Air pollution is one of the main hazards for human health worldwide, especially in cities. Surfac... more Air pollution is one of the main hazards for human health worldwide, especially in cities. Surface emissions are the main responsible for the presence of pollutants in the near atmosphere, but meteorological conditions typically play a fundamental role in their accumulation or dispersion. In this work, we focus on the near-surface atmospheric stability and turbulence, for which data from four field campaigns with meteorological and pollutant measurements belonging to the AIRTEC-CM project(*) have been analysed. Available data correspond to the winter and summer seasons of 2020 and 2021 at two public sites located in the city centre of Madrid: a University (ETSII) and a Hospital (HCSC). The evolution of turbulence and stability and their relationships with pollutants such as NO2, PM2,5 and PM10 are investigated. To study turbulence, an analysis of friction velocity and turbulent kinetic velocity is carried out, while the stability parameter (Obukhov length) and the Richardson number ...
<p&amp... more <p>The temperature in the cities is affected by both global climate change and local changes due to human activities and the different land use compared to rural surroundings. These local changes, which modify the surface energy budget in urban areas, include the replacement of the natural surfaces by buildings and pavements and the heat of anthropogenic origin (heating, air conditioning, traffic). Madrid city (Spain) has a current population of near 3.3 million people and a larger metropolitan area reaching around 6.5 million people. Hence, it is affected by the phenomenon called urban heat island (UHI), which indicates that a higher temperature is found in the city compared with the surrounding rural areas. UHI is defined as the temperature difference between the urban observatory and the rural one and especially affects the minimum temperatures since urban areas cool down to a lesser extent than the neighbouring rural sites. Moreover, the intensity of the UHI is modulated by the meteorological conditions (wind, cloudiness, surface pressure, precipitation), highly associated with different synoptic situations. In this work, we use the Madrid-Retiro meteorological station as the urban one, which has regular and homogeneous data from the beginning of XX century; and the station at Barajas airport (12 km from the city centre) as well as other stations out of Madrid city (but within a range of 20 km from the city centre) as the rural stations. They all have a common measuring period from 1961 until present. The main objectives of the work are: 1) to identify temperature trends in the meteorological stations (both urban and rural); 2) to evaluate the intensity of the UHI for the different rural stations; 3) to apply a systematic and objective algorithm to classify each day in different categories (related to synoptic situation) that produce a different degree of UHI intensity; and, 4) to evaluate possible trends in the UHI intensity.</p>
In January 2009 a very intense major midwinter warming (MMW) took place in the boreal polar strat... more In January 2009 a very intense major midwinter warming (MMW) took place in the boreal polar stratosphere. This MMW was unexpected since all the typical external factors that influence the occurrence of this kind of events (QBO phase, sunspot cycle or ENSO) were in favor of an undisturbed and strong polar vortex for the 2008/09 winter. In this work, NCEP/NCAR reanalysis data are used to study this event in more detail and, particularly, the preceding atmospheric state and the wave activity injection into the stratosphere surrounding the date of the MMW 2009. Concerning the wave activity, we have decomposed it into their different contributors (climatological planetary waves, anomalies associated with Rossby wave packets and the interaction between them) according to the diagnostic tools by Nishii et al. (2009). Among other results, we show that, in contrast to previous MMWs, the stratosphere was not preconditioned by a weak vortex during the month before the phenomenon; on the contra...
Temperature anomalies in the lower stratosphere (namely, at 50‐hPa) poleward of 30°N (hereafter, ... more Temperature anomalies in the lower stratosphere (namely, at 50‐hPa) poleward of 30°N (hereafter, T50) are analysed from reanalysis daily products (i.e. ERA‐40 and NCEP/NCAR) in order to detect those regions with statistically significant trends of T50 during the common 1957–2002 period. We also analyse radiosonde data in order to validate the reanalyses results. The analyses are conducted for the extended polar winter (i.e. from November to May) in order to relate T50 changes to the northern polar vortex variability. In relation to the previous literature, the novelty of this study is double: first, temporal evolution is considered according to regions with similar T50 temporal variability in the Northern Hemisphere; second, trend analyses of stratospheric temperatures are obtained with the use of running windows with variable width of each principal component series computed from monthly mean values. Two main stratospheric regions were identified from both reanalyses, with a statis...
