Space Climate: Radiation, Particles & Response (WG6)

Solar Working Group 6 is an interdisciplinary group that is critical to the HAO mission “to understand the impact of solar variability on the Earth’s atmosphere across temporal scales," through the study and understanding of drivers and responses of the coupled Sun-Earth system, and in particular, the impact of solar variability on the terrestrial and space climate and its interaction with anthropogenic change from monthly to decadal and longer time-scales.

Scientific Highlights - 2018

The main scientific achievements during FY18 are described below. They include: modeling of the quasi periodic 1- to 2-year bursts of solar activity, starting the organization of a new solar minimum campaign, constructing an irradiance scenarios for a Grand Solar Minimum using MHD radiative codes and running corresponding atmospheric simulations, and using WACCM-X for climate change studies.

Solar Modeling - Seasons of the Sun (Mausumi Dikpati)

MHD-SWT is a non-linear MHD shallow water model of the solar tachocline. Quasi-periodic oscillations with periods of 2–20 months can be generated by the exchange of energy among differential rotation, magnetic field, and Rossby waves. Spot-producing "bulges" in the tachocline form when Rossby wave energy grows to its maximum and produce enhanced bursts of activity, called the seasons of the Sun. The periodicity decreases with the increase of the field strength and also with the increase in the effective gravity of the tachocline, but decreases with the migration of the toroidal magnetic band to lower and lower latitudes.

Two perspective snapshots of top-surface (color-shade) of a tachocline fluid shell, viewed respectively along longitude (left panel) and latitude (right panel), during its MHD evolution; red/orange represents swelling of the fluid and blue/sky-blue the depression. Yellowish-green represents neutral thickness. The shallow-water tachocline model has a rigid bottom and deformable top; vertical extent denotes the tachocline thickness (20 times enlarged). Portions of the toroidal magnetic bands (two white tubes one each in the North and South hemispheres) that coincide with swelled fluid are shown encircled by black ellipses—these portions start entering the convection zone, and hence are more likely to buoyantly erupt at the surface.

Solar Minimum Campaign (Sarah Gibson and Giuliana de Toma)

The international Whole Sun Month (WSM; 1996) and Whole Heliosphere Interval (WHI; 2008) were coordinated observing and modeling efforts to characterize the three-dimensional, interconnected solar-heliospheric system, down to the Earth's space environment and upper atmosphere, during quiet times. These campaigns were held during a selected Carrington rotation(s) to better coordinate observations and to focus modeling efforts.

A third solar minimum campaign is planned for Carrington rotation 2019 (June 29-July 26, 2019): the Whole Heliosphere and Planetary Interactions (WHPI). This time interval was chosen because is expected to coincide with the minimum of solar cycle 24 and overlaps with the July 2, 2019, total solar eclipse, which will be a well-observed and modeled time period. If the minimum at the end of solar cycle 24 will be an extended minimum, similar to the one at the end of solar cycle 23, we will select a second Carrington rotation in late 2019 or early 2020.

The previous campaigns have extended their discipline range with each iteration—from Sun-Solar wind (WSM) to Sun-Solar-wind-Geospace (WHI). It was thus appropriate that WHPI will broaden the emphasis further to include planetary magnetospheres and atmospheres, and in particular, planetary space weather. Continuation of this community effort is important because it allows comparative studies of solar minima and identification of long-term trends.

Grand Minimum Modeling (Matthias Rempel, Hanli Liu, Stan Solomon, Joe McInerney)

The aim of this NASA/LWS-funded project was to construct a realistic solar spectral irradiance scenario from physics-based models for extreme solar minimum conditions and to model the response through the entire atmosphere.

