Impact of geomagnetic excursions on atmospheric chemistry and dynamics

Abstract

Abstract. Geomagnetic excursions, i.e. short periods in time with much weaker geomagnetic fields and substantial changes in the position of the geomagnetic pole, occurred repeatedly in the Earth's history, e.g. the Laschamp event about 41 kyr ago. Although the next such excursion is certain to come, little is known about the timing and possible consequences for the state of the atmosphere and the ecosystems. Here we use the global chemistry climate model SOCOL-MPIOM to simulate the effects of geomagnetic excursions on atmospheric ionization, chemistry and dynamics. Our simulations show significantly increased concentrations of nitrogen oxides (NO x ) in the entire stratosphere, especially over Antarctica (+15 %), due to enhanced ionization by galactic cosmic rays. Hydrogen oxides (HO x ) are also produced in greater amounts (up to +40 %) in the tropical and subtropical lower stratosphere, while their destruction by reactions with enhanced NO x prevails over the poles and in high altitudes (by −5 %). Stratospheric ozone concentrations decrease globally above 20 km by 1-2 % and at the northern hemispheric tropopause by up to 5 % owing to the accelerated NO x -induced destruction. A 5 % increase is found in the southern lower stratosphere and troposphere. In response to these changes in ozone and the concomitant changes in atmospheric heating rates, the Arctic vortex intensifies in boreal winter, while the Antarctic vortex weakens in austral winter and spring. Surface wind anomalies show significant intensification of the southern westerlies at their poleward edge during austral winter and a pronounced northward shift in spring. Major impacts on the global climate seem unlikely.

A global environmental crisis 42,000 years ago

“…In the Southern Hemisphere, decreasing stratospheric O 3 appears to be associated with small changes in the mid-latitude airflow (Fig. 3) and subtropical precipitation patterns (see supplementary material) (8). Because the significance is <10%, an ensemble of longer model runs is required to confirm this finding.…”

“…Studies of Greenland ice cores have failed to reveal marked impacts in high-latitude paleoclimate associated with Laschamps (5,6), and this observation has underpinned the current view that there is no relationship between geomagnetic reversals and climate or environmental changes. However, the markedly increased levels of solar and cosmic radiation reaching Earth's atmosphere because of the weakened geomagnetic field are likely to have increased atmospheric ionization and decreased stratospheric ozone levels, potentially generating regional climatic impacts, particularly in lower latitudes (7)(8)(9). In this regard, it is notable that many environmental records around the Pacific Basin appear to detail a major (and often sustained) change in behavior ~40 to 42 ka, including local glacial maxima in Australasia and the Andes (7,10), long-term shifts in atmospheric circulation patterns (11,12), and continent-wide aridification and megafaunal extinction in Australia (4,(13)(14)(15)(16).…”

A simple model for geomagnetic field excursions and inferences for palaeomagnetic observations

“…A greater understanding of the range of geomagnetic field behavior exhibited during excursions is essential to a fuller understanding of geodynamo processes and the applicability of excursions as global or regional stratigraphic markers (Merrill and McFadden, 2005). In addition, the strength of the geomagnetic field and its global morphology are important components in the interaction between the geomagnetic field, the palaeomagnetosphere and space climate (Constable and Korte, 2006;Vogt et al, 2007;Stadelmann et al, 2010), the production of cosmogenic radionuclides (e.g., Baumgartner et al, 1998;Wagner et al, 2000;McCracken, 2004;Muscheler et al, 2005) and may influence atmospheric chemistry and dynamics (Suter et al, 2014).…”

The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals

“…Certain ozone‐depleting agents (such as nitrogen oxides) are produced naturally by energetic particle precipitation from solar wind, particularly during solar proton events, and therefore, times of low geomagnetic field strength lead to higher ozone depletion (Randall et al, , ). Atmospheric modeling implies substantial increases in hydrogen and nitrogen oxide concentrations due to enhanced ionization by GCRs during the Laschamp excursion, with significant decrease in stratospheric ozone particularly at high latitudes (Suter et al, ). Modeling of ozone depletion during polarity reversals, based on a geomagnetic field intensity ~10% of the present value, leads to enhanced UVR flux at the Earth's surface, particularly at higher latitudes, that is 3‐5 times that resulting from the anthropogenic ozone hole (Glassmeier & Vogt, ; Winkler et al, ).…”