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  • Open access
  • 10 Reads
Impact of Wildfires on Atmospheric Ammonia Concentrations in the US: Coupling Satellite and Ground Based Measurements

Gaseous ammonia plays a crucial role in the earth’s atmosphere. Major sources of atmospheric ammonia include agriculture and fires. As the climate continues to change, the pattern of fires across the US will also change, leading to changes in ammonia emissions. This study examines four major science questions using satellite and in-situ data from 2010–2014: (1) How have concentrations of ammonia changed across the US? (2) How have the strength and frequency of fires changed? (3) How has this change in fires impacted ammonia emissions? (4) How does the US EPA NEI compare with the calculated emissions? Satellite and in-situ data were used to evaluate the annual concentrations of ammonia and to calculate the total ammonia emissions across the continental US. The results of this study showed that ammonia concentrations have slightly increased over the five-year period. The total fire number and the average fire radiative power have decreased, while the total yearly burn area has increased. The calculated ammonia emissions from fires on a national scale show an increasing trend and when compared with the US EPA NEI for ammonia emissions from fires, annual ammonia emissions are, on average, a factor of 0.49 higher than the NEI.

  • Open access
  • 11 Reads
Average Path Profile of Atmospheric Temperature and Humidity Structure Parameters from a Microwave Profiling Radiometer

The values of the key atmospheric turbulence parameters (structure constants) for temperature and water vapor, i.e., CT2, and CQ2, are highly dependent upon the vertical height within the atmosphere thus making it necessary to specify profiles of these values along the atmospheric propagation path. The remote sensing method suggested and described in this work makes use of a rapidly integrating microwave profiling radiometer to capture profiles of temperature and humidity through the atmosphere. The integration times of currently available profiling radiometers are such that they are approaching the temporal intervals over which one can possibly make meaningful assessments of these key atmospheric parameters. These integration times, coupled with the boundary effects of the Earth’s surface are, however, unconventional for turbulence characterization; the classical Kolmogorov turbulence theory and related 2/3 law for structure functions prevalent in the inertial sub-range are no longer appropriate. An alternative to this classical approach is derived from first principles to account for the nuances of turbulent mechanics met with using radiometer sensing, i.e., the large-scale turbulence driven by the various possible boundary conditions within the buoyancy sub-range. Analytical expressions connecting the measured structure functions to the corresponding structure parameters are obtained. The theory is then applied to an experimental scenario involving radiometric profile measurements of temperature and shows very good results.

  • Open access
  • 12 Reads
Time Series Clustering to Estimate Particulate Matter Contributions from Deserts

Exploratory analysis of time series (TS) data is an important approach in experimental studies, with a large range of applications in many different fields, including air pollution studies. To identify structures in single (univariate) TS, main clustering analyses are based on general-purpose clustering algorithms (e.g., k-means, hierarchical clustering methods) and made the assumption that the samples (data) of a TS are independent, ignoring the correlations in consecutive sample values in time. This is specially the case of air pollutant studies based on monitoring data. Air pollutants TS can be studied using TS clustering techniques and as a result, pollution profiles or concentration regimes detected as well as the dependency structure between consecutive data is preserved. Once TS clustering applied over the TS data stream, a set of clusters group the data according to their similar concentration values, and therefore, different pollution profiles can be defined and their estimated range of concentration values. Hidden Markov Models (HMMs) are flexible general-purpose models for univariate and multivariate TS. The TS data are assumed to have a Markov property, and may be viewed as the results of a probabilistic walk along a fixed set of (no directly observable) states. This class of approach considers that each TS is generated by a mixture of underlying probability distributions, typically the Gaussian ones. In this study, HMMs were applied to cluster daily average particulate matter with aerodynamic diameter of 10 μm or less (PM10) TS collected at background monitoring stations from the Iberian Peninsula and Canarian Archipelago (Spain). As a result, PM10 concentration regimes were studied and in particular, the contribution to PM10 ambient concentration levels from the regimes associated to transport of air masses from North Africa deserts was estimated. Regarding this last contribution, we later compared to those obtained using the monthly moving 40th percentile (P40) method over the same TS and no significant quantitative differences were detected. However, the results obtained with HMMs seem to correct the net load of PM10 given by the P40 method, and attributes less impact on areas suffering greater influence from African episodes. The method proposed in this work to estimate PM10 from deserts could improve the P40 method in two ways since it avoids: (i) the smoothed effect which is implicit in the P40 methods after applying a mobile procedure in the TS treatment; and (ii) the empirical approach based on a correlation analysis applied in order to select this particular percentile (40th). Moreover, the use of statistical replicative techniques (bootstrap) together with HMMs has let to obtain an interval confidence in the PM10 contribution estimates from North African deserts. This methodology may be used to estimate particulate matter contributions from any desert; however, a consensus among experts is required to give the regimes obtained with HMMs a definition.

