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DOE OSTI2020

Materials Data on YbMoO5 by Materials Project

YbMoO5 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Yb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Yb–O bond distances ranging from 2.29–2.56 Å. Mo is bonded in a distorted tetrahedral geometry to five O atoms. There are a spread of Mo–O bond distances ranging from 1.76–2.38 Å. There are five inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to two equivalent Yb, one Mo, and one O atom. The O–O bond length is 2.00 Å. In the second O site, O is bonded in a distorted trigonal planar geometry to two equivalent Yb and one Mo atom. In the third O site, O is bonded in a distorted trigonal planar geometry to two equivalent Yb and one Mo atom. In the fourth O site, O is bonded in a linear geometry to one Yb and one Mo atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Yb and one Mo atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaBe4Mo by Materials Project

Be4TaMo crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are three inequivalent Be sites. In the first Be site, Be is bonded to six equivalent Be and six equivalent Mo atoms to form BeBe6Mo6 cuboctahedra that share corners with twelve equivalent BeTa3Be6Mo3 cuboctahedra, edges with six equivalent BeBe6Mo6 cuboctahedra, and faces with twenty BeTa6Be6 cuboctahedra. All Be–Be bond lengths are 2.27 Å. All Be–Mo bond lengths are 2.66 Å. In the second Be site, Be is bonded to six equivalent Be and six equivalent Ta atoms to form BeTa6Be6 cuboctahedra that share corners with twelve equivalent BeTa3Be6Mo3 cuboctahedra, edges with six equivalent BeTa6Be6 cuboctahedra, and faces with twenty BeBe6Mo6 cuboctahedra. All Be–Be bond lengths are 2.31 Å. All Be–Ta bond lengths are 2.68 Å. In the third Be site, Be is bonded to six Be, three equivalent Ta, and three equivalent Mo atoms to form BeTa3Be6Mo3 cuboctahedra that share corners with eighteen BeBe6Mo6 cuboctahedra, edges with six equivalent BeTa3Be6Mo3 cuboctahedra, and faces with eighteen BeBe6Mo6 cuboctahedra. There are two shorter (2.22 Å) and two longer (2.33 Å) Be–Be bond lengths. There are two shorter (2.64 Å) and one longer (2.72 Å) Be–Ta bond lengths. There are one shorter (2.61 Å) and two longer (2.66 Å) Be–Mo bond lengths. Ta is bonded in a 1-coordinate geometry to twelve Be, three equivalent Ta, and one Mo atom. All Ta–Ta bond lengths are 2.83 Å. The Ta–Mo bond length is 2.72 Å. Mo is bonded in a 10-coordinate geometry to twelve Be and one Ta atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3AlSnMo3 by Materials Project

Nb3Mo3AlSn crystallizes in the trigonal R3 space group. The structure is three-dimensional. Nb is bonded in a 2-coordinate geometry to two equivalent Mo, two equivalent Al, and two equivalent Sn atoms. There are one shorter (2.54 Å) and one longer (2.62 Å) Nb–Mo bond lengths. There are one shorter (2.86 Å) and one longer (2.89 Å) Nb–Al bond lengths. There are one shorter (2.88 Å) and one longer (2.91 Å) Nb–Sn bond lengths. Mo is bonded in a 2-coordinate geometry to two equivalent Nb, two equivalent Al, and two equivalent Sn atoms. There are one shorter (2.86 Å) and one longer (2.88 Å) Mo–Al bond lengths. Both Mo–Sn bond lengths are 2.89 Å. Al is bonded to six equivalent Nb and six equivalent Mo atoms to form AlNb6Mo6 cuboctahedra that share edges with six equivalent AlNb6Mo6 cuboctahedra and faces with eight equivalent SnNb6Mo6 cuboctahedra. Sn is bonded to six equivalent Nb and six equivalent Mo atoms to form SnNb6Mo6 cuboctahedra that share edges with six equivalent SnNb6Mo6 cuboctahedra and faces with eight equivalent AlNb6Mo6 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg16Al12Mo by Materials Project

