Paulina Ordóñez

Abstract In this paper, we propose a new method based on the detection of jet cores with the aim to describe the climatological features of the jet streams and to estimate their trends in latitude, altitude, and velocity in the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and 20th Century reanalysis data sets. Due to the fact that the detection method uses a single grid point to define the position of jet cores, our results reveal a greater latitudinal definition allowing a more accurate picture of the split flow configurations and double jet structures. To the best of our knowledge, these results provide the first multiseasonal and global trend analysis of jet streams based on a daily‐resolution 3‐D detection algorithm. Trends have been analyzed over 1958–2008 and during the post‐satellite period, 1979–2008. We found that, in general, trends in jet velocities and latitudes have been faster for the Southern Hemisphere jets and especially for the southern polar front jet which has experienced the fastest velocity increase and poleward shift over 1979–2008 during the austral summer and autumn. Results presented here show an acceleration and a poleward shift of the northern and southern winter subtropical jets over 1979–2008 that occur at a faster rate and over larger zonally extended regions during this latter period than during 1958–2008.

Abstract. In winter of 2009–2010 south-western Europe was hit by several destructive windstorms. The most important was Xynthia (26–28 February 2010), which caused 64 reported casualties and was classified as the 2nd most expensive natural hazard event for 2010 in terms of economic losses. In this work we assess the synoptic evolution, dynamical characteristics and the main impacts of storm Xynthia, whose genesis, development and path were very uncommon. Wind speed gusts observed at more than 500 stations across Europe are evaluated as well as the wind gust field obtained with a regional climate model simulation for the entire North Atlantic and European area. Storm Xynthia was first identified on 25 February around 30° N, 50° W over the subtropical North Atlantic Ocean. Its genesis occurred on a region characterized by warm and moist air under the influence of a strong upper level wave embedded in the westerlies. Xynthia followed an unusual SW–NE path towards Iberia, France and central Europe. The role of moist air masses on the explosive development of Xynthia is analysed by considering the evaporative sources. A lagrangian model is used to identify the moisture sources, sinks and moisture transport associated with the cyclone during its development phase. The main supply of moisture is located over an elongated region of the subtropical North Atlantic Ocean with anomalously high SST, confirming that the explosive development of storm Xynthia had a significant contribution from the subtropics.

Abstract The aim of this study is to understand how the Madden–Julian oscillation (MJO) modulates the bimodal seasonal rainfall distribution across the regions in Mexico where the midsummer drought (MSD) occurs. The MSD is characterized by a precipitation decrease in the middle of the rainy season. Relative frequencies of each active phase of the Real-time Multivariate MJO index were calculated at each grid point in the high-resolution Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) rainfall dataset for the first (MAX1) and second (MAX2) rainfall peaks and the MSD minimum (MIN). In addition, standardized anomalies of precipitation (from the CHIRPS dataset) and 300-hPa omega, 500-hPa geopotential height, and 850-hPa u- and υ-wind components (from the Climate Forecast System Reanalysis) were calculated for each MJO phase and each month in the rainy season. Results show that the MIN (MAX2) occurs more frequently during the dry (wet) MJO phases, while the MJO seems not to influence MAX1 significantly. Anomalous anticyclonic (cyclonic) circulations at 850 hPa, positive (negative) 500-hPa geopotential height anomalies, northeast (southwest) 850-hPa wind anomalies over southern Mexico, and a low-level westward (eastward) flow in the northeastern tropical Pacific support the MIN (MAX2) pattern under the influence of the dry (wet) MJO phases. These features are more clearly observed in the MSDs of 1- and 2-month duration and over the southern half of Mexico. The results suggest that the bimodal distribution is less influenced by the MJO in regions of northeastern Mexico.