A radiation MHD model (MURaM code) was used to put physical constraints on possible irradiance scenarios. To this end we computed 4 cases: A non-magnetic (HD) reference, a current quiet sun reference (small-scale dynamo with ~67G unsigned flux at optical depth of unity—SSD67), a “low-activity” quiet sun (~ 44G unsigned flux—SSD44), as well as a “high-activity” quiet sun (~86 G unsigned flux—SSD86). Comparing these simulations we found a TSI sensitivity of about 0.17% per 10G of unsigned flux in the photosphere. This implies that a variation of the current day quiet sun would lead to a TSI change comparable to the current day solar Min to Max variability. On the one hand, this put strong additional indirect constraints on the current day quiet sun variability with the solar cycle, on the other hand, the question if the quiet sun is a stable reference over long time-scales or not is significant for long-term irradiance reconstructions. In addition to the TSI, we also computed SSI in the 200–10,000 nm spectral range using Kurucz/Castelli Opacity Distribution Functions (ODFs). We use the difference between the nominal current day QS and the “low-activity” QS to derive solar spectral irradiances for a hypothetical Grand Minimum. To elucidate the mechanisms in the sun-climate connection, both SSI spectra from HD and the low-activity QS setups have been used to drive WACCM (with coupled ocean) simulations (200 years each). Between 121nm (Lyman-alpha) and 200nm, the SSI is deduced from an empirical scaling relationship. The scaling of SSI relative to nominal solar minimum condition is presented in Figure 2. The corresponding TSI for these two setups are 1349.9 W/m2 and 1354.7 W/m2, 0.76% and 0.41% lower than the nominal solar minimum TSI value (1360.27 W/m2). We are currently analyzing the simulation results.

Relative difference between SSI under nominal solar minimum conditions (SSI_smin) and SSI calculated under non-magnetic convection conditions (SSI_HD) (red), and between SSI_min and SSI for reduced strength quiet sun conditions (SSI_QS).

WACCM-X Climate Simulation (Stan Solomon and the WACCM-X team)

We simulated anthropogenic global change through the entire atmosphere, including the thermosphere and ionosphere, using the Whole Atmosphere Community Climate Model - eXtended. The basic result was that even as the lower atmosphere gradually warms, the upper atmosphere rapidly cools. The simulations employed constant low solar activity conditions to remove the effects of variable solar and geomagnetic activity. Global mean annual mean temperature increased at a rate of +0.2 K/decade at the surface and +0.4 K/decade in the upper troposphere, but decreased by about -1 K/decade in the stratosphere-mesosphere, and -2.8 K/decade in the thermosphere. Near the mesopause, temperature decreases were small compared to the interannual variation, so trends in that region are uncertain. Results were similar to previous modeling confined to specific atmospheric levels, and compared favorably with available measurements. These simulations demonstrate the ability of a single comprehensive numerical model to characterize global change throughout the atmosphere.

Model calculations of the zonal mean annual mean changes in temperature under low solar activity conditions, as a function of latitude and pressure, for the 29-year simulation period between five-year ensembles (1972–1976 to 2001–2005). Negative contours, ranging from -9 to -1 K, with a 1 K interval, are shown in white; positive contours, at +1 and +2 K, are shown in red. The zero-change line is shown in black.


Dikpati, Mausumi, Paul S. Cally, Scott W.McIntosh, Eyal Heifetz, The Origin of the "Seasons" in Space Weather Nature, 7, id. 14750, 2018, doi: 10.1038/s41598-017-14957-x.

Dikpati, Mausumi, Scott W.McIntosh, Gregory Bothun, Paul S. Cally, Siddhartha S. Ghosh, Peter A. Gilman, Orkan M. Umurhan, Role of Interaction between Magnetic Rossby Waves and Tachocline Differential Rotation in Producing Solar Seasons, ApJ, 853, article id. 144, 2018, doi: 10.3847/1538-4357/aaa70d.

Dikpati, Mausumi, Bernadett Belucz, Peter A. Gilman, Scott W.McIntosh, Phase Speed of Magnetized Rossby Waves that Cause Solar Seasons, ApJ, 862, article id. 159, 2018, doi: 10.3847/1538-4357/aacefa.