Mg16MoAl12 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are five inequivalent Mg sites. In the first Mg site, Mg is bonded in a 12-coordinate geometry to seven Mg and five Al atoms. There are a spread of Mg–Mg bond distances ranging from 2.96–3.11 Å. There are a spread of Mg–Al bond distances ranging from 2.98–3.13 Å. In the second Mg site, Mg is bonded in a 12-coordinate geometry to six Mg, one Mo, and five Al atoms. There are two shorter (3.17 Å) and two longer (3.30 Å) Mg–Mg bond lengths. The Mg–Mo bond length is 3.03 Å. There are a spread of Mg–Al bond distances ranging from 2.95–3.17 Å. In the third Mg site, Mg is bonded in a distorted single-bond geometry to three equivalent Mg, one Mo, and twelve Al atoms. All Mg–Mg bond lengths are 3.14 Å. The Mg–Mo bond length is 2.79 Å. There are a spread of Mg–Al bond distances ranging from 3.13–3.20 Å. In the fourth Mg site, Mg is bonded in a 10-coordinate geometry to four Mg and six Al atoms. Both Mg–Mg bond lengths are 3.03 Å. There are a spread of Mg–Al bond distances ranging from 3.09–3.17 Å. In the fifth Mg site, Mg is bonded in a 12-coordinate geometry to five Mg and five Al atoms. There are a spread of Mg–Al bond distances ranging from 2.87–3.13 Å. Mo is bonded in a 10-coordinate geometry to four Mg and six equivalent Al atoms. All Mo–Al bond lengths are 2.81 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 11-coordinate geometry to eight Mg and three Al atoms. There are one shorter (2.68 Å) and two longer (2.82 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a distorted q6 geometry to eight Mg and three Al atoms. Both Al–Al bond lengths are 2.76 Å. In the third Al site, Al is bonded in a 12-coordinate geometry to seven Mg, one Mo, and three Al atoms. There are one shorter (2.62 Å) and one longer (2.64 Å) Al–Al bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U7Mo by Materials Project

U7Mo crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. there are five inequivalent U sites. In the first U site, U is bonded in a 10-coordinate geometry to six U and two equivalent Mo atoms. There are four shorter (2.98 Å) and two longer (2.99 Å) U–U bond lengths. Both U–Mo bond lengths are 2.96 Å. In the second U site, U is bonded in a 4-coordinate geometry to four equivalent U and four equivalent Mo atoms. All U–U bond lengths are 2.86 Å. All U–Mo bond lengths are 2.98 Å. In the third U site, U is bonded in a distorted q6 geometry to ten U atoms. There are a spread of U–U bond distances ranging from 2.98–3.08 Å. In the fourth U site, U is bonded to ten U and two equivalent Mo atoms to form a mixture of distorted edge, face, and corner-sharing UU10Mo2 cuboctahedra. Both U–U bond lengths are 3.00 Å. Both U–Mo bond lengths are 3.55 Å. In the fifth U site, U is bonded in a distorted q6 geometry to ten U atoms. Both U–U bond lengths are 3.00 Å. Mo is bonded in a distorted body-centered cubic geometry to twelve U atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zn9Ga3Mo2 by Materials Project

Mo2Zn9Ga3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Mo is bonded to nine Zn and three equivalent Ga atoms to form corner-sharing MoZn9Ga3 cuboctahedra. There are six shorter (2.75 Å) and three longer (2.79 Å) Mo–Zn bond lengths. All Mo–Ga bond lengths are 2.65 Å. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded in a 10-coordinate geometry to two equivalent Mo and eight Zn atoms. There are four shorter (2.70 Å) and four longer (2.75 Å) Zn–Zn bond lengths. In the second Zn site, Zn is bonded in a 10-coordinate geometry to two equivalent Mo, six Zn, and two equivalent Ga atoms. There are two shorter (2.63 Å) and two longer (2.86 Å) Zn–Zn bond lengths. Both Zn–Ga bond lengths are 2.77 Å. In the third Zn site, Zn is bonded in a 10-coordinate geometry to two equivalent Mo, six Zn, and two equivalent Ga atoms. There are a spread of Zn–Zn bond distances ranging from 2.63–2.86 Å. Both Zn–Ga bond lengths are 2.77 Å. Ga is bonded in a 10-coordinate geometry to two equivalent Mo, four equivalent Zn, and four equivalent Ga atoms. All Ga–Ga bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeNiMo3N by Materials Project