  • Open access
  • 6 Reads
A Satellite View of the Atmospheric Dry Intrusion and its Influences on the Mid-Latitude Disastrous Weather

Dry intrusion is an important mid-latitude atmosphere phenomenon within the upper troposphere and lower stratosphere. It is always found to be related to the cyclogenesis, rainstorm, as well as convection generation and precipitation enhancement. Since the atmosphere environment for any of these above-mentioned weather is terribly complicated, those preexisting popular schemes which takes no account of water vapor may not suitable for detecting the dry intrusion related to these weathers. With regard to the merits and demerits of the current preexisting schemes, a new scheme based on Fengyun-2E geo-stationary satellite data is presented in this study to detect the atmospheric dry intrusion. The scheme is set up based on the statistical relationship between water vapor at high level troposphere, the general moist potential vorticity, ozone concentration and upper-level jet. After using the total amount of ozone and ozone profile operational products retrieved by Fengyun-3 Polar Orbiting Meteorological Satellites and the potential vorticity calculated by ECMWF Interim data for validation, this scheme is applied to analyze two typical middle-latitude weather processes. One is the famous Beijing extreme rainfall of 21 July 2012 and the other is a hailstorm occurred on the eastern China during March 19, 2014. A good application effect in both cases suggests that our new method of detecting dry intrusion is feasible and can be helpful in middle-latitude disastrous weather monitoring and forecasting.

  • Open access
  • 10 Reads
Interannual Variation of a 12,760 km Transequatorial Ionospheric Channel Availability and Its Dependence on Ionization

The ionosphere provides a channel able for long-haul and Non-Line-Of-Sight (NLOS) communications. Nonetheless, the amount of ionization depends on the Sun activity, whose diurnal and seasonal cycles transform the channel constantly. La Salle and the Observatori de l’Ebre have been sounding a 12,760 km ionospheric channel from Antarctica (62.7°S, 299.6°E) to Spain (41.0°N, 1.0°E) in order to find this evidence and to analyze the characteristics of this particular channel. The final goal of the project is to establish a stable communications link to be used as backup or for low rate data transmission. The aim of this paper is to prove the relation between the channel availability and the Sun phenomena affecting the ionization in four consecutive sounding campaigns.

  • Open access
  • 13 Reads
Tracking the Origin of Moisture (and Moisture for Precipitation) over the Danube River Basin through a Lagrangian Approach

In this study we investigate the sources of moisture (and moisture for precipitation) over the Danube River Basin (DRB) through a Lagrangian approach which uses the FLEXPART V9.0 Lagrangian particle dispersion model together with ERA-Interim reanalysis data to track changes in atmospheric moisture along 10-day trajectories. This approach computes the budget of evaporation minus precipitation by calculating changes in specific humidity along forward and backward trajectories. We considered a temporal period of 34 years, from 1980 to 2014 which allowed identifying climatological sources and moisture transport towards the basin at interannual scale. Results showed that the DRB receives moisture mainly from seven different oceanic, maritime and terrestrial moisture source regions: North Atlantic Ocean, North Africa, Mediterranean Sea, Black Sea, Caspian Sea, Danube River Basin and Central and Eastern Europe. The contribution of these sources differs with the season. During the Wet season (October–March) the main moisture source for the DRB is the Mediterranean Sea, while during the Dry season (April–September) the dominant source of moisture in the DRB itself. Moisture coming from each source has a different contribution for the precipitation in the DRB. Between the studied sources results show that the moisture coming from the Mediterranean Sea provides the highest values for precipitation in the basin during both seasons, extending to the whereas the whole basin for the Wet season and more confined to the western side during the Dry one. Moisture coming from the Caspian Sea and the Black Sea was that less contribute to precipitation.

