Daytime Winter Research Articles

Longitudinal features of day- and night-time ionospheric annual variations during the solar cycles 23 and 24

We present a study concerning the ionospheric annual variations (IAV) using the global ionospheric maps (GIMs). In this regard, the corresponding regional electron content (REC) is computed in four longitudinal sectors, namely Asia, Africa, America and Pacific. The features of day- and night-time IAV are investigated using (i) band-pass filters and (ii) summer to winter (SW) ratio of REC. The results indicate that IAV are stronger in the southern hemisphere as compared to its northern counterpart. The asymmetry in the amplitude of IAV is maximum for the Pacific region, followed by America, Africa and Asia. The IAV in southern hemisphere are regular ionospheric variations (RIAV) with positive and negative peaks occurring in the months of December and June, respectively. The northern hemisphere and latitudinal regions exhibit a day-time anomalous ionospheric annual variations (AIAV), during the peak years of the considered solar cycles, in which maxima (minima) occurs in local winter (summer). In this regard, the phase of AIAV is found to vary with solar activity. The night-time IAV show anomalous behavior in the northern hemisphere during the solar minimum. The SW ratio of day-time REC is less than unity at northern hemisphere during the peak of a solar cycle. However, the said ratio is always greater than one in southern counterpart. The fitting curve for day-time SW ratio has a strong negative slope in the northern hemisphere. The threshold of SSN (sunspot number) indicating the presence of the daytime winter anomaly at low- latitudes is found to be 25, 80, and 115 in the Africa, Asia-Pacific, and American regions, respectively. Additionally, this anomaly becomes observable in the mid-latitudes region of America and the Pacific region for SSN values exceeding 100 and 150, respectively. On the other hand, the correlation and fitting analysis demonstrate that night-time SW ratio enhances with increase in the solar activity. This result predicts that night- time winter anomaly can only be present during the periods of minimum and low solar activity. However, our analysis revealed that the night-time winter anomaly is observable only in the African low-latitude region for SSN < 85.

Seasonal gaseous elemental mercury fluxes at a terrestrial background site in south-eastern Australia

Terrestrial air-surface exchange of mercury (Hg) forms an important component of the global Hg cycle, with drivers varying across spatial and temporal scales. These drivers include substrate properties, atmospheric chemistry, and meteorological factors. Vegetation uptake represents the dominant pathway of atmospheric Hg deposition to terrestrial surfaces. This study investigated the drivers of net ecosystem exchange of gaseous elemental mercury (Hg0) across multiple seasons in order to gain an understanding of the influence of vegetation and other environmental parameters on the Hg0 air-surface exchange. Measurements were made continuously using a micrometeorological aerodynamic flux gradient method at a low-vegetated background site in south-eastern Australia, over 14 months. Mean Hg fluxes and atmospheric concentrations across the entire study period were 0.002 ng m–2 h–1 (SD ± 14.23 ng m2 h–1) and 0.68 ng m–3 (SD ± 0.22 ng m–3), respectively. Variability was observed across seasons, with the highest average rate of emissions occurring in austral summer (December, January, February) (0.69 ng m–2 h–1) and the highest rate of deposition observed in autumn (March, April, May) (–0.50 ng m–2 h–1). Vegetation uptake dominated Hg flux during the winter and spring when meteorological conditions were cold and light levels were low. This is supported by CO2 flux data, with a daytime winter mean of 0.80 µmol m–2 h–1 and a spring daytime mean of 1.54 µmol m–2 h–1. Summer Hg fluxes were dominantly emission due to higher solar radiation and temperature. Climatic conditions at Oakdale allowed plant production to occur year-round, however the hot dry conditions observed in the warmer months increased evasion, allowing this site to be a small net source of Hg0 to the atmosphere.

Model of the Ionospheric Trough for Daytime Winter Conditions Based on Data from Interkosmos-19 and Champ Satellites

