Where to Decar a Value Read by and Isr

Incoherent Scatter Radar

Incoherent scatter radar is a relatively contempo technique for observing the ionosphere (run across Hargreaves [1992]).

From: World'south Magnetosphere , 2011

Atmospheric effects and signatures of high-energy electron atmospheric precipitation

Robert A. Marshall , Chris Thou. Cully , in The Dynamic Loss of World's Radiation Belts, 2020

seven.four.ii.2 Ground-based incoherent besprinkle radar

The incoherent scatter radar (ISR) technique to observe precipitation is discussed in particular in Chapter 6; here we provide a very brief overview. Radar observations of the ionosphere were pioneered by Gordon (1958), with the evolution of the ISR technique and the structure of the Arecibo facility, which opened in 1963. ISR relies on the manual of high-power radio waves in the loftier-to-ultrahigh-frequency range; for example, the effective radiated power of the Arecibo UHF (430   MHz) radar is two.5 TW. The radar wave scatters incoherently from the free electrons in the ionosphere, and the return power yields the electron density. In addition, the spectrum of the radar return can provide the electron and ion temperatures and the ion drift velocity.

The D-region, even so, has electron densities that are 3–four orders of magnitude lower than the F-region; therefore the radar returns are generally much weaker. Mathews (1984, 1986) provide overviews of D-region remote sensing using ISR. Mathews (1984) points out that Arecibo, until recently the most sensitive ISR in the world, tin can achieve a point-to-racket ratio (SNR) of 3.0 for a unmarried pulse. All other radars crave pulse averaging to collect a useful signal from the D-region.

Over the past few decades, a number of studies have utilized ISR to measure the D-region electron density for a broad range of scientific purposes. Turunen et al. (1988) measured D-region enhancements during auroral precipitation and were able to fit the measured radar spectra to extract electron densities, ion-neutral collision frequencies, neutral temperatures, and ion mass and density. Other D-region observations using European Incoherent Scatter Scientific Association (EISCAT) information have included Polar Mesospheric Summer Echoes (e.g., Cho and Kelley, 1993; Röttger et al., 1988), polar cap absorption events (east.chiliad., Hargreaves et al., 1987), and EPP (e.g., Kirkwood and Osepian, 1995; Miyoshi et al., 2015). Using a simplified ion chemical science model, Kirkwood and Osepian (1995) were able to reproduce the electron density contour measured by EISCAT and hence infer the precipitating electron spectrum. This assay was applied to electrons of both moderate-free energy 1–100   keV events likewise as energetic >MeV atmospheric precipitation events.

D-region remote sensing with ISR has been conducted at the Poker Flat ISR (PFISR) for the past few years; PFISR is an electronically steerable, phased-array radar that can steer its beam in the sky with every pulse. Janches et al. (2009) showed observations of D-region ionization enhancements and were able to use these to extract atmospheric winds and tides. In recent years, researchers have made observations of EPP from the radiation belts using PFISR (Kaeppler et al., 2015), though those observations have not yet been published. These results demonstrate that ISR holds great potential as a method for D-region remote sensing of EPP.

The benefits of ISR for D-region measurements are its accuracy, time resolution, spatial resolution (though express to a few hundred km in range), and continuous observing ability. When the SNR is strong plenty, the ISR returns provide a direct measurement of the altitude-resolved electron density. Since the ISR tin can transmit pulses every millisecond, it is possible to develop a high-time resolution measurement of the changing electron density profile. As for spatial resolution, with electronically steerable radar such as PFISR, the radar can "pigment" a series of beams on the sky very rapidly, providing both spatial and temporal resolution (though the latter suffers equally the former improves). Finally, as a ground-based instrument, the ISR tin monitor a single location in the ionosphere for long periods of fourth dimension.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978012813371200007X

High-resolution approaches to ionospheric exploration

Joshua Semeter , in The Dynamical Ionosphere, 2020

3.3 Global navigation satellite systems

ISR and GNSSs provide complementary data almost the ionosphere. ISR tin can be used to construct multidimensional images of the overlying electron density field through analysis of echoes collected in multiple directions (Nicolls and Heinselman, 2007; Semeter et al., 2009), while signals collected by dual frequency GNSS receivers can be used to compute path integrals through this field (Sardon et al., 1994). These 2 physical parameters are related through the definite integral,

(11) $\begin{array}{l}\hfill \text{TEC}={\int }_{\mathbf{a}}^{\mathbf{b}}N(\mathbf{r})ds\end{array}$

where Northward(r) is the instantaneous electron density field in ${\mathbb{R}}^3$ , and TEC is the "total electron content" for a given transmitter-receiver pair. Position vectors a and b could refer to a satellite and footing-receiver, or two satellites (i.eastward., occultation geometry).

The propagation of the GNSS point through the conducting ionosphere leads to a grouping (lawmaking) filibuster and a phase advance that are proportional to TEC,

(12) $\begin{array}{l}\hfill \tau \approx \frac{z}{c}+\frac{\mathrm{40.iii}}{c{f}^{\mathrm{two}}}\text{TEC}\varphi \approx \frac{2\pi fr}{c}-\frac{80.6\pi }{cf}\text{TEC}\end{array}$

The changed problem of determining TEC from grouping delay measured at ii frequencies simultaneously yields the TEC and the path correction information technology produced. Provided the transmitted frequencies are much greater than the plasma frequency, to a good approximation,

(13) $\begin{array}{l}\hfill \text{TEC}=\frac{c({\tau }_2-{\tau }_{\mathrm{ane}})}{\mathrm{xl.3}\left(\frac{1}{f_{\mathrm{two}}^2}-\frac{1}{f_{\mathrm{one}}^2}\right)}\frac{d}{dt}\text{TEC}=\frac{cf}{80.6\pi }\left(\frac{2\pi f}{c}\frac{dr}{dt}-\frac{d\varphi }{dt}\right)\end{array}$

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780128147825000157

Breathless scatter radar observations of x–100keV atmospheric precipitation: review and outlook