Mo3FeNiN crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Mo is bonded in a distorted bent 150 degrees geometry to three equivalent Fe, three equivalent Ni, and two equivalent N atoms. There are a spread of Mo–Fe bond distances ranging from 2.67–2.86 Å. There are a spread of Mo–Ni bond distances ranging from 2.76–2.79 Å. Both Mo–N bond lengths are 2.09 Å. Fe is bonded to nine equivalent Mo and three equivalent Ni atoms to form FeNi3Mo9 cuboctahedra that share corners with six equivalent FeNi3Mo9 cuboctahedra, corners with nine equivalent NiFe3Mo9 cuboctahedra, edges with three equivalent NMo6 octahedra, faces with four equivalent NiFe3Mo9 cuboctahedra, faces with six equivalent FeNi3Mo9 cuboctahedra, and faces with four equivalent NMo6 octahedra. All Fe–Ni bond lengths are 2.47 Å. Ni is bonded to nine equivalent Mo and three equivalent Fe atoms to form NiFe3Mo9 cuboctahedra that share corners with six equivalent NiFe3Mo9 cuboctahedra, corners with nine equivalent FeNi3Mo9 cuboctahedra, edges with three equivalent NMo6 octahedra, faces with four equivalent FeNi3Mo9 cuboctahedra, faces with six equivalent NiFe3Mo9 cuboctahedra, and faces with four equivalent NMo6 octahedra. N is bonded to six equivalent Mo atoms to form distorted NMo6 octahedra that share corners with six equivalent NMo6 octahedra, edges with three equivalent FeNi3Mo9 cuboctahedra, edges with three equivalent NiFe3Mo9 cuboctahedra, faces with four equivalent FeNi3Mo9 cuboctahedra, and faces with four equivalent NiFe3Mo9 cuboctahedra. The corner-sharing octahedral tilt angles are 26°.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Stepwise impregnation of bimetallic catalysts for carbon nanotube synthesis

Supported bimetallic catalysts are widely used for carbon nanotube (CNT) synthesis, yet the effects of impregnation procedure remain underexplored. Here, we investigated how the sequence of metal impregnation affects CNT synthesis. We prepared cobalt-molybdenum (Co-Mo) bimetallic catalysts on alumina supports via co- and stepwise impregnation, then compared their CNT synthesis performance under identical conditions. Stepwise-impregnated catalysts exhibited higher carbon yields than those prepared by co-impregnation. Notably, impregnating Mo after Co achieved the highest yield despite the lowest BET surface area. Synchrotron X-ray diffraction and visible/UV-Raman spectroscopy revealed that only this catalyst contained Al 2 (MoO 4 ) 3 with a MoO 4 structure. X-ray photoelectron spectroscopy clarified the surface chemistry: the catalyst with the highest CNT productivity exposed Mo entirely as Mo 6+ in Al 2 (MoO 4 ) 3 and CoMoO 4 , whereas the others contained both Mo 4+ and Mo 6+ . The MoO x species like Al 2 (MoO 4 ) 3 is known to suppress Co sintering during CNT synthesis, delaying catalyst deactivation and enhancing the carbon yield. Moreover, an inverse relationship was observed between carbon yield and the CoMoO 4 content. This is attributed to the consumption of catalytically active Co during CoMoO 4 formation, which reduces active sites for CNT growth. ICP-OES further confirmed higher Co and Mo loadings for stepwise catalysts, contributing to superior catalyst performance. The extent of CoMoO 4 formation strongly depended on the metal introduction sequence. In conclusion, this trend is illustrated by considering the relationship between the point of zero charge of support and the pH of the metal precursor solutions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

X-ray absorption spectroscopic study of the alumina supported Fe and FeMo catalysts for methane dehydrogenation