The leading European winter precipitation anomalous pattern, connected to a NAO-like structure, h... more The leading European winter precipitation anomalous pattern, connected to a NAO-like structure, has been related to a sea surface temperature structure which subtropical branch presents a significant persistence from the previous five months, having an important predictive value. Also, the Northern polar vortex presents a significant predictive skill describing this precipitation structure with 20 days in advance. These two indices
ABSTRACT In the last decades, several studies have identified how the sea surface temperature (SS... more ABSTRACT In the last decades, several studies have identified how the sea surface temperature (SST) variability in the Tropical North Atlantic (TNA) area is linked with relevant phenomena, in particular the El Niño Southern Oscillation (ENSO). Some mechanisms have been proposed to explain this connection that involves atmospheric circulation anomalies in the tropics and extratropics. Besides, recent analyses evidence that ENSO has a large impact on the North Atlantic late-winter atmospheric circulation, pointing to sea-level pressure anomalies modulated by stratospheric changes. In the present study, we explore the covariability between SST in the TNA and the wintertime atmospheric circulation in the Euro-Atlantic sector in the period 1957/58-2000/01 and we analyze the possible differences in this covariability before and after the Pacific climate shift. Atmospheric and sea surface fields are taken from ERA-40 and ERSSTv3 datasets, respectively. For the whole period, our results show that a connection exists between the ENSO phenomenon and SST anomalies in the TNA through changes in the tropospheric and stratospheric circulation. In particular, a wavenumber-2 pattern at the mid-stratosphere over high latitudes in late winter (Jan-Mar) appears linked with intense anomalies in equatorial Pacific SST during previous months (Nov-Jan) and with a strong SST zonal gradient in the tropical North Atlantic during the following spring (Mar-May). After the climate shift, we identify a change in this connection being this period characterized by a weaker coupling between the troposphere and stratosphere.
ABSTRACT Quasi-horizontal transport in the lower stratosphere over Antarctica has been studied in... more ABSTRACT Quasi-horizontal transport in the lower stratosphere over Antarctica has been studied in the past by means of several approaches, such as contour dynamics or Lyapunov exponents. In this work the problem is explored by means of a new Lagrangian descriptor M, which has already been shown to be a powerful technique to studies of ocean flows. Specifically, from an initial time t, the function M measures the length of the particle trajectories advected by the wind field over the interval [t-τ, t+τ]. The focus of this work is on the southern spring of 2005, which allows for a comparison with 1) observations of quasi-Lagrangian drifters in the lower stratosphere gathered during the VORCORE campaign, and 2) previous analyses based on Lyapunov exponents. With the methodology based on the function M, key Lagrangian features of the stratospheric polar vortex are much sharper depicted. Hyperbolic trajectories on both sides of the jet stream are associated to irreversible deformation of material contours due to Rossby wave breaking, and routes of large-scale horizontal transport across the vortex edge are successfully captured. Our results highlight the importance of lobe dynamics as transport mechanism across the Antarctic polar vortex.
Recently, several studies have pointed out the seasonal predictability of the winter anomalous pr... more Recently, several studies have pointed out the seasonal predictability of the winter anomalous precipitation in Europe and North of Africa from the Subtropical North Atlantic summer Sea Surface Temperature (SST) anomalies with five months lag. This work analyses the anomalous SST cases in the Subtropical North Atlantic area associated with the extreme precipitation events. For these extreme cases, we will
The stratospheric circulation has been recently proposed to play an important role in transmittin... more The stratospheric circulation has been recently proposed to play an important role in transmitting the ENSO signal to the Euro-Atlantic region, which projects on annular-like patterns. In this context, the influence of the ENSO polarity on the winter circulation modes in the stratosphere-troposphere system over the Northern Hemisphere is studied. Principal Component Analysis of the geopotential at different levels is
An Atmospheric Boundary Layer campaign was developed in Spain along June 2008 at the CIBA (Resear... more An Atmospheric Boundary Layer campaign was developed in Spain along June 2008 at the CIBA (Research Centre for the Lower Atmosphere) site which is placed on a fairly homogeneous terrain in the centre of an extensive plateau (41°49' N, 4°56' W). Different instrumentation at several levels was available on a new 10m meteorological mast, including temperature and humidity sensors, wind
Air pollution is one of the main hazards for human health worldwide, especially in cities. Surfac... more Air pollution is one of the main hazards for human health worldwide, especially in cities. Surface emissions are the main responsible for the presence of pollutants in the near atmosphere, but meteorological conditions typically play a fundamental role in their accumulation or dispersion. In this work, we focus on the near-surface atmospheric stability and turbulence, for which data from four field campaigns with meteorological and pollutant measurements belonging to the AIRTEC-CM project(*) have been analysed. Available data correspond to the winter and summer seasons of 2020 and 2021 at two public sites located in the city centre of Madrid: a University (ETSII) and a Hospital (HCSC). The evolution of turbulence and stability and their relationships with pollutants such as NO2, PM2,5 and PM10 are investigated. To study turbulence, an analysis of friction velocity and turbulent kinetic velocity is carried out, while the stability parameter (Obukhov length) and the Richardson number ...
