Near‐Earth Solar Wind Forecasting Using Corotation From L5: The Error Introduced By Heliographic Latitude Offset

Owens, M. J.; Riley, Pete; Lang, Matthew; Lockwood, Mike

doi:10.1029/2019sw002204

Cited by 20 publications

(33 citation statements)

References 41 publications

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“…30 gives the photospheric magnetic field configuration on the Sun using magnetic field extrapolations from GONG data marking open and closed field lines. With such inevitable differences in the latitude between the measuring spacecraft, rather large uncertainties in the 1 AU measured speed of a particular coronal hole are obtained (see Hofmeister et al 2018;Owens et al 2019). Recent studies suggest that solar wind forecasting based on persistence models may work best when using a combination of spacecraft located behind Earth (L5 position or STEREO data from time-varying spacecraft position) and empirical or numerical solar wind modeling (see e.g., Opitz et al 2010;Temmer et al 2018;Owens et al 2019;Bailey et al 2020).…”

Section: Background Solar Windmentioning

confidence: 99%

Space weather: the solar perspective

Temmer

2021

Living Rev Sol Phys

187

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The Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA’s Parker Solar Probe (launched in 2018) and ESA’s Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews article by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.

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Section: Background Solar Windmentioning

confidence: 99%

Space weather: the solar perspective

Temmer

2021

Living Rev Sol Phys

187

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“…Recently, we used magnetogram-constrained simulations of the solar wind to estimate the difference in solar wind speed encountered at Earth and the L5 position, 60°behind Earth in its orbit, owing entirely to the small time-varying difference in latitude (Owens et al, 2019a, hereafter "Paper 1"). While the latitudinal difference is small, varying from 0°to approximately 7°over the year, it can lead to sampling significantly different solar wind streams at the two locations, even under the perfectly steady-state approximation.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the latitudinal representivity of in situ solar wind observations

Owens

Lang

Riley

et al. 2020

J. Space Weather Space Clim.

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Advanced space-weather forecasting relies on the ability to accurately predict near-Earth solar wind conditions. For this purpose, physics-based, global numerical models of the solar wind are initialized with photospheric magnetic field and coronagraph observations, but no further observation constraints are imposed between the upper corona and Earth orbit. Data assimilation (DA) of the available in situ solar wind observations into the models could potentially provide additional constraints, improving solar wind reconstructions, and forecasts. However, in order to effectively combine the model and observations, it is necessary to quantify the error introduced by assuming point measurements are representative of the model state. In particular, the range of heliographic latitudes over which in situ solar wind speed measurements are representative is of primary importance, but particularly difficult to assess from observations alone. In this study we use 40+ years of observation-driven solar wind model results to assess two related properties: the latitudinal representivity error introduced by assuming the solar wind speed measured at a given latitude is the same as that at the heliographic equator, and the range of latitudes over which a solar wind measurement should influence the model state, referred to as the observational localisation. These values are quantified for future use in solar wind DA schemes as a function of solar cycle phase, measurement latitude, and error tolerance. In general, we find that in situ solar wind speed measurements near the ecliptic plane at solar minimum are extremely localised, being similar over only 1° or 2° of latitude. In the uniform polar fast wind above approximately 40° latitude at solar minimum, the latitudinal representivity error drops. At solar maximum, the increased variability of the solar wind speed at high latitudes means that the latitudinal representivity error increases at the poles, though becomes greater in the ecliptic, as long as moderate speed errors can be tolerated. The heliospheric magnetic field and solar wind density and temperature show very similar behaviour.

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“…L5 reaches a maximum |Δθ| of around 5° with Earth (at times close to the summer and winter solstices), meaning that the latitudinal variation can be largely disregarded. Owens et al (2019) showed that there is a time-of-year variation in the modeled impact of |Δθ| on MAE. This is not investigated here due to data limitations.…”

Section: Discussionmentioning

confidence: 99%

The Influence of Spacecraft Latitudinal Offset on the Accuracy of Corotation Forecasts

et al. 2021

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Knowledge of the ambient solar wind is important for accurate space-weather forecasting. A simple-but-effective method of forecasting near-Earth solar-wind speed is "corotation", wherein solar-wind structure is assumed to be fixed in the reference frame rotating with the Sun. Under this approximation, observations at a source spacecraft can be rotated to a target location, such as Earth. Forecast accuracy depends upon the rate of solar-wind evolution, longitudinal and latitudinal separation between the source and target, and latitudinal structure in the solar wind itself. The time-evolution rate and latitudinal structure of the solar wind are both strongly influenced by the solar cycle, though in opposing ways. A latitudinal separation (offset) between source and target spacecraft is typically present, introducing an error to corotation forecasts. In this study, we use observations from the STEREO and near-Earth spacecraft to quantify the latitudinal error. Aliasing between the solar cycle and STEREO orbits means that individual contributions to the forecast error are difficult to isolate. However, by considering an 18month interval near the end of solar minimum, we find that the latitudinal-offset contribution to corotation-forecast error cannot be directly detected for offsets < 6 • , but is increasingly important as offsets increase. This result can be used to improve solarwind data assimilation, allowing representivity errors in solar-wind observations to be correctly specified. Furthermore, as the maximum latitudinal offset between L5 and Earth is ≈ 5 • , corotation forecasts from a future L5 spacecraft should not be greatly affected by latitudinal offset.

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Near‐Earth Solar Wind Forecasting Using Corotation From L5: The Error Introduced By Heliographic Latitude Offset

Cited by 20 publications

References 41 publications

Space weather: the solar perspective

Space weather: the solar perspective

Quantifying the latitudinal representivity of in situ solar wind observations

The Influence of Spacecraft Latitudinal Offset on the Accuracy of Corotation Forecasts

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