High-latitude Phenomena Research Articles

On the colour of noctilucent clouds

Abstract. The high-latitude phenomenon of noctilucent clouds (NLCs) is characterised by a silvery-blue or pale blue colour. In this study, we employ the radiative transfer model SCIATRAN to simulate spectra of solar radiation scattered by NLCs for a ground-based observer and assuming spherical NLC particles. To determine the resulting colours of NLCs in an objective way, the CIE (International Commission on Illumination) colour-matching functions and chromaticity values are used. Different processes and parameters potentially affecting the colour of NLCs are investigated, i.e. the size of the NLC particles, the abundance of middle atmospheric O3 and the importance of multiply scattered solar radiation. We affirm previous research indicating that solar radiation absorption in the O3 Chappuis bands can have a significant effect on the colour of the NLCs. A new result of this study is that for sufficiently large NLC optical depths and for specific viewing geometries, O3 plays only a minor role for the blueish colour of NLCs. The simulations also show that the size of the NLC particles affects the colour of the clouds. Cloud particles of unrealistically large sizes can lead to a reddish colour. Furthermore, the simulations show that the contribution of multiple scattering to the total scattering is only of minor importance, providing additional justification for the earlier studies on this topic, which were all based on the single-scattering approximation.

A Space Hurricane Spotted Above the Polar Cap

Researchers have identified a high-latitude phenomenon that looks remarkably like a tropospheric hurricane, with spinning arms of plasma and a shower of electrons.

Total Electron Content Measurements in the Ionosphere Disturbed by High-Power High-Frequency Waves by the Methods of Incoherent Scattering of Radio Waves and Radio Sounding by Glonass Satellite Signal

We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar (Tromso, Norway) during modification of the high-latitude ionosphere in the magnetic zenith direction by high-frequency radio waves of the EISCAT/Heating facility (Tromso, Norway). The measurements were performed during two experiment campaigns in October 2013 and in October 2018. In general, the total electron content variations obtained from the radar data in the altitude range 100–400 km were consistent with the total electron content variations from the GLONASS satellites. The efficiency of using GLONASS satellites for observations of high-latitude phenomena was shown. The anomalous increase in the total electron content by 4 TECU obtained from the incoherent scatter radar when the ionosphere was heated in the region close to the magnetic zenith is considered. The GLONASS satellite data show the total electron content reduction in the same region. To explain the disagreement between measurements by these two methods, the effect of smallscale electron-density irregularities arising in the region modified by high-power HF radio waves is considered. It is shown that when the electron density in artificial irregularities exceeds the background density of the medium by 2 ・ 10−3 times in relative units, scattering by irregularities with spatial scales of the order of 16 cm becomes predominant in the reflected signal.

Statistical characteristics of low-latitude ionospheric scintillation over China

The Global Positioning System (GPS) L-band ionospheric scintillation produced by electron density irregularities in the ionospheric E- and F-regions, is mainly a low- and high-latitude phenomenon. In this study, the statistical behavior of GPS ionospheric scintillation over a Chinese low-latitude station Sanya (18.3°N, 109.6°E; dip lat: 12.8°N) has been investigated. A detailed study on the seasonal and solar activity dependence of scintillation occurrence during July 2004–December 2012 show that the amplitude scintillation pattern, with a maximum occurrence during equinox of solar maximum, agrees with plasma bubble observations by in situ satellites in this longitude. A few daytime periodic scintillation events are found during June solstice months of solar minimum. Interestingly, a significant equinoctial asymmetry of scintillation onset time is found in 2011–2012. The initiation of scintillation during September–October is on average earlier than that of March–April about 25min. Meanwhile, the zonal drifts of irregularities estimated using two spatially separated GPS receivers over Sanya show a similar behavior during the two equinoxes, slowly decreasing from 150m/s at post-sunset to 50m/s near midnight. The possible mechanisms responsible for the occurrence characteristics of GPS scintillation over Sanya, and relevant aspects of the zonal drifts of the irregularities are discussed.

