08年处暑节气期间环流形势展望

将臣

气候值上的处暑，是北方冷空气开始活动的节气，是副高开始南落的节气，是南海季风走向衰弱的节气。

对于华南，粤东有句老话“七热八热热处内”，七八是指农历七八月的高温，“处内”，是指处暑的高温，连屋里也热了。所以，处暑也是南方秋老虎的节气。

今年处暑又会怎样？欢迎大家讨论预测。

sam160

讲笑咁讲，我希望北方较强冷空气能够突破南岭的阻挡南下
98W的出现，有可能会改写这几天的天气

将臣

突破南岭先不说，在暖化背景下的拉尼娜滞后期，目前环流存在以下特征：

1.北冰洋东半球面积仍然相对较大
2.阻塞反复，副高面积波动性偏大，西脊点东西摆动
3.南半球经向趋势持续，110-120E季风假相当位温，在25-30N存在持续正距区域

虽然ENSO和04年不一样，但下一个西风阻塞，副高增强期，华西有重现04年川渝9.3洪灾的风险，现在起到秋分，极夜、海冰面积最小前后的冷暖对峙阶段，都必须留意环流发展。

特别是当副高弱点存在TC时，必须留意TC下沉协同南亚高压，对副高西环和高低空形势的复杂反馈作用，及早预警，避免一夜成灾。

dnt02

引述一位在NOAA的專家在8月30日於自己網誌的意見
An equatorial trade wind surge during July initiated an upwelling oceanic Kelvin wave leading to the negative equatorial subsurface anomalies greater than 3C at roughly 150m depth/150W per TAO buoy data. Another strong trade wind surge (~5m/s 15N-S) is occurring west of the Dateline. Whether or not another upwelling Kelvin wave is generated is unclear. As discussed below, there is some evidence of our low AAM “La-Nina” base state returning.
七月赤道的信風增強引發一個向上流(upwelling)的開爾文波,導致西經150度海平面以下~150m的深海出現3度的負距平
另一股信風增強出現在換日線以西(南北緯15度左右),未知會否出現新一股向上流(upwelling)的開爾文波
不過根據下面討論,有證據顯示低大氣角動量(AAM)的"拉尼娜狀態"可能回歸..

With the all important interannual component left in, since about 6 August there has been ~2 sigma MJO projection in octant 2 of WH (2004) phase space. Phase 2 of the MJO 250mb psi composite anomaly represents the current tropical circulation anomalies, including a favorable environment for Atlantic Ocean tropical cyclogenesis. Some eastward propagation of this MJO signal has occurred during the last week or so. In fact, tropical convection has been moving east along the equator across Indonesia at ~7m/s. However, having my reasons, I am suspicious the latter is only a transient component within a generally quasi-stationary situation of (extremely complicated) tropical forcing.
目前MJO處於Phase2,大氣形勢包括為大西洋旋生帶來合適環境..MJO信號在過去一週有東移..熱帶對流以~7m/s速度移至印尼..不過筆者認為MJO信號仍會少動

dnt02

Synoptically a Northern Hemisphere response has been a “Branstator (2002) like” circumglobal teleconnection of anomalous midlatitude ridges during the last several days. This was the pattern observed, on average, during the boreal 2007-08 cold season, and is typical of La-Nina (defined globally, not just from Nino 3.4!!!).
現時北半球形勢和07-08冬季類似,一個典型拉尼娜形勢

The bottom line is I think we have an important weather-climate signal to offer at least reasonable week 1-3 predictions. Whether or not La-Nina returns in some form is unclear, especially since there are endless scenarios I can offer to the contrary. However, this is an example of the serious rigorous daily subseasonal monitoring issues that exist, utilizing the WB (2007) GSDM and WB (2008) GWO frameworks.
未來1-3週的天氣-氣候信號至少可以提供一個合理預測..不過拉尼娜事件會否回歸仍然不明朗..

Intense to severe tropical thunderstorm activity is probable to continue from the central and eastern equatorial Indian Ocean into Indonesia and the monsoon systems week-1. Unlike the past 2 subseasonal events, this area of rainfall is probable to stay farther south, consistent with the seasonal cycle. How far east the enhanced tropical convection coherently moves is unclear. However, a transient component impacting the west central and TNWP is a possibility anytime until further notice, including at least hybrid tropical cyclones. There may be a reduced risk for significant East Pacific Ocean tropical cyclone development at least week-1, while the tropical Americas have generally climatology for rainfall. Finally equatorial Africa is likely to remain wet with intense easterly wave activity at least weeks 1-2.
劇烈熱帶雷暴(對流)發展在未來一週可能持續在中東印度洋赤道的海域至印尼出現
不過降雨會偏南
對流會否東移發展至西北太平洋仍然不明朗
未來一週,東太平洋熱帶氣旋發展機會比較低
未來1-2週,赤道附近非洲持續潮濕伴隨劇烈東風波發展