Interannual Changes of the Stratospheric Circulation: Influence on the Tropics and Southern Hemisphere

This study identifies a new triggering mechanism of the Indian Ocean Dipole (IOD) from the Southern Hemisphere. This mechanism is independent from the El Ni&#241;o/Southern Oscillation (ENSO) and tends to induce the IOD before its canonical peak season. The joint effects of this mechanism and ENSO may explain different lifetimes and strengths of the IOD. During its positive phase, development of sea surface temperature cold anomalies commences in the southern Indian Ocean, accompanied by an anomalous subtropical high system and anomalous southeasterly winds. The eastward movement of these anomalies enhances the monsoon off Sumatra-Java during May-August, leading to an early positive IOD onset. The pressure variability in the subtropical area is related with the Southern Annular Mode, suggesting a teleconnection between high-latitude and mid-latitude climate that can further affect the tropics. To include the subtropical signals may help model prediction of the IOD event.

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Southern Hemisphere Blocking Onsets Associated with Upper-Tropospheric Divergence Anomalies

Journal of the Atmospheric Sciences ◽

10.1175/jas3421.1 ◽

2005 ◽

Vol 62 (5) ◽

pp. 1614-1625 ◽

Cited By ~ 12

Author(s):

F. Javier Sáez de Adana ◽

Stephen J. Colucci

Keyword(s):

Southern Hemisphere ◽

Nonlinear Effect ◽

Local Development ◽

Relative Vorticity ◽

Convective Activity ◽

Early Winter ◽

Horizontal Advection ◽

Blocking Activity ◽

The Tropics ◽

Blocking Index

Abstract Upper-tropospheric divergence anomalies and divergence tendencies prior to and during the onset of blocking have been investigated for selected cases over the Southern Hemisphere in search of links between the upper-tropospheric response to tropical convective activity and the onset of blocking in midlatitudes. Climatologies of blocking, defined by an objective index, and divergence are established for the Southern Hemisphere and the southern Pacific, respectively. Relative blocking frequency versus longitude reveals a region of maximum blocking activity between 160°E and 75°W. Blocking frequencies for each ENSO phase indicate a shift toward the late austral fall and early winter during the warm phase, whereas during the cold and neutral phases the highest frequencies are in June and July, respectively. Composites of area-averaged divergence anomalies for the selected blocking cases reveal more anomalous divergence than during nonblocking periods over the blocking regions and the immediate upstream regions in midlatitudes. A full divergence tendency equation is utilized to diagnose the local development of divergence preceding the onset of blocking. Results indicate that divergence tendencies over midlatitudes in the block-onset region were forced primarily by horizontal advection, ageostrophic relative vorticity, and a nonlinear effect. In the region directly upstream from the block-onset region, ageostrophic relative vorticity had the greatest contribution followed by the horizontal advection. In the Tropics, divergence tendencies appear to be driven primarily by horizontal advection. Correlations of calculated divergence tendencies with the blocking index suggest that ageostrophic vorticity may locally generate divergence that in turn may force anticyclonic vorticity associated with blocking. Lag correlations with a blocking index during blocking reveal the importance of horizontal advection in driving divergence anomalies, implying divergence-induced vorticities, toward the incipient block.

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Zonal Wave 3 Pattern in the Southern Hemisphere generated by tropical convection

10.21203/rs.3.rs-320008/v1 ◽

2021 ◽

Author(s):

Rishav Goyal ◽

Martin Jucker ◽

Alex Sen Gupta ◽

Harry Hendon ◽

Matthew England

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

Southern Hemisphere ◽

Ocean Circulation ◽

General Circulation ◽

Deep Convection ◽

Circulation Model ◽

Hadley Cell ◽

Wave Source ◽

The Tropics

Abstract A distinctive feature of the Southern Hemisphere (SH) extratropical atmospheric circulation is the quasi-stationary zonal wave 3 (ZW3) pattern, characterized by three high and three low-pressure centers around the SH extratropics. This feature is present in both the mean atmospheric circulation and its variability on daily, seasonal and interannual timescales. While the ZW3 pattern has significant impacts on meridional heat transport and Antarctic sea ice extent, the reason for its existence remains uncertain, although it has long been assumed to be linked to the existence of three major land masses in the SH extratropics. Here we use an atmospheric general circulation model to show that the stationery ZW3 pattern is instead driven by zonal asymmetric deep atmospheric convection in the tropics, with little to no role played by the orography or land masses in the extratropics. Localized regions of deep convection in the tropics form a local Hadley cell which in turn creates a wave source in the subtropics that excites a poleward and eastward propagating wave train which forms stationary waves in the SH high latitudes. Our findings suggest that changes in tropical deep convection, either due to natural variability or climate change, will impact the zonal wave 3 pattern, with implications for Southern Hemisphere climate, ocean circulation, and sea-ice.