Modification of the high-latitude ionosphere by high-power hf radio waves. 2. Results of coordinated satellite and ground-based observations

We present the results of coordinated satellite and ground-based observations of the high-latitude ionospheric phenomena induced by high-power high-frequency (HF) radio waves. The ion outflow phenomenon accompanied by a strong increase in the electron temperature and thermal expansion of plasma was observed in the evening hours, when the high-latitude ionospheric F region was heated by high-power O-mode HF radio waves. The DMSP F15 satellite recorded an increase in the ion number density O+ at an altitide of about 850 km in that period. Ultralow-frequency (ULF) radiation at the modulation frequency 3 Hz of the high-power HF radio waves, which was generated in the ionosphere irradiated by high-power O-mode HF radio waves and accompanied by a strong increase in the electron temperature and the generation of artificial small-scale ionospheric irregularities, was recorded by the CHAMP satellite during the heating experiment in Tromso in November 5, 2009. The results of the DEMETER satellite observations of extremely low frequency (ELF) radiation at the modulation frequency 1178 Hz of the high-power radio waves in the heating experiments were analyzed using the event of March 3, 2009 as an example.

Present-day South American climate

This paper documents the main features of the climate and climate variability over South America, on the basis of instrumental observations gathered during the 20th Century. It should provide a modern reference framework for paleoclimate research in South America, targeting high-resolution proxies over the past few centuries. Several datasets suitable for present-day climate research are first described, highlighting their advantages as well as their limitations. We then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans. In particular, the diversity of precipitation, temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large-scale circulation caused by the Andes cordillera, the contrasting oceanic boundary conditions and the landmass distribution. Similarly, the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence, as some regions are more influenced by large-scale phenomena rooted in the tropical oceans while others are more influenced by high-latitude phenomena. The impact of these large-scale phenomena over South America is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields. We have included a discussion on the seasonality and long-term stability of such impacts, and complemented our general description by an updated review of the literature on climate variability over specific regions.

International Space Station supports International Polar Year

The International Space Station (ISS) provides an excellent venue for observing Earth systems. Starting in March 2007 and coinciding with the beginning of the International Polar Year (IPY), NASA's Crew Earth Observations (CEO) payload invites IPY investigators to submit requests for relevant imagery be collected from the ISS.Every day, ISS astronauts photograph designated sites and dynamic events on the Earth's surface using digital cameras equipped with a variety of lenses. Depending on observation parameters, astronauts can collect high‐resolution (4–6 meter pixel size; see J. Robinson and C. Evans, Eos Trans. AGU, 83(17), 185, 2002) or synopticview (lower resolution but covering very large areas) digital data in three (red‐greenblue) color bands.

Book Review: Space Weather, Environment and Societies

Book Review: Space Weather, Environment and Societies

Mid-Latitude Pc1, 2 Pulsations Induced by Magnetospheric Compression in the Maximum and Early Recovery Phase of Geomagnetic Storms

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT andlast more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1, 2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

THERMOHALINE CIRCULATION: High-Latitude Phenomena and the Difference Between the Pacific and Atlantic

▪ Abstract Deepwater formation, the process whereby surface water is actively converted into deep water through heat and freshwater exchange at the air-sea interface, is known to occur in the North Atlantic but not in the North Pacific. As such, the thermohaline circulation is fundamentally different in these two regions. In this review we provide a description of this circulation and outline a number of reasons as to why deep water is formed in the North Atlantic but not in the North Pacific. Special emphasis is given to the role of interactions with the Arctic Ocean. We extend our analysis to discuss the observational evidence and current theories for decadal-interdecadal climate variability in each region, with particular focus on the role of the ocean. Differences between the North Atlantic and North Pacific are highlighted.

