Ríos Atmosféricos y Transporte de Humedad Tropical: Relevancia para la Precipitación Extrema y la Ciclogénesis Explosiva

La presente tesis doctoral estudia el fenómeno del río atmosférico desde una perspectiva holística. Se analiza, primeramente, el origen de la humedad asociada a estos eventos, su variabilidad interanual e interestacional sobre el Atlántico Norte, así como su implicación en los procesos de ciclogénesis explosiva sobre las cuencas oceánicas atlántica y pacífica. Finalmente, se estudia la relevancia de la fenomenología para la precipitación extrema sobre el margen atlántico ibérico, y el fenómeno de la inundación en Galicia

Tagging moisture sources with Lagrangian and inertial tracers: application to intense atmospheric river events

Two Lagrangian tracer tools are evaluated for studies on atmospheric moisture sources and pathways. In these methods, a moisture volume is assigned to each particle, which is then advected by the wind flow. Usual Lagrangian methods consider this volume to remain constant and the particle to follow flow path lines exactly. In a different approach, the initial moisture volume can be considered to depend on time as it is advected by the flow due to thermodynamic processes. In this case, the tracer volume drag must be taken into account. Equations have been implemented and moisture convection was taken into account for both Lagrangian and inertial models. We apply these methods to evaluate the intense atmospheric rivers that devastated (i) the Pacific Northwest region of the US and (ii) the western Iberian Peninsula with flooding rains and intense winds in early November 2006 and 20 May 1994, respectively. We note that the usual Lagrangian method underestimates moisture availability in the continent, while active tracers achieve more realistic resultsERA-Interim data were supported by the ECMWF. This work was financially supported by Ministerio de Economía, Industria y Competitividad (CGL2017-89859-Rand CGL2013-45932-R), with contributions by the COST Action MP1305 and CRETUS strategic partnership (AGRUP2015/02). All these programs are co-funded by the ERDF (EU)S

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

A new 3-D tracer tool is coupled to the WRF model to analyze the origin of the moisture in two extreme atmospheric river (AR) events: the so-called Great Coastal Gale of 2007 in the Pacific Ocean and the Great Storm of 1987 in the North Atlantic. Results show that between 80 and 90 % of moisture advected by the ARs, and a high percentage of the total precipitation produced by the systems have a tropical origin. The tropical contribution to precipitation is in general above 50 % and largely exceeds this value in the most affected areas. Local convergence transport is responsible for the remaining moisture and precipitation. The ratio of tropical moisture to total moisture is maximized as the cold front arrives on land. Vertical cross sections of the moisture content suggest that the maximum in tropical humidity does not necessarily coincide with the low-level jet (LLJ) of the extratropical cyclone. Instead, the amount of tropical humidity is maximized in the lowest atmospheric level in southern latitudes and can be located above, below or ahead of the LLJ in northern latitudes in both analyzed casesThis work has been founded by the Ministerio de Economía y Competitivad (CGL2013-45932-R) from the Spanish Government and its mobility grants for pre-doc researchers. Funding for Dominguez and Hu comes from NASA grant NNX14AD77GS

On the assessment of the moisture transport by the Great Plains low-level jet

Low-level jets (LLJs) can be defined as wind corridors of anomalously high wind speed values located within the first kilometre of the troposphere. These structures are one of the major meteorological systems in the meridional transport of moisture on a global scale. In this work, we focus on the southerly Great Plains low-level jet, which plays an important role in the moisture transport balance over the central United States. The Gulf of Mexico is the main moisture source for the Great Plains low-level jet (GPLLJ), which has been identified as a key factor for rainfall modulation over the eastern and central US. The relationship between moisture transport from the Gulf of Mexico to the Great Plains and precipitation has been well documented in previous studies. Nevertheless, a large uncertainty still remains in the quantification of the moisture amount actually carried by the GPLLJ. The main goal of this work is to address this question. For this purpose, a relatively new tool, the regional atmospheric Weather Research and Forecasting Model with 3-D water vapour tracers (WRF-WVT; Insua-Costa and Miguez-Macho, 2018) is used together with the Lagrangian model FLEXPART to estimate the load of precipitable water advected within the GPLLJ. Both models were fed with data from ERA Interim. From a climatology of jet intensity over a 37-year period, which follows a Gaussian distribution, we select five cases for study, representing the mean and 1 and 2 standard deviations above and below it. Results show that the jet is responsible for roughly 70 %–80 % of the moisture transport occurring in the southern Great Plains when a jet event occurs. Furthermore, moisture transport by the GPLLJ extends to the north-east US, accounting for 50 % of the total in areas near the Great Lakes. Vertical distributions show the maximum of moisture advected by the GPLLJ at surface levels and maximum values of moisture flux about 500 m above, in coincidence with the wind speed profile.Ministerio de Economía | Ref. CGL2015-65141-RXunta de Galicia | Ref. EDB481B 2018/069Xunta de Galicia | Ref. ED431C 2017/64-GR

