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Accueil du site → Doctorat → États-Unis → 2003 → Mineral dust variability and the parameterization of emission due to unresolved circulations

COLUMBIA UNIVERSITY (2003)

Mineral dust variability and the parameterization of emission due to unresolved circulations

Cakmur, Reha Vakif

Titre : Mineral dust variability and the parameterization of emission due to unresolved circulations

Auteur : Cakmur, Reha Vakif

Université de soutenance : COLUMBIA UNIVERSITY

Grade : Doctor of Philosophy (PhD) 2003

Résumé
The first part of this thesis compares the seasonal cycle and interannual variability of Advanced Very High Resolution Radiometer (AVHRR) and Total Ozone Mapping Spectrometer (TOMS) satellite retrievals over the Northern Hemisphere subtropical Atlantic Ocean, where soil dust aerosols make the largest contribution to the aerosol load, and are assumed to dominate the variability of each data set. The correlation of monthly anomalies is low at most locations. However, when the monthly anomalies are constructed using only days common to both data sets, the correlation is substantially increased. This suggests that data availability limits the agreement of the original anomalies. Because the two retrievals have only a few days in the common per month, these restricted monthly averages have a large uncertainty. Calculations suggest that at least 7 to 10 daily images are needed to estimate reliably the average dust load during any particular month. The second part of the dissertation analyzes dust emission in an atmospheric general circulation model (ALCM), where realistic simulation is inhibited by the model’s coarse resolution compared to the scale of the circulations observed to mobilize dust. The model originally incorporates the effect of subgrid circulations by tuning the threshold wind speed at each grid box so that AGCM emission matches the value from a tracer transport model with a globally uniform threshold, but whose surface winds are derived from high-resolution reanalyses. We apply a globally uniform threshold to the AGCM, and model subgrid fluctuations in wind speed using information from the AGCM’s parameterizations of the planetary boundary layer, along with dry and moist convection. When subgrid scale variability is inferred from the AGCM meteorology, dust emission shows significant improvement especially over the Sahara and Asia. Emission associated with subgrid wind fluctuations is dominated by dry convection. When the model precipitation is brought to closer agreement with the observations, the AGCM accurately estimates dust loading over the Caribbean region, suggesting that rainfall errors cause the overestimation of wet deposition over the Atlantic. The mechanistic representation of dust emission allows its simulation under different climates, where high resolution surface wind reanalyses are not available for tuning.

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Page publiée le 19 avril 2004, mise à jour le 3 février 2019