Nanoscale Fe (5%Fe/Al 2 O 3 ) and FeMo (4.5%Fe-0.5%Mo/Al 2 O 3 ) catalysts are prepared by precipitating metal components onto alumina and then reducing in hydrogen at 700 °C for 2 hrs. Here, the catalysts are characterized before and after their exposures to methane at 700 °C, employing ex-situ X-ray absorption spectroscopy (XAS) and X-ray diffraction techniques. XAS data of the as-prepared catalysts shows that, iron precipitates onto alumina as 6L-ferrihydrite, and Mo is present as molybdate (Mo(VI)O 4 2- ). The molybdate, which binds the alumina in the as-prepared FeMo catalyst, is partially reduced to MoO 2 . The reduction of iron to metallic state is incomplete because the ferrous iron binds the alumina, forming hercynite. After several hrs of methane exposure to both the catalysts at 700 °C, a major Fe 3 C and a graphite phase are observed only in the FeMo catalyst. The observation confirms that the Mo promotes more iron to an active Fe metal, a part of that metal converts to Fe 3 C and austenite (Fe x C). Concurrently, the MoO 2 converts to Mo-oxycarbide (MoO x C y ), the latter then carburize to Mo 2 C in the FeMo catalyst. The Fe metal, Mo-oxycarbide and metal carbides are mainly responsible for the conversion of methane to H 2 and carbon. At reaction temperature > 900 °C, the Mo carbide particles agglomerate, and the excess carbon deposits on this agglomerate leading to catalyst deactivation. The deactivated catalyst is regenerated with CO 2 treatment at 1000 °C to restore its initial oxide structure.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Structural dependence of hydrogen evolution reaction on transition metal catalysts sputtered at different temperatures in alkaline media

In the present article, we studied the catalytic activity of magnetron sputtered Mo, V, Ni, and Co thin films for hydrogen evolution reaction (HER) in the alkaline electrolyte. Here, we find that the HER potentials (η 10 ) of the Mo and V thin film catalysts sputtered at 800 °C shift positive with respect to those of the film catalysts sputtered at 25°C. For Mo metal the observed shift of η 10 was 280 mV and for V metal observed shift of η 10 was 390 mV. On the other hand, minimal effect of sputtering temperature on both Ni and Co thin film catalyst activity for HER was observed. Structural analysis reveals that Mo and V prepared at 800 °C have uncommon face centered cubic (fcc, 0.74 packing density) structure as opposed to room-temperature sputtered Mo and V thin films which have common body centered cubic (bcc, 0.68 packing density) structure, resulting in significant increases of the packing densities when they are prepared at 800 °C. On the other hand, the high-temperature prepared thin films of Ni and Co retained fcc structures, resulting in no density changes compared to the room-temperature prepared fcc Ni and hexagonal close packed (hcp, 0.74 packing density) Co. Impedance spectroscopy shows that fcc Mo is a better catalyst than fcc Ni, which is considered an industry standard for non-noble pure metal-based catalysts in alkaline media. Stability tests also suggest that fcc Mo thin film catalysts prepared at 800 °C are more durable than fcc Ni thin films. Our study points out that structure phases of catalysts can be a key factor governing the activities of transition metals for HER in alkaline media.

08 HYDROGEN↗
DOE OSTI2020

New Synthesis Strategies to Improve Co-Free LiNi0.5Mn0.5O2 Cathodes: Early Transition Metal d0 Dopants and Manganese Pyrophosphate Coating

In this work, we report solution-based doping and coating strategies to improve the electrochemical performance of the Co-free layered oxide cathode LiNi0.5Mn0.5O2 (LNMO). Small amounts of d0 dopants (e.g., Mo6+and Ti4+, 0.5-1 at. %) increase the cathode’s specific capacity, cycling stability, and rate capability. More specifically, a Mo-doped cathode with the nominal composition LiNi0.495Mn0.495Mo0.01O2 achieves a high reversible capacity of 180 mAh/g at 20 mA/g with good retention at higher rates (e.g., 120 mAh/g at 100 mA/g). Effects of 1 at.% Mo dopant on the cathode structure were studied using a suite of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). These measurements demonstrate that Mo6+ reduces Li+/Ni2+cation mixing and mitigates undesirable phase transformations near the cathode surface during cycling. This work also reports the use of an inorganic Mn2P2O7 coating which enhances cycling stability, presumably through formation of a stable cathode electrolyte interphase (CEI) layer. Overall, the synthesis approaches reported herein are quite general and can potentially be expanded to other high voltage LIB cathodes.