On the relationship between atmospheric rivers, weather types and floods in Galicia (NW Spain)

Atmospheric rivers (ARs) – long and narrow structures of anomalously high water vapor flux located in the warm sector of extratropical cyclones – have been shown to be closely related to extreme precipitation and flooding. In this paper we analyze the connection between ARs and flooding in the northwestern Spanish region of Galicia under a variety of synoptic conditions represented by the so-called “weather types”, a classification of daily sea-level pressure patterns obtained by means of a simple scheme that adopts the subjective procedure of Lamb. Flood events are identified from official reports conducted by the Spanish emergency management agency (Protección Civil) from 1979 to 2010. Our results suggest that, although most flood events in Galicia do not coincide with the presence of an overhead AR, ARs are present in the majority of severe cases, particularly in coastal areas. Flood events associated with ARs are connected to cyclonic weather types with westerly and southwesterly flows, which occur mostly in winter months. The link between ARs and severe flooding is not very apparent in inland areas or during summer months, in which case heavy precipitation is usually not frontal in nature but rather convective. Nevertheless, our results show that, in general, the amount of precipitation in flood events in Galicia more than doubles when an AR is present.Ministerio de Economía y Competitividad | Ref. CGL2013-45932-RXunta de Galicia | Ref. ED431C 2017/64-GR

A rama atmosférica do ciclo hidrolóxico. Dende a evaporación oceánica ata a precipitación nos continentes

Este libro presenta unha caracterización da rama atmosférica do ciclo hidrolóxico baseada na relación entre fontes e sumidoiros e o transporte de humidade. Nela analízanse os principais mecanismos e procesos relacionados co transporte de humidade e revísase a localización das principais fontes oceánicas e terrestres e as rexións influenciadas por elas. Ademais, faise fincapé nos extremos hidrometeorolóxicos (secas e inundacións) e as suas principais causas ademais do efecto do cambio climático nesta rama do ciclo hidrolóxico. Esta monografía pretende de realizar unha síntese dos principais factores involucrados no ciclo hidrolóxico e no transporte de humidade cara os continentes; resultando nun libro de consulta especialmente indicado para o alumnado de materias medioambientais tanto de grao coma mestrado, así coma para o alumnado de doutoramento ou persoas que queiran iniciarse na investigación da vertente atmosférica do ciclo hidrolóxico

Significant increase of global anomalous moisture uptake feeding landfalling Atmospheric Rivers

One of the most robust signals of climate change is the relentless rise in global mean surface temperature, which is linked closely with the water-holding capacity of the atmosphere. A more humid atmosphere will lead to enhanced moisture transport due to, among other factors, an intensification of atmospheric rivers (ARs) activity, which are an important mechanism of moisture advection from subtropical to extra-tropical regions. Here we show an enhanced evapotranspiration rates in association with landfalling atmospheric river events. These anomalous moisture uptake (AMU) locations are identified on a global scale. The interannual variability of AMU displays a significant increase over the period 1980-2017, close to the Clausius-Clapeyron (CC) scaling, at 7 % per degree of surface temperature rise. These findings are consistent with an intensification of AR predicted by future projections. Our results also reveal generalized significant increases in AMU at the regional scale and an asymmetric supply of oceanic moisture, in which the maximum values are located over the region known as the Western Hemisphere Warm Pool (WHWP) centred on the Gulf of Mexico and the Caribbean SeaMinisterio de Ciencia, Innovación y Universidades | Ref. RTI2018-095772-B-I00Xunta de Galicia | Ref. ED431C 2017/64-GRCMinisterio de Economía y Competitividad | Ref. CGL2015-65141-RXunta de Galicia | Ref. EDB481B 2018/069Fundação para a Ciência e a Tecnologia | Ref. PTDC/CTA-MET/29233/2017Fundação para a Ciência e a Tecnologia | Ref. CEECIND/00027/201