The principles and algorithm for the construction of an empirical model of the ionospheric trough for quiet (Kр = 2) daytime (06−18 LT) winter conditions in the Northern and Southern Hemispheres are described. The model consists of models of the trough position and shape. The model of the trough position describes longitudinal variations of the trough position in terms of the geographic latitude for fixed moments of local time. The model of the trough shape describes the latitudinal–longitudinal variations of foF2 within the interval of geographic latitudes 40°−85° in both hemispheres. The model of the ionospheric trough is probabilistic, since the trough is not always observed under midday conditions. In other words, the problem consists of the construction of a model of foF2 in the daytime, high-latitude ionosphere that would describe the trough structure. Data from the Interkosmos-19 and CHAMP satellites were used to solve this problem. The IRI international model of the ionosphere was also widely used; however, according to the tests, the constructed model more adequately describes the diurnal, longitudinal, and latitudinal variations of foF2 than IRI-2016. This model, together with the previously constructed model of the nighttime trough, makes it possible to speak of the creation of a complete model of foF2 in the winter ionosphere. Soon, the complete foF2 model will be accessible at the IZMIRAN site http://www.izmiran.ru/ionosphere/sm-mit/ . The model make it possible to calculate the longitudinal variations of the trough position and the latitudinal–longitudinal variations of foF2 for any local time and any level of solar activity within the range F10.7 = 70−200 for all winter months.

Equivalent slab thickness of the ionosphere over Europe as an indicator of long-term temperature changes in the thermosphere

Simultaneous measurements of the total electron content (TEC) and the peak electron density NmF2 at vertical sounding stations enable the estimation of the equivalent slab thickness of the ionosphere. This shape parameter, defined as the ratio of the observables TEC and NmF2 of the vertical electron density profile, is closely related to the neutral gas scale height under steady-state conditions at daytime. In this paper we present for the first time a long term trend (LTT) analysis of the equivalent slab thickness for estimating long term trends of thermospheric temperature changes. The analysis is made for 5 vertical sounding stations located in the latitude range 40–70°N in Europe and covers the entire solar cycle 23 during the years 1995–2009. The observations indicate a long term decrease of the equivalent slab thickness at all ionosonde stations considered here from 11 to 62km/decade with increasing tendency towards higher latitudes. Since the seasonal dynamics of the slab thickness clearly overestimates expected temperature changes, it has been found that composition changes, in particular the atomic oxygen/molecular nitrogen density ratio, contribute essentially to the high dynamics of the equivalent slab thickness closely associated with the occurrence of the well-known daytime winter anomaly in Northern mid-latitudes. In analogy, to explain remaining temperature overestimates in the long term trends of the equivalent slab thickness, it is assumed that a long term increase of the atomic oxygen/molecular nitrogen density ratio exist. So the contraction (decrease of scale height and equivalent slab thickness) and the lowering (decrease of the peak density height hmF2) of the electron density profile can be understood in a consistent manner. It is demonstrated that a permanent monitoring of the equivalent slab thickness can contribute to explore long term changes of the thermosphere. To get quantitative estimates of thermospheric temperature changes based on this new LTT monitoring technique, more detailed studies including first principles models are needed.

Region of permanent generation of large-scale irregularities in the daytime winter ionosphere of the Southern Hemisphere

With the use of data from topside sounding on board the Interkosmos-19 (IK-19) satellite, the region of permanent generation of large-scale irregularities in the daytime winter ionosphere of the Southern Hemisphere is differentiated. This region is characterized by low values of foF2 and hmF2 and occupies a rather large latitudinal band, from the equatorial anomaly ridge to ~70° S within the longitudinal range from 180° to 360°. Irregularities with a dimension of hundreds kilometers are regularly observed in the period from 0700–0800 to 1800–1900 LT, i.e., mainly in the daytime. In the IK-19 ionograms, they normally appear in the form of an extra trace with a critical frequency higher than that of the main trace reflected from the ionosphere with lower density. The electron density in the irregularity maximum sometimes exceeds the density of the background ionosphere by nearly a factor of 3. A model of the ionosphere with allowance for its irregular structure was created, and it was shown on the basis of trajectory calculations how the IK-19 ionograms related to these irregularities are formed. A possible mechanism of the generation of large-scale irregularities of the ionospheric plasma is discussed.

Anomalous variations of &amp;lt;I&amp;gt;Nm&amp;lt;/I&amp;gt;F2 over the Argentine Islands: a statistical study

