Even though I published a post on this blog a few months ago [LINK] about my intuitions about climates of the world that do a much better job of explaining actual climates than any prior posts about climate on this blog (so I will not link to those posts within this one except for specific reasons) and therefore made me feel satisfied with my understanding of the climates of the world, there was one bit of dissatisfaction that lingered. At the end of that post, I alluded to creating a new climate classification system that would address some of the problems that I have seen in the Köppen & Trewartha climate classification systems. My specific problems with those climate classification systems are in the middle latitudes: at these latitudes, in the Köppen categorization, the climate type "Cfa" commonly found in North America almost never transitions within the same continent to the climate type "Cfb" commonly found in Europe, and in the Trewartha categorization, the Mid-Atlantic & Northwest regions of the US are assigned the climate type "Do" despite having extremely different climates (the latter particularly having noticeably drier & cooler summers, which the the Köppen categorization does a much better job of capturing). Even my modification of the Trewartha categorization didn't fully satisfy me, as there is still almost never any geographic continuity from the climate types "Dfak" to "Dfbk".
The actual new climate classification system that I have in mind will be the subject of a future post. However, thinking through my new climate classification system involved me looking at climate data from various places, and in that process, I saw that in the middle latitudes in South America, locations along the east coast have significantly higher annual average temperatures than locations along the west coast at the same latitudes due to having shorter & warmer winters. This is a significant contrast to the middle latitudes in North America & Eurasia (which are the only other continents that have significant landmass in the middle latitudes), where locations along the east coast have significantly lower annual average temperatures than locations along the west coast at the same latitudes due to having longer & colder winters. This can be seen in the following table of continents, latitudes, locations, and annual average temperatures.
| Latitude (degrees) | Continent | ||
|---|---|---|---|
| South America | North America | Eurasia | |
| 38 | West: 11.5 degrees Celsius (Lebu, Chile) East: 14.0 degrees Celsius (Mar del Plata, Argentina) |
West: 12.7 degrees Celsius (Bodega Bay, US) East: 13.3 degrees Celsius (Ocean City (Maryland), US) |
West: 16.3 degrees Celsius (Sines, Portugal) East: 12.8 degrees Celsius (Sendai, Japan) |
| 38.75 | West: 12.3 degrees Celsius (Temuco, Chile) East: 15.4 degrees Celsius (Bahía Blanca, Argentina) |
West: 11.9 degrees Celsius (Point Arena (California), US) East: 13.9 degrees Celsius (Rehoboth Beach, US) |
West: 17.4 degrees Celsius (Lisbon, Portugal) East: 11.4 degrees Celsius (Minamisanriku, Japan) |
| 42.5 | West: 11.6 degrees Celsius (Castro, Chile) East: 13.6 degrees Celsius (Puerto Madryn, Argentina) |
West: 12.2 degrees Celsius (Gold Beach (Oregon), US) East: 11.1 degrees Celsius (Boston, US) |
West: 14.8 degrees Celsius (Pontevedra, Spain) East: 7.9 degrees Celsius (Tomakomai, Japan) |
| 46 | West: 7.1 degrees Celsius (Balmaceda, Chile) East: 13.2 degrees Celsius (Comodoro Rivadavia, Argentina) |
West: 10.8 degrees Celsius (Astoria (Oregon), US) East: 6.2 degrees Celsius (Sydney, Canada) |
West: 13.5 degrees Celsius (Rochefort, France) East: 7.0 degrees Celsius (Wakkanai, Japan) |
| 49.25 | West: 5.8 degrees Celsius (El Chaltén, Argentina) East: 9.8 degrees Celsius (Puerto San Julián, Argentina) |
West: 9.5 degrees Celsius (Tofino, Canada) East: 4.4 degrees Celsius (Eastport, Canada) |
West: 11.0 degrees Celsius (Cherbourg, France) East: 0.9 degrees Celsius (Poronaysk, Russia) |
That table shows that consistently poleward of 40 degrees in latitude, the west coast of South America is colder than the east coast of South America at the same latitudes, whereas the opposite holds for North America & Eurasia at the same latitudes (in the other hemisphere). Especially given that the warm current along the western edge of the Atlantic Ocean in the southern hemisphere turns away from the east coast of South America at a latitude of approximately 40 degrees even around the southern hemisphere summer solstice such that the water temperatures of 10-16 degrees Celsius at those latitudes are comparable to the water temperature along the west coast of South America at the same latitudes (in contrast to North America around the northern hemisphere summer solstice, where the water temperatures of 18-22 degrees Celsius along the east coast are much warmer than the temperatures along the west coast at the same latitudes) and given that the poleward tapering of the shape of South America means that the climates in that latitude range are dominated by the prevailing westerlies blowing throughout the year, this was a surprising result for me. Moreover, although the Gulf Stream being so warm even at the latitudes of Europe along with the seasonal system of high pressure from the settling of much colder air thereby being much stronger over North Asia compared to North America certainly amplifies the temperature difference seen in Eurasia, it does not fully explain this distinction, as the water temperatures along the west coast of North America at those latitudes are similar to those along the west coast of South America at those latitudes (in the other hemisphere). Again, I am not a trained climatologist or meteorologist; I can't guarantee that this information is accurate, and I can only say that my intuitions seem through my limited understanding to align with superficial aspects of more detailed explanations. Follow the jump to see the explanation.
