scholarly journals Halley’s Comet: From Remote Ultraviolet Spectroscopy to In-Situ Studies

1988 ◽  
Vol 102 ◽  
pp. 25-35
Author(s):  
A.-C. Levasseur-Regourd
Keyword(s):  
Space Missions ◽  
Satellite Observations ◽  
Ultraviolet Spectroscopy ◽  
The Sun ◽  
In Situ Studies ◽  
Halley's Comet ◽  
In Situ Observations ◽  
Comet Halley

Due to the success of the March 1986 space missions to comet Halley, and to the large amount of ground, rocket or satellite observations, numerous papers have recently been published, and new and exciting problems have raised. It should nevertheless be kept in mind that the development of cometary physics is much prior to the last return to perihelion of Halley. One of the most remarkable results of the space missions has been to demonstrate that the nucleus, the coma (transient atmosphere which expands when the comet approaches the Sun), and the tails models that had been inferred from various astrophysical methods were rather in agreement with in situ observations.

scholarly journals The Global Interaction of Comets with the Solar Wind

1991 ◽  
Vol 116 (2) ◽  
pp. 1125-1144 ◽  
Author(s):  
K. R. Flammer
Keyword(s):  
Solar Wind ◽  
Heliocentric Distance ◽  
Theoretical Models ◽  
Bow Shock ◽  
Flow Transition ◽  
The Sun ◽  
In Situ Observations ◽  
Comet Halley

AbstractThe global interaction of the solar wind with a comet as it orbits the Sun is reviewed. After a brief survey of the flow transition regions observed at comet Halley is presented, theoretical models are given for the cometocentric distance of the bow shock, the cometopause, and the ionopause. In addition, predictions are made as to what heliocentric distance these boundaries should form at. The results of these models are compared with the in situ observations at comet Halley.

scholarly journals Halley’S Comet (Part I): Ground-based Observations

1989 ◽  
Vol 8 ◽  
pp. 3-16
Author(s):  
Richard M. West
Keyword(s):  
Space Missions ◽  
In Situ Measurements ◽  
Time Interval ◽  
Short Time Interval ◽  
International Programme ◽  
Halley's Comet ◽  
Large Telescopes ◽  
Short Time ◽  
Comet Halley

AbstractSince the recovery in October 1982, an extensive, international programme to observe Comet Halley with ground-based instruments has been co-ordinated by the International Halley Watch (IHW), and a comprehensive archive is now in the final phases of preparation. The observations were carried out at more than 150 observatories and with all available methods. A special effort was made to support the space missions during the comet encounters in early March 1986. Whereas the spacecraft provided detailed in-situ measurements over a short time interval, ground-based observers have so far followed the development of the comet over a period of nearly six years, and a number of spectacular events near the nucleus and in the tail have been documented in great detail. These observations still continue. This article gives an overview of the most important results obtained from the ground and also mentions the prospects for further observations with large telescopes during the next years.

scholarly journals International Arctic Systems for Observing the Atmosphere: An International Polar Year Legacy Consortium

2016 ◽  
Vol 97 (6) ◽  
pp. 1033-1056 ◽  
Author(s):  
Taneil Uttal ◽  
Sandra Starkweather ◽  
James R. Drummond ◽  
Timo Vihma ◽  
Alexander P. Makshtas ◽  
...  
Keyword(s):  
United States ◽  
The United States ◽  
Satellite Observations ◽  
The Arctic ◽  
International Polar Year ◽  
Network Measurements ◽  
International Polar ◽  
In Situ Observations ◽  
Arctic Atmosphere