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Solar Influences on Stratospheric Circulation Patterns

10.5194/egusphere-egu2020-5287 ◽

2020 ◽

Author(s):

Yonatan Givon ◽

Chaim Garfinkel

Keyword(s):

Zonal Wind ◽

Wind Anomaly ◽

Zonal Wind Anomaly ◽

Circulation Patterns ◽

Downward Propagation ◽

P Flux ◽

Stratospheric Circulation ◽

The Tropics ◽

The Impact ◽

Transformed Eulerian Mean

The impact of the solar cycle on the NH winter stratospheric circulation is analyzed using simulations of a Model of an idealized Moist Atmosphere (MiMA). By comparing solar minimum periods to solar maximum periods, the solar impact on the stratosphere is evaluated: Solar maximum periods are accompanied by warming of the tropics that extends into the midlatitudes due to an altered Brewer Dobson Circulation. This warming of the subtropics and the altered Brewer Dobson Circulation leads to an increase in zonal wind in midlatitudes, which is then followed by a decrease in E-P flux convergence near the winter pole which extends the enhanced westerlies to subpolar latitudes. We use the transformed Eulerian mean framework to reveal the processes that lead to the formation of this sub-polar zonal wind anomaly and its downward propagation from the top of the stratosphere to the tropopause.

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Simuliidae of the Buganda, Eastern and Western Provinces of Uganda

Bulletin of Entomological Research ◽

10.1017/s0007485300038438 ◽

1937 ◽

Vol 28 (2) ◽

pp. 289-309 ◽

Cited By ~ 8

Author(s):

E. G. Gibbins

Keyword(s):

Southern Hemisphere ◽

East Coast ◽

Northern Province ◽

African Continent ◽

River Nile ◽

High Mountains ◽

The West ◽

Number Of Species ◽

The Tropics

Five years ago, when a study was commenced of the Simuliid fauna of Uganda, 24 species were known from the whole of Africa. To-day, Uganda can claim more than that number within its own boundaries. In fact 30 species are known to occur in the country. And yet it is probable that many more species remain to be discovered, particularly as the investigation has not included the Northern Province, which will undoubtedly prove to be one of the richest in Simulium, since within its confines are the River Nile and its many subsidiary tributaries. Quite a number of species found in Uganda occur in other parts of the African continent. Some extend their distribution over to the west and also to the east coast, while other species do not confine their range to the tropics and are found as far afield as the Transvaal and Natal in the Southern Hemisphere. Early observations (1934) indicated a specialised Simuliid fauna on each of the high mountains in Uganda, and while this may still be true in the case of some species, subsequent investigations have shown that several have a wider distribution.

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II. Descriptions of New and Rare Diatoms from the Tropics and Southern Hemisphere

Transactions of the Botanical Society of Edinburgh ◽

10.1080/03746606609468620 ◽

1866 ◽

Vol 8 (1-4) ◽

pp. 436-440 ◽

Cited By ~ 3

Author(s):

R. K. Greville

Keyword(s):

Southern Hemisphere ◽

The Tropics

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Interaction between the MJO and Polar Circulations

Journal of Climate ◽

10.1175/jcli-d-11-00508.1 ◽

2013 ◽

Vol 26 (11) ◽

pp. 3562-3574 ◽

Cited By ~ 38

Author(s):

Maria Flatau ◽

Young-Joon Kim

Keyword(s):

Indian Ocean ◽

Southern Hemisphere ◽

Warm Season ◽

Cold Season ◽

The Arctic ◽

Boreal Winter ◽

Annular Modes ◽

The Indian Ocean ◽

The Arctic Oscillation ◽

The Tropics

Abstract A tropical–polar connection and its seasonal dependence are examined using the real-time multivariate Madden–Julian oscillation (MJO) (RMM) index and daily indices for the annular modes, the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). On the intraseasonal time scale, the MJO appears to force the annular modes in both hemispheres. On this scale, during the cold season, the convection in the Indian Ocean precedes the increase of the AO/AAO. Interestingly, during the boreal winter (Southern Hemisphere warm season), strong MJOs in the Indian Ocean are related to a decrease of the AAO index, and AO/AAO tendencies are out of phase. On the longer time scales, a persistent AO/AAO anomaly appears to influence the convection in the tropical belt and impact the distribution of MJO-preferred phases. It is shown that this may be a result of the sea surface temperature (SST) changes related to a persistent AO, with cooling over the Indian Ocean and warming over Indonesia. In the Southern Hemisphere, the SST anomalies are to some extent also related to a persistent AAO pattern, but this relationship is much weaker and appears only during the Southern Hemisphere cold season. On the basis of these results, a mechanism involving the air–sea interaction in the tropics is suggested as a possible link between persistent AO and convective activity in the Indian Ocean and western Pacific.

