Global trends in visibility: implications for dust sources

نویسنده

  • N. M. Mahowald
چکیده

There is a large uncertainty in the relative roles of human land use, climate change and carbon dioxide fertilization in changing desert dust source strength over the past 100 years, and the overall sign of human impacts on dust is not known. We used visibility data from meteorological stations in dusty regions to assess the anthropogenic impact on long term trends in desert dust emissions. We did this by looking at time series of visibility derived variables and their correlations with precipitation, drought, winds, land use and grazing. Visibility data are available at thousands of stations globally from 1900 to the present, but we focused on 357 stations with more than 30 years of data in regions where mineral aerosols play a dominant role in visibility observations. We evaluated the 1974 to 2003 time period because most of these stations have reliable records only during this time. We first evaluated the visibility data against AERONET aerosol optical depth data, and found that only in dusty regions are the two moderately correlated. Correlation coefficients between visibility-derived variables and AERONET optical depths indicate a moderate correlation (0.47), consistent with capturing about 20% of the variability in optical depths. Two visibility-derived variables appear to compare the best with AERONET observations: the fraction of observations with visibility less than 5 km (VIS5) and the surface extinction (EXT). Regional trends show that in many dusty places, VIS5 and EXT are statistically significantly correlated with the Palmer drought severity index (based on precipitation and temperature) or surface wind speeds, consistent with dust temporal variability being largely driven by meteorology. This is especially true for North African and Chinese dust sources, but less true in the Middle East, Australia or South America, where there are not consistent patterns in the correlations. Climate indices such as El Nino or the North Atlantic Oscillation are not correlated with Correspondence to: N. M. Mahowald ([email protected]) visibility-derived variables in this analysis. There are few stations where visibility measures are correlated with cultivation or grazing estimates on a temporal basis, although this may be a function of the very coarse temporal resolution of the land use datasets. On the other hand, spatial analysis of the visibility data suggests that natural topographic lows are not correlated with VIS5 or EXT, but land use is correlated at a moderate level. This analysis is consistent with land use being important in some regions, but meteorology driving interannual variability during 1974–2003.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Effective Synoptic Structures in the Supporting Dust Storms over the Persian Gulf

In the paper, the atmospheric conditions in the Persian Gulf region and southwest of Iran were studied by analyzing several case studies in cold and warm seasons. For this purpose, three case studies were selected from the dust events occurred between September and March and have been studied using meteorological stations data, satellite imagery, ECMWF global data, and HYSPLIT and DREAM outputs...

متن کامل

Interactive comment on “Global trends in visibility: implications for dust sources” by N. M. Mahowald et al

Response to reviewers: The reviewers make excellent suggestions and comments that substantially improve the text. For the most part we modify the text to better reflect their comments. There are a few exceptions, where we do not do as suggested, in which case we explain why we did not. Comments by Reviewer # 1 (Ron Miller) “There seem to be four main conclusions. First, surface extinction, wher...

متن کامل

بررسی رابطه بین پارامتر‌های اقلیمی و وقوع ریزگردها (مطالعه موردی: استان خوزستان)

Since climate has a major impact on dust generation, it is essential to identify the climatic parameters affecting this phenomenon. In this study, climatic parameters including temperature, relative humidity, rainfall, maximum wind speed and direction were selected and their relationship with visibility data and also dust storm days (recorded at meteorological stations) was analyzed on monthly ...

متن کامل

بررسی تغییرات پوشش‌گیاهی در کانون‌های داخلی و خارجی ریزگردها با استفاده از تصاویر ماهواره‌ای MODIS (مطالعه موردی: استان کرمانشاه)

Vegetation is one of the most important components of ecosystem, which plays an important role in protecting soil and preventing its rise. So, monitoring and evaluating its changes in planning to control the dust storm is effective. The purpose of this study was to investigate the changes of vegetation in the internal and external dust storm sources of Kermanshah province and dust extension are...

متن کامل

Thirteen Most Common Trends Shaping Automobile Dependence Worldwide and the Global Implications of these Trends Kenya

Walking being the oldest form of urban transport, and until the advent of major transformationsin transport technology in the nineteenth century, most cities were structured in ways that supported walkability.Today, there is a change in transportation which emphasizes, the traditional pedestrian paths which are increasinglybecoming non-regulated spaces when compared to the urban spaces for auto...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2007