Abstract. We present a statistical study of variations in the F2-layer peak electron density, NmF2, and altitude, hmF2, over the Argentine Islands ionosonde. The critical frequencies, foF2, and, foE, of the F2 and E-layers, and the propagation factor, M(3000)F2, measured by the ionosonde during the 1957–1959 and 1962–1995 time periods were used in the statistical analysis to determine the values of NmF2 and hmF2. The probabilities to observe maximum and minimum values of NmF2 and hmF2 in a diurnal variation of the electron density are calculated. Our study shows that the main part of the maximum diurnal values of NmF2 is observed in a time sector close to midnight in November, December, January, and February exhibiting the anomalous diurnal variations of NmF2. Another anomalous feature of the diurnal variations of NmF2 exhibited during November, December, and January when the minimum diurnal value of NmF2 is mainly located close to the noon sector. These anomalous diurnal variations of NmF2 are found to be during both geomagnetically quiet and disturbed conditions. Anomalous features are not found in the diurnal variations of hmF2. The statistical study of the NmF2 winter anomaly phenomena over the Argentine Islands ionosonde was carried out. The variations in a maximum daytime value, R, of a ratio of a geomagnetically quiet daytime winter NmF2 to a geomagnetically quiet daytime summer NmF2 taken at a given UT and for approximately the same level of solar activity were studied. The conditional probability of the occurrence of R in an interval of R, the most frequent value of R, the mean expected value of R, and the conditional probability to observe the F2-region winter anomaly during a daytime period were calculated for low, moderate, and high solar activity. The calculations show that the mean expected value of R and the occurrence frequency of the F2-region winter anomaly increase with increasing solar activity.

Prehospital temperature control

We have increasingly noted that patients with traumatic injuries attended by the paramedic response unit of the Durban University of Technology, South Africa are hypothermic. Daytime winter temperatures in Kwa-Zulu...

Carrion – It's What's for Dinner: Wolves Reduce the Impact of Climate Change

The Big Bad Wolf Humans have viewed wolves as competitors, threats to personal safety, and symbols of evil throughout history. By the early part of the 20th century, gray wolves (Canis lupus) had been eradicated from 42% of their historic range in North America (Laliberte & Ripple, 2004). In Yellowstone National Park, gray wolves were hunted to local extinction by 1926, but were reintroduced in 1995 after a decades-long process involving biologists, politicians, ranchers, and the general public (Table 1). By the end of 2006, the wolf population in the park was at least 136 wolves in 13 packs (Smith et al., 2007). In this activity, high school students use mathematical models to explore how the presence of wolves buffers other carnivores and scavengers from the effects of climate change. By the end of the lesson, students should be able to: * define and give examples of keystone species. * demonstrate, using mathematical models, that ecosystems are more resilient to environmental change when they contain a full complement of species, including top carnivores. * recognize that math is a vital tool in scientific investigations. Background From an ecological perspective, it was important to restore the gray wolf to Yellowstone because it is a keystone species. Keystone species, which are usually top predators, affect their communities or ecosystems in a much larger way than expected based on abundance alone (Steneck, 2005). The presence, abundance, and productivity of a wide array of species in Yellowstone National Park are indirectly affected by interactions of wolves with elk and coyotes (Figure 1). For example, the reintroduction of wolves has facilitated the recovery of beavers in Yellowstone. In the 1800s, human trappers decimated beaver populations. After wolves were removed from the park, elk populations grew and competition for willow--the preferred food and construction material of beavers--became intense (Ripple & Beschta, 2003). Although beavers had been protected from trapping since the early 1920s, and beaver reintroduction efforts were underway, competitive pressure from elk suppressed recovery (Baker et al., 2005). Since wolves were restored to Yellowstone, predation, hunting, and drought have reduced elk populations. But elk also have changed their behavior (Creel et al., 2005): When elk detect wolves in a general area, they move toward conifer forests (where they have good protection from wolves) and away from open areas and streams (where they have less protection from wolves; Figure 2). Because of the combined effect of fewer elk and reduced use of willow habitat, the number of beaver colonies (five to six beavers per colony) on the northern range of Yellowstone increased from one in 1996 to nine in 2003 (D.W. Smith, 2006, personal communication). [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] Winter on the Northern Range In Yellowstone National Park, daytime winter temperatures range from -40[degrees]C to -5[degrees]C and snow depths can exceed 7m at high elevations (NPS, 2006). Every autumn, the northern Yellowstone elk herd migrates from high-elevation summer habitat within the park to milder habitat in the northern range, a 1,530 [km.sup.2]-area that includes a portion of the park and some adjacent public and private land (Singer & Mack, 1999). Even so, winter isn't easy. Elk search for grasses and other herbaceous plants by digging in the snow with their hooves. When the snow is deep or covered by a hard crust, digging becomes more difficult, as does the simple act of moving through the snow (Gese et al., 1996). Furthermore, the plants under the snow are less nutritious than in the summer (Jenkins & Starkey, 2003). In severe winters, elk regularly starve to death (Wisdom & Cook, 2000). They also can suffer the same fate during mild winters if conditions during the previous summer were poor (Vucetich et al. …

Features of annual and semiannual variations derived from the global ionospheric maps of total electron content