The Intra–Americas Seas region is known for its relevance to air–sea interaction processes, the contrast between large water masses and a relatively small continental area, and the occurrence of extreme events. The differing weather systems and the influence of variability at different spatio–temporal scales is a characteristic feature of the region. The impact of hydro–meteorological extreme events has played a huge importance for regional livelihood, having a mostly negative impact on socioeconomics. The frequency and intensity of heavy rainfall events and droughts are often discussed in terms of their impact on economic activities and access to water. Furthermore, future climate projections suggest that warming scenarios are likely to increase the frequency and intensity of extreme events, which poses a major threat to vulnerable communities. In a region where the economy is largely dependent on agriculture and the population is exposed to the impact of extremes, understanding the climate system is key to informed policymaking and management plans. A wealth of knowledge has been published on regional weather and climate, with a majority of studies focusing on specific components of the system. This study aims to provide an integral overview of regional weather and climate suitable for a wider community. Following the presentation of the general features of the region, a large scale is introduced outlining the main structures that affect regional climate. The most relevant climate features are briefly described, focusing on sea surface temperature, low–level circulation, and rainfall patterns. The impact of climate variability at the intra–seasonal, inter–annual, decadal, and multi–decadal scales is discussed. Climate change is considered in the regional context, based on current knowledge for natural and anthropogenic climate change. The present challenges in regional weather and climate studies have also been included in the concluding sections of this review. The overarching aim of this work is to leverage information that may be transferred efficiently to support decision–making processes and provide a solid foundation on regional weather and climate for professionals from different backgrounds.

A new index, namely the African Southwesterly Index (ASWI), based on the persistence of the low‐level southwesterly winds in the region (29°–17°W; 7–13°N) is developed to characterise the strength of the West African Monsoon. The ASWI is significantly correlated with the monsoonal precipitation in the Sahel in the 1900–2013 period ( r = + 0.57, r = + 0.66 and r = + 0.53 for July, August and September respectively). By using historical wind direction measurements it has been possible to compute the ASWI back to 1790 for July and to 1839 for August and September, thus providing the first instrumental record of the West African Monsoon strength for a large portion of the nineteenth century. Since the 1970s, the Sahel has experienced a strong and persistent drought. During this period the West African Monsoon has been weaker than normal and its correlation with different climatic patterns such as the ENSO has changed. The analysis of our new series indicates that this anomalous behaviour of the West African Monsoon has no precedent in the last 170 years. Our results also show that the period 1839–1890 was characterised by a stronger than average monsoon, resulting in relatively wet conditions in the Sahel. Notwithstanding, two of the few dry years within this period were concurrent with large volcanic eruptions in the Northern Hemisphere. This latter result supports the recently described relationship between major volcanic eruptions and the occurrence of isolated drought episodes in the Sahel.

Abstract Although the identification of the moisture sources of a region is of prominent importance to characterize precipitation, the origin and amount of moisture towards the Indian Subcontinent and its relationship with the occurrence of precipitation are still not completely understood. In this article, the origin of the atmospheric water arriving to the Western and Southern India during a period of 5 years (1 January 2000–31 December 2004) is investigated by using a Lagrangian diagnosis method. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity of thousands of air particles aimed to the study area following the observed winds. During the summer monsoon, the main supply of moisture is the Somali Jet, which crosses the equator by the West Indian Ocean. The recycling process is the main water vapour source in winter. Two additional moisture sources located over northwestern India and the Bay of Bengal are identified. A 30% increase in the moisture flux from the Indian Ocean has been related to the occurrence of strong precipitation in the area, and at the end of the monsoon, the recycling became a significant contribution to the last part of the wet season of Western and Southern India. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract The Indian summer monsoon onset is one of the most expected meteorological events of the world, affecting the lives of hundreds of millions of people. The India Meteorological Department has dated the monsoon onset since 1901, but its original methodology was considered subjective and it was updated in 2006. Unfortunately, the new method relies on OLR measurements, which impedes the construction of an objective onset series before the 1970s. An alternative approach is the use of the wind field, but the development of such an index is limited to the period covered by reanalysis products. In this paper historical wind records taken on board ships are used to develop a new onset series using only wind direction measurements, providing an objective record of the onset since the late nineteenth century. The new series captures the rapid precipitation increase associated with the onset, correlates well with previous approaches, and is robust against anomalous (bogus) onsets. A tendency for later-than-average onsets during the 1900–25 and 1970–90 periods and earlier-than-average onsets between 1940 and 1965 was found. A relatively stable relationship between ENSO and Indian monsoon onset dates was found; however, this link tends to be weaker during decades characterized by prevalent La Niña conditions. Furthermore, it was found that the link between the Pacific decadal oscillation (PDO) and the onset date is limited to the phases characterized by a shift from negative to positive PDO phases.