Coupling the plasma interaction at Io to Jupiter

Io's interaction with the jovian magnetosphere causes auroral and radio emissions. This interaction can not be modeled as either an Alfvén wave or a steady current loop alone. Given the Galileo measurement of low flow velocities in Io's wake, we argue that the interaction begins as an Alfvénic disturbance but as the disturbance is convected downstream it has time to evolve into a steady current loop. We associate high latitude phenomena with different phases of the interaction.

Distinctive ozone structure in the high‐latitude stratosphere: Measurements by the Millimeter‐Wave Atmospheric Sounder

MAS (Millimeter‐wave Atmospheric Sounder) observations from the shuttle ATLAS spacelab pallet have revealed some little known (and unexplained) structure in stratospheric ozone mixing ratio profiles at sub‐polar latitudes, of both hemispheres. Qualitatively similar features are observed by UARS instruments. Another possibly related feature has been observed by ground‐based remote sensing from the South Pole over an extended season. In all these cases, it seems likely that active photochemistry and highly structured horizontal and vertical transport play important roles. Some evidence of a similar feature is also present in a current 2‐D photochemical model. This high latitude phenomenon is both an intriguing challenge for current 3‐D models and potentially useful test for validating remote sensing experiments.

Incoherent scatter radar contributions to high latitude D-region aeronomy

Recent aeronomical work on the high latitude D-region is reviewed, restricting the discussion to observations of the D-region by the incoherent scatter technique. Emphasis is given to chemical aeronomy, which governs part of the coupling between the neutral atmosphere and the ionosphere, and forms the basis for the global role of the high latitude D-region. Details of the dynamics of the high latitude D-region, and thus the actual coupling with regions below and above, are, however, not discussed in this context. The aeronomical consequences of special high-latitude phenomena are discussed. These include the effects of the polar summer, precipitation of high energy electrons during auroral substorms and high ionization of the D-region during solar proton events. A detailed discussion is given on selected studies concerning the series of solar proton events that occurred in 1989. Problems of ion and neutral chemistry are readily accessible with incoherent scatter measurements through chemical modelling of the D-region. In this way the continuous nature of incoherent scatter measurements can be utilized to expand our knowledge of the D-region, which earlier was mainly based on momentarily sounding rocket experiments. However, it is pointed out how the interpretation of incoherent scatter data from the D-region strongly benefits from multi-instrument configurations. An outline is given of a possible new development based on the combined use of the Tromsø heating facility and the EISCAT incoherent scatter radars.

Ulysses at high latitudes: An overview of recent results

After its fly-by of the planet Jupiter in February 1992, the Ulysses spacecraft is now in a highly inclined heliocentric orbit that will bring it above the south polar regions of the Sun in September 1994. The high-latitude phenomena observed to date have been strongly influenced by the near-minimum solar activity conditions encountered during this phase of the mission. In late April 1993, when Ulysses was at ∼29°S heliographic latitude, the recurrent high speed solar wind stream that had been observed at the location of the spacecraft for 11 consecutive solar rotations underwent a dramatic change. The wind speed in the valleys between successive peaks increased in a single step from ∼420 km s −1 to ∼560 km s −1. This change in solar wind flow was accompanied by the disappearance at the spacecraft of the magnetic sector structure that had been observed until then. Both these findings are consistent with Ulysses having climbed beyond the latitude of the coronal streamer belt in which is embedded the heliospheric current sheet (HCS). In its subsequent poleward journey, no further evidence for an encounter with the HCS has been seen at Ulysses. Other phenomena observed include the evolution with latitude of corotating interaction regions (CIRs) and their influence on the acceleration of energetic particles, and the characteristics of the solar wind flows emanating from the south polar coronal hole. In this paper, we present details of the above observations. Finally, while the polar passes of the prime mission will take place near solar minimum, an extended mission will bring Ulysses back over the poles near the maximum of the next cycle. A summary of scientific goals for Ulysses at solar maximum is given.

