“Exploring the Earth’s Time-Variable Gravity Field using Satellite Observations” – Pro ISSI Talk with Adrian Jäggi

A new era in satellite gravimetry was initiated with the launch of dedicated gravity missions such as CHAMP (2000–2010), GRACE (2002–2017), GOCE (2009–2013), and the still on-going GRACE Follow-On (GRACE-FO) mission that was launched in 2018. Whereas CHAMP and GOCE significantly improved our knowledge of the Earth’s static gravity field, GRACE and GRACE-FO were/are mainly devoted to measure its tiny variations in time by providing monthly snapshots of the Earth’s gravity field.

Time-variable gravity as derived from ultra-precise GRACE/GRACE-FO inter-satellite ranging is the only observable to provide integrative measures of total water storage variations on a global scale, i.e., the sum of groundwater, soil moisture, snow, ice, and surface water bodies. As such it is of great interest for large user communities in hydrology, climate modeling, ice observation, geodetic, geophysical, oceanographic, atmospheric, and environmental sciences.

Moreover, it is paramount for separating the variations of individual compartments that are not well accessible by combining the total water storage variations with other remote sensing data. In this talk an overview of the underlying principles of the challenging GRACE/GRACE-FO data analysis will be given and selected key scientific results will be highlighted. A special focus will be on the relevance of European and international initiatives, and in particular also on the important role of ISSI in this context, to further exploit and promote this unique observable to continuously monitor the on-going changes in our Earth system.

This talk was organised by the Association Pro ISSI and was recorded on March 24, 2021.

Global Change in Africa: Role of Space Observations (Remote Workshop | 11-15 January 2021)

The objective of the workshop is to investigate the benefit of using Earth Observation data to monitor and understand global environmental changes due to natural phenomena and anthropogenic forcing factors over the African continent, and highlight a number of associated applications of high societal relevance. The main topics addressed concern water resource; land use & land cover change, and implications for agriculture and deforestation; exploitation of mineral resources and environmental impacts; floods, droughts and desertification; coastal zones changes. The workshop will offer an opportunity to discuss with scientists from different horizons on the role of space-based observations for monitoring and understanding global changes in Africa, and investigate how this knowledge can be communicated to stakeholders to mitigate associated societal impacts. A large variety of remote sensing data can indeed help addressing these topics, e.g., multi-mission satellite altimetry, including the SWOT mission to be launched in 2021, SMOS, GRACE, radar and optical imagery from the Copernicus Sentinel missions, future missions of the Earth Explorer program of ESA, as well as Earth Observation missions from other space agencies worldwide.

Workshop Webpage >>

“The Sun from SOHO, and First Glimpses of Parker Solar Probe and Solar Orbiter“ with Daniel Müller (Solar Orbiter Project Scientist, ESA – ESTEC, The Netherlands)

SOHO, the Solar and Heliospheric Observatory, is a cooperative project of ESA and NASA to study the Sun, from its deep core to the outer corona, the solar wind, and energetic particles. Together with Cluster it forms the Solar-Terrestrial Science Programme (STSP), the first cornerstone of ESA’s long-term science program “Horizon 2000.” SOHO was launched on 2 December 1995 and inserted into a halo orbit around the L1 Lagrangian point in February 1996. The twelve instruments on SOHO have provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind and its interaction with the interstellar medium. SOHO’s findings have been documented in over 5900 scientific publications in the refereed literature, authored by more than 4000 scientists worldwide. SOHO provided the first images of structures and flows below the Sun’s surface and of activity on the far side of the Sun. It discovered sunquakes and has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsurface zonal and meridional flows, sub-convection zone mixing, and very slow polar rotation. It provided evidence for upward transfer of magnetic energy from the surface to the corona through a “magnetic carpet” and revealed an extremely dynamic solar atmosphere where plasma flows play an important role. It discovered new dynamic phenomena such as coronal waves, measured the acceleration profiles of the slow and fast solar wind, and identified the source regions and acceleration mechanisms of the latter. It revolutionized our understanding of solar-terrestrial relations and dramatically boosted space weather forecasting capabilities by providing, in a near-continuous stream, a comprehensive suite of images covering the dynamic atmosphere and extended corona. SOHO observed and characterized over 40,000 coronal mass ejections and, as a byproduct, became the most prolific discoverer of comets in astronomical history, with over 4000 comets found in SOHO observations, most of them by citizen scientists accessing SOHO real-time data via the Internet.

Control of the spacecraft was lost in June 1998 due to an unfortunate series of events during a spacecraft maneuver, but restored three months later in a dramatic recovery operation. Miraculously, all twelve instruments were still usable, most with no ill effects, despite the enormous temperatures they were exposed to during the time contact with SOHO was lost. Despite subsequent failures of all three gyroscopes (the last in December 1998), new gyroless control software installed by February 1999 allowed the spacecraft to return to full scientific operations. This made SOHO the first three-axis stabilized spacecraft operated without gyroscopes.

While SOHO is still operating today with 7 of its 12 instruments at almost full capability, two new solar missions have joined it recently. In 2018 the Parker Solar Probe was launched by NASA and already has approached the Sun closer than any spacecraft before. In February 2020 ESA launched its Solar Orbiter that will approach the Sun to as close as 0.28 AU and will use a series of Venus fly-bys to work its way to higher and higher latitudes, thus obtaining an unprecedented view onto the solar polar regions. The future game changers are underway, but they stand on the shoulders of a giant – SOHO.

