Global Structure of Brunt Vaisala Frequency as revealed by COSMIC GPS Radio Occultation

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Eileen King
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1 ICGPSRO, May 14-16, 2013, Taiwan Session 3A; U3-2B :10-14:25, May 14 Global Structure of Brunt Vaisala Frequency as revealed by COSMIC GPS Radio Occultation Noersomadi National Institute of Aeronautics and Space (LAPAN), Indonesia (Toshitaka Tsuda, RISH, Kyoto University, Japan)

2 Background GPS-RO provides accurate temperature profiles with very good height resolution (a few hundred meters). Index of atmospheric stability, N 2, (Brunt-Vaisala frequency squared) can be obtained from the height derivative of atmospheric temperature profiles. N 2 is an important parameter that is closely related to various characteristics of the atmosphere. Turbulence diffusion coefficient: D=ε/N 2 Gravity wave (potential) energy: Ep=½ (g/n) 2 (T /T) 2 Saturated gravity wave spectrum: F(m) ~N 2 /m 3 We report in this paper a preliminary study of the N2 distributions using COSMIC GPS-RO data.

3 Outline of the results Background conditions of N 2, Brunt-Vaisala frequency squared from COSMIC GPS RO Height versus Latitude section of N 2 Relationship with the QBO phase in the equator The Polar Night Jet in the Southern Hemisphere Sudden Stratospheric Warming (SSW) in the Northern Hemisphere Eastward propagation of atmospheric waves Horizontal structure of N 2 in the stratosphere

4 Background conditions of Brunt Vaisala frequency from COSMIC GPS Radio Occultation Altitude - Longitude section of average of N 2 in the equator region (15S 15N ) showed a very stable conditions in the stratosphere.

5 Norhtern Hemisphere Southern Hemisphere 20 o 40 o 60 o 90 o The stable conditions are also seen in the stratosphere over the mid latitude and high latitude. Near the surface, N 2 seems to become smaller over continents.

6 Height versus Latitude section of N 2 Over E

Relationship with the QBO phase in the equator Height time section of deviation of N 2 in the equator (15S 15N) for the entire longitude overlayed by zonal mean wind

7 Relationship with the QBO phase in the equator Height time section of deviation of N 2 in the equator (15S 15N) for the entire longitude overlayed by zonal mean wind from NCEP reanalysis (eastward represented by dashed line). It described that the atmospheric stability related to the QBO which is decreasing during eastward phase.

8 Time longitude section of Brunt Vaisala frequency over 15S 15N. Annual oscillation of N 2 in the equator is seen at 17 km. The atmosphere over the tropical region become more stable during middle year and vice versa. It seems related to annual oscillation of tropopause height.

9 The Polar Night Jet in the Southern Hemisphere Height time section of deviation of N 2 at 60S 90N composited with mean zonal wind from NCEP reanalysis (eastward and westward are represented by solid and dot-dashed line respectively).

o N Temperature Sudden Stratosphere Warming event in 2009 was starting from 21

10 Sudden Stratospheric Warming in the Northern Hemisphere Height time section of temperature and Brunt Vaisala frequency over Lon : 90 o 150 o E Lat : 60 o 90 o N Temperature Sudden Stratosphere Warming event in 2009 was starting from 21 Jan and affecting on atmospheric stability conditions. Brunt Vaisala frequency

Eastward propagation in the mid latitude northern hemisphere Time longitude section of N 2 over 20N 40N at 15 km Data were averaged three days centered at the middle and

11 Eastward propagation in the mid latitude northern hemisphere Time longitude section of N 2 over 20N 40N at 15 km Data were averaged three days centered at the middle and shifted oneday. The figure showed decreasing stability during summer months over Eurasia including Tibetan Pletau. Effects by eastward propagating waves are seen in winter months.

12 Horizontal structure of 5 days running mean N 2 at selected altitude 10 km 15 km 20 km 25 km Note : the interval of colorbar of top and bottom panels are different

13 Summary The atmospheric stability in the equator region are related to the QBO which depict larger value of N 2 during westward phase of QBO. It has been described an annual oscillation of N 2 at 17 km for the entire longitude that related to the oscillation of tropopause height. The polar night jet in the southern hemisphere and sudden stratosphere warming in the northern hemisphere also affect the stability condition. Eastward propagation of planetary waves are seen in the mid latitude of northern hemisphere during winter months. N 2 become smaller in summer.

Global observations of stratospheric gravity. comparisons with an atmospheric general circulation model

Global observations of stratospheric gravity waves made with COSMIC GPS RO and comparisons with an atmospheric general circulation model S. P. Alexander 1, T. Tsuda 2, Y. Kawatani 3, M. Takahashi 4, K.