Comparing radiosonde and COSMIC atmospheric profile datato quantify differences among radiosonde types and the effectsof imperfect collocation on comparison statistics

摘要

Collocated global atmospheric temperature, humidity, and refractivity profiles fromradiosondes and from Constellation Observing System for Meteorology, Ionosphere, andClimate (COSMIC) radio occultation data for April 2008 to October 2009 are comparedfor two purposes. The first is to quantify the error characteristics of 12 radiosondetypes flown in the global operational network, as a function of height and for both dayand nighttime observations, for each of the three variables. The second is to determinethe effects of imperfect temporal and spatial collocation on the radiosonde-COSMICdifferences, for application to the general problem of satellite calibration and validationusing in situ sounding data. Statistical analyses of the comparisons reveal differencesamong radiosonde types in refractivity, relative humidity, and radiation-correctedtemperature data. Most of the radiosonde types show a dry bias, particularly in the uppertroposphere, with the bias in daytime drier than in nighttime. Weather-scale variability,introduced by collocation time and distance mismatch, affects the comparison ofradiosonde and COSMIC data by increasing the standard deviation errors, which aregenerally proportional to the size of the time and distance mismatch within the collocationwindow of 6 h and 250 km considered. Globally, in the troposphere (850-200 hPa), thecollocation mismatch impacts on the comparison standard deviation errors for temperatureare 0.35 K per 3 h and 0.42 K per 100 km and, for relative humidity, are 3.3% per 3h and 3.1% per 100 km, indicating an approximate equivalence of 3 h to 100 km in termsof mismatch impact.