Analysis of the main source regions of moisture transport events with the new ESA CCI/CM‐SAF total column water vapour climate data record (v2)

This study makes use of the new total column water vapour data record (CDR‐2 (v2)), developed by the European Space Agency (ESA) in coordination with the Satellite Application Facility on Climate Monitoring (CM SAF), to analyse the adequacy of the integrated vertical water vapour column (IWV) data provided by the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA5 and ERA‐Interim reanalyses in regions of critical interest for moisture transport mechanisms. This information is critical for the initialization of moisture transport models—both Eulerian and Lagrangian—used to study the main mechanisms and predict the future evolution of moisture transport events. In particular, almost 40,000 atmospheric river (AR) and nocturnal low‐level jet (NLLJ) events identified on a global scale between 2002 and 2017 have been used to study the variability between the cited reanalyses and CDR‐2, in terms of both bias in the observed values of IWV during each particular event and daily temporal correlation fields. Although some notable discrepancies are reported in the main tropical rainforest regions, it is observed that, in regions of high interest for both ARs and NLLJs, the degree of agreement between the reanalyses and CDR‐2 is high. The bias observed in the regions of interest is generally low, and the temporal correlation in the IWV fields is above 0.8 in most areas. ERA5 appears to show slightly better performance than ERA‐Interim when resolving the moisture column, and both show greater similarity to CDR‐2 in the midlatitudes compared with tropical regions. The probability density functions constructed on an event‐to‐event basis reinforce these ideas. We conclude that the evaluations presented here using CDR‐2 serve to strengthen avaliable evidence that the ECMWF reanalyses can safely be used in the initializations of Lagrangian dispersion models and Eulerian moisture tracer simulations—commonly used for the analysis of main advection mechanisms—in the vast majority of regions critical to the study of ARs and LLJs. They can also safely be used for the detection of moisture source–sink regions in the study of the global hydrological cycle in these regions

Changes in moisture sources of atmospheric rivers landfalling the Iberian Peninsula with WRF-FLEXPART

This paper makes use of a combination of FLEXPART-WRF simulations forced with ERA5 and the CESM2 model—incorporated in the CMIP6 project—to infer a series of changes over the present century in the behavior of the landfalling atmospheric rivers (ARs) arriving to the Iberian Peninsula. In addition, future changes in the intensity and position of their main moisture sources are studied. In overall terms, there is a noticeable increase in the amount of moisture transported by ARs in the study region, particularly accentuated by the end of the century. However, no significant changes in the number of events are observed. A northward shift of both the mean position of the ARs as well as their main sources of moisture is also detected, particularly for the end of the century, and in the summer and fall months. In relation to the latter, an increase in the contribution of moisture contribution is also observed, quantitatively compatible with Clausius-Clapeyron amplification.Agencia Estatal de Investigación | Ref. PID2021-122314OB-I00Xunta de Galicia | Ref. ED481A‐2020/193Xunta de Galicia | Ref. ED431C 2021/44Universidade de Vigo/CISU

Extreme precipitation events

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThe effect of increased populations concentrated in urban areas, coupled with the ongoing threat of climate change, means that society is becoming increasingly vulnerable to the effects of extreme precipitation. The study of these events is therefore a key topic in climate research, in their physical basis, in the study of their impacts, and in our adaptation to them. From a meteorological perspective, the main questions are related to the definition of extreme events, changes in their distribution and intensity both globally and regionally, the dependence on large-scale phenomena including the role of moisture transport, and changes in their behavior due to anthropogenic pressures. In this review article, we address all these points and propose a set of challenges for future research.Agencia Estatal de Investigación | Ref. RTI2018‐095772‐B‐I00Xunta Galicia | Ref. D431C 2021/4