Stephen R. Kaeppler , ... Pablo M. Reyes , in The Dynamic Loss of Globe's Radiation Belts, 2020

6.four D-region incoherent besprinkle radar mode

PFISR is a remotely operated, phased-array radar capable of beam steering on a pulse-to-pulse footing (Kelly and Heinselman, 2009). PFISR has run nigh continuously since 2007 and produces a depression-duty cycle data product of alternating code and long-pulse information called the IPY fashion. While this manner is useful for long-term studies of the auroral ionosphere and thermosphere, information technology is not an optimal fashion for studies of D-region ionization. Dougherty (1963) and Dougherty and Farley (1963) derived the theory for the incoherent scatter radar spectrum in the presence of ion-neutral collisions, which are the conditions found in the D-region ionosphere. When collisions are dominant, the backscattered power spectrum is described as a Lorentzian distribution,

(6.23) $\sigma \left({\omega }_0+\omega \right)\propto \frac{({\nu }_{in}/k)}{1+{({\nu }_{i\mathrm{north}}/k)}^2{(\omega /k)}^2}$

where k=λ/4π is the radar wave number corresponding to the Bragg status for backscatter, ω ₀ is the angular radar frequency, ω is the angular Doppler shift frequency, and ν _in is the ion-neutral standoff frequency. The spectral half-width at half maximum of the Lorentzian distribution can be written as (e.m., Dougherty and Farley, 1963; Nicolls et al., 2010),

(six.24) $\mathrm{\Delta }\omega \approx \frac{16\pi m_{B}T}{{\lambda }^2{m}_i{\nu }_{i\mathrm{due\; north}}}$

where T is the temperature, assuming thermal equilibrium between ions, electrons, and neutrals, which is more often than not true in the D-region (due east.g., Kelley, 2009; Schunk and Nagy, 2004), and m _i is the ion mass. Given typical D-region parameters, the effective spectral width is on the order of tens to hundreds of Hz, which is in contrast with typical E- and F-region spectral bandwidths, which are on the club of kHz. By the Wiener–Khintchine theorem, this narrow-bandwidth signal in the D-region corresponds to a long decorrelation lag in the time domain. This long decorrelation time, combined with the reduced range of the relatively nearby target (l–100   km), ways that that pulse-to-pulse range Doppler radar processing techniques (e.m., Richards et al., 2010a) can exist practical to the D-region. Fig. 6.eleven shows an example of the median spectral power from April 23, 2008 at 1705–1721   UT from the vertical directed axle. The exponential decrease in the spectral width can be seen beneath 85   km distance, consistent with the expected change in the ion-neutral collision frequency (eastward.g., Nicolls et al., 2010).

Figure 6.11. An instance of the median of the PFISR spectral ability from Apr 23, 2008, at 1705–1721   UT, from the vertical directed beam. The exponential decrease in the spectral width tin can be seen below 85   km altitude, consistent with the theory by Dougherty (1963) and Dougherty and Farley (1963).

Two modes were designed to specifically probe the D-region electron density and besides to derive winds. These modes use four beam-steering directions like to the IPY mode—vertical, field-aligned, northwest-directed, and northeast-directed, labeled as beams 1, 2, 3, and 4, respectively. Fig. 6.12 shows a layout of the beam placement. The difference between the two modes is the coding scheme: one manner uses a 13-baud Barker code with 10   µs baud length and the other scheme uses a 47-baud pseudo-random coded pulse with a 4   µs baud length. The difference in the baud length corresponds to a 1.5   km and 600   m range resolution, respectively. The IPP of 2   ms determines the maximum unambiguous range of 300   km and the maximum frequency of 250   Hz, respectively. For this style, 256 pulses are integrated to produce a unmarried spectral approximate every 0.512   seconds, having a corresponding spectral resolution of 3.9   Hz. Tabular array 6.3 summarizes the modes that were run at PFISR from 2015 to the present.

Figure 6.12. Placement of PFISR beams. Beam 2 is aligned with the local geomagnetic field, axle ane is looking at the zenith, axle 3 is directed toward the northwest, and beam four is directed toward the northeast. The black outline denotes the phased-array grating lobes that grade the limit of region the ISR can probe. Any axle tin can be formed within the grating lobes.

Table 6.3. Summary of the modes run at PFISR to quantify E- and D-region ionization.

Pulse blueprint	Range resolution	Spectral resolution (Hz)	Nyquist frequency (Hz)	Dates
thirteen   baud, x   µs/baud	1.5   km	3.9	250	<02/2015>xi/2016
Barker code
47   baud, 4   µs/baud	600   m	3.nine	250	02/2015<t<11/2016
Pseudo-random code

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128133712000068

Ionospheric conjugate point science: Hemispheric coupling

Michael Mendillo , in The Dynamical Ionosphere, 2020

ii Electrobuoyancy cohabit science

Breathless besprinkle radar (ISR) observations at the Arecibo Observatory discovered unusual corrugations in ionospheric densities with horizontal scale size of 100  due south of kilometers (Behnke, 1979). The starting time optical studies of these midlatitude structures were carried out using an all-sky imager at the Arecibo Observatory (Mendillo et al., 1997; Miller et al., 1997). The wavelengths and speeds observed were typical of medium-calibration traveling ionospheric disturbances (MSTIDs) associated with waves in the neutral atmosphere. Yet, the structures observed at Arecibo did not propagate over the full range of azimuths constitute with before studies of MSTIDs—rather, they had a narrow range of northeast-to-southwest propagation vectors. Those characteristics led to the suggestion that a specific type of plasma instability seemed to be involved (Perkins, 1973), only 1 non fully consistent with observations, and thus the phrase "Perkins-like" came into use. A more than general name was suggested (electro-buoyancy-waves) by Kelley et al. (2000) in order to distinguish them from the ionospheric corrugations driven by waves in the neutral atmosphere (gravity waves) that propagate in all directions. Unfortunately, information technology has not been widely adopted. The MSTID designation is still used, as volition be washed here.