Abstract Intense extra‐tropical cyclones are often associated with strong winds, heavy precipitation and socio‐economic impacts. Over southwestern Europe, such storms occur less often, but still cause high economic losses. We characterize the large‐scale atmospheric conditions and cyclone tracks during the top‐100 potential losses over Iberia associated with wind events. Based on 65 years of reanalysis data, events are classified into four groups: (1) cyclone tracks crossing over Iberia on the event day (‘Iberia’), (2) cyclones crossing further north, typically southwest of the British Isles (‘North’), (3) cyclones crossing southwest to northeast near the northwest tip of Iberia (‘West’), and (4) so called ‘Hybrids’, characterized by a strong pressure gradient over Iberia because of the juxtaposition of low and high pressure centres. Generally, ‘Iberia’ events are the most frequent (31–45% for top‐100 vs top‐20), while ‘West’ events are rare (10–12%). Seventy percent of the events were primarily associated with a cyclone. Multi‐decadal variability in the number of events is identified. While the peak in recent years is quite prominent, other comparably stormy periods occurred in the 1960s and 1980s. This study documents that damaging wind storms over Iberia are not rare events, and their frequency of occurrence undergoes strong multi‐decadal variability.

Abstract. This work examines the origin of atmospheric water vapor arriving to the western North American monsoon (WNAM) region over a 34-year period (1981–2014) using a Lagrangian approach. This methodology computes budgets of evaporation minus precipitation (E−P) by calculating changes in the specific humidity of thousands of air particles advected into the study area by the observed winds. The length of the period analyzed (34 years) allows the method to identify oceanic and terrestrial sources of moisture to the WNAM region from a climatological perspective. During the wet season, the WNAM region itself is on average the main evaporative source, followed by the Gulf of California. However, water vapor originating from the Caribbean Sea, the Gulf of Mexico, and terrestrial eastern Mexico is found to influence regional-scale rainfall generation. Enhanced (reduced) moisture transport from the Caribbean Sea and the Gulf of Mexico from 4 to 6 days before precipitation events seems to be responsible for increased (decreased) rainfall intensity on regional scales during the monsoon peak. Westward propagating mid- to upper-level inverted troughs (IVs) seem to favor these water vapor fluxes from the east. In particular, a 200 % increase in the moisture flux from the Caribbean Sea to the WNAM region is found to be followed by the occurrence of heavy precipitation in the WNAM area a few days later. Low-level troughs off the coast of northwestern Mexico and upper-level IVs over the Gulf of Mexico are also related to these extreme rainfall events.

This study aims to improve the understanding of the role of the Madden-Julian Oscillation (MJO) in modulating the midsummer drought (MSD) in Mexico. First, the main moisture sources for the MSD region in Mexico during the summer were identified using the Lagrangian particle dispersion model FLEXPART for the period 1979–2017. From this analysis, the Caribbean Sea was identified as one of the main moisture sources, particularly the area where the core of the Caribbean low-level jet (CLLJ) is located. Second, the water vapour flux transported by the CLLJ to Mexico was then analysed. It was found that the summer seasonal cycle of the CLLJ is associated with the bimodal precipitation pattern in Mexico through the seasonal variability of the moisture contribution from the CLLJ to precipitation over the MSD region, thereby confirming the CLLJ as a key element in the occurrence of the MSD in the Americas. Third, the influence of the MJO on this transport was examined. This analysis showed that the locally dry phases of the MJO decrease the contribution of moisture from the CLLJ core towards the MSD region, while the locally wet phases increase it. Moreover, phases 1 and 2 of the MJO were found to influence the first precipitation peak that occurs in the southwestern region of Mexico by increasing the contribution of moisture from the northeastern tropical Pacific. The study ends by proposing, for the first time, a mechanism by which the MJO modulates the MSD in Mexico.