<p&amp... more <p>The temperature in the cities is affected by both global climate change and local changes due to human activities and the different land use compared to rural surroundings. These local changes, which modify the surface energy budget in urban areas, include the replacement of the natural surfaces by buildings and pavements and the heat of anthropogenic origin (heating, air conditioning, traffic). Madrid city (Spain) has a current population of near 3.3 million people and a larger metropolitan area reaching around 6.5 million people. Hence, it is affected by the phenomenon called urban heat island (UHI), which indicates that a higher temperature is found in the city compared with the surrounding rural areas. UHI is defined as the temperature difference between the urban observatory and the rural one and especially affects the minimum temperatures since urban areas cool down to a lesser extent than the neighbouring rural sites. Moreover, the intensity of the UHI is modulated by the meteorological conditions (wind, cloudiness, surface pressure, precipitation), highly associated with different synoptic situations. In this work, we use the Madrid-Retiro meteorological station as the urban one, which has regular and homogeneous data from the beginning of XX century; and the station at Barajas airport (12 km from the city centre) as well as other stations out of Madrid city (but within a range of 20 km from the city centre) as the rural stations. They all have a common measuring period from 1961 until present. The main objectives of the work are: 1) to identify temperature trends in the meteorological stations (both urban and rural); 2) to evaluate the intensity of the UHI for the different rural stations; 3) to apply a systematic and objective algorithm to classify each day in different categories (related to synoptic situation) that produce a different degree of UHI intensity; and, 4) to evaluate possible trends in the UHI intensity.</p>
In January 2009 a very intense major midwinter warming (MMW) took place in the boreal polar strat... more In January 2009 a very intense major midwinter warming (MMW) took place in the boreal polar stratosphere. This MMW was unexpected since all the typical external factors that influence the occurrence of this kind of events (QBO phase, sunspot cycle or ENSO) were in favor of an undisturbed and strong polar vortex for the 2008/09 winter. In this work, NCEP/NCAR reanalysis data are used to study this event in more detail and, particularly, the preceding atmospheric state and the wave activity injection into the stratosphere surrounding the date of the MMW 2009. Concerning the wave activity, we have decomposed it into their different contributors (climatological planetary waves, anomalies associated with Rossby wave packets and the interaction between them) according to the diagnostic tools by Nishii et al. (2009). Among other results, we show that, in contrast to previous MMWs, the stratosphere was not preconditioned by a weak vortex during the month before the phenomenon; on the contra...
Temperature anomalies in the lower stratosphere (namely, at 50‐hPa) poleward of 30°N (hereafter, ... more Temperature anomalies in the lower stratosphere (namely, at 50‐hPa) poleward of 30°N (hereafter, T50) are analysed from reanalysis daily products (i.e. ERA‐40 and NCEP/NCAR) in order to detect those regions with statistically significant trends of T50 during the common 1957–2002 period. We also analyse radiosonde data in order to validate the reanalyses results. The analyses are conducted for the extended polar winter (i.e. from November to May) in order to relate T50 changes to the northern polar vortex variability. In relation to the previous literature, the novelty of this study is double: first, temporal evolution is considered according to regions with similar T50 temporal variability in the Northern Hemisphere; second, trend analyses of stratospheric temperatures are obtained with the use of running windows with variable width of each principal component series computed from monthly mean values. Two main stratospheric regions were identified from both reanalyses, with a statis...