From a conjugate-point perspective, a miracle controlled by electrodynamics must map from one hemisphere to the other post-obit magnetic field patterns (Otsuka et al., 2004). The airglow signatures of an MSTID are vivid and night bands moving from northeast to southwest in the northern hemisphere, and thus should be from southeast to northwest in the southern hemisphere. The offset coordinate airglow and GPS observations of MSTID structures simultaneously seen at Arecibo and its conjugate point (Mercedes, Argentina) were described by Martinis et al. (2010, 2011). The NE-to-SW motion in the northern hemisphere and the SE-to-NW movement in the southern hemisphere thus showed them to be hemispherically coherent, electrodynamical phenomena.

An example of conjugate point MSTIDs is given in Fig. 2. Similarities and differences are noted—in this case, contrasting seasonal differences between northern winter and southern summertime. In exploring such receptor status differences, diverse components of a complex arrangement are immediately apparent. It has been proposed that lesser-side ionospheric processes control MSTID occurrence patterns (Kelley et al., 2003). Specifically, their origin is in the summer hemisphere where low-altitude plasma tin can persist after sunset and/or appear in sudden sporadic layers—and thus structures in the nighttime summer hemisphere can be mapped to the contrary (wintertime) hemisphere. Such electrodynamical coupling from one hemisphere to the other must exist afflicted past nonuniform B-field conditions versus longitude. With MSTID propagation vectors not perpendicular to magnetic meridians, and those meridians having different orientations (declinations) with respect to geographic meridians, a complex longitude-dependent propagation blueprint can emerge (Martinis et al., 2018, 2019). Clearly, new approaches from the ionospheric complexity perspective are needed to advance our understanding of the electrobuoyancy/MSTID wave phenomena.

Fig. 2. Example of a Medium-Calibration Traveling Ionospheric Disturbance (MSTIDs) captured in 630.0-nm images from Boston University all-sky imagers at the Arecibo Observatory (Puerto Rico) and the Mercedes Observatory (Argentina). Similarities and departure occur at these conjugate points.

From Martinis, C., Baumgardner, J., Wroten, J., Mendillo, M., 2018. All-sky-imaging capabilities for ionospheric space atmospheric condition research using geomagnetic conjugate point observing sites. Adv. Space Res. 61 (7), 1636–1651. https://doi.org/ten.1016/j.asr.2017.07.021.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128147825000030

RADAR | Incoherent Besprinkle Radar

M.P. Sulzer , in Encyclopedia of Atmospheric Sciences (2nd Edition), 2015

Introduction

The incoherent besprinkle radar (ISR) technique is a powerful ground-based tool used to measure various backdrop of the ionized part of the upper temper called the ionosphere. All radars transmit radio waves at a target and receive much weaker waves generated when electrons, the lightest charged component of the target thing, accelerate in response to the incident waves and reradiate the signal. Reflection and besprinkle are terms used to describe the reradiation, depending upon the degree and nature of the system of the electrons in the target. Incoherent scatter returns come from costless electrons in the ionospheric gas, or plasma, usually with a strong influence from the ions. ISRs can exist used to measure electron and ion temperatures and velocities, and the number densities of the electrons and the various ions. ISR has remained a useful technique for ionospheric studies during the last 40 years, because a complete, authentic, and elegant theory describes the spectrum of the scattered indicate, and because inexpensive and easily implemented digital signal processing makes the use of new radar techniques practical and allows new and meliorate data analysis methods. Information assay consists of comparison measured spectra with model spectra, adjusting the model parameters for a skilful friction match using nonlinear least-squares fitting. The main job of ISRs is the global study of the effects of energy inputs into the ionosphere and upper atmosphere, that is, solar radiation and particles inbound forth the Earth'south magnetic field lines from to a higher place, and energy, ofttimes in the form of waves, from the denser atmosphere below. ISRs verify many aspects of the behavior of the ionospheric plasma, including plasma instabilities generated naturally and artificially. ISRs also make measurements in the middle atmosphere, and can function every bit MST (mesosphere–stratosphere–thermosphere) radars in the lower atmosphere.

The required hardware is large: one or more antennas, 30–300   m in bore, and a powerful transmitter, 1   MW or more, capable of transmitting for several pct of the time. Near radars are monostatic, using the same antennas for transmission and reception. Each ISR is the consequence of different compromises in design, trading away the less needed characteristics in social club to lower the price. The Arecibo radar (18.3° Due north, 293.two° E) obtains a very loftier sensitivity at 430   MHz by using a fixed spherical dish 305   chiliad in bore synthetic in a sinkhole in Puerto Rico. Energy focuses to a line rather than a bespeak as with a parabolic antenna, and the original blueprint used a long line feed antenna. Today, a Gregorian feed with secondary and tertiary reflectors is used to correct the spherical aberration. With such a large antenna the feed is moved rather than the dish, with zenith angles of 20° accessible at Arecibo. The Jicamarca observatory in Peru (−12.0° N, 283.one° E) uses a big assortment of dipoles operating at 50   MHz to obtain a similar sensitivity. It has a express range of pointing angles nearly perpendicular to the magnetic field and is used to written report the electrodynamics and other features of the ionosphere at the magnetic equator.

Radars requiring full sky coverage use movable parabolic dishes, and accept lower sensitivity equally a issue of the smaller antenna. The Millstone Hill facility in Massachusetts, USA (42.6° E, 288.5° N) operates at 440   MHz and has ii parabolic dishes, 1 fixed in the vertical direction (68   g) and the other (46   m) rapidly steerable over most of the heaven. The Sondrestrom facility in Greenland (67.0° N, 309.0° E) operates at about 1100   MHz and besides uses a steerable parabolic dish (32   m). This radar has moved from the Stanford Campus to Alaska and then to Greenland in response to the needs of the scientific customs. These four radars course a longitudinal chain operated under the CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) programme of the U.s.a. National Science Foundation (NSF).

