我最初的回答后,和一些在评论中来回,结果我得到了正确的答案有点傻瓜运气,我们整理出来…问题是,尽管通量通常被认为是在物理学表明[BetterExplained.com][1]: >时间:我们测量通量在一个时间点。冻结时间和问>“现在,此时此刻,有多少东西是经过我的>表面吗?”。如果你的场不随时间变化,那么一切都好。>如果你的领域确实改变了,那么你需要选择一个时间点>测量通量。但是,相当的直觉相反的对许多人来说,气象模型通常,尽管命名变量变化(如sshf…* * * * urface * *年代* * ensible * * h * *吃* * * *通量),实际上存储* *积累* *。(这个ECMWF白皮书)[2]对归档数据规范解释说:>物理通量存档的ECMWF模式>开始以来积累的相关预测,因此在单位> $ \ mathrm {Jm ^{−2}} $(美元\ mathrm {W m ^ {−2} \ cdot年代}$)。因此,每天>的意思是(在$ \ mathrm {W m ^{−2}} $)通过检索>美元累积通量\ mathrm {t_1 = t} $和$ \ mathrm {t_2 = t} + \ mathrm{24 \;小时}$美元(> \ mathrm {t} $的时间开始的平均),采取差异>,除以86400,一天的秒数。因此,虽然直觉,你可能认为表面显热通量在6小时就是sshf变量在6小时文件中,它不是。 To get the best estimate of the flux, you'd need to calculate it as: $$\mathrm{\frac{fluxvar_{(this\;timestep)} - fluxvar_{(previous\;timestep)}}{timestep_{(in\;hours)}\cdot3600}}$$ So if you want to find the average flux between hours 3 and 6, you'd do: $$\mathrm{\frac{fluxvar_{(t=6hr)} - fluxvar_{(t=3hr)}}{3\cdot3600}}$$ A couple of questions that Vidhi asked about that may be worthwhile understanding to others: 1. Why did the website quoted show the calculation as $\mathrm{({fluxvar_{(t=6hr)} - fluxvar_{(t=3hr)})/10800}}$, but not $\mathrm{({fluxvar_{(t=3hr)} - fluxvar_{(t=0hr)})/10800}}$... instead just using $\mathrm{{fluxvar_{(t=3hr)}}/10800}$ - Because indeed, in this strange accumulation form $\mathrm{fluxvar_{(t=0hr)}}$ by definition is zero. The variable may or may not exist in the $\mathrm{t=0hr}$ file, but if it does, it should be pointless to include as it had better be 0 if it is indeed accumulation. 2. The site quoted only mentions hours 3, 6, 9, and 12. I have 15, 18, and 21 as well, how do I deal with this? - The same math applies... but remember, if you're dealing with forecast model archive (rather than reanalysis data), you want to use the shortest future hour possible. So actually, rather than use 00Z's $\mathrm{t=12hr}$, you want to be using 12Z's $\mathrm{t=0hr}$, such that, when calculating the 9Z to 12Z flux average, best is$\mathrm{({fluxvar_{(12Z\;t=0hr)} - fluxvar_{(00Z\;t=9hr)})/10800}}$. Anytime derived values (variables that aren't in the model itself, but require a formula to determine) need calculating, such as total surface heat flux, just make sure that when you combine the variables (in this case the shortwave, longwave, sensible, and latent heats), you only divide by the timestep once (don't divide by 10800 in the separate input variables beforehand, then divide by 10800 again after combining them). The models are strange to many, but hopefully this helps some confused people! [1]: https://betterexplained.com/articles/flux/ [2]: https://www.ecmwf.int/sites/default/files/radiation_in_mars.pdf [3]: http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/