Abstract. In the present work we use the NASA-JPL global ionospheric maps of total electron content (TEC), firstly to construct TEC maps (TEC vs. magnetic local time MLT, and magnetic latitude MLAT) in the interval from 1999 to 2005. These TEC maps were, in turn, used to estimate the annual-to-mean amplitude ratio, A1, and the semiannual-to-mean amplitude ratio, A2, as well as the latitudinal symmetrical and asymmetrical parts, A' and A" of A1. Thus, we investigated in detail the TEC climatology from maps of these indices, with an emphasis on the quantitative presentation for local time and latitudinal changes in the seasonal, annual and semiannual anomalies of the ionospheric TEC. Then we took the TEC value at 14:00 LT to examine various anomalies at a global scale following the same procedure. Results reveal similar features appearing in NmF2, such as that the seasonal anomaly is more significant in the near-pole regions than in the far-pole regions and the reverse is true for the semiannual anomaly; the winter anomaly has least a chance to be observed at the South America and South Pacific areas. The most impressive feature is that the equinoctial asymmetry is most prominent at the East Asian and South Australian areas. Through the analysis of the TIMED GUVI columnar [O/N2] data, we have investigated to what extent the seasonal, annual and semiannual variations can be explained by their counterparts in [O/N2]. Results revealed that the [O/N2] variation is a major contributor to the daytime winter anomaly of TEC, and it also contributes to some of the semiannual and annual anomalies. The contribution to the anomalies unexplained by the [O/N2] data could possibly be due to the dynamics associated with thermospheric winds and electric fields.

Delineation of precipitation areas from MODIS visible and infrared imagery with articial neural networks

AbstractAn important phase in a nowcasting system is the diagnosis of the forecast variables. This work focuses on the diagnosis of precipitation. The Nimrod automatic nowcasting system at the Met Office (UK) has long used Meteosat visible and infrared data to supplement the data it receives from the UK weather radar network to produce rainfall analyses. With the advent of Meteosat Second Generation (MSG) attention has focused on how best to use the larger range of spectral information from MSG to improve the rainfall analyses. Earlier work at the Met Office had suggested artificial neural networks (ANNs) to be a useful tool for such applications. Pending the availability of data from MSG, ANNs were used to process data from appropriate visible and infrared channels on the MODIS instrument. Sixty daytime winter cases were collected, and Nimrod radar rainfall analyses provided ‘ground truth’ for both training and testing the ANNs. The optimal combination of MODIS channels was investigated and it was found that almost all the skill in rain/no rain discrimination was provided by the radiance values from six selected spectral channels. A notable result was that the 1.64 µm channel had no value as a discriminator when used alone, but produced a large increase in skill when used in conjunction with a visible channel. The ANN with MODIS data was found to outperform the corresponding Nimrod look‐up table technique applied to Meteosat data. Application of the technique to SEVIRI data is proposed, as is extension to other seasons. Copyright © 2005 Royal Meteorological Society

Analytical representation of the plasmasphere electron temperature distribution based on Akebono data

A new approach is used to reveal the average thermal structure of plasmasphere at altitudes between 1000 and 10,000 km. This paper only considers the plasmasphere inside L = 3, and this region of space is sliced at L = 2 to one internal (denoted as equatorial) and one external (denoted as midlatitude) part. Each of these parts is divided into four altitude/local time zones: northern and southern daytime and northern and southern nighttime. Electron temperature (Te) distribution measured along every individual orbit within each zone is approximated by simple expressions that are functions of the geomagnetic latitude or L. The fitting is performed independently to each zone, and two coefficients are extracted from the individual fits: Te value at the equatorward border and the coefficient scaling the latitudinal shape. These coefficients are accumulated in each zone in order to obtain its average Te structure as a function of altitude. The fitting coefficients exhibit large scatter, which reflects the large day‐to‐day variability of plasmasphere Te. The fitting error is estimated at 6% and 12% for the equatorial and midlatitude zones, respectively. The average fit coefficients are used to check for seasonal variations in each zone and for a possible hemispheric asymmetry. It is determined that the winter sunlit plasmasphere is hotter than the summer one; the case for nighttime is reverse. The day/night amplitude is larger in the winter than in the summer, and the seasonal differences are more pronounced in the Southern Hemisphere. The latitude gradients of Te reveal a hemispheric asymmetry, which is largest during northern daytime winter. Solar activity is found to affect the plasmasphere Te. During the day at 3000 km and L = 2, Te increases by ∼2000°K when F10.7 changes from 70 to 300. The nighttime increase is ∼1000°K. At the equator, Te shows weaker dependence on solar activity. The average heat flux through 3000 km altitude is estimated at 3.7 × 109 (eV cm−2 s−1) during the day and 1.6 × 108 (eV cm−2 s−1) during the night.