The EISCAT (European Incoherent Scatter) Clan, a consortium of six European countries and Japan, operates the newest facilities. These are 931   MHz radar with transmitting and receiving facilities in Tromsø, Norway (69.vi° Northward, xix.2° East) and receiving sites in Kiruna, Sweden, and Sodankylä, Finland, a and so-called tristatic system. The Tromsø site too has a monostatic 224   MHz system using a cylindrical paraboloidal antenna with mechanical steering in i plane and electrical pointing past means of phasing in the other plane. The newest EISCAT radar is located in the Svalbard archipelago on the island of Spitzbergen (78° North, twenty° E) and has two parabolic dishes. The Institute of Ionosphere in Kharkov, Ukraine, operates a facility at 150   MHz with a 100   one thousand fixed vertical dish and a 25   thou steerable dish. The Institute of Solar-Terrestrial Physics operates a radar virtually Irkutsk (53° N, 103° E) in Russia (Siberia) which steers by irresolute the frequency betwixt 154 and 162   MHz. The EISCAT, NSF, and Kharkov radars frequently operate together on 'World Days' that allow global studies of the ionosphere and infinite weather events. Originally designed for middle atmospheric studies, the MU radar almost Shigaraki, Nippon, has regularly been used in the ISR mode in contempo years.

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780123822253003303

MULTISCALE GEOSPACE PHYSICS IN CANADA

William Liu , ... Andrew Yau , in Multiscale Coupling of Sun-Globe Processes, 2005

4.three AMISR

The Avant-garde Modular Incoherent Scatter Radar (AMISR) is a major $44 Grand upper atmospheric research facility funded by the US National Scientific discipline Foundation in August 2003. Featuring a novel modular design, AMISR offers the scientists ii advantages: relocatability to different locations around the earth to facilitate comparative studies, and remote steering and control to permit scientists to zoom in on interesting auroral and ionospheric features in real time.

Two of the three gigantic AMISR "faces" (each 32 m2 in size, with 128 modular panels) will be built at Resolute Bay, Canada, where a host of Canadian and international basis instruments already operate, making information technology one of the best locations to report the underexplored polar cap region. Many polar cap phenomena are straight signatures of solar wind-magnetosphere interaction, and proxies of magnetospheric topology (theta auroral, auroral patches, and traveling vortices); the argue on convection topology under northward IMF weather condition is seen by many as a litmus test of competing theories of dayside reconnection. Still, the absence of an incoherent radar facility in the polar cap has express the study of how these large- and meso-calibration structures cascade to modest scales. AMISR volition fill this gap by providing information on how ionospheric instabilities can exist excited by external forcing and how the resulting wave-particle interactions may control polar wind dynamics, among other potential effects.

Canada's involvements in AMISR is still developing. The poleward extension of the HF radar network, accordingly named PolarDARN, is one such possibility. The complementarity between PolarDARN and AMISR can be appreciated by the post-obit consideration. AMISR is a powerful instrument to probe ionospheric waves and instabilities on the meso and small scales; however, its limited field of view does non allow it to see the context in which these processes occur. For instance, not knowing whether the convection is four-jail cell or two-cell limits one's power to connect ionospheric observations to magnetospheric reconnection and convection. PolarDARN is an ideal complement in giving the big-calibration information, much similar the complementary value of THEMIS GBO to the overall mission. Other potential Canadian support instruments include Canadian Avant-garde Digital Ionosonde (CADI) and optical instrumentation

(including potentially THEMIS-type imagers) placed in strategic locations to allow stereoscopic imaging of auroral features underlying AMISR observations.

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/commodity/pii/B9780444518811500368

Electromagnetic energy input and dissipation

Stephen R. Kaeppler , ... Weijia Zhan , in Cross-Scale Coupling and Energy Transfer in the Magnetosphere-Ionosphere-Thermosphere System, 2022

5.five Recent observations from the Poker Flat Incoherent Scatter Radar

The Poker Flat Incoherent Scatter Radar (PFISR) is an avant-garde modular incoherent scatter radar, which is a monostatic electronically steerable phased-assortment radar that is capable of beam steering on a pulse-to-pulse ground ( Kelly and Heinselman, 2009) and PFISR is located nearly Poker Flat, Alaska, the United States (Longitude: 147.47°W, Longitude: 65.12°N). Since 2007, PFISR has been operating in a four-beam one% duty cycle background mode called the "IPY mode," which has provided nearly continuous observations of the E- and F-region ionosphere. Higher duty bike modes are also run during defended experiments. Alternating codes are used to resolve the E-region ionospheric land parameters (Lehtinen and Haggstrom, 1987). PFISR experiments use a 16-baud randomized strong alternating code (east.chiliad., Lehtinen and Haggstrom, 1987) with 30   μs (4.5   km) bauds. The information are oversampled at 10   μs and processed using fractional lag processing (e.grand., Huuskonen et al., 1996). For the F-region, a long-pulse experiment using a 480 or 330   μs uncoded pulses are gated to have a spacing of 36 and 24.5   km with a range resolution of 72 and 49   km, respectively.

Nosotros present results of Joule heating derived from PFISR observations. The total database of neutral winds and Joule heating parameters are calculated from March 2010 to June 2019; we present a small-scale, but representative, ready of examples from these data. The estimation of the electric field and neutral winds used methods described in Heinselman and Nicolls (2008) and discussed in Section 5.4.i.one. For the neutral winds, estimates of the geographic zonal, meridional, and vertical winds were produced as a function of time and on a uniform altitude grid that spanned from xc to 130   km in five   km increments. The electron density observed by PFISR was used to calculate the Hall and Pedersen conductivity using Eq. (five.11). As described in Section 5.3.1, the perpendicular electric current density, Pedersen conductivity, electrical field, and neutral winds were used in Eqs. (5.15), (5.17), and (5.xviii) to calculate the Joule heating charge per unit, the passive energy degradation rate, and the mechanical free energy transfer rate. These values were then integrated with respect to altitude to produce the integrated Joule heating charge per unit, integrated passive energy deposition rate, and the integrated mechanical energy transfer rate.

