Representation of the Tropical Stratospheric Zonal Wind in Global Atmospheric Reanalyses

Abstract. This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis datasets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50–70 hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the eastern Pacific, where few in situ observations are available. At 10–20 hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed at Singapore. In addition, the timing of the easterly-to-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly mean zonal wind near the equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from mid-latitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered (1979–2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

Download Full-text

Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-6681-2016 ◽

2016 ◽

Vol 16 (11) ◽

pp. 6681-6699 ◽

Cited By ~ 31

Author(s):

Yoshio Kawatani ◽

Kevin Hamilton ◽

Kazuyuki Miyazaki ◽

Masatomo Fujiwara ◽

James A. Anstey

Keyword(s):

Phase Transitions ◽

Zonal Wind ◽

Phase Changes ◽

Stationary Waves ◽

Central Pacific ◽

Strong Constraint ◽

Quasi Biennial Oscillation ◽

Zonal Wavenumber ◽

In Situ Observations

Abstract. This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis data sets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height, and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50–70 hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the central Pacific, where few in situ observations are available. At 10–20 hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed in Singapore. In addition, the timing of the easterly-to-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly-mean zonal wind near the Equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from midlatitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the Equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered (1979–2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

Download Full-text

Representation of the Equatorial Stratopause Semiannual Oscillation in Global Atmospheric Reanalyses

10.5194/acp-2020-73 ◽

2020 ◽

Author(s):

Yoshio Kawatani ◽

Toshihiko Hirooka ◽

Kevin Hamilton ◽

Anne K. Smith ◽

Masatomo Fujiwara

Keyword(s):

Zonal Wind ◽

Good Representation ◽

Polar Regions ◽

Quasi Biennial Oscillation ◽

Amplitude Maximum ◽

Systematic Improvement ◽

Stratospheric Circulation ◽

Biennial Oscillation ◽

Semiannual Oscillation

Abstract. This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere among six major global atmospheric reanalysis datasets and with recent satellite SABER and MLS observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD is minimum near the equator and largest in the polar regions. Along the equator the zonal wind SD is smallest around the longitude of Singapore where consistently high-quality near-equatorial radiosonde observations are available. Interestingly the near-Singapore minimum in SD is evident to at least ~ 3 hPa, i.e. considerably higher than the usual ~ 10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as its detailed time variation and the displacement off the equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa. One of the reanalyses in our study also has a version produced without assimilating satellite observations and a comparison of the SAO in these two versions demonstrates the very great importance of satellite derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.

Download Full-text

Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-9115-2020 ◽

2020 ◽

Vol 20 (14) ◽

pp. 9115-9133

Author(s):

Yoshio Kawatani ◽

Toshihiko Hirooka ◽

Kevin Hamilton ◽

Anne K. Smith ◽

Masatomo Fujiwara

Keyword(s):

Zonal Wind ◽

Good Representation ◽

Polar Regions ◽

Quasi Biennial Oscillation ◽

Amplitude Maximum ◽

Broadband Emission ◽

Systematic Improvement ◽

Stratospheric Circulation ◽

Semiannual Oscillation

Abstract. This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysis datasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO-dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD reaches a minimum near the Equator and is largest in the polar regions. Along the Equator, the zonal wind SD is smallest around the longitude of Singapore, where consistently high-quality near-equatorial radiosonde observations are available. Interestingly, the near-Singapore minimum in SD is evident to at least ∼3 hPa, i.e., considerably higher than the usual ∼10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as its detailed time variation and the displacement off the Equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa. One of the reanalyses in our study also has a version produced without assimilating satellite observations, and a comparison of the SAO in these two versions demonstrates the very great importance of satellite-derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.

Download Full-text

In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.6b01555 ◽

2016 ◽

Vol 120 (39) ◽

pp. 22571-22584 ◽

Cited By ~ 42

Author(s):

Bernhard C. Bayer ◽

David A. Bosworth ◽

F. Benjamin Michaelis ◽

Raoul Blume ◽

Gerlinde Habler ◽

...

Keyword(s):

Phase Transitions ◽

Carbon Nanocomposites ◽

Nickel Carbide ◽

In Situ Observations

Download Full-text

An investigation into the temperature phase transitions of synthesized materials with Al- and Mg-doped lithium manganese oxide spinels by in situ powder X-ray diffraction

Powder Diffraction ◽

10.1017/s088571561600066x ◽

2016 ◽

Vol 32 (1) ◽

pp. 23-30

Author(s):

C. D. Snyders ◽

E. E. Ferg ◽

D. Billing

Keyword(s):

Phase Transitions ◽

Intermediate Phase ◽

Phase Changes ◽

Synthesis Process ◽

Temperature Phase ◽

Gravimetric Analysis ◽

Spinel Oxide ◽

X Ray Diffraction ◽

X Ray

Three spinel materials were prepared and characterized by in situ powder X-ray diffraction (PXRD) techniques to track their phase changes that occurred in the typical batch synthesis process from a sol–gel mixture to the final crystalline spinel oxide. The materials were also characterized by thermal gravimetric analysis, whereby the materials decomposition mechanisms that were observed as the precursor, was gradually heated to the final oxide. The results showed that all the materials achieved their total weight loss at about 400 °C. The in situ PXRD analysis showed the progression of the phase transitions where certain of the materials changed from a crystalline precursor to an amorphous intermediate phase and finally to the spinel cathode oxide (Li1.03Mg0.2Mn1.77O4). For other materials, the precursor would start as an amorphous phase and upon heating, convert into an impure intermediate phase (Mn2O3) before forming the final spinel oxide (Li1.03Mn1.97O4). On the other hand, the LiAl0.4Mn1.6O4 would start with an amorphous precursor, with no intermediate phases and immediately formed the final spinel oxide phase. The in situ PXRD study also showed the increases in the materials respective lattice parameters of the crystalline unit cells upon heating and the significant increases in their crystallite sizes when heated above 600 °C.

Download Full-text