A new model of meteoric calcium in the mesosphere and lower thermosphere

Abstract

Abstract. Meteoric ablation produces layers of metal atoms in the mesosphere and lower thermosphere (MLT). It has been known for more than 30 years that the Ca atom layer is depleted by over 2 orders of magnitude compared with Na, despite these elements having essentially the same elemental abundance in chondritic meteorites. In contrast, the Ca + ion abundance 15 is depleted by less than a factor of 10. To explain these observations, a large data-base of neutral and ion-molecule reaction kinetics of Ca species, measured over the past decade, was incorporated into the Whole Atmosphere Community Climate Model (WACCM). A new meteoric input function for Ca and Na, derived using a chemical ablation model that has been tested experimentally with a Meteoric Ablation Simulator, shows that Ca experiences significant differential ablation, by almost 1 order of magnitude, with respect to Na. WACCM-Ca simulates the seasonal Ca layer satisfactorily when compared with lidar 20 observations, but tends to overestimate Ca + measurements made by rocket mass spectrometry and lidar. A key finding is that CaOH and CaCO3 are very stable reservoir species because they are involved in essentially closed reaction cycles with O2 andO. This has been demonstrated experimentally for CaOH, and in this study for CaCO3 using electronic structure and statistical rate theory. Most of the neutral Ca is therefore locked in these reservoirs, enabling rapid loss through polymerization into meteoric smoke particles and explaining the extreme depletion of Ca. 25

A Comparison of the Midlatitude Nickel and Sodium Layers in the Mesosphere: Observations and Modeling

“…It is worth noting that the seasonal variation of Ni, Na, and Fe is quite different from the semi‐annual seasonal variations of the Ca and K layers at mid‐latitudes, which exhibit maxima in summer and winter, and minima in spring and autumn. The column abundance of the Ca layer measured at midlatitudes (Kühlungsborn, 54°N) is 2.1 × 10 7 cm −2 (Plane et al., 2018), which is smaller than the Ni column abundance by a factor of 14.8, despite the CI abundance of Ca being 1.2 times larger than that of Ni (Asplund et al., 2009). This reflects the very refractory nature of Ca in a silicate melt (Carrillo‐Sánchez et al., 2020).…”

“…WACCM6 extends vertically from the Earth's surface to the lower thermosphere at ∼140 km. For this study, we used a specific dynamics (SD) version of WACCM6 (Plane et al., 2018), nudged with NASA's ModernEra Retrospective Analysis for Research and Applications (MERRA2) (Molod et al., 2015). The model has a horizontal resolution of 1.9° latitude × 2.5° longitude and 88 vertical model levels (height resolution ∼3.5 km in the MLT).…”

First Lidar Profiling of Meteoric Ca+ Ion Transport From ∼80 to 300 km in the Midlatitude Nighttime Ionosphere

“…The continuity equation given in the TIMt modeling study by Chu and Yu (2017) can be utilized to study metallic ions (Mt + ) including Ca + : $$$\frac{\partial {N}_{M{t}^{+}}}{\partial t}=S+Q-L-\nabla \cdot \left({N}_{M{t}^{+}}{\overrightarrow{V}}_{M{t}^{+}}\right)$$$ where S represents the external sources from direct meteoric deposition of Mt + via collisional ionization during meteor ablation, Q is the chemical production of Mt + via charge transfer with NO + and O 2 + ions, photoionization, and dissociative release, and L is the chemical loss of Mt + via direct recombination with electrons and reactions with O 3 , N 2 , CO 2 , and H 2 O molecules (Plane et al., 2018). The last term in is the vertical and horizontal transport of Mt + ions (Chu & Yu, 2017).…”

Meteor‐Ablated Aluminum in the Mesosphere‐Lower Thermosphere

“…Reaction R36 in Table 1 is a set of polymerization reactions which account for the permanent loss of the significant neutral Al‐containing molecules AlO, AlOH and, to a lesser extent, Al(OH) 2 (see Section 4) to form meteoric smoke particles (MSPs). We have used this type of reaction in previous models of the Na (Marsh et al., 2013), K (Plane et al., 2014), Fe (Feng et al., 2013), Mg (Langowski et al., 2015), SiO (Plane et al., 2016), Ca (Plane et al., 2018), and Ni (Daly et al., 2020) layers. In this case, k 36 is set to 5.8 × 10 −8 cm 3 s −1 , which is ∼80 times larger than a typical dipole‐dipole capture rate for these metallic molecules.…”

“…WACCM6 has a vertical extension from the Earth’s surface to the lower thermosphere at ∼140 km. Although the model can be nudged by a reanalysis data set, as we have done with other meteoric metals where measurements are available for comparison (Plane et al., 2015, 2018), for the present study we used a free‐running version of WACCM6 with a reduced tropospheric chemical mechanism. The model has a horizontal resolution of 1.9° latitude × 2.5° longitude, and 70 vertical model layers (∼3 km vertical resolution in the MLT region).…”