The leading European winter precipitation anomalous pattern, connected to a NAO-like structure, h... more The leading European winter precipitation anomalous pattern, connected to a NAO-like structure, has been related to a sea surface temperature structure which subtropical branch presents a significant persistence from the previous five months, having an important predictive value. Also, the Northern polar vortex presents a significant predictive skill describing this precipitation structure with 20 days in advance. These two indices
ABSTRACT In the last decades, several studies have identified how the sea surface temperature (SS... more ABSTRACT In the last decades, several studies have identified how the sea surface temperature (SST) variability in the Tropical North Atlantic (TNA) area is linked with relevant phenomena, in particular the El Niño Southern Oscillation (ENSO). Some mechanisms have been proposed to explain this connection that involves atmospheric circulation anomalies in the tropics and extratropics. Besides, recent analyses evidence that ENSO has a large impact on the North Atlantic late-winter atmospheric circulation, pointing to sea-level pressure anomalies modulated by stratospheric changes. In the present study, we explore the covariability between SST in the TNA and the wintertime atmospheric circulation in the Euro-Atlantic sector in the period 1957/58-2000/01 and we analyze the possible differences in this covariability before and after the Pacific climate shift. Atmospheric and sea surface fields are taken from ERA-40 and ERSSTv3 datasets, respectively. For the whole period, our results show that a connection exists between the ENSO phenomenon and SST anomalies in the TNA through changes in the tropospheric and stratospheric circulation. In particular, a wavenumber-2 pattern at the mid-stratosphere over high latitudes in late winter (Jan-Mar) appears linked with intense anomalies in equatorial Pacific SST during previous months (Nov-Jan) and with a strong SST zonal gradient in the tropical North Atlantic during the following spring (Mar-May). After the climate shift, we identify a change in this connection being this period characterized by a weaker coupling between the troposphere and stratosphere.
ABSTRACT Quasi-horizontal transport in the lower stratosphere over Antarctica has been studied in... more ABSTRACT Quasi-horizontal transport in the lower stratosphere over Antarctica has been studied in the past by means of several approaches, such as contour dynamics or Lyapunov exponents. In this work the problem is explored by means of a new Lagrangian descriptor M, which has already been shown to be a powerful technique to studies of ocean flows. Specifically, from an initial time t, the function M measures the length of the particle trajectories advected by the wind field over the interval [t-τ, t+τ]. The focus of this work is on the southern spring of 2005, which allows for a comparison with 1) observations of quasi-Lagrangian drifters in the lower stratosphere gathered during the VORCORE campaign, and 2) previous analyses based on Lyapunov exponents. With the methodology based on the function M, key Lagrangian features of the stratospheric polar vortex are much sharper depicted. Hyperbolic trajectories on both sides of the jet stream are associated to irreversible deformation of material contours due to Rossby wave breaking, and routes of large-scale horizontal transport across the vortex edge are successfully captured. Our results highlight the importance of lobe dynamics as transport mechanism across the Antarctic polar vortex.
Recently, several studies have pointed out the seasonal predictability of the winter anomalous pr... more Recently, several studies have pointed out the seasonal predictability of the winter anomalous precipitation in Europe and North of Africa from the Subtropical North Atlantic summer Sea Surface Temperature (SST) anomalies with five months lag. This work analyses the anomalous SST cases in the Subtropical North Atlantic area associated with the extreme precipitation events. For these extreme cases, we will
The stratospheric circulation has been recently proposed to play an important role in transmittin... more The stratospheric circulation has been recently proposed to play an important role in transmitting the ENSO signal to the Euro-Atlantic region, which projects on annular-like patterns. In this context, the influence of the ENSO polarity on the winter circulation modes in the stratosphere-troposphere system over the Northern Hemisphere is studied. Principal Component Analysis of the geopotential at different levels is
An Atmospheric Boundary Layer campaign was developed in Spain along June 2008 at the CIBA (Resear... more An Atmospheric Boundary Layer campaign was developed in Spain along June 2008 at the CIBA (Research Centre for the Lower Atmosphere) site which is placed on a fairly homogeneous terrain in the centre of an extensive plateau (41°49' N, 4°56' W). Different instrumentation at several levels was available on a new 10m meteorological mast, including temperature and humidity sensors, wind
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