In Fig. 5.four, nosotros nowadays an case of the ii days of PFISR observations for June 18, 2017 and June 19, 2017 which show a day with a Joule heating event and a typical quiet day, respectively. Fig. 5.4A and B shows the passive free energy deposition rate and the Joule heating rate as a function of altitude, respectively. Fig. 5.ivC shows the percentage difference betwixt the passive energy deposition rate and the Joule heating rate, normalized to Joule heating rate; −100% corresponds to the limiting case, where only the neutral winds are contributing to the Joule heating charge per unit. This ratio gives an indication equally to the event of the electric field on the Joule heating charge per unit. Fig. 5.ivD shows the meridional and zonal electric fields every bit orange and blue, respectively. Note that the left column and correct column have unlike magnitudes. Fig. 5.fourE and F shows the altitude-resolved zonal and meridional neutral winds, respectively. All of these data are plotted with respect to magnetic local time. At PFISR, magnetic midnight occurs at ∼11 UT, solar local time (LT) is ∼UT-nine.8   h, and LT is +1.2   h ahead of MLT.

Fig. five.4. An instance of ii days that include a Joule heating effect and a typical quiet day. The left and correct column are June 18, 2017 and June 19, 2017, which correspond to the active and tranquillity weather, respectively. Rows A and B are the passive energy deposition rate and the Joule heating rate, respectively. Row C is the percent difference between the passive energy deposition rate and the Joule heating rate. Row D is the zonal and meridional electric fields shown as blueish and orange, respectively. Rows E and F correspond to the distance-resolved zonal and meridional winds, respectively.

On June 18, 2017, there are two maxima in the passive energy deposition rate and the Joule heating rate, one that occurs in the evening sector, 1600–2100   MLT, and the other which occurs in the morning time sector, 0000–0400   MLT. There is a minimum which occurs near magnetic midnight, which has been reported in the previous observational papers (e.grand., Fujii et al., 1999; Thayer, 2000; Aikio et al., 2012; Cai et al., 2013) and has been attributed to the reversal of plasma drifts associated with the Harang discontinuity (eastward.m., Aikio et al., 2012; Cai et al., 2013). The Joule heating rate on the morningside extends down to lower altitudes, relative to the eveningside; this effect could be could be partially attributed to the harder auroral precipitation observed in the morningside associated with diffuse and pulsating aurora (eastward.g., Jones et al., 2009; Hosokawa and Ogawa, 2015). For June 18, 2017, Fig. five.ivD shows that the meridional electric field has a larger magnitude in the evening sector relative to the morning sector. Although on the morningside, Fig. v.fourC shows the electric field has a stronger touch on on the Joule heating charge per unit at lower altitudes in the dawn sector, equally indicated by the positive magnitude, relative to the evening sector. Fig. 5.4C suggests that the winds may reduce the Joule heating rate on the morningside. On the eveningside, near 2100–2300   MLT, there is ∼two–three   h delay in MLT between the peak meridional electrical field and the largest percent difference in the Joule heating, as shown in Fig. 5.4C.

For the Due east-region neutral winds, a one-h running boilerplate window was applied to the information that are presented. During the interval 0600–1800   MLT which corresponds to the daytime, the winds are somewhat noisy, which is mostly attributed to the low duty cycle IPY mode, relative to the college duty cycle modes run during the nightside MLT sector.

June xix, 2017 shows a typical tranquility day. There is an isolated morningside event well-nigh 0200   MLT; even so, the rest of the day shows small-scale passive energy deposition and Joule heating rates. In these cases, the Joule heating rate does not simply cease, but due to the neutral winds and the weak electric field, some energy transfer occurs, fifty-fifty if the magnitude is small-scale. As shown on June 19, 2017, not every day has an associated Joule heating event, such as the event shown on June 18, 2017.

Fig. 5.5 shows statistical results for the whole month of June 2017. Approximately 400   h of information were used to generate Fig. five.v. The data are subdivided by columns into geomagnetically quiet and active weather condition, corresponding to AE ≤ 200 and AE > 200, respectively. Fig. 5.fiveA and B shows the occurrence rates for the passive energy deposition charge per unit and the Joule heating charge per unit, respectively. The occurrence rate is a percentage relative to the total number of hours for June 2017 per distance and is represented as a discrete, normalized color bar. We encounter that for the active conditions, the occurrence rates bear witness the evening and dawnside enhancements, while for quiet conditions, there is an eveningside enhancement that peaks at 2100   MLT. For agile conditions, the eveningside enhancement is also broader in MLT and extends to lower altitudes relative to the tranquillity times.

Fig. 5.five. Median results are presented for the month of June 2017. Rows A and B prove the occurrence rate for the passive energy deposition rate and the Joule heating rate, respectively. Rows C, D, and E, are the median distance-resolved passive energy degradation rate, Joule heating rate, and mechanical energy transfer rate. Row F shows the median integrated passive energy deposition charge per unit, Joule heating charge per unit, and mechanical free energy transfer rate as blue, dark-green, and crimson, respectively. The shaded regions correspond to the 25% and 75% quartiles. Row G shows the per centum difference betwixt the integrated passive energy deposition rate relative to the Joule heating charge per unit. More than details can be institute in the text.

Fig. 5.5C–E shows the median passive free energy deposition charge per unit, Joule heating rate, and the mechanical energy transfer rate for tranquility and agile conditions as columns, respectively. The passive energy degradation rate and the Joule heating rate are plotted on a logarithmic scale to show the full range. For quiet conditions, there is an enhancement in the passive free energy transfer charge per unit associated with the electric fields near ∼2100   MLT, which correlates with the larger occurrence rate. However, nosotros meet the median Joule heating charge per unit, which includes the neutral current of air contribution, has a contribution during all MLT sectors down to 110   km, and to slightly lower altitudes near ∼2100   MLT.