Co-free cathodes, d0 cation, pyrophosphate coating↗
DOE OSTI2022

MoO x S y /Ni 3 S 2 Microspheres on Ni Foam as Highly Efficient, Durable Electrocatalysts for Hydrogen Evolution Reaction

Hydrogen energy derived from water splitting is the cleanest renewable energy source, but it is also very challenging to achieve because the hydrogen evolution reaction (HER) requires highly efficient and low-cost electrocatalysts. Here, we have fabricated a novel hierarchical system of amorphous molybdenum oxy/sulfide microspheres with crystalline Ni 3 S 2 intergrown in situ on Ni foam (MoO x S y /Ni 3 S 2 /NF) as an outstanding electrocatalyst for HER. The MoO x S y /Ni 3 S 2 /NF demonstrates an ultra-low overpotential of 58 mV at a current density of 10 mA cm -2 and extremely durable stability (>200 h), suggesting superior performance comparable to that of Pt-C/NF under acidic conditions. The X-ray absorption fine structure (XAFS) determines the average valence state of Mo to be +(5 + δ), with a coordination motif by O and S. To explain such high HER activity, a [Mo 2 O 2 (S,O) 4 ] dimer-based periodic model structure with the average composition of [Mo 4 O 8 S 4 ] interfaced with the Ni 3 S 2 (101) surface is proposed. The interactions between the Ni of Ni 3 S 2 and bridging S/O of [Mo 4 O 8 S 4 ] result in an average formal Mo charge state between +5 and +6, and significant charge transfer from Ni 3 S 2 to [Mo 4 O 8 S 4 ] activates the Mo = O bonds. The calculated |ΔG H* | of less than 50 meV suggests that the double-bonded O is the most active site. This work points to the importance of oxy/sulfides with Mon+ (+5 < n < +6) as exceptional electrochemical catalysts for HER.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Size and Stoichiometry Effects on the Reactivity of MoCy Nanoparticles Towards Ethylene

Molybdenum carbides are promising catalysts alternative to Pt-group metals for the hydrogenation of unsaturated hydrocarbons. Nanostructuring has been shown to be an efficient way to boost the catalytic activity of these materials with MoCy nanoparticles (NPs) exhibiting a good performance when encapsulated inside zeolites or dispersed on inert supports such as carbon or gold. In this work, we focus on a systematic DFT study of the interaction of MoCy NPs with ethylene (C 2 H 4 ), as a general and simple approach for examining binding and activation of C≡C bonds. Models for 14 NPs, with a Mo/C ratio in the 0.67 to 2.00 range, have been built following a cascade procedure. Several chemical descriptors, including the adsorption energy, structural NPs distortion, C≡C deformation, and C 2 H 4 attachment energy have been analyzed along with a meticulous geometric and electronic characterization of bare NPs and C2H4 binding. The present results show that 1:1 stoichiometric Mo 6 C 6 , Mo 12 C 12 , and Mo 24 C 24 , and the non-stochiometric Mo 4 C 6 , Mo 8 C 12 (MetCar), and Mo 14 C 13 (Nanocube) are excellent systems for the binding and activation of ethylene, exhibiting a much bigger reactivity than a bulk δ-MoC(001) surface with a similar Mo:C ratio. In addition, C 2 H 4 binding on the NPs with a Mo/C < 1.08 is advantageous since, apart from a rather large adsorption energy, implies low energy values for NPs deformation (from 0.00 to 0.31 eV), C≡C distortion (from 0.30 to 0.52 eV), and C 2 H 4 attachment (from -2.12 to -2.58 eV). These theoretical results point to the ideal MoCy size and composition for C 2 H 4 binding, providing a background for further experimental studies aimed at the preparation of MoCy NPs as hydrogenation catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Molybdenum-99 from Molten Salt Reactor as a Source of Technetium-99m for Nuclear Medicine: Past, Current, and Future of Molybdenum-99