I think that this distinction is because of the lack of a large landmass in South America at poleward middle latitudes that would support seasonal systems of high pressure from the settling of cold air during the winter half of the year. Such systems of high pressure would lead to cold fronts regularly moving eastward & toward the equator. In their absence, the only prevailing winds in South America at those latitudes come from the prevailing westerlies generated by the subtropical ridge over the Pacific Ocean to the west, and those winds have temperatures moderated by moisture from the ocean. Orographic lifting precipitation means that locations in South America at middle latitudes leeward (east) of the Andes Mountains get warmer & drier air in the winter half of the year than locations windward (west) of the Andes Mountains at the same latitudes.
By contrast, in North America in the winter half of the year, seasonal systems of high pressure from the settling of cold air would generate prevailing westerlies that do not become warmer as they move east because they are generated from air over land that starts out very cold (as opposed to milder air over the ocean). This certainly holds for such systems of high pressure east of the Rocky Mountains, as there is comparatively little elevation change from the Midwest of the US & Canada to their respective east coasts at the same latitudes except for the Appalachian Mountains, so there is little overall adiabatic compressive warming that can happen from the air falling overall. This even holds for such systems of high pressure east of the Rocky Mountains, as there is still not a huge elevation change from the Great Basin plateaus to the east coast. The latter point contrasts with the huge elevation drop from the Tibetan Plateau to the southwest coast of India that allows for significant adiabatic compressive warming, which (along with India's position closer to the equator) explains why the seasonal system of high pressure from the settling of cold air over the Tibetan Plateau rarely leads to cold snaps in India fully leeward of the Himalayas.
Furthermore, the east coast of Japan has much lower average annual temperatures in this latitude range than the west coast of the Iberian Peninsula in Europe at the same latitudes. This is despite the fact that the separation of Japan from the mainland of Eurasia by the Sea of Japan should be analogous to the Pacific Ocean west of South America. This is also despite the fact that the mountains of Japan should make the northwesterly winds in the winter half of the year carrying moisture from the Sea of Japan cool less quickly on the windward side than dry air would due to heat released from condensation leading to orographic lifting precipitation, such that those winds then become warmer upon crossing those mountains, similar to how the air is relatively warmer on the east coast of South America than on the west coast of South America at the same latitudes (due to condensation & orographic lifting precipitation releasing heat on the windward side followed by adiabatic compressive warming on the leeward side as that air crosses the Andes Mountains). Ultimately, this is because the land in North Asia supporting that seasonal system of high pressure contains much colder air compared to the air generated by the subtropical ridge over the Pacific Ocean to the west of North America, the Sea of Japan being much colder during the northern hemisphere winter than the Pacific Ocean to the west of South America at the same latitudes (in the opposite hemisphere) during the southern hemisphere winter means that the northwesterly winds entering Japan are still cold & carry less moisture after having traveled over the Sea of Japan compared to the prevailing westerlies entering Chile after having been generated over the Pacific Ocean, and the fact that the land in North Asia supporting that seasonal system of high pressure is close to sea level (like the east coast of Japan) means that there can be little further adiabatic compressive warming from the overall elevation of that land being higher than the east coast of Japan.