[1] Recent studies suggest that there is a strong linkage between the moisture uptake over the equatorial area of the Somali low level jet (SLLJ) and the rainfall variability over most of continental India. Additionally, the Madden-Julian Oscillation (MJO) strongly modulates the intraseasonal variability of the Indian summer monsoon rainfall, since the northward propagation of the boreal summer MJO is closely associated with the active and break phases of monsoon rainfall. But a question remains open: is there a relationship between the moisture transported by the SLLJ and the MJO evolution? In this paper, a Lagrangian approach is used to track the evaporation minus precipitation (E − P) evolution along trajectories of particles initially situated over the equatorial region of SLLJ. The impact of the MJO on the water budget transport of the SLLJ is examined by making composites of the obtained (E-P) fields for the different MJO phases. The spatial structures of the boreal summer intraseasonal oscillation are revealed in our results, which strongly suggest that the main responsible for the rainfall variability associated to the MJO in these regions are the changes in the moisture advected by the SLLJ. In order to assess the MJO-SLLJ interaction, an analysis of the total-column mass and the total-column specific humidity transported by the SLLJ during the MJO life cycle is performed. While a systematic difference between air mass advected to India during active and break phases of MJO is not detected, changes in the moisture of particles are found, with wet (dry) anomalies over enhanced (suppressed) convection region. This result implicitly leads to assume air-sea interaction processes.

<h2>Abstract</h2> Atmospheric pollution in cities is due to several human factors, for instance the number of cars in circulation, fuel efficiency and industrial waste, as well as orographic and meteorological conditions that determine air circulation. Ozone contingencies cause health disorders on the population, making it important to understand the factors that trigger such contingencies. Here, we analyze meteorological (wind, temperature, relative humidity) and atmospheric composition (ozone, and NOx) data of five atmospheric monitoring stations on Mexico City, from March 2004 to May 2018, comparing normal days with the extreme days in the 90th percentile of ozone. Moreover, we present the synoptic patterns of the seasonal differences of geopotential height at 500 hPa between extreme and control days. We found that, in the dry-hot season (from March to May) an atmospheric blockage with meteorological conditions of almost no wind, low relative humidity, and small temperature fluctuations occurs. Because the air in the city permanently contains large amounts of ozone precursors like NOx, this meteorological scenario raises ozone levels to those of an environmental contingency. Thus, during the dry-hot season on Mexico City, ozone contingencies are triggered by atmospheric blocking. This scenario will be present in cities surrounded by mountains with high levels of Ozone precursors.

In the past, several works addressed the impact of El Niño-Southern Oscillation (ENSO) on Mexican precipitation by using relative scarce observations of the National Weather Service of Mexico or reanalysis data. In this work, we reassessed the ENSO signal in Mexican rainfall by using four precipitation databases (CHIRPS, GPCC, GPCP and CMAP) over a 34-yr period (1981-2014) and three different ENSO indices. Results obtained with different datasets are consistent among them and with previous studies, showing strong positive precipitation anomalies along the winter over the northern Mexico for El Niño events. In contrast, during the summer, negative rainfall anomalies can be found over most of central and southern Mexico, being stronger in August. During La Niña years, the anomalies show approximately the opposite pattern to those observed during El Niño. A Lagrangian approach is used to track the evaporation minus precipitation (E-P) along trajectories followed by the atmospheric particles that will take precipitable water to the areas with a precipitation amount modulated by ENSO phases. Then, composites of the obtained (E-P) fields are examined for the strong phases of El Niño and La Niña. Finally, the synoptic conditions associated with ENSO-related anomalous atmospheric water vapor fluxes are studied for a better understanding of the origin of the ENSO impact on the Mexican precipitation.

Abstract. Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H2O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H2O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H2O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6–10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H2O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H2O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of δD are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal δD variations, the results suggest that in the current data versions, the calculated isotopic composition (δD) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological δD composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these δD observations.

Abstract This work aims to define an index to declare rainy season onset and withdrawal dates for the Mexico Valley Basin, located in central Mexico. The onset/withdrawal is obtained using only precipitation for the study period 1981-2020. The onset is defined as the first day, between May 1st and July 15th, of the first 20 consecutive days having a 20-day average precipitation over the Basin of at least 2.5 mm/day. The withdrawal is defined as the last day, between September 1st and November 15th, of the last 20 consecutive days having a 20-day average precipitation of at least 1.7 mm/day. The mean onset is June 6, with a standard deviation of 14.3 days; the mean withdrawal date is October 15, with a standard deviation of 16.1 days; and the average length of the rainy season is 131 days, with a standard deviation of 22.7 days. These criteria maximize the precipitation change slope during onset/withdrawal. We categorized pre- and post-onset/withdrawal periods to investigate mean circulation characteristic changes. Besides a stark increase (decrease) in rainfall over the Basin during onset (withdrawal), we found that vertically integrated moisture transport over the Caribbean Low-Level Jet core region increases (decreases). The onset/withdrawal dates derived show interannual trends, while a late (early) withdrawal is associated with a positive (negative) ENSO Index, and a strong (weak) Caribbean Lower Level Jet (CLLJ) is associated with a late (early) onset.