Technitium-99m ( 99m Tc), a widely used radioisotope, is used in tens of millions of medical diagnostic procedures annually. However, it is hard to store and must be immediately used upon production due to its short half-life (i.e., 6 h); thus, it is currently produced from 99 Mo, which itself is a result of 235 U fission. The majority of 99 Mo supplies to U.S. patients are currently provided by foreign producers and produced using highly enriched uranium (HEU). In order to minimize the proliferation risks of HEU-based medical isotope production, the U.S. Department of Energy’s National Nuclear Security Administration has funded a program to accelerate the development of technologies to produce 99 Mo without the use of HEU. Today, the global supply of 99 Mo depends on a limited number of nuclear reactors, and production has been interrupted unexpectedly since 2009 due to the fleet’s advanced age. Herein, alternative options for 99 Mo production are discussed, and one potential option is to obtain 99m Tc from molten salt reactors (MSRs). A MSR is a nuclear fission reactor that can operate at or close to atmospheric pressure with liquid fuel, which allows for producing isotopes in a timely manner. In this paper, the past and current production of 99 Mo via nuclear reactors is described, and the future of 99 Mo production by MSRs is discussed. The behavior and chemical properties of molybdenum in fluoride salts in MSRs and the possible extraction methods are also examined in addition to the limitation of current studies.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2023

Electrically enhanced thermochemical cycles for hydrogen generation

In two-step metal-oxide (MO) solar thermochemical cycles, high temperature solar thermal energy is first converted to chemical energy in the form of a reduced MO. The reduced MO is then reoxidized in a second step with steam (or carbon dioxide) to produce hydrogen (or carbon monoxide) at a lower temperature. Solar thermochemical cycles of this type circumvent heat-to-electrical conversion required for electrochemical water splitting and promise high efficiencies. However, significant challenges remain to implementation. Ultra-high temperatures and efficiency-sapping low per-cycle conversion stand out as particularly difficult hurdles. Hybrid approaches utilizing both thermal and electrical energy provide some of the advantages of each, and can facilitate lower temperature operation and offer better per-pass utilization than thermochemical alone. However, early concepts for implementing the thermo-electrochemical approach introduced substantial new challenges including difficult separations, corrosive environments, and energy losses from large temperature swings and phase changes. We are currently investigating two different options for implementation. In the first, a MO that reduces at lower temperature is selected. As the reduced MO lacks the full thermodynamic driving force to effectively split water, the reaction is driven forward by an electrically-assisted proton-conducting membrane that separates and recovers hydrogen as it is produced. This approach produces a pure hydrogen stream, is mechanically simple, and has unique thermodynamic advantages. The second option seeks to more directly couple the electrical boost to the solid MO to drive either the reduction or oxidation step, or both, through the utilization of layered MO materials and advanced reactors. This approach could be applied to both water and carbon dioxide splitting. The results of process modeling and optimization will be presented, and progress towards demonstrating the concepts at the laboratory scale will be discussed.

08 HYDROGEN↗
NASA NTRS1994

Global QBO in circulation and ozone. Part 1: Reexamination of observational evidence