Dr. Daniel Müller holds a Ph.D. in Physics from the Albert-Ludwigs-Universität Freiburg, Germany. After a Marie Curie Fellowship at the University of Oslo, Norway, he joined ESA’s SOHO team at NASA’s Goddard Space Flight Center, where he became Deputy Project Scientist of SOHO. In 2010, he moved to ESTEC to start working on Solar Orbiter, and has been serving as the mission’s Project Scientist since 2012. In addition to his scientific and project management work, he has a strong interest in high-performance scientific data visualization. In particular, he is coordinating the development of the open-source Helioviewer software and is the ESA Lead of the ESA/NASA Helioviewer Project.

This seminar was recorded on October 1, 2020

“Juno: Revealing the Mysteries of Jupiter” with Ravit Helled (University of Zurich, Switzerland)

Juno was launched in August 2011 to arrive at Jupiter almost five years later. Juno is the first Jupiter mission on a polar orbit. It is a NASA New Frontiers mission and its goals are to understand the origin and the evolution of the planet, to study Jupiter’s interior structure, in particular look for evidence for a heavy-element core and determining its bulk composition, map the gravity and magnetic fields of the planet and map the magnetosphere, measure water and ammonia in the planet’s deep atmosphere, and observe auroras. The mission is ongoing and scheduled to end by having Juno deorbit and dive into Jupiter’s atmosphere in July next year where the spacecraft would be destroyed. Juno’s orbit has a large eccentricity and thus the mission is particularly suited to explore the planet’s magnetosphere and gravity field. Juno is the first mission to Jupiter that relies solely on solar energy thanks to its orbit. The orbit is also well suited to deal with the strong radiation level around the planet.

The question of heavy-element cores in giant planets is one of long-standing interest in planetary science due to its direct connection to planet formation theory. Before the Juno mission, some models of the interior structure allowed cores of masses of several times the Earth’s mass (or even larger), while other models concluded that a core is not necessary to explain the planet’s gravity field features. Juno gravity data imply that Jupiter’s interior is inhomogeneous in composition, and that it is likely to have a “fuzzy” core.

Another question of long-standing interest is the origin of Jupiter’s magnetic field. It is undisputed that a dynamo is at work – in some way similar to the dynamo that generates the Earth’s magnetic field in its core. But the dynamo is not located in Jupiter’s core but at depths where hydrogen becomes metallic and behaves like a metal. It is also still unknown how the dynamo is powered. Accurately mapping Jupiter’s magnetic field helps to understand the dynamo mechanism and can also be used to further constrain the internal structure.

The Juno spacecraft carries a plaque remembering Galileo Galilei and three mini Lego figures (but made of aluminum rather than plastic because of the more challenging space environment) representing Galileo and the roman gods Jupiter and Juno.

Prof. Ravit Helled is professor at the Center for Theoretical Astrophysics and Cosmology of the Institute for Computational Science at the University of Zurich. She is a member of the Juno science team and a highly cited and respected expert for the interior structure of giant planets and their formation in the solar system and beyond.

This Seminar was recorded on September 10, 2020

New selected International Teams in Space and Earth Sciences 2020

Thirty-two International Teams have been selected by the ISSI Science Committee for implementation from the proposals received in response to the 2020 call. 

As one of ISSI’s and ISSI-BJ’s tools, International Teams of up to 15 scientists address specific self-defined problems in the Space and Earth Sciences, analyzing data and comparing these with models and theories. The teams  work together in an efficient and flexible format with typically 2-3 one-week meetings over two years. The results of the studies are published in the peer-reviewed literature.  

New International Teams 2020 >>

A word from the ISSI executive Director

Dear friends of ISSI,
Dear visitors of our web page,

The ISSI web page has been renovated recently thanks to Andrea Fischer and Saliba Saliba. ISSI is proud to present itself to the interested reader with a fresher look but keeping the organization of the website clearly structured and familiar so that interested users can find what they need easily and quickly.

I hope you and your loved ones are safe in this time of crisis! As many others, ISSI and its activities have been hit by the pandemic, but fortunately, no staff member has become ill. We have turned to teleworking as of March 17th and will remain so at least until the end of the eastern recess. But the ISSI office can be reached by phone and mail will be checked daily thanks to the presence of at least one ISSI staff on duty. The easiest way to reach us these days, though, is by email.

ISSI teams and workshops up to mid-May have been postponed. We will be watching the situation and adjust as it will evolve. Decisions about postponements have and will be taken together with the team leaders and the conveners at least six weeks prior to the scheduled event. As of today, there are no postponements of decisions on proposals and applications submitted to ISSI.

We all hope that the damage to the ISSI program can be kept to a minimum; we will resume as soon as the situation and the authorities will allow. ISSI will step-up its activities after the crisis to allow postponed meetings to occur as soon as possible.

In the meantime, our thoughts and sympathies are with those all over the world hit by COVID 19!

Stay safe and hope to meet you all in person at ISSI sometime soon!

Tilman Spohn

ISSI executive Director