The Atmospheric Hydrologic Cycle over the Arctic Basin from Reanalyses. Part I: Comparison with Observations and Previous Studies

Abstract

The atmospheric moisture budget is evaluated for the region 70°N to the North Pole using reanalysis datasets of the European Centre for Medium-Range Weather Forecasts (ECMWF; ERA: ECMWF Re-Analysis) and the collaborative effort of the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR). For the forecast fields of the reanalyses, the ERA annually averaged P ? E (precipitation minus evaporation/sublimation) field reproduces the major features of the basin perimeter as they are known, while the NCEP?NCAR reanalysis forecast fields contain a spurious wave pattern in both P and E. Comparisons between gauge data from Soviet drift camp stations and forecast P values of the reanalyses show reasonable agreement given the difficulties (i.e., gauge accuracy, translating location). When averaged for 70°?90°N, the ERA and NCEP?NCAR forecast P ? E are similar in the annual cycle. Average reanalysis forecast values of E for the north polar cap are found to be 40% or more too large based on comparisons using surface latent heat flux climatologies. Differences between a synthesized average moisture flux across 70°N from rawinsonde data of the Historical Arctic Rawinsonde Archive (HARA) and the reanalysis data occur in the presence of rawinsonde network problems. It is concluded that critical deficiencies exist in the rawinsonde depiction of the summertime meridional moisture transport. However, it remains to be seen whether the rawinsonde estimate can be rectified with a different method. For 70°?90°N, annual moisture convergence (P ? E) values from the ERA and NCEP?NCAR are very similar; for both reanalyses, annual P ? E values obtained from forecast fields are much lower than those obtained from moisture flux convergence by about 60%, indicating severe nonclosure of the atmospheric moisture budget. The nonclosure primarily results from anomalously large forecast E values. In comparison with other studies, reanalyses moisture convergence values are much more reasonable. A synthesis of the reanalysis moisture convergence values and more recent studies yields a value of 18.9 ± 2.3 cm yr?1 for the north polar cap.