Ireland. Given that we know of no systematic changes in measurement practice that would affect multiple series simultaneously at this time, it may be that this break point is due to a natural cause. Therefore we do not make any adjustments to the series here. We also emphasise that the identified break suggests that the pre-1913 series may be artificially low. As we are assessing low precipitation totals and droughts, we note that if adjustments were to lift the early series, it would make the spring 2020 totals even more remarkable in the long-term context.

 

Figure 2 Annual precipitation totals for Phoenix Park 1837-2019. The black line represents low frequency variability in the series using a lowess smoothing function. The vertical black lines represents the timing of the possible breakpoint identified using both the Pettit test and the SNHT.

 

Record Rainfall

We extracted precipitation totals for spring [MAM] and all spring months from 1837 to 2020. These are plotted in Figure 3. Evident is the very low total for Spring 2020 (52.6 mm), by far and away the lowest spring total in the entire record. Totals for each month have been low, especially in April and May, but not record breakers on their own. Figure 4 shows just how extreme the spring 2020 totals have been, far lower than any other total recorded in the entire series. While March totals (30.7 mm) were below average, both April (13.6 mm) and especially May (just 8.3 mm) have been extremely low. These numbers are not just remarkable for Spring. The combined April and May total is the driest consecutive two-month total ever recorded (at any time of the year) at Phoenix Park. The total for May 2020 lies in the top 1% of driest months ever recorded at the station back to 1837. The total for the three months of March, April and May mark the 5^th driest three-month period ever recorded across the record.

 

Figure 3 Precipitation totals for Spring [MAM] (top) and for each spring month (bottom) recorded at Phoenix Park, Dublin 1837-2020. Red line is a lowess smoothing function.

 

  Figure 4 Histograms of spring [MAM] precipitation and for the months of March, April and May at Phoenix Park, Dublin 1837-2020. The red lines show the location of 2020 totals.

 

Drought Conditions

 

To examine drought conditions at Phoenix Park we use the Standardised Precipitation Index (SPI) (McKee et al. 1993). SPI is one of the most widely used drought indices and can be used to examine drought of various accumulations. Here we derived SPI-3 to examine how deficits accrued during spring 2020 compare to other droughts in the record. SPI-3 is widely used to measure agricultural drought and soil moisture deficits. SPI values between 0.99 and −0.99 are generally considered to be near normal, −1.00 to −1.49 is moderate drought, −1.50 to −1.99 is severe drought and less than −2.00 is defined as an extreme drought (Noone et al., 2017).

 

Figure 5 shows the SPI-3 index applied to all months since 1837. Evident is the extreme nature of the drought in which we currently find ourselves. In terms of three month accumulated deficits, the current drought has already surpassed the minimum SPI-3 values for the summer 2018 drought at Phoenix Park. It has done so more than a month earlier also. Across the entire record May 2020 and April 1854 are ranked joint fourth most extreme (SPI-3 = -3.24) drought events. March 1891 is ranked second (SPI-3 = -3.53) and April 1938 ranked as the most extreme (SPI-3 = -3.76). It is worth noting that the current drought event is ongoing and with no end in sight. It is already in the top 5 most extreme droughts in the series.

Figure 5 SPI-3 series for Phoenix Park 1837-2020. Blue shows wetter than average periods, red drier than average. The grey dashed horizontal line shows the threshold for severe drought, the black dashed line is the threshold for extreme drought.

 

Figure 6 shows just the Spring SPI-3 series (SPI-3 extract for month of May) from 1837 to present. May 2020 is by far the most extreme Spring drought (SPI-3= -3.24) experienced at Phoenix Park in more than 180 years. No other event comes close. This is despite the fact that over the long-term there is a statistically significant trend towards less extreme Spring droughts. This should highlight the danger of planning based on the extrapolation of trends. Table 1 shows the top ten ranked spring droughts in the Phoenix Park record, with spring 2020 head and shoulders above the rest.

Figure 6 SPI-3 series for spring (May SPI-3) for Phoenix Park 1837-2020. The series shows a statistically significant trend (p=0.02) towards increased SPI-3 values over the long term (i.e. less extreme droughts). Despite this the May 2020 SPI-3 value is by far the most extreme on record.