Abstract International Arctic Systems for Observing the Atmosphere (IASOA) activities and partnerships were initiated as a part of the 2007–09 International Polar Year (IPY) and are expected to continue for many decades as a legacy program. The IASOA focus is on coordinating intensive measurements of the Arctic atmosphere collected in the United States, Canada, Russia, Norway, Finland, and Greenland to create synthesis science that leads to an understanding of why and not just how the Arctic atmosphere is evolving. The IASOA premise is that there are limitations with Arctic modeling and satellite observations that can only be addressed with boots-on-the-ground, in situ observations and that the potential of combining individual station and network measurements into an integrated observing system is tremendous. The IASOA vision is that by further integrating with other network observing programs focusing on hydrology, glaciology, oceanography, terrestrial, and biological systems it will be possible to understand the mechanisms of the entire Arctic system, perhaps well enough for humans to mitigate undesirable variations and adapt to inevitable change.

scholarly journals Transforming in-situ observations of CME-driven shock accelerated protons into the shock's reference frame.

2005 ◽  
Vol 23 (5) ◽  
pp. 1931-1941 ◽  
Author(s):  
I. M. Robinson ◽  
G. M. Simnett
Keyword(s):  
Solar Physics ◽  
Solar Energetic Particle ◽  
Transport Processes ◽  
Solar Energetic Particle Event ◽  
The Sun ◽  
Proton Acceleration ◽  
Angle Scattering ◽  
Peak Energy ◽  
In Situ Observations

Abstract. We examine the solar energetic particle event following solar activity from 14, 15 April 2001 which includes a "bump-on-the-tail" in the proton energy spectra at 0.99 AU from the Sun. We find this population was generated by a CME-driven shock which arrived at 0.99 AU around midnight 18 April. As such this population represents an excellent opportunity to study in isolation, the effects of proton acceleration by the shock. The peak energy of the bump-on-the-tail evolves to progressively lower energies as the shock approaches the observing spacecraft at the inner Lagrange point. Focusing on the evolution of this peak energy we demonstrate a technique which transforms these in-situ spectral observations into a frame of reference co-moving with the shock whilst making allowance for the effects of pitch angle scattering and focusing. The results of this transform suggest the bump-on-the-tail population was not driven by the 15 April activity but was generated or at least modulated by a CME-driven shock which left the Sun on 14 April. The existence of a bump-on-the-tail population is predicted by models in Rice et al. (2003) and Li et al. (2003) which we compare with observations and the results of our analysis in the context of both the 14 April and 15 April CMEs. We find an origin of the bump-on-the-tail at the 14 April CME-driven shock provides better agreement with these modelled predictions although some discrepancy exists as to the shock's ability to accelerate 100 MeV protons. Keywords. Solar physics, astrophysics and astronomy (Energetic particles; Flares and mass ejections) – Space plasma physics (Transport processes)

In-Situ Observations of Cometary Pick-Up Ions ≥0.2 Au Upstream of Comet Halley: Ice Observations

2013 ◽  
pp. 861-864
Author(s):  
K.-P. Wenzel ◽  
T.R. Sanderson ◽  
I.G. Richardson ◽  
S.W.H. Cowley ◽  
R.J. Hynds ◽  
...  
Keyword(s):  
In Situ Observations ◽  
Comet Halley

scholarly journals Deriving Arctic 2 m air temperatures over snow and ice from satellite surface temperature measurements

2021 ◽  
Author(s):  
Pia Nielsen-Englyst ◽  
Jacob L. Høyer ◽  
Kristine S. Madsen ◽  
Rasmus T. Tonboe ◽  
Gorm Dybkjær ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Arctic Region ◽  
Satellite Observations ◽  
The Arctic ◽  
Clear Sky ◽  
Ice Surface ◽  
Air Temperatures ◽  
In Situ Observations ◽  
The Arctic Region