During the agile interval, the dusk and dawn enhancements in the median passive energy transfer charge per unit and the Joule heating rate are articulate. The mechanical energy transfer charge per unit shown in Fig. 5.fiveE shows that during quiet times, at altitudes in a higher place 110   km, the sign of the mechanical energy transfer rate is negative which means that the neutral winds are doing the work on the plasma. For active atmospheric condition, especially between ∼1800 and 2200   MLT, at altitudes above 110   km, the piece of work is being done past the plasma onto the neutral wind, which is acting equally an free energy sink.

Fig. five.vF shows the median integrated passive energy degradation charge per unit, Joule heating rate, and mechanical energy transfer rate as blue, green, and blood-red, respectively. The shaded region corresponds to the 25% and 75% quartiles. For quiet times, this illustrates that the neutral winds are responsible for the Joule heating charge per unit for almost MLT sectors, except for an interval most ∼2100   MLT where the electric field does provide some contribution to the Joule heating charge per unit. The mechanical energy transfer term, equally shown as the red line, is negative indicating that the winds are doing work and thus acting as an energy source. The median integrated Joule heating rate provided by the winds is of the society of 1–2   mW/m² during placidity intervals. During active conditions, the median integrated Joule heating charge per unit and the integrated passive energy deposition rate are approximately equal in the evening sector, while in the morn sector the median Joule heating rate is larger than the passive energy degradation charge per unit. The median Joule heating charge per unit and passive free energy transfer rate are a factor of ∼2–5 larger during active intervals relative to quiet times. Likewise, during active intervals, the mechanical energy transfer charge per unit becomes positive for a pocket-sized interval well-nigh 2100   MLT, which indicates that the winds are acting as an free energy sink.

Fig. five.5Thousand shows the percent deviation between the integrated passive free energy deposition charge per unit and the Joule heating rate. Again, for interpretation, if the ratio is −100% that indicates that the neutral winds are the only factor contributing to the integrated Joule heating rate. In this case, we meet that for quiet weather, the neutrals are the primary energy dissipation machinery, with the electric field contributing a very small magnitude, await near ∼2100   MLT when the electric field produces an appreciable contribution to the free energy deposition. For the active interval, the neutral winds are the ascendant in the morning time sector from 0000 to 0500   MLT, while in the evening sector the integrated Joule heating rate and the integrated passive energy degradation charge per unit are approximately equal from 1500 to 2400   MLT, except about 2100   MLT. About 2100   MLT, the energy deposition is dominated by the ionospheric electrical field, as indicated by the ∼100% enhancement in the passive free energy deposition rate.

Read total chapter

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780128213667000068

MESOSPHERE | Ionosphere

Chiliad.C. Kelley , in Encyclopedia of Atmospheric Sciences (2nd Edition), 2015

A Day in the Life of the Midlatitude Ionosphere

The most powerful single tool for ionospheric studies is an incoherent scatter radar that detects the microscopic fluctuation due to thermal motions in the ionosphere. The first such instrument, and still the largest of the eleven now in employ worldwide, is near Arecibo, Puerto Rico. The dish is i km in circumference and tin can 'see' the ionosphere out to several k km altitude. In Effigy 4, we show the plasma content measured by the radar over a full 24-hour interval. The discussion in the Section Sources and Cardinal Features of the Ionosphere explains the basic graphic symbol of this plot, but not at all its details. Nosotros see that the density is loftier during the day, even at 100 km. At night the lower ionosphere rapidly – and almost completely – disappears, so much and so that to encounter annihilation at all we must change the altitude and gray scale. Then slowly during the nighttime, the density decays to low values just earlier sunrise, when the cycle begins again. Simply what about the wiggles? Why does the layer moves upwardly and down? And what is the origin of the weak ionization layers seen at depression altitudes?

Figure 4. Ionospheric plasma density over Arecibo during a 24-h menstruation (xvi–17 September 1999; fourth dimension is Atlantic Standard Time). The lack of plasma below 250 km at night is due to recombination of molecular ions. The high-altitude plasma and interesting thin layers are due to ions such as O1, Mg1, and Fe1, which have long lifetimes.

These effects in large part are due to horizontal winds and waves in the thermosphere. With a very hot atmosphere on the dayside (>one thousand Yard) in full sunlight and a very absurd i at nighttime (<800 K), information technology is not surprising that potent winds accident from day to dark continuously all over the globe. Different the thick lower atmosphere, the thermosphere has no thermal inertia. The winds simply blow continuously, acting as a huge atmospheric thermal tide. Speeds of 200 1000 s^{− one} (720 km h⁻¹) are not uncommon. It is very hard to move the plasma beyond the magnetic field lines, but such winds easily move the ionosphere up and down the magnetic field lines. At Arecibo, the management of the magnetic field is at an angle of 45° to the vertical (pointing n and downwardly). When the air current blows due south, the ionosphere moves upward, much similar a ping-pong brawl held up against gravity on an inclined airplane by a hair dryer, as shown in Figure 5.

Effigy 5. An illustration showing the illustration between the midlatitude ionosphere on the correct, with atmospheric winds pushing the ionosphere up the magnetic field, and a lite object suspended on an inclined plane.

At high altitude in that location is very piddling neutral gas, and recombination is weak. If the air current ceases or blows north, the ionosphere falls due to gravity into regions where reaction [5a,b] tin can swallow abroad at it. So a south air current not only elevates the ionosphere, it besides keeps it high out of reach of the losses due to the thermosphere. Some of what we come across at nighttime in Figure four is due to these winds.

The more sharp changes in height may be due to the electrical forces that act on the ionosphere. These electric fields have associated voltages as high as 200 000 V and ionospheric currents every bit great equally one 000 000 A, yielding ability levels of two × 10¹¹ Watts, more power than any artificial generator on globe. Two major generators provide this electrification and both involve move of a usher across a magnetic field, exactly the manner by which generators convert mechanically rotating machines into electric energy. The solar wind is the about powerful of the two, generating hundreds of kilovolts beyond the world'south polar regions and causing 1 of nature'southward nearly spectacular visual displays – the aurora borealis and australis (meet the next section). The second generator is the motion of the earth'due south temper, described in previous paragraphs. Tides, winds, and gravity waves in the atmosphere all drive currents and generate electric fields by the dynamo effect. Considering the magnetic field lines behave like conducting wires, the only voltage easily immune is beyond magnetic field lines. Figure 6 illustrates what happens if a single positive particle is subjected to orthogonal electric and magnetic fields. Initially, the particle is accelerated parallel to the electric field by the force qE.