 

Rank	year	Month	Phoenix Park  SPI-3
1st	2020	5	-3.24
2nd	1929	5	-2.16
3rd	1944	5	-2.08
4th	1875	5	-2.02
5th	1990	5	-1.90
6th	2007	5	-1.90
7th	1893	5	-1.88
8th	1938	5	-1.84
9th	1855	5	-1.73
10th	2011	5	-1.73

Table 1. Top ten ranked SPE-3 Spring (MAM) at Phoenix park 1837-2020

 

Outlook from here

It is important to note that this drought is ongoing. The passing of a season causes excitement for us to tally numbers, but the drought continues. The numbers are exceptional to date but large soil moisture deficits exist. It will take a considerable amount of rain to bring this drought event to an end. Continued dry conditions will make the 2020 drought an even more remarkable event. While forecasts for the coming weeks show some chance of rain, the totals for now look to be small. The longer-term seasonal forecasts for summer, while uncertain, suggest a drier and hotter summer than average over western Europe. The impacts of the 2018 drought live large in the memory. While the drought of 2020 is more limited in spatial scale thus far, affecting the east most intensely, the unfolding situation needs to be carefully monitored. Unlike 2018 we now find ourselves in the midst of a global pandemic where water has taken on a new public health importance and created new vulnerabilities.

 

 

References

McKee TB, Doesken NJ, Kleist J. 1993. The relationship of drought frequency and duration of time scales. In Eighth Conference on Applied Climatology. Am. Meteorol. Soc. January 17–23, 1993, Anaheim CA, 179–186.

Noone, S., Murphy, C., Coll, J., Matthews, T., Mullan, D., Wilby, R.L. and Walsh, S., 2016. Homogenization and analysis of an expanded long‐term monthly rainfall network for the Island of Ireland (1850–2010). International Journal of Climatology, 36(8), pp.2837-2853.

Noone, S., Broderick, C., Duffy, C., Matthews, T., Wilby, R.L. and Murphy, C., 2017. A 250‐year drought catalogue for the island of Ireland (1765–2015). International Journal of Climatology, 37, pp.239-254.

 

 

  

Supporting Information

Screenshot of monthly rainfall totals for Phoenix Park, accessed 30/5/2020

Seasonal Forecast-ECMWF shows the likely predominance of high pressure over western Europe for summer 2020.

 

Hurricanes, Ireland and Lorenzo

There has been a lot of discussion around hurricanes and Ireland this past week and a bit, associated with the remnants of Hurricane Lorenzo, coming as it has climatologically speaking hot on the heels of ex-hurricane Ophelia. Lorenzo ended up having relatively minor impacts upon the island of Ireland and there have been accusations it was over-hyped. There have also been, frankly wild, messages around hurricanes, climate change and the future impacts on Ireland bandied around. I thought it may be useful to put some thoughts down on the matter.

Was Lorenzo unusual?

While there are records for parts of the North Atlantic basin that go back for in excess of a Century, we only started observing the whole basin with the advent of satellite records in the 1970s. The eastern Atlantic basin before this time was fitfully observed, which means we can't be certain about earlier behaviour. Hurricanes are also infrequent events and it is thus hard to know whether single events are unusual in the context of a short record - did we just not observe such events by chance in the short record rather than them actually being truly unusual?

Caveats out of the way, Lorenzo was by far and away an outlier geographically in where Category 5 hurricanes (the strongest classification) have been known to have occurred. You'll note that for the <24 hours it was likely at category 5 it was very far away from Ireland.

Unusualness of the position of Lorenzo when category 5 in a historical record context. Source: Robert Rohde (@RArohde)

Other aspects of Hurricane Lorenzo were far more typical. The storm started out as a disturbance coming off Africa, moved westwards, strengthened, recurved to the north then north-east before becoming entrained in the mid-latitude circulation and transitioning to a post-tropical storm.

Storm histories for all recorded historical systems including their genesis, intensification and eventual decay either in-situ in the tropics or as extra-tropical systems. Colours denote intensity (see colour bar). Source: NOAA

Were the potential impacts on Ireland overhyped?

Let's start with the official forecasts from Met Eireann, which as the national meteorological service should be seen as the sole source for authoritative information (similarly the UK Met Office for Northern Ireland). From about a week out it was consistently suggested by the premier global forecast model from ECMWF that the post-tropical remnants of Lorenzo could impact Ireland.