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Hydrogen cyanide in the upper troposphere: GEM-AQ simulation and comparison with ACE-FTS observations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-2165-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 2165-2194 ◽

Cited By ~ 1

Author(s):

A. Lupu ◽

J. W. Kaminski ◽

L. Neary ◽

J. C. McConnell ◽

K. Toyota ◽

...

Keyword(s):

Southern Hemisphere ◽

Atmospheric Chemistry ◽

Hydrogen Cyanide ◽

Weather Forecasting ◽

Boreal Summer ◽

Air Quality Model ◽

Quality Model ◽

Upper Troposphere ◽

Mixing Ratios ◽

The Tropics

Abstract. We investigate the spatial and temporal distribution of hydrogen cyanide (HCN) in the upper troposphere through numerical simulations and comparison with observations from a space-based instrument. To perform the simulations, we used the Global Environmental Multiscale Air Quality model (GEM-AQ), which is based on the three-dimensional global multiscale model developed by the Meteorological Service of Canada for operational weather forecasting. The model was run for the period 2004–2006 on a 1.5°×1.5° global grid with 28 hybrid vertical levels from the surface up to 10 hPa. Objective analysis data from the Canadian Meteorological Centre were used to update the meteorological fields every 24 h. Fire emission fluxes of gas species were generated by using year-specific inventories of carbon emissions with 8-day temporal resolution from the Global Fire Emission Database (GFED) version 2. The model output is compared with HCN profiles measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument onboard the Canadian SCISAT-1 satellite. High values of up to a few ppbv are observed in the tropics in the Southern Hemisphere; the enhancement in HCN volume mixing ratios in the upper troposphere is most prominent in October. Low upper-tropospheric mixing ratios of less than 100 pptv are mostly recorded at middle and high latitudes in the Southern Hemisphere in May–July. Mixing ratios in Northern Hemisphere peak in the boreal summer. The amplitude of the seasonal variation is less pronounced than in the Southern Hemisphere. Our model results show that in the upper troposphere GEM-AQ performs well globally for all seasons, except at Northern high and middle latitudes in summer, where the model has a large negative bias, and in the tropics in winter and spring, where it exhibits large positive bias. This may reflect inaccurate emissions or possible inaccuracies in the emission profile. The model is able to explain most of the observed variability in the upper troposphere HCN field, including the interannual variations in the observed mixing ratio. The estimated average global emission equals 1.3 Tg N yr−1. The average atmospheric burden is 0.53 Tg N, and the corresponding lifetime is 4.9 months.

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Evaluation of ozonesondes, HALOE, SAGE II and III, Odin-OSIRIS and SMR, and ENVISAT-GOMOS, -SCIAMACHY and -MIPAS ozone profiles in the tropics from SAOZ long duration balloon measurements in 2003 and 2004

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-10087-2006 ◽

2006 ◽

Vol 6 (5) ◽

pp. 10087-10152 ◽

Cited By ~ 4

Author(s):

F. Borchi ◽

J.-P. Pommereau

Keyword(s):

Southern Hemisphere ◽

Ozone Concentration ◽

Measuring Instruments ◽

Near Ir ◽

Solar Occultation ◽

Long Duration ◽

Stellar Occultation ◽

Tropical Troposphere ◽

The Tropics ◽

Balloon Measurements

Abstract. The performances of satellite and sondes ozone measuring instruments available in the tropics between 10 and 26 km during the southern hemisphere summer in 2003 and 2004, have been investigated by comparison with series of profiles obtained by solar occultation in the visible Chappuis bands using a SAOZ UV-Vis spectrometer carried by circumnavigating long duration balloons. When compared to SAOZ, systematic positive or negative altitude shifts could be observed in satellite profiles, varying from <50 m for the GOMOS stellar occultation instrument, followed by +100/200 m for solar occultation systems (SAGE II, HALOE above 22 km), but as large as −900 m or +2000 m for limb viewing systems (OSIRIS, SCIAMACHY). The ozone relative biases are generally limited, between −4% and +4%, for measurements in the visible Chappuis bands (SAGE II and III, GOMOS above 22 km and OSIRIS), the near IR (HALOE above 22 km) and the ozonesondes, but increase to −7% in the UV (SCIAMACHY), and +7% in the mid-IR (MIPAS) and the submillimetric range (SMR). Regarding precision, evaluated statistically from the zonal variability of ozone concentration, the best measurements are found to be those of SAGE II (2%), followed by HALOE above 22 km (3–4%), then the ozonesondes, SAGE III moon and OSIRIS (4–5%), GOMOS above 22 km and SCIAMACHY (~6%), MIPAS (8.5%) and finally SMR (16%). Overall, all satellite ozone measurements appear little reliable in the tropical troposphere except those of SAGE II (and eventually SAGE III), though low biased by 50% and of limited (50%) precision.

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