This study presents the first multidecadal climatology of cutoff low systems in the Northern Hemisphere. The climatology was constructed by using 41 yr of NCEP-NCAR reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low (the 200-hPa geopotential minimum, cutoff circulation, and the specific structure of both equivalent thickness and thermal front parameter fields).Several results were confirmed and climatologically validated: 1) the existence of three preferred areas of cutoff low occurrence (the first one extends through southern Europe and the eastern Atlantic coast, the second one is the eastern North Pacific, and the third one is the northern China-Siberian region extending to the northwestern Pacific coast; the European area is the most favored region); 2) the known seasonal cycle, with cutoff lows forming much more frequently in summer than in winter; 3) the short lifetime of cutoff lows, most cutoff lows lasted 2-3 days and very few lasted more than 5 days; and 4) the mobility of the system, with few cutoff lows being stationary. Furthermore, the long study period has made it possible (i) to find a bimodal distribution in the geographical density of cutoff lows for the European sector in all the seasons (with the exception of winter), a summer displacement to the ocean in the American region, and a summer extension to the continent in the Asian region, and (ii) to detect northward and westward motion especially in the transitions from the second to third day of occurrence and from the third to fourth day of occurrence.The long-term cutoff low database built in this study is appropriate to study the interannual variability of cutoff low occurrence and the links between cutoff lows and jet stream systems, blocking, or major modes of climate variability as well as the global importance of cutoff low in the stratosphere-troposphere exchange mechanism, which will be the focus of a subsequent paper.

Elevated stratopause (ES) events occurring during Northern Hemisphere winter are identified in four climate simulations of the period 1953–2005 made with the Whole Atmosphere Community Climate Model (WACCM). We find 68 ES events in 212 winters. These events are found in winters when the middle atmosphere is disturbed and there are zonal wind reversals in the stratosphere at high latitudes. These disturbances can be associated with both major and minor stratospheric sudden warming events (SSWs). The ES events occur under conditions where the stratospheric jet, the gravity wave forcing, and the residual circulation remain reversed longer than in those winters where an SSW occurs without an ES. We compare ES events with the type of SSW (vortex splitting and vortex displacement) and find that 68% of ES events form after vortex splitting events. We also present a climatology of ES events based on NASA's Modern‐Era Retrospective Analysis for Research and Applications reanalysis data from 1979 to 2012 and compare it to the model results. WACCM composites of major SSW and ES also show enhanced Eliassen‐Palm flux divergences in the upper mesosphere after the stratospheric warming, immediately before the formation of an ES. However, the formation of an ES in WACCM is due primarily to adiabatic heating from gravity wave‐driven downwelling, which follows the reestablishment of the eastward jet in the upper stratosphere. We find nine winters where an ES forms in the absence of any significant planetary wave activity in the upper mesosphere and illustrate one such event.

[1] This study examines various climatological features related to multiple tropopause events (MT events). The analysis is based on the lapse rate definition of the tropopause and is performed on a radiosonde data subset taken from the Integrated Global Radiosonde Archive database. The global statistics of MT events are analyzed, taking into consideration both their seasonal and geographical variations. Our results are in moderate qualitative agreement with those of earlier studies. They reinforce the analytical findings of other researchers, but at the same time highlight important differences in both the number and position of the maximum occurrence of MT events. We found a latitudinal band of multiple tropopause occurrence in the Northern Hemisphere and three centers in the Southern Hemisphere, which coincided with identified zones of maximum cyclogenesis. The climatological features of pressure, temperature, and vertical separation of MT events revealed the complexity of these phenomena, which behave very differently according to latitude and season.

Previous attempts to use fly ash as a soil amendment have had limited success because of its low nutrient value, low cation exchange capacity (CEC), and elevated levels of toxic trace elements. However, treating fly ash with NaOH or KOH at an elevated temperature converts the ash into zeolite minerals and solubilizes the toxic trace elements, which are removed in the base solution. The CEC of the untreated fly ash was <100 mmolC kg-1 but increased to over 3000 mmolC kg-1 when heated for 3 days at 100 °C in 3 M NaOH. The dominant zeolites formed at 100 °C in NaOH were zeolite Na-Pl and zeolite P-C, and at temperatures of 150−250 °C, the mineralogy changed to zeolite X and pectolite. In KOH at 100 °C, zeolite K-G (potassium chabazite) was formed. The fly ash zeolites had a high affinity for K+, Ca2+, and NH4 +, although attempts to use the treated ash to remove NH4 + and heavy metals from wastewater and electroplating wastes were only partially successful. Potential uses of the treated ash were limited due to the high pH that resulted from the dissolution of the zeolite minerals. At pH 4 and pH 5, the rate of fly ash zeolite dissolution was 1000 times faster than most aluminosilicate minerals. Attempts to produce a zeolitic material with NH4OH or fluorides were not successful.

In this study the depth of the atmospheric boundary layer (ABL) over the Tibetan Plateau was measured during a regional radiosonde observation campaign in 2008 and found to be deeper than indicated by previously measurements. Results indicate that during fair weather conditions on winter days, the top of the mixed layers can be up to 5 km above the ground (9.4 km above sea level). Measurements also show that the depth of the ABL is quite distinct for three different periods (winter, monsoon-onset, and monsoon seasons). Turbulence at the top of a deep mixing layer can rise up to the upper troposphere. As a consequence, as confirmed by trajectory analysis, interaction occurs between deep ABLs and the low tropopause during winter over the Tibetan Plateau.