scholarly journals Historical variability and lifecycles of North Atlantic midlatitude cyclones originating in the tropics

2021 ◽  
Author(s):  
Alexander J. Baker ◽  
Kevin I. Hodges ◽  
Reinhard K. H. Schiemann ◽  
Pier Luigi Vidale
Keyword(s):  
North Atlantic ◽  
The Tropics ◽  
Midlatitude Cyclones

scholarly journals Lagrangian formation pathways of moist anomalies in the trade-wind region during the dry season: two case studies from EUREC<sup>4</sup>A

2021 ◽  
Author(s):  
Leonie Villiger ◽  
Heini Wernli ◽  
Maxi Boettcher ◽  
Martin Hagen ◽  
Franziska Aemisegger
Keyword(s):  
Long Range ◽  
North Atlantic ◽  
Large Scale ◽  
Cold Front ◽  
Trade Wind ◽  
Long Range Transport ◽  
The North ◽  
Range Transport ◽  
The North Atlantic ◽  
The Tropics

Abstract. Shallow clouds in the trade-wind region over the North Atlantic contribute substantially to the global radiative budget. In the vicinity of the Caribbean island Barbados, they appear in different mesoscale organisation patterns with distinct net cloud radiative effects (CRE). Cloud formation processes in this region are typically controlled by the prevailing large-scale subsidence. However, occasionally weather systems from remote origin cause significant disturbances. This study investigates the complex cloud-circulation interactions during the field campaign EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) from 16 January to 20 February 2020, using a combination of Eulerian and Lagrangian diagnostics. Based on observations and ERA5 reanalyses, we identify the relevant processes and characterise the formation pathways of two moist anomalies above the Barbados Cloud Observatory (BCO), one in the lower (~1000–650 hPa) and one in the middle troposphere (~650–300 hPa). These moist anomalies are associated with strongly negative CRE values and with contrasting long-range transport processes from the extratropics and the tropics, respectively. The low-level moist anomaly is characterised by an unusually thick cloud layer, high precipitation totals and a strongly negative CRE. Its formation is connected to an “extratropical dry intrusion” (EDI) that interacts with a trailing cold front. A quasi-climatological (2010–2020) analysis reveals that EDIs lead to different conditions at the BCO depending on how they interact with the associated cold front. Based on this climatology, we discuss the relevance of the strong large-scale forcing by EDIs for the low-cloud patterns near the BCO and the related CRE. The second case study about the mid-tropospheric moist anomaly is associated with an extended and persistent mixed-phase shelf cloud and the lowest daily CRE value observed during the campaign. Its formation is linked to “tropical mid-level detrainment” (TMD), which refers to detrainment from tropical deep convection near the melting layer. The quasi-climatological analysis shows that TMDs consistently lead to mid-tropospheric moist anomalies over the BCO and that the detrainment height controls the magnitude of the anomaly. However, no systematic relationship was found between the amplitude of this mid-tropospheric moist anomaly and the CRE at the BCO. Overall, this study reveals the important impact of the long-range transport, driven by dynamical processes either in the extratropics or the tropics, on the variability of the vertical structure of moisture and clouds, and on the resulting CRE in the North Atlantic winter trades.

Uncertainty in different precipitation products in the case of two atmospheric river events

2021 ◽  
Author(s):  
Alexandre M. Ramos ◽  
Rémy Roca ◽  
Pedro M.M. Soares ◽  
Anna M. Wilson ◽  
Ricardo M. Trigo ◽  
...  
Keyword(s):  
North Atlantic ◽  
Daily Precipitation ◽  
Climate Extremes ◽  
Research Programme ◽  
Late Glacial ◽  
Atmospheric Rivers ◽  
Atmospheric River ◽  
Western Us ◽  
Weather And Climate ◽  
The Tropics