Figure vi. In crossed electrical and magnetic fields in vacuum, ions and electrons exhibit the motion shown schematically. The ion path is specifically shown to be similar to that of a dot on the rim of a rolling bike.

But in one case it attains a velocity, the magnetic force, q 5 ×B, deflects it to the right. Eventually, it comes to rest and the wheel starts over. The pattern is the aforementioned as a dot on the edge of a rolling, nonslipping bike moving to the right at a velocity EB ^−one. A negatively charged particle (electron) starts out in the opposite direction, just is also deflected to the correct, and drifts on average at the aforementioned speed as the positive ions. Since at that place are equal numbers of positive ions and electrons, there is no cyberspace current – just a net velocity. Higher up about 150 km, collisions are so rare that Figure six describes the motion quite well – electric fields are one-to-one, related to the motion of the ionosphere across the magnetic field lines, whereas winds, gravity, and diffusion dominate along the direction of the magnetic field. An eastward electrical field over Arecibo, for example, causes an (Due east ×B)B ⁻ⁱⁱ drift northward and upward at an angle of 45°. Some of the precipitous top changes visible in Figure 4 are due to such electric field–induced motions.

The abrupt summit changes might be temporal or spatial or a combination of both; it is difficult to tell with a single measurement. But the fact that carmine lite is emitted in reactions [5a] and [5b] allows us to visualize the plasma in two dimensions. The information in Figure 7 were obtained on this same night using a bare, backlit charge-coupled device chip illuminated by a fisheye (all-heaven) lens. A narrow (630 ± 1 nm) filter was inserted in the path and the chip was exposed for 90 s. There were $1024\times 1024$ pixels in the prototype, which, at a pinnacle of 250 km, covers a 1000-km diameter circle. The image has been corrected for the lens furnishings, vignetting, etc., and projected equally if we were above the earth looking down rather than up (hence the map of the Caribbean in its usual geometry). We see intricate patterns of low-cal and dark regions, with one of the night zones positioned right over the Arecibo Observatory. The ionosphere is highly structured this nighttime and is far unlike than would be predicted if but product, loss, gravity, and diffusion were operating. The sequence of images taken this night shows the nighttime bands surging poleward from well south of Puerto Rico and and so drifting toward the west. This unexpected behavior demonstrates that we have much to larn about even the most well-behaved regions of the ionosphere.

Figure 7. The 630 nm airglow for 17–18 February 1999, superimposed on a map of the Caribbean islands with Puerto Rico in the heart. The regions depleted of airglow (shown black) commenced in the SE and surged to the NW on this dark.

Reproduced past permission of the American Geophysical Union from Kelley, M.C., Makela, J.J., Swartz, Westward.E., Collins, S.C., Thonnard, Due south., Aponte, N., Tepley, C.A., 2000. Caribbean Ionosphere Campaign, year one: airglow and plasma observations during two intense midlatitude spread-F events. Geophysical Enquiry Messages 27, 2825.

Read total chapter

URL:

https://world wide web.sciencedirect.com/science/commodity/pii/B9780123822253001845

Density, irregularity, and instability

In Cross-Scale Coupling and Energy Transfer in the Magnetosphere-Ionosphere-Thermosphere Organisation, 2022

Incoherent scatter radar

A type of radar arrangement that is unremarkably used to resolve plasma density enhancements is the incoherent scatter radar (ISR). The ISR technique uses the backscatter power generated past ionospheric plasma to deduce the ionosphere's state parameters including plasma density, ion and electron, and majority plasma velocity. The spatial resolution of ISR measurements varies depending on the system, but is typically of the gild of tens of kilometers, with a temporal resolution of the guild of 1–5  min. Dissimilar ionosondes, ISR measurements are not restricted to the bottomside ionosphere and tin can provide observations in multiple directions well into the topside ionosphere. Withal, ISRs are extremely sophisticated and, therefore, very expensive instruments. Accordingly, only a few ISRs have been built and are operating in the world at the moment.

An example of ISR measurements of plasma density irregularities is provided in Fig. 3.i, which shows data spanning approximately 18   h collected by the Resolute Bay Incoherent Scatter Radar—Northward (RISR-Northward) (Bahcivan et al., 2010), which faces northwards, and RISR-Canada (RISR-C), which faces southwards (Gillies et al., 2016). Fig. 3.ane shows RISR-C data collected by a axle directed at an azimuth of −157.0 degrees of acme bending of 55 degrees, and RISR-N data from a beam directed at an azimuth of 26.0 degrees of meridian angle of 55 degrees. Note that these beams were directed in opposite directions—their azimuths were separated by approximately 180 degrees. These radars operate at radio frequencies well in a higher place the ionosphere'south critical frequency, and then their narrow radar beams practise not suffer from refractive effects.

Fig. three.1. September 29–30, 2019 observations from RISR-C and -Due north equally a office of Universal Time (UT). (left) RISR-C observations at azimuth = −157.0 degrees and peak = 55.0 degrees. (right) RISR-Northward observations at azimuth = 26.0 degrees and tiptop = 55.0 degrees. In each subfigure: (i + ii) plasma density (3 + iv) the median plasma density between 200 and 400   km (a 15   min median filter has been practical), where orange corresponds to the beam of interest and blue is a similarly directed beam at an tiptop bending of 75.0 degrees (v + vi) line-of-sight plasma velocity, where positive is away (red) from the radar and negative is toward (blue) the radar (7 + viii) electron temperature. Dashed lines indicate the locations of local apex (19:45 UT) and local midnight (7:45 UT). A Python program used to generate panels (i), (ii), and (5)–(viii) has been supplied in the supplementary information available at https://doi.org/10.1016/B978-0-12-821366-7.00001-9.

