The remote sensing of radiative forcing by light-absorbing particles (LAPs) in seasonal snow over northeastern China
oleh: W. Pu, J. Cui, T. Shi, X. Zhang, C. He, X. Wang, X. Wang
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2019-08-01 |
Deskripsi
<p>Light-absorbing particles (LAPs) deposited on snow can decrease snow albedo and affect climate through snow-albedo radiative forcing. In this study, we use MODIS observations combined with a snow-albedo model (SNICAR – Snow, Ice, and Aerosol Radiative) and a radiative transfer model (SBDART – Santa Barbara DISORT Atmospheric Radiative Transfer) to retrieve the instantaneous spectrally integrated radiative forcing at the surface by LAPs in snow (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="0ffdcf32e6c12ae1f536438a8d04133c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00001.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00001.png"/></svg:svg></span></span>) under clear-sky conditions at the time of MODIS Aqua overpass across northeastern China (NEC) in January–February from 2003 to 2017. <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="ec04f9fb00bc29e4c51e76c0ee4d17cb"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00002.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00002.png"/></svg:svg></span></span> presents distinct spatial variability, with the minimum (22.3 W m<span class="inline-formula"><sup>−2</sup></span>) in western NEC and the maximum (64.6 W m<span class="inline-formula"><sup>−2</sup></span>) near industrial areas in central NEC. The regional mean <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="5a2b24db0c569e0c3f9a78c7081b764c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00003.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00003.png"/></svg:svg></span></span> is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>∼</mo><mn mathvariant="normal">45.1</mn><mo>±</mo><mn mathvariant="normal">6.8</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="4b28a528847c453147ed6055557a9edf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00004.svg" width="60pt" height="10pt" src="acp-19-9949-2019-ie00004.png"/></svg:svg></span></span> W m<span class="inline-formula"><sup>−2</sup></span> in NEC. The positive (negative) uncertainties of retrieved <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="330ae56179f5f0f4b2ab991eeafdce99"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00005.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00005.png"/></svg:svg></span></span> due to atmospheric correction range from 14 % to 57 % (<span class="inline-formula">−14</span> % to <span class="inline-formula">−47</span> %), and the uncertainty value basically decreases with the increased <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="e8aae5d7d6dc978944870391cc138dec"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00006.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00006.png"/></svg:svg></span></span>. We attribute the variations of radiative forcing based on remote sensing and find that the spatial variance of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="4d757ce65e7fade4491b604cd8723d3f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00007.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00007.png"/></svg:svg></span></span> in NEC is 74.6 % due to LAPs and 21.2 % and 4.2 % due to snow grain size and solar zenith angle. Furthermore, based on multiple linear regression, the BC dry and wet deposition and snowfall could explain 84 % of the spatial variance of LAP contents, which confirms the reasonability of the spatial patterns of retrieved <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="27f74a816d615d97c0813d4744e738a1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00008.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00008.png"/></svg:svg></span></span> in NEC. We validate <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="08235846b325d7830c039e8f382f52f6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00009.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00009.png"/></svg:svg></span></span> using in situ radiative forcing estimates. We find that the biases in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi mathvariant="normal">RF</mi><mi mathvariant="normal">MODIS</mi><mi mathvariant="normal">LAPs</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="43pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="2833dc67d2fe3c35cca32c84bc5aa4a2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9949-2019-ie00010.svg" width="43pt" height="17pt" src="acp-19-9949-2019-ie00010.png"/></svg:svg></span></span> are negatively correlated with LAP concentrations and range from <span class="inline-formula">∼5</span> % to <span class="inline-formula">∼350</span> % in NEC.</p>