  • Open access
  • 8 Reads
Sensitivity Analysis of Climate Change Projection to the Grid Size Resolution over Mediterranean

In this study the Weather Research and Forecasting (WRF) model is used to dynamically downscale NASA Goddard Institute for Space Studies (GISS) GCM ModelE simulations over the Mediterranean in order to assess the grid size selection effect on the estimated climate change in this region. Results are presented for Athens (Greece) and Rome (Italy), the biggest cities at the
south-southeast Europe, which are located close to the sea. A multinesting approach is used with grid resolutions of 108 km, 36 km, 12 km, 4 km and 1.3 km. The NASA GISS GCM ModelE is used to simulate current and future climate using the RCP4.5 emissions scenario while WRF simulations are performed for October of 2010 and 2050. The sensitivity analysis assesses the estimated changes in temperature, precipitation and wind speed for the related cell in each grid that corresponds to the cities of Athens and Rome. The results show that increasing grid resolution significantly improves the spatial distribution of the examined parameters but does not add much value on the average projected change of the variable.

  • Open access
  • 7 Reads
On the Isobaric Surface Shape in the Geostrophic State of the Atmosphere

The paper presents a theoretical study of the disturbed isobaric surface shape in the geostrophic state of the atmosphere. It has been shown that depending on the overheat sign at the equator the isobaric surface has the shape of an oblate or prolate geoid. If the geostrophic wind velocity is nonzero at the poles, the local pressure extrema (minima for oblate geoid and maxima for prolate geoid) appear at the poles in the geostrophic state. This result correlates with the well-known polar vortex phenomenon and possibly can refine our understanding and interpretation of the phenomenon. In other words, the existence of polar minima and maxima of the pressure field can be the peculiarity of the geostrophic state of the atmosphere. It has been found that air must be colder than surrounding atmosphere for initiation of the zonal eastward transport. For warm air mass only easterly winds will be observed.

  • Open access
  • 15 Reads
Extreme Sea Ice Loss over the Arctic: An Analysis Based on Anomalous Moisture Transport

Recently, the Arctic system has been suffering an extreme reduction in its sea ice extension. 2007 and 2012 represent those years showing the maximum sea ice loss. This rapid decrease has been suggested to have important implications on climate not only over the system itself but also globally. Understanding the causes of this sea ice loss is key to analyzing how future changes related to climate change can affect the Arctic system and the global system. For this purpose, we have applied the Lagrangian model FLEXPART to study the anomalous transport of moisture for these years and to analyze the implications on the sea ice it may produce. Throughout this model, we will analyze the variation in the sources of moisture for the system (backward analysis), and how the moisture supply from these sources is affected (forward analysis). From the results an anomalous transport of moisture have been proved to occur for both years. However, the pattern is different for each event, being the anomalous moisture supply different in both intensity and spatial distribution from every source.

  • Open access
  • 21 Reads
Moisture Sources Identification of Tropical Cyclones in the North Atlantic

In this study, we identified the moisture sources of 110 tropical cyclones with cyclogenesis within the area comprised between 15–45°W and 8–20°N. We used the Lagrangian FLEXPART model to perform the analysis that computes the changes in the specific humidity of ten days before the day of cyclogenesis of each tropical cyclone and its contribution to the moisture budget of the region of interest. Then we calculated the anomaly values of the results to identify the main regions of moisture sources: The African coasts in the North Atlantic, the continental region over western Africa and the area along the South Atlantic from the Equator to the Southern Africa coast.

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