Karak, Bydia Biani, Miesch Mark, Long-term variability of the solar cycle in the Babcock-Leighton dynamo framework, ApJ, 2018, 860, L26, doi: 10.3847/2041-8213/aaca97.

Liu, H.-L., et al., Development and validation of the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X v. 2.0), J. Adv. Mod. Earth Sys., 10, 381, doi:10.1002/2017MS001232, 2018.

Liu, J., et al., First results from the ionospheric extension of WACCM-X during the deep solar minimum year of 2008, J. Geophys. Res. Space Physics, 123, 1534, doi:10.1002/2017JA025010, 2018.

Solomon, S. C., H.-L. Liu, D. R. Marsh, J. M. McInerney, L. Qian, and F. M. Vitt, Whole atmosphere simulation of anthropogenic climate change, Geophys. Res. Lett., 45, 1567, doi:10.1002/2017GL076950, 2018.

Solomon, S. C., L. Qian, and A. J. Mannucci, Ionospheric electron content during solar cycle 23, J. Geophys. Res. Space Physics, 123, 5223, doi:10.1029/2018JA025464, 2018.

Upton, Lisa A., and David H. Hathaway, An Updated Solar Cycle 25 Prediction With AFT: The Modern Minimum GRL, 2018, doi: 10.1029/2018GL078387.

Webb, D., S. E. Gibson, I. M. Hewins, R. H. McFadden, B. A. Emery, A. Malanushenko, T. A. Kuchar, Evolution of the global solar magnetic field over 4 solar cycles: Use of the McIntosh Archive, Frontiers in Solar and Space Sciences, 31,, 2018.


Dikpati, M., Forecasting phase-by-phase progression of a solar cycle using data assimilation and machine learning, IAU Symposium, Jaipur, India, Feb. 2018.

Dikpati, M., Solar tsunami to give birth to new cycle’s sunspots by 2020, ISSI team meeting on “Rossby waves in astrophysics,” Bern, Switzerland, June 2018.

Dikpati, M., (D2.4-0015-18) On forecasting seasonal-to-decadal-to-millennial time-scale solar magnetic activity, COSPAR, 2018 42nd Assembly, Pasadena, CA, July 2018.

Liu, H.-L., S. C. Solomon, and the WACCM-X team, NCAR Whole Atmosphere Community Climate Model with thermosphere/ionosphere Extension(WACCM-X 2.0): Development and research, Triennial Earth-Sun Summit, Leesburg, Virginia, May 2018.

McIntosh, S. W., Does the Sun Have A Polar Dynamo? AGU Fall Meeting 2017, abstract #SH11C-02.

McIntosh, S. W., R. J. Leamon, Y. Fan, M. Rempel, M. Dikpati, Terminator 2020: Get Ready for the "Event" of The Next Decade, AGU Fall Meeting 2017, abstract #SH22B-06.

Qian, L., et al., Thermosphere Mass Density Variations From Solar Flare to Solar Cycle Time Scales, 42nd COSPAR Assembly, Pasadena, California, July 2018.

Solomon, S. C., et al., Whole Atmosphere Simulation of Anthropogenic Climate Change, Climate Variability and Change Working Group Meeting, Boulder, Colorado, January 2018.

Solomon, S. C., H.-L. Liu, D. R. Marsh, J. McInerney, L. Qian, and F. Vitt, Whole Atmosphere Simulation of Anthropogenic Climate Change, TREND-2018 Workshop, Hefei, China, 2018 (invited).

Solomon, S. C., Atmospheric Modeling using Solar Irradiance Estimates, Triennial Earth-Sun Summit, Leesburg, Virginia, 2018 (invited).

Solomon, S. C., H.-L. Liu, D. R. Marsh, J. M. McInerney, and L. Qian, Simulation of Climate Change from the Surface to the Exobase, CEDAR Workshop, Santa Fe, New Mexico, 2018 (invited).

Wang, W. and L. Qian, Trend in Ionospheric Temperatures, 10th Workshop on Long-tern Changes and Trends in the Atmosphere, Hefei, Anhui, China, May 2018.