Zonal asymmetries in middle atmospheric ozone and water vapour derived from Odin satellite data 2001-2010

Stationary wave patterns in middle atmospheric ozone (O3) and water vapour (H2O) are an important factor in the atmospheric circulation, but there is a strong gap in diagnosing and understanding their configuration and origin. Based on Odin satellite data from 2001 to 2010 we investigate the stationary wave patterns in O3 and H2O as indicated by the seasonal long-term means of the zonally asymmetric components O*/3=O3-[O3] and H2O* =H2O-[H2O] ([O3], [H2O]: zonal means). At mid- and polar latitudes we find a pronounced wave one pattern in both constituents. In the Northern Hemisphere, the wave patterns increase during autumn, maintain their strength during winter and decay during spring, with maximum amplitudes of about 10–20% of the zonal mean values. During winter, the wave one in O*/3 shows a maximum over the North Pacific/Aleutians and a minimum over the North Atlantic/Northern Europe and a double-peak structure with enhanced amplitude in the lower and in the upper stratosphere. The wave one in H2O* extends from the lower stratosphere to the upper mesosphere with a westward shift in phase with increasing height including a jump in phase at upper stratosphere altitudes. In the Southern Hemisphere, similar wave patterns occur mainly during southern spring. By comparing the observed wave patterns in O*/3 and H2O* with a linear solution of a steady-state transport equation for a zonally asymmetric tracer component we find that these wave patterns are primarily due to zonally asymmetric transport by geostrophically balanced winds, which are derived from observed temperature profiles. In addition temperature-dependent photochemistry contributes substantially to the spatial structure of the wave pattern in O*/3. Further influences, e.g., zonal asymmetries in eddy mixing processes, are discussed

Climate change between the mid and late Holocene in northern high latitudes - Part 1: Survey of temperature and precipitation proxy data

We undertake a study in two parts, where the overall aim is to quantitatively compare results from climate proxy data with results from several climate model simulations from the Paleoclimate Modelling Intercomparison Project for the mid-Holocene period and the pre-industrial, conditions for the pan-arctic region, north of 60 degrees N. In this first paper, we survey the available published local temperature and precipitation proxy records. We also discuss and quantifiy some uncertainties in the estimated difference in climate between the two periods as recorded in the available data. The spatial distribution of available published local proxies has a marked geographical bias towards land areas surrounding the North Atlantic sector, especially Fennoscandia. The majority of the reconstructions are terrestrial, and there is a large over-representation towards summer temperature records. The available reconstructions indicate that the northern high latitudes were warmer in both summer, winter and the in annual mean temperature at the mid-Holocene (6000 BP +/- 500 yrs) compared to the pre-industrial period (1500 AD +/- 500 yrs). For usage in the model-data comparisons (in Part 1), we estimate the calibration uncertainty and also the internal variability in the proxy records, to derive a combined minimum uncertainty in the reconstructed temperature change between the two periods. Often, the calibration uncertainty alone, at a certain site, exceeds the actual reconstructed climate change at the site level. In high-density regions, however, neighbouring records can be merged into a composite record to increase the signal-to-noise ratio. The challenge of producing reliable inferred climate reconstructions for the Holocene cannot be underestimated, considering the fact that the estimated temperature and precipitation fluctuations during this period are in magnitude similar to, or lower than, the uncertainties the reconstructions. We advocate a more widespread practice of archiving proxy records as most of the potentially available reconstructions are not published in digital form

What caused the exceptional mid-latitudinal Noctilucent Cloud event in July 2009?

Noctilucent Clouds (NLCs) are rarely observed at mid-latitudes. In July 2009, strong NLCs were recorded from both Paris and Nebraska, located at latitudes 48 degrees N and 41 degrees N, respectively. The main focus of this work is on the atmospheric conditions that have led to NLCs at these latitudes. We investigate to what extent these clouds may be explained by local formation or by transport from higher latitudes. The dynamical situation is analyzed in terms of wind fields created from Aura/MLS temperature data and measured by radar. We discuss possible tidal effects on the transport and examine the general planetary wave activity during these days. The winds do not seem sufficient to transport NLC particles long southward distances. Hence a local formation is rather likely. In order to investigate the possibility of local NLC formation, the CARMA microphysical model has been applied with temperature data from MLS as input. The results from the large-scale datasets are compared to NLC observations by Odin and to local NLC, temperature and wind measurements by lidar and radar. The reason for the exceptional NLC formation is most likely a combination of local temperature variations by diurnal tides, advantageously located large-scale planetary waves, and general mesospheric temperature conditions that were 5-10 K colder than in previous years. The results also point to that NLCs are very unlikely to occur at latitudes below 50 degrees N during daytime. This conclusion can be made from a tidal temperature mode with cold temperatures during nighttime and temperatures above the limit for NLC occurrence during daytime. The best time for observing mid-latitude NLCs is during the early morning hours