An Overview of Energetic Particle Measurements in the Jovian Magnetosphere with the EPAC Sensor on Ulysses

Observations of ions and electrons of probable Jovian origin upstream of Jupiter were observed after a corotating interplanetary particle event. During the passage of Ulysses through the Jovian bow shock, magnetopause, and outer magnetosphere, the fluxes of energetic particles were surprisingly low. During the passage through the "middle magnetosphere," corotating fluxes were observed within the current sheet near the jovimagnetic equato. During the outbound pass, fluxes were variably directed; in the later part of the flyby, they were probably related to high-latitude phenomena.

On the Use of Satellites in Molniya Orbits for Meteorological Observation of Middle and High Latitudes

Time and space sampling is an increasingly critical aspect of Earth observation satellites. The highly eccentric orbit used by Soviet Molniya satellites functions much like a high-latitude geostationary orbit. Meteorological instruments placed on a satellite in a Molniya orbit would improve the temporal frequency of observation of high-latitude phenomena such as polar lows. Consideration of this new sampling strategy is suggested for future systems such as the “Earth Probe” satellites in the Mission to Planet Earth program as well as for operational meteorological satellite programs.

Characterizing the Multipath and Doppler Spreads of the High-Latitude Meteor Burst Communication Channel

High-latitude propagation phenomena, such as scatter from the aurora and sporadic- E propagation, can alter the communication characteristics of the meteor communication channel. This paper describes an experiment in which the fading and multipath profiles of the high-latitude meteor communication channel were characterized. The effects of high-latitude propagation phenomena on the capacity and reliability of meteor burst communication are discussed.

The Hydrology of Alaskan Wetlands, U.S.A.: A Review

Alaska's wetland resources are vast and the literature dealing directly with any given aspect of Alaskan wetland hydrology is sparse. This review focuses on hydrological function and pays particular attention to (1) hydrologic inputs to and outputs from wetlands, and (2) the influence of wetlands on peak flow regulation. The influence of several characteristic high-latitude phenomena (permafrost, glaciers, and seasonal stream icings) on the overall water balance and the volume, areal distribution, rate, and timing of water release are discussed. We find that (1) measured annual precipitation exceeds calculated annual evapotranspiration in most areas of the state, creating conditions suitable for the development of ombrotrophic wetlands; (2) during snowmelt, which is the principal event in the annual hydrologic cycle in most areas of the state, wetland soils typically have high ice contents, and thus probably do not contribute significantly to either flood storage or groundwater recharge, and (3) the exist...

Currents associated with abnormal quiet days in Sq(H)

Summary Declination data have been analysed on NQDs and AQDs for the years 1963-64-65. Such an analysis indicates that there is a larger southward current in the morning and a larger northward current in the afternoon on NQDs than AQDs in both the northern and southern hemispheres. The strength of this current is found to be IMF-dependent. Taken in conjunction with the previous analyses of the H-data it is concluded that on AQDs the Sq(H) amplitude is affected by a reduction in the current of a large current vortex which extends over both hemispheres and is part of the normal Sq(H) current system. Such a current is driven by diurnal winds, variations in the strength of the wind thus contributing to the day-to-day variability of the Sq(H) amplitudes. AQDs therefore represent days of small amplitude in the general day-to-day variability. The IMF-dependence arises due to complicated current systems that flow on AQDs and which are associated with high latitude phenomena and generally have their focus at latitudes 60°, similar to those found by Takeda & Araki.

The structure of the atmosphere up to 150 kilometre

Abstract New techniques and organized observing programmes have maintained the impetus to geophysical research proviclcd by the IGY in 1957–58. A selection of research techniques and results are discussed which illustrate this statement. Mcteorological rockets and satellites, sounding rocket observations, high-latitude phenomena and upper atmosphere structure are the main topics dealt with. Reference is made to a new COSPAR International Reference Atmosphere (CIRA 1972) which reviews and tabulates atmospheric structure above 25 km and brings the material of the previous (1965) edition up to date.