Abstract. The Arctic region is responding heavily to climate change, and yet, the air temperature of ice covered areas in the Arctic is heavily under-sampled when it comes to in situ measurements, resulting in large uncertainties in existing weather- and reanalysis products. This paper presents a method for estimating daily mean clear sky 2 meter air temperatures (T2m) in the Arctic from satellite observations of skin temperature, using the Arctic and Antarctic ice Surface Temperatures from thermal Infrared (AASTI) satellite dataset, providing spatially detailed observations of the Arctic. The method is based on a linear regression model, which has been tuned against in situ observations to estimate daily mean T2m based on clear sky satellite ice surface skin temperatures. The daily satellite derived T2m product includes estimated uncertainties and covers clear sky snow and ice surfaces in the Arctic region during the period 2000–2009, provided on a 0.25 degree regular latitude-longitude grid. Comparisons with independent in situ measured T2m show average biases of 0.30 °C and 0.35 °C and average root mean square errors of 3.47 °C and 3.20 °C for land ice and sea ice, respectively. The associated uncertainties are verified to be very realistic for both land ice and sea ice, using in situ observations. The reconstruction provides a much better spatial coverage than the sparse in situ observations of T2m in the Arctic, is independent of numerical weather prediction model input and it therefore provides an important supplement to simulated air temperatures to be used for assimilation or global surface temperature reconstructions. A comparison between in situ T2m versus T2m derived from satellite and ERA-Interim/ERA5 estimates shows that the T2m derived from satellite observations validate similar or better than ERA-Interim/ERA5 in the Arctic.

scholarly journals On the performance of satellite-based observations of <i>CO</i><sub>2</sub> in capturing the NOAA Carbon Tracker model and ground-based flask observations over Africa land mass

2019 ◽  
Author(s):  
Anteneh Getachew Mengistu ◽  
Gizaw Mengistu Tsidu
Keyword(s):  
Model Simulation ◽  
Satellite Observation ◽  
Satellite Observations ◽  
Lower Altitude ◽  
Equatorial Africa ◽  
In Situ Observations ◽  
The Mean ◽  
Data Gap ◽  
Good Agreement

Abstract. Africa is one of the most data-scarce regions as satellite observation at the equator is limited by cloud cover and there are a very limited number of ground-based measurements. As a result, the use of simulations from models are mandatory to fill this data gap. A comparison of satellite observation with model and available in-situ observations will be useful to estimate the performance of satellites in the region. In this study, GOSAT XCO2 is compared with the NOAA CT2016 and six flask observations over Africa using five years of data covering the period from May 2009 to April 2014. Ditto for OCO-2 XCO2 against NOAA CT16NRT17 and eight flask observations over Africa using two years of data covering the period from January 2015 to December 2016. The analysis shows that the XCO2 from GOSAT is higher than XCO2 simulated by CT2016 by 0.28 ppm whereas OCO-2 XCO2 is lower than CT16NRT17 by 0.34 ppm on African landmass on average. The mean correlations of 0.83 and 0.60 and average RMSD of 2.30 and 2.57 ppm are found between the model and the respective datasets from GOSAT and OCO-2 implying the existence of a reasonably good agreement between CT and the two satellites over Africa's land region. However, significant variations were observed in some regions. For example, OCO-2 XCO2 are lower than that of CT16NRT17 by up to 3 ppm over some regions in North Africa (e.g., Egypt, Libya, and Mali) whereas it exceeds CT16NRT17 XCO2 by 2 ppm over Equatorial Africa (10° S–10° N). This regional difference is also noted in the comparison of model simulations and satellite observations with flask observations over the continent. For example, CT shows a better sensitivity in capturing flask observations over sites located in Northern Africa. In contrast, satellite observations have better sensitivity in capturing flask observations in lower altitude island sites. CT2016 shows a high spatial mean of seasonal mean RMSD of 1.91 ppm during DJF with respect to GOSAT while CT16NRT17 shows 1.75 ppm during MAM with respect to OCO-2. On the other hand, low RMSD of 1.00 and 1.07 ppm during SON in the model XCO2 with respect to GOSAT and OCO-2 are determined respectively indicating better agreement during autumn. The model simulation and satellite observations exhibit similar seasonal cycles of XCO2 with a small discrepancy over Southern Africa and during wet seasons over all regions.

