Winter warmings, tides and planetary waves: comparisions between CMAM (with interactive chemistry) and MFR-MetO observations and data

Abstract

Abstract. Following earlier comparisons using the Canadian Middle Atmosphere Model (CMAM, without interactive chemistry), the dynamical characteristics of the model are assessed with interactive chemistry activated. Timesequences of temperatures and winds at Tromsø (70 • N) show that the model has more frequent and earlier stratospheric winter warmings than typically observed. Wavelets at mesospheric heights (76, 85 km) and from equator to polar regions show that CMAM tides are generally larger, but planetary waves (PW) smaller, than medium frequency (MF) radar-derived values.Tides modelled for eight geographic locations during the four seasons are not strikingly different from the earlier CMAM experiment; although monthly data now allow these detailed seasonal variations (local combinations of migrating and non-migrating components) within the mesosphere (circa 50-80 km) to be demonstrated for the first time. The dominant semi-diurnal tide of middle latitudes is, as in the earlier papers, quite well realized in CMAM. Regarding the diurnal tide, it is shown here and in an earlier study by one of the authors, that the main characteristics of the diurnal tide at low latitudes (where the S (1,1) mode dominates) are well captured by the model. However, in this experiment there are some other unobserved features for the diurnal tide, which are quite similar to those noted in the earlier CMAM experiment: low latitude amplitudes are larger than observed Finally, the seasonal variations of planetary wave (PW) activity available from CMAM and the MFR show quite good agreement, apart from the amplitude differences (smaller in CMAM above 70 km). A major difference for the 16-d PW is that CMAM shows large amplitudes before the winter solstice; and for the 2-d PW, while both CMAM and MFR show summer and winter activity, the observed summer mesopause and winter mesospheric wave activities are stronger and more extended in height.Models such as CMAM, operated without dataassimilation, are now able to provide increasingly realistic climatologies of middle atmosphere tides and PW activity. Differences do exist however, and so discussion of the various factors affecting tidal and PW characteristics in atmospheres, modelled and observed, is provided. Other diagnostics of model-characteristics and of future desirable model experiments are suggested.

Comment on "Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)" by Pancheva et al. (2009)

“…We move finally to new results from the Canadian Middle Atmosphere Model (CMAM, Manson et al, 2006). At this time the Data Assimilation System (DAS) has been developed as an option (Ren et al, 2008), and results for the year 2006 are being used here.…”

“…The effects of the increased ionization due to the "winter anomaly" (Manson, 1981;Garcia et al, 1986) were also generally considered in the production of contour-plots of amplitudes and phases of the semidiurnal tides as functions of height and time i.e. as in Manson et al (2006) and earlier papers referenced there. In fact, the winter anomaly was found to have a positive influence on the MFR by enhancing the quantity of day-time data during winter in the lower D-region/upper mesosphere (Manson and Meek, 1987).…”

Regional stratospheric warmings in the Pacific-Western Canada (PWC) sector during winter 2004/2005: implications for temperatures, winds, chemical constituents and the characterization of the Polar vortex

“…This warmer region is not a prominent feature of empirical models such as CIRA-86, or general circulation models (e.g. Manson et al, 2006), unless they include effective tropospheric data assimilation. It seems that the studies of Labitzke (1972) and Hitchman et al (1989) have been forgotten by some.…”

Characteristics of Arctic winds at CANDAC-PEARL (80° N, 86° W) and Svalbard (78° N, 16° E) for 2006–2009: radar observations and comparisons with the model CMAM-DAS

“…We use two MWR (Meteor Wind) radars of similar design (Hall et al, 2003;Hocking and Hocking, 2002 Manson et al, 2006) are included in two sections of this paper: provision of "polar-projection" plots up into the mesosphere, to help understand longitudinal variability of background winds in the broad hemispheric context (Sect. 3); and then in Sects.…”