Two branches of day-time winter ionospheric trough according to Cosmos-900 data at F2-layer heights

With the large data set of the Cosmos-900 satellite it is shown that in the low-altitude day-time winter ionosphere, besides the high-latitude trough two other troughs are often observed: the “daytime main trough” and the “Muldrew trough”. The first trough is observed in the shadow region as a continuation of the nighttime main trough close but equatorwards of the auroral oval. The second trough is observed at sunlit longitudes. Developing in the stagnation region (at 17–18 MLT) it is then transported by the westward drift into the day-time sector of the auroral oval, but equatorwards of the day-side cusp. The variations of their characteristic features are different in the Northern and Southern hemispheres creating an asymmetry of the high-latitude ionospheres.

Quantification of nitro- and hydroxylated nitro-aromatic/polycyclic aromatic hydrocarbons in selected ambient air daytime winter samples

Two ambient air samples, both collected in a northern latitude city during winter daytimes, are compared here with regard to NO 2-AR/PAH levels and OH-NO 2-AR levelsfrom filter and XAD-2 extracts. Detection of a previously unreported environmental constituent, tentatively identified as a NO 2-azulene isomer, is discussed. The levels of the OH-NO 2-AR were, in general, at least 4 times higher than levels of the corresponding NO 2-AR. As with NO 2-AR/PAH, OH-NO 2-AR appear to be both primary source emissions and secondary photochemical products. The filter-collected para-substituted OH-NO 2-AR in these samples appear to be the source emissions, while the XAD-collected ortho- and para-substituted OH-NO 2-AR may be products of photochemical reactions. Other pollutant and meteorological data, including NO, NO 2, HONO, sunlight intensity and fine-particle Pb and K concentrations, are also used to discuss differences between these samples.

Mobile measurements of SO 2 in heavy traffic in London

Regular surveys of SO 2 were made along the A10 and A23 roads through Central London with 2 vehicles during the Winter of 1983–1984. After spatial averaging, a strong correlation between SO 2 concentration and meterological variables was found allowing extrapolation of the results to predict a daytime Winter mean SO 2 concentration of 107 μg m −3. This is twice what is measured at National Survey sites in Central London. It is suggested that the difference arises from motor vehicle emissions. This is consistent with the sulphur content of petrol and Diesel fuel and the measured concentrations of CO and black smoke.

Prediction of total electron content using the international Reference Ionosphere

Comparisons are presented between the values of total electron content (TEC) observed at 31°S and those predicted using the Australian Ionospheric Prediction Service's version of the International Reference Ionosphere. Although discrepancies sometimes exceed 30% they are usually less than 20%. The predicted TEC values tend to be too low in daytime summer, too high in daytime winter, and have an incorrect diurnal variation during winter days. Although the predicted TEC was sensitive to the errors in the foF2 values used, the major discrepancies remained.

The light ion trough

A distinct feature of the ion composition results from the OGO-2, 4 and 6 satellites is the light ion trough, wherein the mid latitude concentrations of H + and He + decrease sharply with latitude, dropping to levels of 10 3 ions/cm 3 or less near 60° dipole latitude ( L=4). In contrast to the ‘main trough’ in electron density, N e , observed primarily as a nightside phenomenon, the light ion trough persists during both day and night. For daytime winter hemisphere conditions and for all seasons during night, the mid latitude light ion concentration decrease is a pronounced feature. In the dayside summer and equinox hemispheres, the rate of light ion decrease with latitude is comparatively gradual, and the trough boundary is less well defined, particularly for quiet magnetic conditions. In response to magnetic storms, the light ion trough minimum moves equatorward, and deepens, consistent with earlier evidence of the contraction of the plasmasphere in response to storm time enhancements in magnetospheric plasma convection. The fact that a pronounced light ion trough is observed under conditions for which the dominant ion O + may exhibit little or no simultaneous decrease appears to explain why earlier studies of the ‘main trough’ in topside distributions of N e and N i may, at times, have been inconclusive in relating the total ionization minimum with the mechanism of the plasmapause. In particular, the topside distribution of N i appears to be the complex resultant of several variables within the ion composition, being governed by the competing processes of chemical production and loss, loss through magnetospheric convection, and large-scale dynamic transport resulting from neutral winds and electric fields. The net result is that in general, the light ion trough, rather than N i , provides a more fundamental parameter for examining the structure and behavior of the plasmapause.