Stratospheric aftermath of the 2010 Storm on Saturn as observed by the TEXES instrument. I. Temperature structure

We present a retrieval analysis of TEXES (Texas Echelon Cross Echelle Spectrograph (Lacy et al., 2002)) spectra of Jupiter's high latitudes obtained on NASA's Infrared Telescope Facility on December 10-11th 2014. The vertical temperature profile and vertical profiles of C 2 H 2 , C 2 H 4 and C 2 H 6 were retrieved at both high-northern and high-southern latitudes and results were compared in 'quiescent' regions and regions known to be affected by Jupiter's aurora in order to highlight how auroral processes modify the thermal structure and hydrocarbon chemistry of the stratosphere. In qualitative agreement with Sinclair et al. (2017a), we find temperatures in auroral regions to be elevated with respect to quiescent regions at two discrete pressures levels at approximately 1 mbar and 0.01 mbar. For example, in comparing retrieved temperatures at 70• N, 60• W (a representative quiescent region) and 70• N, 180• W (centred on the northern auroral oval), temperatures increase by 19.0 ± 4.2 K at 0.98 mbar, 20.8 ± 3.9 K at 0.01 mbar but only by 8.3 ± 4.9 K at the intermediate level of 0.1 mbar. We conclude that elevated temperatures at 0.01 mbar result from heating by joule resistance of the atmosphere and the energy imparted by electron and ion precipitation. However, temperatures at 1 mbar are considered to result either from heating by shortwave radiation of aurorally-produced haze particulates or precipitation of higher energy population of charged particles. Our former conclusion would be consistent with results of auroral-chemistry models, that predict the highest number densities of aurorally-produced haze particles at this pressure level (Wong et al., 2000(Wong et al., , 2003. C 2 H 2 and C 2 H 4 exhibit enrichments but C 2 H 6 remains constant within uncertainty when comparing retrieved concentrations in the northern auroral region with quiescent longitudes in the same latitude band. At 1 mbar, C 2 H 2 increases from 278.4 ± 40.3 ppbv at 70• N, 60• W to 564.4 ± 72.0 ppbv at 70• N, 180• W and at 0.01 mbar, over the same longitude range at 70• N, C 2 H 4 increases from 0.669 ± 0.129 ppmv to 6.509 ± 0.811 ppmv. However, we note that non-LTE (local thermodynamic equilibrium) emission may affect the cores of the strongest C 2 H 2 and C 2 H 4 lines on the northern auroral region, which may be a possible source of error in our derived concentrations. We retrieved concentrations of C 2 H 6 at 1 mbar of 9.03 ± 0.98 ppmv at 70• N, 60• W and 7.66 ± 0.70 ppmv at 70• N, 180• W. Thus, C 2 H 6 's concentration appears constant (within uncertainty) as a function of longitude at 70• N.

Section: Radiance Differencessupporting

confidence: 55%

Jupiter’s auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014

Sinclair

Orton

Greathouse

et al. 2018

“…Sudden stratospheric warming on Earth's high and mid-latitude regions are associated with downward wind propagation anomalies of the Quasi-Biennial Oscillation (Lu et al, 2008). Is it possible that the extremely warm stratospheric disturbance in the aftermath of the Great White Storm of 2010-2011 (Fletcher et al, 2011(Fletcher et al, , 2012Fouchet et al, 2016) is due to a disruption of the downward propagation of the equatorial oscillation on Saturn? Conversely, Cassini observations showed that the occurrence of this huge storm disturbed the equatorial oscillations (Fletcher et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Global climate modeling of Saturn’s atmosphere. Part IV: Stratospheric equatorial oscillation