&lt;p&gt;One of the World Climate Research Programme Grand Challenges is to evaluate whether existing observations are enough to underpin the assessment of weather and climate extremes. In this study, we focus on extreme associated with Atmospheric Rivers (ARs). ARs are characterized by intense moisture transport usually from the tropics to the extra-tropics. They can either be beneficial, providing critical water supply, or hazardous, when excessive precipitation accumulation leads to floods. Here, we examine the uncertainty in gridded precipitation products included in the Frequent Rainfall Observations on GridS (FROGS) database during two atmospheric river events in distinct Mediterranean climates: one in California, USA, and another in Portugal. FROGS is composed of gridded daily-precipitation products on a common 1&amp;#8728;&amp;#215;1&amp;#8728; grid to facilitate intercomparison and assessment exercises. The database includes satellite, ground-based and reanalysis products. Results show that the precipitation products based on satellite data, individually or combined with other products, perform least well in capturing daily precipitation totals over land during both cases studied here. The reanalysis and the gauge-based products show the best agreement with local ground stations. As expected, there is an overall underestimation of precipitation by the different products. For the Portuguese AR, the multi-product ensembles reveal mean absolute percentage errors between -25% and -60%. For the Western US case, the range is from -60% to -100 %.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgments&lt;/p&gt;&lt;p&gt;The financial support for this work was possible through the following FCT project: HOLMODRIVE&amp;#8212;North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017). A.M. Ramos was supported by the Scientific Employment Stimulus 2017 from Funda&amp;#231;&amp;#227;o para a Ci&amp;#234;ncia e a Tecnologia (FCT, CEECIND/00027/2017).&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

On the Role of Atmospheric Teleconnections in Climate

2008 ◽  
Vol 21 (12) ◽  
pp. 2990-3001 ◽  
Author(s):  
Anastasios A. Tsonis ◽  
Kyle L. Swanson ◽  
Geli Wang
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Recent Application ◽  
The North ◽  
The Pacific ◽  
Atmospheric Teleconnections ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Tropics

Abstract In a recent application of networks to 500-hPa data, it was found that supernodes in the network correspond to major teleconnection. More specifically, in the Northern Hemisphere a set of supernodes coincides with the North Atlantic Oscillation (NAO) and another set is located in the area where the Pacific–North American (PNA) and the tropical Northern Hemisphere (TNH) patterns are found. It was subsequently suggested that the presence of atmospheric teleconnections make climate more stable and more efficient in transferring information. Here this hypothesis is tested by examining the topology of the complete network as well as of the networks without teleconnections. It is found that indeed without teleconnections the network becomes less stable and less efficient in transferring information. It was also found that the pattern chiefly responsible for this mechanism in the extratropics is the NAO. The other patterns are simply a linear response of the activity in the tropics and their role in this mechanism is inconsequential.

scholarly journals In the field: an interview with Holly Shiels

2020 ◽  
Vol 223 (17) ◽  
pp. jeb233601
Keyword(s):  
New Brunswick ◽  
North Atlantic ◽  
Master's Degree ◽  
Stanford University ◽  
Cardiac Physiology ◽  
Senior Lecturer ◽  
The University ◽  
The Tropics ◽  
University Of Manchester ◽  
Simon Fraser University

Holly Shiels is a Reader at The University of Manchester, UK, where she investigates cardiac physiology in ectotherms. She completed her undergraduate degree in Biology at University of Western Ontario, Canada, before moving to Simon Fraser University, Canada, to complete her Master's degree and PhD. After postdoctoral studies at Stanford University, USA, and the University of Leeds, UK, Shiels moved to the University of Manchester, UK, first as a Lecturer and then Senior Lecturer. Telling us about her first experience of fieldwork on the coast of New Brunswick, Canada, Shiels describes the highs and lows of research on the ocean in the tropics and North Atlantic.

scholarly journals Is the decadal variability in the tropical Atlantic a precursor to the NAO?

2008 ◽  
Vol 26 (12) ◽  
pp. 4075-4080 ◽  
Author(s):  
I. Wainer ◽  
J. Servain ◽  
G. Clauzet
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
Periodic Oscillation ◽  
Tropical Atlantic ◽  
The Past ◽  
The North ◽  
Decadal Scale ◽  
Decadal Variations ◽  
The North Atlantic Oscillation ◽  
The Tropics

Abstract. In the past two decades climate research in the tropical Atlantic with respect to the inter-hemispheric gradient of sea surface temperature (SST) emphasized the predominance of decadal-scale variability. Our results show that this mode of variability is prevalent only for part of the last 130-years record (the 1880s, the 1920s and, especially, the 1970s). There is a lag of a few months between the decadal variations of the inter-hemispheric gradient of SST and the decadal variability of the North Atlantic Oscillation (NAO). This seems to indicate that the 10-year variability first develops in the tropics and then propagates polewards. The inter-hemispheric gradient of SST mode should be thought as episodic and not as a periodic oscillation.