scholarly journals Magnetic clouds seen at different locations in the heliosphere

2008 ◽  
Vol 26 (2) ◽  
pp. 213-229 ◽  
Author(s):  
L. Rodriguez ◽  
A. N. Zhukov ◽  
S. Dasso ◽  
C. H. Mandrini ◽  
H. Cremades ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Space ◽  
Field Configuration ◽  
Magnetic Clouds ◽  
Magnetic Characteristics ◽  
The Sun ◽  
Source Regions ◽  
Plasma Species ◽  
In Situ Observations

Abstract. We analyze two magnetic clouds (MCs) observed in different points of the heliosphere. The main aim of the present study is to provide a link between the different aspects of this phenomenon, starting with information on the origins of the MCs at the Sun and following by the analysis of in-situ observations at 1 AU and at Ulysses. The candidate source regions were identified in SOHO/EIT and SOHO/MDI observations. They were correlated with H-α images that were obtained from ground-based observatories. Hints on the internal magnetic field configuration of the associated coronal mass ejections are obtained from LASCO C2 images. In interplanetary space, magnetic and plasma moments of the distribution function of plasma species (ACE/Ulysses) were analyzed together with information on the plasma composition, and the results were compared between both spacecraft in order to understand how these structures interact and evolve in their cruise from the Sun to 5 AU. Additionally, estimates of global magnitudes of magnetic fluxes and helicity were obtained from magnetic field models applied to the data in interplanetary space. We have found that these magnetic characteristics were well kept from their solar source, up to 5 AU where Ulysses provided valuable information which, together with that obtained from ACE, can help to reinforce the correct matching of solar events and their interplanetary counterparts.

Understanding Solar Wind Formation by Identifying the Origins of In Situ Observations 

2021 ◽  
Author(s):  
Samantha Wallace ◽  
Nicholeen M. Viall ◽  
Charles N. Arge
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Source Region ◽  
Heliospheric Current Sheet ◽  
Slow Solar Wind ◽  
The Sun ◽  
Flux Transport ◽  
Model Driven ◽  
In Situ Observations

&lt;p&gt;Solar wind formation can be separated into three physical steps &amp;#8211; source, release, and acceleration &amp;#8211; that each leave distinct observational signatures on plasma parcels.&amp;#160; The Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) time-dependent photospheric field maps now has the ability to connect in situ observations more rigorously to their precise source at the Sun, allowing us to investigate the physical processes involved in solar wind formation. &amp;#160;&amp;#160;In this talk, I will highlight my PhD dissertation research in which we use the ADAPT-WSA model to either characterize the solar wind emerging from specific sources, or investigate the formation process of various solar wind populations. &amp;#160;In the first study, we test the well-known inverse relationship between expansion factor (f&lt;sub&gt;s&lt;/sub&gt;) and observed solar wind speed (v&lt;sub&gt;obs&lt;/sub&gt;) for solar wind that emerges from a large sampling of pseudostreamers, to investigate if field line expansion plays a physical role in accelerating the solar wind from this source region.&amp;#160; We find that there is no correlation between f&lt;sub&gt;s&lt;/sub&gt; and v&lt;sub&gt;obs&lt;/sub&gt; at pseudostreamer cusps. In the second study, we determine the source locations of the first identified quasiperiodic density structures (PDSs) inside 0.6 au. Our modeling provides confirmation of these events forming via magnetic reconnection both near to and far from the heliospheric current sheet (HCS) &amp;#8211; a direct test of the Separatrix-web (S-web) theory of slow solar wind formation.&amp;#160; In the final study, we use our methodology to identify the source regions of the first observations from the Parker Solar Probe (PSP) mission.&amp;#160; Our modeling enabled us to characterize the closest to the Sun observed coronal mass ejection (CME) to date as a streamer blowout.&amp;#160; We close with future ways that ADAPT-WSA can be used to test outstanding questions of solar wind formation.&lt;/p&gt;

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