LAUSR

Lapse rates of near-surface (2 m) air temperature are important parameters in hydrologic and climate simulations, especially for the mountainous areas without enough in-situ observations. In Xinjiang, northwestern China, the elevations range from higher than 7000 m to lower than sea level, but the existing long-term meteorological measurements are limited and distributed unevenly. To calculate lapse rates in Xinjiang, the daily data of near-surface air temperature (Tmin, Tave, and Tmax) were measured by automatic weather stations from 2012 to 2014. All the in situ observation stations were gridded into a network of 1.5° (latitude) by 1.5° (longitude), and the spatial distribution and the daily, monthly, seasonal variations of lapse rates for Tmin, Tave, and Tmax in Xinjiang are analyzed. The Urumqi River Basin has been considered as a case to study the influence of elevation, aspect, and the wet and dry air conditions to the Tmin, Tave, and Tmax lapse rates. Results show that (1) the lapse rates for Tmin, Tave, and Tmax vary spatially during the observation period. The spatial diversity of Tmin lapse rates is larger than that of Tave, and that of Tmax is the smallest. For each season, Tmax lapse rates have more negative values than Tave lapse rates which are steeper than Tmin lapse rates. The weakest spatial diversity usually appears in July throughout a year. (2) The comparison for the three subregions (North, Middle, and South region) exhibits that lapse rates have similar day-to-day and month-to-month characteristics which present shallower values in winter months and steeper values in summer months. The Tave lapse rates in North region are shallower than those in Middle and South region, and the steepest Tave lapse rates of the three regions all appear in April. Tmin lapse rates are shallower than Tmax lapse rates. The maximum medians of Tmin and Tmax lapse rates for each grid in the three regions all appear in January, whereas the minimum medians all concentrate in July. (3) The seasonality of Tmin, Tave, and Tmax in Xinjiang is also observed. An increasing trend from summer to winter and a decreasing trend from winter to next summer can be seen clearly. (4) The inversion phenomenon is obvious in the Urumqi River Basin and appears in March, November, December, January, and February. The great inversion phenomenon days (24 days) and persistent inversion phenomenon days (12 days) present in January. The influences of elevation and aspect are complex. Lapse rates for Tave, Tmin, and Tmax are steeper under humid air conditions, while dry air conditions lead to shallower lapse rates.