scholarly journals A Global Climatology of Tropospheric Inertial Instability

2018 ◽  
Vol 75 (3) ◽  
pp. 805-825 ◽  
Author(s):  
Callum F. Thompson ◽  
David M. Schultz ◽  
Geraint Vaughan
Keyword(s):  
North Atlantic ◽  
North Atlantic Ocean ◽  
Western Pacific Subtropical High ◽  
Synoptic Scale ◽  
Coriolis Parameter ◽  
Local Maxima ◽  
The North ◽  
Inertial Instability ◽  
The North Atlantic ◽  
The Tropics

Abstract A climatology of tropospheric inertial instability is constructed using the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) at 250, 500, and 850 hPa. For each level, two criteria are used. The first criterion is the traditional criterion of absolute vorticity that is opposite in sign to the local Coriolis parameter. The second criterion, referred to as the gradient criterion, is the traditional criterion with an added term incorporating flow curvature. Both criteria show that instability, on all pressure levels, occurs most frequently in the tropics and decreases toward the poles. Compared to the traditional criterion, the gradient criterion diagnoses instability much more frequently outside the tropics and less frequently near the equator. The global distribution of inertial instability also shows many local maxima in the occurrence of instability. A sample of these local maxima is investigated further by constructing composites of the synoptic-scale flow associated with instability. The composites show that instability occurs in association with cross-equatorial flow in the North Atlantic Ocean, the Somali jet, tip jets off northern Madagascar, the western Pacific subtropical high, gap winds across Central America, upper-level ridging over western North America, and the North Atlantic polar jet. Furthermore, relatively long-lived synoptic-scale regions of instability are found within the midlatitude jet streams.

scholarly journals Changes in Seasonal Predictability due to Global Warming

2014 ◽  
Vol 27 (1) ◽  
pp. 300-311 ◽  
Author(s):  
Timothy DelSole ◽  
Xiaoqin Yan ◽  
Paul A. Dirmeyer ◽  
Mike Fennessy ◽  
Eric Altshuler
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Teleconnection Pattern ◽  
Future Climate ◽  
Quantitative Relation ◽  
Seasonal Predictability ◽  
Climate System Model ◽  
The North ◽  
The Tropics ◽  
Standard Techniques

Abstract The change in predictability of monthly mean temperature in a future climate is quantified based on the Community Climate System Model, version 4. According to this model, the North Atlantic overtakes the El Niño–Southern Oscillation (ENSO) as the dominant area of seasonal predictability by 2095. This change arises partly because ENSO becomes less variable and partly because the ENSO teleconnection pattern expands into the Atlantic. Over land, the largest change in temperature predictability occurs in the tropics and is predominantly due to a decrease in ENSO variability. The southern peninsula of Africa and northeast South America are predicted to experience significant drying in a future climate, which decreases the effective heat capacity and memory, and hence increases variance independently of ENSO changes. Extratropical land areas experience enhanced precipitation in a future climate, which decreases temperature variance by the same mechanism. Finally, the model predicts that surface temperatures near the poles will become more predictable and less variable in a future climate, primarily because melting sea ice exposes the underlying sea surface temperature, which is more predictable owing to its longer time scale. Some of these results, especially the change in ENSO variance, are known to be model dependent. This paper also advances the use of information theory to quantify predictability, including 1) deriving a quantitative relation between predictability of the first and second kinds; 2) showing how differences in predictability can be decomposed in two dramatically different ways, facilitating physical interpretation; and 3) proposing a sample estimate of mutual information whose significance can be tested using standard techniques.

scholarly journals A twenty-year study on natural and manmade global interannual fluctuations of cirrus cloud cover

2007 ◽  
Vol 7 (1) ◽  
pp. 93-126 ◽  
Author(s):  
K. Eleftheratos ◽  
C. S. Zerefos ◽  
P. Zanis ◽  
D. S. Balis ◽  
G. Tselioudis ◽  
...  
Keyword(s):  
Relative Humidity ◽  
North Atlantic ◽  
Annual Cycle ◽  
Cloud Cover ◽  
Cirrus Cloud ◽  
The North ◽  
Long Term Trends ◽  
The North Atlantic ◽  
The Tropics