Observational evidence for a global quasi-biennial oscillation (QBO) pattern is reviewed. In particular, the presence of an extratropical, as well as an equatorial, component of the QBO signal in column ozone is established. It is found that the ozone interannual variability is such that as one moves away from the Tropics, the frequency spectrum of the anomaly changes from one that is dominated by the equatorial QBO frequency of 1/30 mo to a two-peak spectrum around the two frequencies: 1/30 mo and 1/20 mo. Instead of treating the 1/20 mo frequency as a separate phenomenon to be filtered away in extracting the QBO in the extratropics, as was previously done, the authors argue that both peaks are integral parts of the extratropical QBO phenomenon. The 1/20 mo frequency happens to be the difference combination of the QBO frequency 1/30 mo and the annual frequency 1/12 mo. Therefore, it can represent the result of the QBO modulating an annual cycle. The authors suggest that previous methods of extracting the extratropical QBO signal severely underestimated the contribution of the QBO to the interannual variability of ozone when data are filtered to pass only the component with the period of equatorial QBO. Further, it is argued that the transport of equatorial QBO ozone anomaly by a non-QBO circulation can at most account for 6-8 Dobson units (DU) of the observed interannual variability of column ozone in the extratropics. The remaining variability (up to 20 DU) probably cannot be produced without an anomaly in the transporting circulation in the extratropics.

Tung, K. K.↗
NASA NTRS2007

Anticipating Cycle 24 Minimum and Its Consequences

On the basis of the 12-mo moving average of monthly mean sunspot number (R) through November 2006, cycle 23 has persisted for 126 mo, having had a minimum of 8.0 in May 1996, a peak of 120.8 in April 2000, and an ascent duration of 47 mo. In November 2006, the 12-mo moving average of monthly mean sunspot number was 12.7, a value just outside the upper observed envelope of sunspot minimum values for the most recent cycles 16-23 (range 3.4-12.3), but within the 90-percent prediction interval (7.8 +/- 6.7). The first spotless day during the decline of cycle 23 occurred in January 2004, and the first occurrence of 10 or more and 20 or more spotless days was February 2006 and April 2007, respectively, inferring that sunspot minimum for cycle 24 is imminent. Through May 2007, 121 spotless days have accumulated. In terms of the weighted mean latitude (weighed by spot area) (LAT) and the highest observed latitude spot (HLS) in November 2006, 12-mo moving averages of these parameters measured 7.9 and 14.6 deg, respectively, these values being the lowest values yet observed during the decline of cycle 23 and being below corresponding mean values found for cycles 16-23. As yet, no high-latitude new-cycle spots have been seen nor has there been an upturn in LAT and HLS, these conditions having always preceded new cycle minimum by several months for past cycles. Together, these findings suggest that cycle 24 s minimum amplitude still lies well beyond November 2006. This implies that cycle 23 s period either will lie in the period "gap" (127-134 mo), a first for a sunspot cycle, or it will be longer than 134 mo, thus making cycle 23 a long-period cycle (like cycle 20) and indicating that cycle 24 s minimum will occur after July 2007. Should cycle 23 prove to be a cycle of longer period, a consequence might be that the maximum amplitude for cycle 24 may be smaller than previously predicted.

Wilson, Robert M.↗
NASA NTRS2017

Comparison of Passive Microwave-Derived Early Melt Onset Records on Arctic Sea Ice

Two long records of melt onset (MO) on Arctic sea ice from passive microwave brightness temperatures (Tbs) obtained by a series of satellite-borne instruments are compared. The Passive Microwave (PMW) method and Advanced Horizontal Range Algorithm (AHRA) detect the increase in emissivity that occurs when liquid water develops around snow grains at the onset of early melting on sea ice. The timing of MO on Arctic sea ice influences the amount of solar radiation absorbed by the ice-ocean system throughout the melt season by reducing surface albedos in the early spring. This work presents a thorough comparison of these two methods for the time series of MO dates from 1979through 2012. The methods are first compared using the published data as a baseline comparison of the publically available data products. A second comparison is performed on adjusted MO dates we produced to remove known differences in inter-sensor calibration of Tbs and masking techniques used to develop the original MO date products. These adjustments result in a more consistent set of input Tbs for the algorithms. Tests of significance indicate that the trends in the time series of annual mean MO dates for the PMW and AHRA are statistically different for the majority of the Arctic Ocean including the Laptev, E. Siberian, Chukchi, Beaufort, and central Arctic regions with mean differences as large as 38.3 days in the Barents Sea. Trend agreement improves for our more consistent MO dates for nearly all regions. Mean differences remain large, primarily due to differing sensitivity of in-algorithm thresholds and larger uncertainties in thin-ice regions.

sea ice↗