<strong class="journal-contentHeaderColor">Abstract.</strong> Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H₂O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H₂O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H₂O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6&ndash;10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H₂O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H₂O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of &delta;D are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal &delta;D variations, the results suggest that in the current data versions, the calculated isotopic composition (&delta;D) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological &delta;D composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these &delta;D observations.

Abstract This work aims to define a procedure to declare rainy season onset and withdrawal dates for the Mexico Valley Basin, located in central Mexico. The onset/withdrawal is obtained using only precipitation for the study period 1981–2020. The onset is defined as the first day, between May 1st and July 15th, of the first 20 consecutive days having a 20-day average precipitation over the Basin of at least 2.5 mm/day. The withdrawal is defined as the last day, between September 1st and November 15th, of the last 20 consecutive days having a 20-day average precipitation of at least 1.7 mm/day. The mean onset is June 6th, with a standard deviation of 14.3 days; the mean withdrawal date is October 15th, with a standard deviation of 16.1 days; and the average length of the rainy season is 131 days, with a standard deviation of 22.7 days. These criteria maximize the precipitation change slope during onset/withdrawal. We categorized pre- and post-onset/withdrawal periods to investigate mean circulation characteristic changes. Besides a stark increase (decrease) in rainfall over the Basin during onset (withdrawal), we found that vertically integrated moisture transport over the Caribbean Low-Level Jet core region increases (decreases). The onset/withdrawal dates derived show interannual trends, while a late (early) withdrawal is associated with a positive (negative) ENSO Index, and a strong (weak) Caribbean Low Level Jet (CLLJ) is associated with a late (early) onset.

<strong class="journal-contentHeaderColor">Abstract.</strong> Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H₂O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H₂O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H₂O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6&ndash;10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H₂O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H₂O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of &delta;D are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal &delta;D variations, the results suggest that in the current data versions, the calculated isotopic composition (&delta;D) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological &delta;D composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these &delta;D observations.

<strong class="journal-contentHeaderColor">Abstract.</strong> Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H₂O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H₂O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H₂O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6&ndash;10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H₂O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H₂O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of &delta;D are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal &delta;D variations, the results suggest that in the current data versions, the calculated isotopic composition (&delta;D) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological &delta;D composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these &delta;D observations.

<strong class="journal-contentHeaderColor">Abstract.</strong> Variations in the isotopological composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapor transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H₂O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H₂O and HDO retrievals from Envisat/MIPAS are compared with data derived from SCISAT/ACE-FTS. Specifically, MIPAS-IMK V5, MIPAS-ESA V8, and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. Stratospheric H₂O and HDO global average coincident profiles reveal good agreement. The smallest biases are found between 20 and 30 km, and the largest biases are exhibited around 40 km both in absolute and relative terms. For HDO, biases between -8.6&ndash;10.6 % are observed among the three databases in the altitudes of 16 to 30 km. However, around 40 km, ACE-FTS agrees better to MIPAS-IMK than MIPAS-ESA, with biases of -4.8 % and -37.5 %, respectively. The HDO bias between MIPAS-IMK and MIPAS ESA is 28.1 % at this altitude. The meridional cross-sections of H₂O and HDO exhibit the expected distribution that has been established in previous studies. The tape recorder signal is present in H₂O and HDO for the three databases with slight quantitative differences. The meridional cross-sections of &delta;D are in good agreement with the previous version of MIPAS-IMK and ACE-FTS data. In the temporal &delta;D variations, the results suggest that in the current data versions, the calculated isotopic composition (&delta;D) from MIPAS-IMK aligns more closely with expected stratospheric behavior for the entire stratosphere. Nevertheless, there are differences in the climatological &delta;D composites between databases that could lead to different interpretations regarding the water vapor transport processes toward the stratosphere, so it is important to intercompare these &delta;D observations.