Bardet

Spiga

Guerlet

et al. 2021

Self Cite

The Composite InfraRed Spectrometer (CIRS) on board Cassini revealed an equatorial oscillation of stratospheric temperature, reminiscent of the Earth's Quasi-Biennial Oscillation (QBO), as well as anomalously high temperatures under Saturn's rings. To better understand these predominant features of Saturn's atmospheric circulation in the stratosphere, we have extended to the upper stratosphere the DYNAMICO-Saturn global climate model (GCM), already used in a previous publication to study the tropospheric dynamics, jets formation and planetary-scale waves activity. Firstly, we study the higher model top impact on the tropospheric zonal jets and kinetic energy distribution. Raising the model top prevents energy and enstrophy accumulation at tropopause levels. The reference GCM simulation with 1/2 • latitude/longitude resolution and a raised model top exhibits a QBO-like oscillation produced by resolved planetary-scale waves. However, the period is more irregular and the downward propagation faster than observations. Furthermore, compared to the CIRS temperature retrievals, the modeled QBO-like oscillation underestimates by half both the amplitude of temperature anomalies at the equator and the vertical characteristic length of this equatorial oscillation. This QBO-like oscillation is mainly driven by westward-propagating waves; a significant lack of eastward waveforcing explains a fluctuating eastward phase of the QBO-like oscillation. We also show that the seasonal cycle of Saturn is a key parameter of the establishment and the regularity of the equatorial oscillation. At 20 • N and 20 • S latitudes, the DYNAMICO-Saturn GCM exhibits several strong seasonal eastward jets, alternatively in the northern and southern hemisphere. These jets are correlated with the rings' shadowing. Using a GCM simulation without rings' shadowing, we show its impact on Saturn's stratospheric dynamics. Both residualmean circulation and eddy forcing are impacted by rings' shadowing. In particular, the QBO-like oscillation is weakened by an increased drag caused by those two changes associated with rings' shadowing.

“…In essence, α represents the relative weights to give to the measurements and to the a priori at each step of the iteration process. Following Fouchet et al (2016), we found that an optimum choice of α (in terms of stability and rapidity of the algorithm) was achieved by equalling the traces of the αKSK T and E matrices. Iterations were performed until convergence -defined by the constancy of the fit quality (rms between observations and models) within 1 % from an iteration to the next one -was reached.…”

Section: Methodsmentioning

confidence: 99%

Detection of CO and HCN in Pluto’s atmosphere with ALMA

Lellouch

Gurwell

Butler

et al. 2017

109

Observations of the Pluto-Charon system, acquired with the ALMA interferometer on June 12-13, 2015, have led to the detection of the CO(3-2) and HCN(4-3) rotational transitions from Pluto (including the hyperfine structure of HCN), providing a strong confirmation of the presence of CO, and the first observation of HCN in Pluto's atmosphere. The CO and HCN lines probe Pluto's atmosphere up to ∼450 km and ∼900 km altitude, respectively, with a large contribution due to limb emission. The CO detection yields (i) a much improved determination of the CO mole fraction, as 515±40 ppm for a 12 µbar surface pressure (ii) strong constraints on Pluto's mean atmospheric dayside temperature profile over ∼50-400 km, with clear evidence for a well-marked temperature decrease (i.e., mesosphere) above the 30-50 km stratopause and a best-determined temperature of 70±2 K at 300 km, somewhat lower than previously estimated from stellar occultations (81±6 K), and in agreement with recent inferences from New Horizons / Alice solar occultation data. The HCN line shape implies a high abundance of this species in the upper atmosphere, with a mole fraction > 1.5×10 −5 above 450 km and a value of 4×10 −5 near 800 km. Assuming HCN at saturation, this would require a warm (>92 K) upper atmosphere layer; while this is not ruled out by the CO emission, it is inconsistent with the Alicemeasured CH 4 and N 2 line-of-sight column densities. Taken together, the large HCN abundance and the cold upper atmosphere imply supersaturation of HCN to a degree (7-8 orders of magnitude) hitherto unseen in planetary atmospheres, probably due to a lack of condensation nuclei above the haze region and the slow kinetics of condensation at the low pressure and temperature conditions of Pluto's upper atmosphere. HCN is also present in the bottom ∼100 km of the atmosphere, with a 10 −8 -10 −7 mole fraction; this implies either HCN saturation or undersaturation there, depending on the precise stratopause temperature. The HCN column is (1.6±0.4)×10 14 cm −2 , suggesting a surface-referred vertically-integrated net production rate of ∼2×10 7 cm −2 s −1 . Although HCN rotational line cooling affects Pluto's atmosphere heat budget, the amounts determined in this study are insufficient to explain the well-marked mesosphere and upper atmosphere's ∼70 K temperature, which if controlled by HCN cooling would require HCN mole fractions of (3-7)×10 −4 over 400-800 km. We finally report an upper limit on the HC 3 N column density (< 2×10 13 cm −2 ) and on the HC 15 N / HC 14 N ratio (< 1/125).