Temperature Climatology

General

Long term measurements from several lidar instruments (Rayleigh and sodium) located at 44ºN (Observatoire de Haute-Provence and Centre d'essai des Landes, France, OHP+CEL), 40.6ºN (Fort-Collins, CO, CSU), 34.4ºN (Table Mountain Faciltiy, CA, TMF), and 19.5ºN (Mauna Loa Observatory, HI, MLO) were used to develop a climatology of middle atmospheric temperature (as of 1998). For each instrument, the measurements on every individual day of the year over the entire long-term record were averaged to build a composite year of temperature profiles. These profiles were then interpolated to provide temperature values at 1 km altitude intervals so that the climatology comprises daily temperature values at integer altitudes between 15 and 110 km, depending on the instrument (Figure 1).

Plate 1
Figure 1: Mean annual temperature climatologies obtained for OHP, CEL, CSU, TMF, and MLO

The climatologies for each lidar were compared to the CIRA-86 model and to each other. Large differences between the lidar temperatures and the CIRA-86 temperatures are identified and explained (Figure 2). When compared to all instruments, CIRA-86 appears systematically much too cold between 90 and 95 km, by 20 K or more, and possibly 6-8 K too warm around 80 km, making its use as a reference atmosphere model questionable at these altitudes.

Plate 2
Figure 2: Temperature difference between the observed lidar climatology and the CIRA-86 climatology (a) (OHP+CEL and CSU), (b) (TMF) and (c) (MLO)

The annual and semi-annual components of the seasonal variability and the 2- to 33-day period variability were investigated. An annual cycle with 6-7 K amplitude in the upper stratosphere, increasing to 15-20 K at 80 km, is observed at mid-latitudes (Figure 3). This cycle is in phase with the solar flux in the stratosphere and in opposite phase in the mesosphere with a very cold summer mesopause at 85 km, in good agreement with previous climatologies. At lower latitudes, a semiannual oscillation (SAO) propagates downward from 85 to 30 km (Figure 4) and is characterized by a stronger first cycle than the second (4 K and 2 K amplitude respectively). The 2- to 33-day variability at mid-latitudes shows a maximum during winter around 40 km and in the mesosphere (Figure 5). The first peak is associated with planetary wave activity and stratospheric warmings, and the second to the occurrence of mesospheric temperature inversions. Finally, sudden seasonal transitions, highly consistent between all instruments, have been observed (Figure 6). In particular, in the early winter mid-latitudes a two-step warming of the winter mesosphere between 65 and 85 km as well as a cooling of the lower mesosphere appear to be real climatological events rather than some short-term geophysical or instrumental random variability.

Plate 3
Figure 3: Temperature deviation from the climatological annual mean (a) (OHP+CEL and CSU), (b) (TMF) and (c) (MLO).

Plate 4
Figure 4: Annual and SAO temperature amplitude (K) and phase (UT)

Plate 5
Figure 5: 2- to 33-day temperature standard deviation

Plate 6
Figure 6: Time-derivative of the lidar temperature measurements

References

Leblanc, T., I. S. McDermid, C. Y. She, D. A. Krueger, A. Hauchecorne, and P. Keckhut, Temperature climatology of the middle atmosphere from long-term lidar measurements at mid- and low-latitudes, J. Geophys. Res., 103., 17,191-17,204, 1998.

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