Abstract. In winter of 2009–2010 Southwestern Europe was hit by several destructive windstorms. The most important was Xynthia (26–28 February 2010), which caused 64 reported casualties and was classified as the 2nd most expensive natural hazard event for 2010 in terms of economic losses. In this work we assess the synoptic evolution, dynamical characteristics and the main impacts of storm Xynthia, whose genesis, development and path were very uncommon. Wind speed gusts observed at more than 500 stations across Europe are evaluated as well as the wind gust field obtained with a regional climate model simulation for the entire North Atlantic and European area. Storm Xynthia was first identified on 25 February around 30° N, 50° W over the subtropical North Atlantic Ocean. Its genesis occurred on a region characterized by warm and moist air under the influence of a strong upper level wave embedded in the westerlies. Xynthia followed an unusual SW–NE path towards Iberia, France and central Europe. The role of moist air masses on the explosive development of Xynthia is analysed by considering the evaporative sources. A lagrangian model is used to identify the moisture sources, sinks, and moisture transport associated with the cyclone during its development phase. The main supply of moisture is located over an elongated region of the subtropical North Atlantic Ocean with anomalously high SST, confirming that the explosive development of storm Xynthia had a significant contribution from the subtropics.

This work provides an assessment of the two most intense seasonal droughts that occurred over the Balsas River Basin (BRB) in the period 1980–2017. The detection of the drought events was performed using the 6 month scale standardized precipitation–evapotranspiration index (SPEI-6) and the 6 month standardized precipitation index (SPI-6) in October. Both indices were quite similar during the studied period, highlighting the larger contribution of precipitation deficits vs. temperature excess to the drought occurrence in the basin. The origin of the atmospheric water arriving to the BRB (1 May 1980–31 October 2017) was investigated by using a Lagrangian diagnosis method. The BRB receives moisture from the Caribbean Sea and the rest of the tropical Atlantic, the Gulf of Mexico, the eastern north Pacific and from three terrestrial evaporative sources: the region north of BRB, the south of BRB and the BRB itself. The terrestrial evaporative source of the BRB itself is by far the main moisture source. The two most intense drought events that occurred in the studied period were selected for further analysis. During the severe drought of 2005, the summertime sea surface temperature (SST) soared over the Caribbean Sea, extending eastward into a large swathe of tropical North Atlantic, which was accompanied by the record to date of hurricane activity. This heating generated a Rossby wave response with westward propagating anticyclonic/cyclonic gyres in the upper/lower troposphere. A cyclonic low-level circulation developed over the Gulf of Mexico and prevented the moisture from arriving to the BRB, with a consequent deficit in precipitation. Additionally, subsidence also prevented convection in most of the months of this drought period. During the extreme drought event of 1982, the Inter Tropical Convergence Zone (ITCZ) remained southern and stronger than the climatological mean over the eastern tropical Pacific, producing an intense regional Hadley circulation. The descent branch of this cell inhibited the development of convection over the BRB, although the moisture sources increased their contributions; however, these were bounded to the lower levels by a strong trade wind inversion.

Abstract. This work examines the origin of atmospheric water vapor arriving to the North American Monsoon (NAM) region over a 34-yr period (1981–2014) by using a Lagrangian diagnosis method. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity of thousands of air particles advected into the study area by the observed winds. During the NAM wet season, on average the recycling process is the main water vapor source, followed by the supply of moisture from the Gulf of California. However, the water vapor transport that generates synoptic-scale rainfall comes primarily from the Caribbean Sea, the Gulf of Mexico and terrestrial eastern Mexico. An additional moisture source over the southwestern US is also identified in association with synoptic rainfall events over the NAM region. A high (low) moisture supply from the Caribbean Sea and the Gulf of Mexico from 4 to 6 days before precipitation events is responsible for high (low) rainfall intensity on synoptic scales during the monsoon peak. Westward propagating mid to upper level inverted troughs (IVs) seem to favor these water vapor fluxes. A 200 % increase in the moisture flux from the Caribbean Sea is related to the occurrence of heavy precipitation in the NAM area, accompanied by a decrease in water vapor advection from the Gulf of California.