 ECMWF deterministic model for 00Z on 4/10 initialised a week in advance. Note the tightly packed isobars off Cork which were the remnants of Lorenzo as forecast at that time. Source: www.wetterzentrale.de

By the start of the week, based upon continued run to run consistency of the forecast for the post-tropical remnants of Lorenzo to be over / near Ireland it was absolutely right of Met Éireann to start providing advice to the public warning of potential disruption. However, there was still considerable uncertainty in the track and intensity which persisted until much nearer the time. This is not unusual - predicting how a tropical storm system will interact with the mid-latitude system is not a simple problem. By 48 hours in advance and with Lorenzo undergoing extra-tropical transition just north of the Azores the predicted state had changed slightly:

Forecast of ex-hurricane Lorenzo initialised 48 hours in advance from ECMWF. Source: www.wetterzentrale.de

However, even this close in there were substantial disagreements between predictions arising from different global modelling groups. ECMWF and the Met Office bought the system in over Donegal / Mayo rapidly weakening as it moved over to Wales and SW England. Several other modelling groups took it up to the west of Scotland or even recorded it toward Greenland.

It was only this close in that Met Eireann issued amber and yellow specific warnings. These were appropriate to what the models were suggesting would occur. These warnings were then updated regularly and downgraded appropriately as it became clear that the system was weakening. Impacts and measured windspeed were clearly entirely consistent with the amber warnings issued. Thus Met Eireann did not overhype the storm or its likely impacts.

Members of the media and certain social media may be less innocent in the matter. Lorenzo was a category 5 hurricane several thousand kilometres and about 7 Days prior to eventual arrival in Ireland. The storm was never going to be that strong anywhere near Ireland. Yet, much reporting implied that it was still a category 5 hurricane. Arguably responsible reporting should have concentrated upon the actual state of the system upon arrival on Irish shores (a strong post-tropical system) rather than what it had been in, meteorologically speaking, a former lifetime.

What Lorenzo actually looked like at landfall in Donegal according to the Met Office analysis: i) confirms the typical post-tropical system structure and ii) the ECMWF model forecast from two days or so prior.

Met Office analysis chart for 00Z on Friday 4th Oct

Could Ireland be hit by an actual hurricane?

There have been some suggestions reported that Ireland could be hit by a hurricane in the near future. Not putting too fine a point on this: those suggestions are utterly false. Hurricanes are warm cored systems that require the sustained availability of ocean waters over 26 degrees to maintain their structure. Present day climatological sea surface temperatures of the surface Ocean (not coastal waters) in the proximity of Ireland are about 16 degrees:

Climatological SSTs for September from NOAA. Hurricanes can only be maintained over regions above 26 degrees (the oranges) which are very far from Ireland.

The 26 degree isotherm is several thousand kilometres to the SW of Ireland. Tropical systems can only transect for a very limited time over ocean surface temperatures below 26 degrees without losing their tropical characteristics:

Model output from the GFS model showing the transition from a warm cored hurricane to an extra-tropical system for Lorenzo. Colours denote temperatures, white lines denote isobars. Note how the system takes on very different structure and how pressure field broadens (weaker peak winds). Source: Simon Lee (@simonleewx)

That is before getting into finer points such as the effects of vertical shear that can rip apart a tropical system. The hurricane season in the North Atlantic is driven by the availability of a low shear environment which is a seasonally occurring phenomenon. Shear in the midlatitudes would tend to tear apart storms even if, somehow, the ocean surface temperature warmed sufficiently.

For a hurricane to hit Ireland would require late summer season sea surface temperatures to be sustained all the way from the tropics to Ireland at or above 26C, along with a sufficiently low shear environment along the path. That would require warming of the North Atlantic basin of the order 10 degrees. Because oceans warm slower than land this would equate to a global mean surface temperature warming of even more - likely somewhere north of 15 degrees. That is a warming not seen in even the most sensitive climate models under the most pessimistic emissions scenarios by 2100.

So, no, Ireland is not about to get hit by a hurricane. It is extremely unlikely to occur within the lifetime of anyone reading this blog irrespective of our collective choices as global society.

There are more than sufficient reasons for concern and subsequent undertaking of meaningful actions to address the significant challenges of climate change. This is not one of them.

But what about Ophelia?

Ophelia was also extra-tropical (an ex-hurricane) when it hit. Despite having hurricane force winds it was not a hurricane when it hit County Cork. It was, however, a very special case, transitioning much closer to Ireland than any known system. This was a very particular dynamical set-up whereby the hurricane interacted with a strong polar jet streak which maintained an outflow aloft and allowed it to retain warm-core tropical characteristics over colder than usual ocean surface temperatures. Even that  somewhat unique circumstance was insufficient to maintain tropical storm structure all the way to Ireland.