The space-time evolution of intraseasonal convection and circulation anomalies in the 10-25-day period range over East Asia and western North-Pacific Monsoon regions are explored for four early summer seasons from 1991 to 1994. The paper primarily focuses on the linkage between tropical convection over the South China Sea, and lower-tropospheric circulation over the East Asian subtropics on this time scale. The composite results show that quasi-periodic fluctuations of convection on the 10-25-day time scale over the South China Sea, are associated with large-scale circulation in the Asian-Pacific region. The development of subtropical circulation and convection takes place through changes in large-scale circulation on this time scale.10-25-day enhanced (suppressed) convection occurs in conjunction with well-organized cyclonic (anticyclonic) circulation anomalies over the South China Sea. A downstream wave train extending from the South China Sea into the North Pacific, is built up in the lower troposphere associated with this convective activity. This wave train is probably interpreted as a Rossby mode response to the anomalous heating (cooling) . Following the peak of enhanced convection, the East Asian subtropical anomalous anti-cyclone maintains its strength as part of this wave train, and couples with enhanced subtropical convection along the northern flank of this anti-cyclonic cell. This development of convection in the subtropical frontal zone is due to an increase in the low-level westerlies at the northern flank of this anti-cyclonic circulation. In addition, this subtropical anomalous anti-cyclone moves southwestward from the subtropics into the South China Sea region, and appears to initiate subsequent suppressed convection. In contrast, the southwestward migration of subtropical cyclonic anomalies also occurs following the inactive convection over the South China Sea, and this behavior appears to trigger the subsequent active convection over this region. These features suggest that mutual interactions between the tropics and the subtropics on this time scale play important roles on the variability of monsoon convection and circulation over East Asia, and western North Pacific.In the upper level strongest divergent outflow (convergent inflow) occurs in the convective (nonconvective) region and the significant wave train is maximally intensified in the mid-latitude at the convective peak. Upper-level circulation also appears to be forced by heating (cooling) located over the South China Sea region. These circulation features confirm that 10-25-day variations of convection over the South China Sea are one of the effective forcings for the large-scale circulation during the early summer season.
Ten years (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995) of ECMWF analyses and NOAA outgoing longwave radiation (OLR) data were used to investigate intraseasonal tropical-extratropical interactions on timescales of 10
Meridional wind surges from the extratropics into the Tropics strongly regulate tropical convective activity. This paper confirms that extratropical forcing manifested as a meridional surge does modulate the tropical atmosphere over the eastern Indian Ocean, and it describes the tropical–extratropical connection in the region. Surges in the lower atmosphere on submonthly (6–25 days) time scales over the eastern Indian Ocean were examined in tandem with associated tropical convection and large-scale atmospheric fields during the Southern Hemisphere (SH) winter (June–August). Data used in this study are NCEP-2 reanalyses and daily NOAA/Climate Diagnostics Center (CDC) outgoing longwave radiation (OLR) data for 23 yr, from 1979 to 2001. A low-level surge index was calculated using the 850-hPa meridional wind component (υ) averaged over a region where sub–monthly scale υ variance shows a local maximum (17.5°–2.5°S, 87.5°–97.5°E). The surge index defines 62 different surge events. Composites of various components were generated based on the index to define relationships between surge events and large-scale fields. Low-level southerly surges over the eastern Indian Ocean originate from midlatitude Rossby waves with strong baroclinic development in the entrance region of a subtropical jet core off Australia’s west coast. Strengthened low-level wind surges cause cross-equatorial flow stretching from the subtropical eastern Indian Ocean to the southern Bay of Bengal. Surges are accompanied by the advection of cold, dry air from midlatitudes into the Tropics. A cold and dry front develops at the leading surge edge during the surge period. Two to four days later, as the surge peaks, negative OLR anomalies develop near the key region. The OLR anomalies indicate a local blow up of convection over the tropical eastern Indian Ocean. Convection reflects increased instability in the surge region, which is caused by low-level dry air advection and near-surface moistening that is forced by enhanced sea surface evaporation associated with the surge. The southerly surge on submonthly time scales is an important bridge linking the Tropics and midlatitudes over the Indian Ocean.
Lipoarabinomannan (LAM) is the major arabinose-and mannose-containing phosphorylated lipopolysaccharide (LPS) in mycobacterial cell walls. LAM preparations from a virulent strain (Erdman) (LAMErdi.a) and an attenuated strain (H37Ra) (LAMH37R.) of Mycobacterium tuberculosis, as well as from M. leprae (a virulent mycobacterium), were analyzed for their effects on various macrophage (MO) effector functions. LAMH37R., like gram-negative LPS, exhibited a dose-dependent ability to induce tumor necrosis factor alpha (TNF-a) production in normal M+, and gamma interferon (IFN-y) priming of the M+ greatly augmented the levels of TNF-c However, the effects of LAMH37R. were unaffected by polymyxin B, which totally abrogated the effects of LPS. LAMErd..a and LAM from M. keprae, on the other hand, induced virtually no TNF-a production. Analysis of M4 mRNA by reverse transcription-polymerase chain reaction revealed that the levels of TNF-a mRNA induced by the various preparations correlated with the levels of TNF-a protein detected. Interestingly, both LAMJI3R,, and LAMEdm..an could block subsequent IFN-yand LPS-induced M+ activation, a previously reported measure of the potent ability of LAM to down-regulate M4 effector functions. Two lines of evidence suggested, however, that M4 cyclooxygenase products did not play a role in this down-regulation. LAMH37R. and LPS could induce the production of N02 in both normal and IFN-y-primed M+, whereas LAMErdman could stimulate N02 production only in primed M+. Both LAMH37R, and
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