The Annual Cycle of the Eddy Momentum Flux Caused by the Planetary-Scale Southern Hemisphere 500-mb Seasonally Forced Waves

Our team is using radio observations of Uranus, collected with the Very Large Array (VLA) telescope, to track seasonal changes in the deep troposphere of Uranus between 1981 and the present. &#160;We previously reported on changes between 1981 and 1994, as the Southern Hemisphere moved from mid- to late-summer (Hofstadter and Butler 2003, Icarus 165, https://doi.org/10.1016/S0019-1035(03)00174-X). &#160;During that time, the distribution of opacity sources in the atmosphere (now thought primarily to be H2S) changed in such a way as to suggest an increase in the strength of the planetary-scale circulation pattern in the 5 to 50 bar region of the atmosphere. &#160;More specifically, using wavelengths from 1 to 20 cm, we found that regions poleward of 45 degrees latitude in the Southern Hemisphere are significantly depleted in absorbers compared to more equatorial latitudes, down to a pressure of about 50 bars (which is near the top of where a liquid water cloud is expected to form). &#160;This opacity distribution could be explained by a planetary-scale circulation pattern, with absorber rich air parcels moving upward in equatorial regions, being depleted in absorbers by condensation at higher altitudes, and then moving poleward and descending, keeping the pole depleted in absorbers. &#160;We found that the opacity difference between the pole and equator increased between the 1980's and the 1990's, suggesting a strengthening of the assumed circulation pattern. &#160;Radio observations by our group and others since 1994 have shown that the Northern Hemisphere is roughly symmetric with the Southern, and that smaller-scale latitudinal banding exists (e.g., Molter et al. 2020 https://arxiv.org/abs/2010.11154). &#160;We are currently analyzing additional Uranus data collected at the VLA, and will present results from a subset of those observations taken in 2012 (during Southern Fall). &#160;We will also discuss plans for extending the time line to the present. &#160;The complete data set will span half a uranian year, allowing all seasons to be observed. &#160;We will also discuss how the composition and chemistry of the ice giant planets (Uranus and Neptune) differ from those of the gas giants (Jupiter and Saturn).

Download Full-text

Phase Alignment of the Tropical Stratospheric QBO in the Annual Cycle

Journal of the Atmospheric Sciences ◽

10.1175/jas3276.1 ◽

2004 ◽

Vol 61 (21) ◽

pp. 2627-2637 ◽

Cited By ~ 16

Author(s):

John Hampson ◽

Peter Haynes

Keyword(s):

Annual Cycle ◽

Momentum Flux ◽

Large Scale ◽

3D Model ◽

Lower Boundary ◽

Oscillation Period ◽

Reanalysis Data ◽

Quasi Biennial Oscillation ◽

Phase Alignment ◽

Equatorial Wave

Abstract This paper investigates the occurrence of phase alignment of the tropical stratospheric quasi-biennial oscillation (QBO) with the annual cycle. First, updating previous studies, observational results are shown for NCEP reanalysis data and Singapore radiosondes: both datasets show strong phase alignment of the QBO at 24.5 km. Phase alignment is investigated in a 3D mechanistic stratospheric model including explicit large-scale planetary waves, forced by a lower boundary geopotential anomaly, and a simple equatorial wave parameterization. The model simulates a QBO-like oscillation, with the period depending on the lower boundary momentum flux of the parameterized waves. Phase alignment is manifested in two different ways. First, simulated oscillations of both integer and noninteger year periods are shown to lock on to a certain phase of the annual cycle. Second, when the magnitude of the lower boundary momentum flux is varied about a range implying oscillation period close to 2 yr, the period of the resulting oscillation is exactly 2 yr for a finite range of such magnitude. Analysis of the 3D model results suggest that the the phase alignment is due largely to the annual cycle in tropical upwelling. This hypothesis is supported by simulations with a 1D equatorial model including both parameterized waves and seasonally varying upwelling. The oscillations in this model show significant phase alignment when the upwelling parameters are tuned to correspond to the 3D model, although the phase alignment is weaker than that seen in the 3D model.

Download Full-text

Energy and Momentum Flux to Nonresonant Forced Waves

Turbulent Fluxes Through the Sea Surface, Wave Dynamics, and Prediction ◽

10.1007/978-1-4612-9806-9_30 ◽

1978 ◽

pp. 457-468

Author(s):

Dieter Hasselmann

Keyword(s):

Momentum Flux ◽

Forced Waves ◽

Energy And Momentum

Download Full-text

Untangling the Annual Cycle of the Tropical Tropopause Layer with an Idealized Moist Model

Journal of Climate ◽

10.1175/jcli-d-17-0127.1 ◽

2017 ◽

Vol 30 (18) ◽

pp. 7339-7358 ◽

Cited By ~ 19

Author(s):

M. Jucker ◽

E. P. Gerber

Keyword(s):

Annual Cycle ◽

Lower Boundary ◽

Boreal Summer ◽

Simple Modification ◽

Tropical Tropopause Layer ◽

Planetary Scale ◽

Tropical Tropopause ◽

Westerly Winds ◽

Cold Point ◽

The Impact

Abstract The processes regulating the climatology and annual cycle of the tropical tropopause layer (TTL) and cold point are not fully understood. Three main drivers have been identified: planetary-scale equatorial waves excited by tropical convection, planetary-scale extratropical waves associated with the deep Brewer–Dobson circulation, and synoptic-scale waves associated with the midlatitude storm tracks. In both observations and comprehensive atmospheric models, all three coexist, making it difficult to separate their contributions. Here, a new intermediate-complexity atmospheric model is developed. Simple modification of the model’s lower boundary allows detailed study of the three processes key to the TTL, both in isolation and together. The model shows that tropical planetary waves are most critical for regulating the mean TTL, setting the depth and temperature of the cold point. The annual cycle of the TTL, which is coldest (warmest) in boreal winter (summer), however, depends critically on the strong annual variation in baroclinicity of the Northern Hemisphere relative to that of the Southern Hemisphere. Planetary-scale waves excited from either the tropics or extratropics then double the impact of baroclinicity on the TTL annual cycle. The remarkably generic response of TTL temperatures over a range of configurations suggests that the details of the wave forcing are unimportant, provided there is sufficient variation in the upward extent of westerly winds over the annual cycle. Westerly winds enable the propagation of stationary Rossby waves, and weakening of the subtropical jet in boreal summer inhibits their propagation into the lower stratosphere, warming the TTL.

Download Full-text