Abstract. The seasonal variability and the interannual variance explained by ENSO and NAO to cirrus cloud cover (CCC) are examined during the twenty-year period 1984–2004. CCC was found to be significantly correlated with vertical velocities and relative humidity from ECMWF/ERA40 in the tropics (correlations up to –0.7 and +0.7 at some locations, respectively) suggesting that variations in large-scale vertical winds and relative humidity fields can be the origin of up to half of the local variability in CCC over these regions. These correlations reflect mostly the seasonal cycle. Although the annual cycle is dominant in all latitudes and longitudes, peaking over the tropics and subtropics, its amplitude can be exceeded during strong El Nino/La Nina events. Over the eastern tropical Pacific Ocean the interannual variance of CCC which can be explained by ENSO is about 6.8% and it is ~2.3 times larger than the amplitude of the annual cycle. Natural long-term trends in the tropics are generally small (about –0.3% cloud cover per decade) and possible manmade trends in those regions are also small. The contributions of NAO and QBO to the variance of CCC in the tropics are also small. In the northern mid–latitudes, on the other hand, the effect of NAO is more significant and can be very important regionally. Over northern Europe and the eastern part of the North Atlantic Flight Corridor (NAFC) there is a small positive correlation between CCC and NAO index during the wintertime of about 0.3. In this region, the interannual variance of CCC explained by NAO is 2.6% and the amplitude of the annual cycle is 3.1%. Long-term trends over this region are about +1.6% cloud cover per decade and compare well with the observed manmade trends over congested air traffic regions in Europe and the North Atlantic as have been evidenced from earlier findings.

scholarly journals Climate feedbacks induced by the North Atlantic freshwater forcing in a coupled model of intermediate complexity

2010 ◽  
Vol 25 (1) ◽  
pp. 103-113 ◽  
Author(s):  
Flávio Barbosa Justino ◽  
Jeferson Prietsch Machado
Keyword(s):  
Heat Transport ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Coupled Model ◽  
The North ◽  
Poleward Heat Transport ◽  
Freshwater Forcing ◽  
Oceanic Response ◽  
The North Atlantic ◽  
The Tropics

Based on coupled model simulations (ECBilt-Clio), we investigate the atmospheric and oceanic response to sustained freshwater input into the North Atlantic under the glacial maximum background state. The results demonstrate that a weakening of the thermohaline circulation triggered by weaker density flux leads to rapid changes in global sea-ice volume and reduced poleward heat transport in the Northern Hemisphere (NH). In the Southern Hemisphere (SH), however, the oceanic heat transport increases substantially. This in turn leads to strong cooling over the North Atlantic whereas the SH extratropical region warms up. The suppression of the NADW also drastically changes the atmospheric circulation. The associated northward wind anomalies over the North Atlantic increase the warm air advection from the tropics and induce the transport of tropical saltier water to mid-latitudes. This negative atmospheric-oceanic feedback should play an important role to resume the NADW, after the freshwater forcing ends up.

scholarly journals The Effect of the Madden–Julian Oscillation on the North Atlantic Oscillation Using Idealized Numerical Experiments

2020 ◽  
Vol 77 (5) ◽  
pp. 1613-1635
Author(s):  
Sebastien Fromang ◽  
Gwendal Rivière
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Nonlinear Effects ◽  
Madden Julian Oscillation ◽  
The North ◽  
Budget Analysis ◽  
The North Atlantic ◽  
Quasigeostrophic Model ◽  
The North Atlantic Oscillation ◽  
The Tropics

Abstract The aim of the paper is to investigate the influence of the Madden–Julian oscillation (MJO) on the North Atlantic Oscillation (NAO) using a quasigeostrophic model on the sphere. A simplified forcing based on potential vorticity anomalies in the tropics is used to mimic the MJO. The idealized nature of our setup allows us to determine the distinct roles played by stationary and synoptic waves. This is done by means of several series of almost 10 000 short runs of 30 days. Ensemble averages and a streamfunction budget analysis are used to study the modifications of the flow induced by the MJO. We find that a stationary Rossby wave is excited in the tropics during MJO phase 3. The western part of the Pacific jet is displaced poleward, which modifies the transient eddy activity in that basin. These changes create a ridge south of Alaska, which favors equatorward propagation of synoptic waves and larger poleward eddy momentum fluxes from the eastern Pacific toward the Atlantic, increasing the frequency of occurrence of the positive NAO events. The situation is essentially reversed following phase 6 of the MJO and conducive to the negative phase of the NAO. For a realistic MJO forcing amplitude, we find increases in both NAO phases to be around 30%, in reasonable agreement with the observations given the model simplicity. Finally, we present a series of experiments to assess the relative importance of linear versus nonlinear effects.

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