Plasma density is plotted in panels i and ii. Panels 3 and iv show the median plasma density along 2 beams from each radar, covering 200 and 400   km distance. The beginning beam has an tiptop angle of 55 degrees (orange), while the 2d has an peak angle of 75 degrees (blue). Both beams are directed forth the same azimuth. Panels v and half dozen show the line-of-sight plasma velocity at a 55 degrees superlative angle, and panels vii and viii show the electron temperature at a 55 degrees elevation angle. In panels i and ii, a diversity of relative density enhancements and minimums are apparent. In general, the plasma density is enhanced on the dayside (between eighteen:00 and 00:00 universal time, UT) relative to the nightside (after 00:00 UT).

The traces in panels iii and 4 show the same trends equally in panels i and ii, respectively. Variations in the median plasma density in both traces, particularly after 03:00 UT, are readily apparent. The sudden drop in electron temperature at approximately 00:00 UT marks local sunset; the lack of electron temperature enhancements afterwards that bear witness at that place is negligible particle precipitation present in either radar's field of view at night. We can, therefore, apply the same logic used in deriving Eq. (3.7) to conclude that the variations detected in panels 2 are the result of F-region plasma density irregularities being transported into the region.

Both radars measure ∂n _i /∂t > 0 simply earlier 04:00 UT (panels iii and iv), followed by a ∂n _i /∂t < 0 signature, consistent with the signature of an enhancement moving toward, and then away from each radar. A comparing of this feature in the higher (blueish) and lower (orange) acme beams of each radar shows that the enhancement is moving away from RISR-C and toward RISR-N, that is, in a southerly direction. This is consequent with the direction of the plasma flows measured by each radar (panels five and half dozen). This move is consistent with the southerly global convection menstruation expected in that region at that fourth dimension of day (Ruohoniemi and Greenwald, 2005). A similar effect tin can exist seen on the dayside, such as nigh 19:00 UT, with the exception that the flows are v _i > 0 for RISR-N and five _i < 0 for RISR-C, suggesting a northerly motion. This motion is also consistent with the global convection flow expected in that region at that time of day.

We feel that it is necessary to point out that, in accordance with contemporary jargon, these enhancements would be referred to as "patches" depending on our definition of the ambient ionosphere. This is one of the several reasons why we feel that the term "patch" is outdated. Instead, language such as "big-calibration plasma density irregularities" is, arguably, more descriptive, without implying that a particular or exceptional procedure is associated with enhancements that are twice as dense equally the groundwork. Furthermore, as Fig. 3.1 illustrates, quantifying the "background or ambience ionosphere" in the polar cap is exceedingly hard.

Finally, panels 7 and eight evidence that overall the dayside plasma has an elevated electron temperature, which is an expected result of photoionization. However, note that the plasma density enhancements are coincident with slight decreases in electron temperature. This is because the thermal capacity of the enhancements is larger than the ambient ionosphere. Under a constant supply of heat to the plasma, the temperature of the enhancements will exist less than the ambience ionosphere, owing to their increased density with respect to the ambience ionosphere. This effect is non as readily apparent under nighttime conditions.

ISRs take, by far, been the subject area of the well-nigh irregularity studies, no uncertainty given their capacity to estimate plasma density and plasma density enhancements. Some of the first high-breadth ISR measurements were performed with an ISR located in Chatanika, Alaska (which was subsequently moved to Greenland and contributed even further to the written report of enhancements) (Kelley et al., 1982; Vickrey et al., 1980), which demonstrated that, indeed, the dark high-latitude ionosphere is replete with plasma density enhancements. Several ISR-based studies (we just provide a few here and suggest to the reader to consider the references contained therein) have followed since and became more common equally more ISR facilities were installed in Scandinavia (Carlson et al., 2004; de la Beaujardière et al., 1986), Nunavut, Canada (Dahlgren et al., 2012; Perry and St.-Maurice, 2018; Ren et al., 2018), and Poker Flat, Alaska (Liang et al., 2018; Nicolls and Heinselman, 2007). Observations by these systems take been pivotal in characterizing plasma irregularities, including enhancements, their generation mechanisms, their dynamic backdrop, and their connection to other M-I-T coupling processes.

Read full affiliate

URL:

https://www.sciencedirect.com/science/article/pii/B9780128213667000019

Microsatellites every bit Research Tools

Due east.A. Essex , ... H.A. Cohen , in COSPAR Colloquia Serial, 1999

INTRODUCTION

The various regions of the ionosphere accept been monitored to dissimilar degrees on a long-term basis. Fifty-fifty instruments such equally incoherent scatter radars, while providing profiles of both the topside and bottom side ionosphere, do not operate on a continuous basis and provides poor resolution for the lower ionosphere. The footing-based ionosondes provide not-homogeneous coverage of the bottom side ionosphere, as they are express to observations from land. This is particularly true in the Southern Hemisphere where the oceans embrace the majority of the Hemisphere. The topside ionosphere and the region above, the plasmasphere are non hands monitored on a long-term basis. Only a few instruments such equally incoherent scatter radars, topside sounders and in situ satellite based diagnostics are able to provide details on the structure, composition and dynamics of the topside ionosphere. The properties of the plasmasphere are even less well known and techniques to explore it are very limited. The appearance of the Global Positioning Arrangement (GPS) with 24 satellites in 12 60 minutes orbits at 20,000 kilometres, provides the opportunity to monitor on a global basis the variation of the ionisation content of the ionosphere and plasmasphere. The recent deployment of space based GPS receivers have demonstrated the feasibility of using satellite to satellite experiments for monitoring the ionosphere. In this paper we discuss some of the satellite to satellite experiments proposed for FedSat1, the Australian satellite to be launched in 2001.

Read full affiliate

URL:

https://www.sciencedirect.com/science/commodity/pii/S0964274999800353

cloudablat1994.blogspot.com

Source: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/incoherent-scatter-radar

Share this post